Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/28/23
Area Forecast Discussion
National Weather Service Indianapolis IN
954 PM EDT Thu Jul 27 2023
.Forecast Update...
Issued at 954 PM EDT Thu Jul 27 2023
Much of the isolated showers and thunderstorms that were across
central Indiana earlier this evening have dissipated with loss of
heating. Most of the convection is now southeast of the area,
associated with a low level convergence axis.
Confidence is lower than desired in chances for convection
overnight. Much of the convection earlier was driven by outflow
boundaries moving through unstable air.
However, some weak upper energy may move across the area into the
early overnight, sparking additional isolated convection. The latest
HRRR has been hinting at this possibility. For now, have just
extended the isolated PoPs a few more hours than the previous
forecast, since confidence is low in specifics of the weak upper
energy. Will keep a close eye on whether they need to be extended
longer.
Additionally, a little stronger push of upper energy will approach
the area late tonight from the west. This will generate convection
that may move into the forecast area in the 09-12Z time frame.
Convective allowing models are struggling with this, and there is no
clear signal yet on how this will develop. Will have to play a
waiting game with this as well. Kept the forecast dry for now.
Adjusted hourly temperatures and dewpoints based on latest
observations, but made no significant changes to low temperatures.
Dewpoints are quite high with many observations showing 79/80 degree
readings.
&&
.Short Term...(This evening through Friday)
Issued at 251 PM EDT Thu Jul 27 2023
* Heat Advisory in effect today and Friday
* Hottest temperatures and heat indices of the Summer expected Friday
* Isolated to scattered storms possible near and south of I-70
through early evening
Sultry afternoon across the region with a few lucky locations
getting a drink from isolated downpours...including KIND. Where rain
has not fallen...afternoon temps have soared into the lower 90s.
Meanwhile here at KIND...temps have been unable to rise above 85 due
to the few downpours that have tracked across the SW Indy metro
since around 16Z. Regardless of the temps...the dewpoints are
absurdly high this afternoon...with much of the area in the mid and
upper 70s. KHUF has even made it the rare 80 deg dewpoint as of 18Z.
Heat indices have maxed in the 105 to 110 range as a result...
especially across the Wabash Valley.
The convection component so far has been a result of some form of a
convergence boundary which has shown up very nicely on satellite as
an axis of towering cu from Vermillion Co E/SE across the southern
Indy metro continuing into Shelby and Rush Cos before persisting
further east into southwest Ohio. There have been a few storms but
as discussed earlier...the lack of shear and storm motions generally
hovering around 10kts at best have led to slow moving and pulse
intensity convection with soaking downpours which has had difficulty
maintaining intensity for any extended period of time. Away from
this boundary...it has been dry so far today across the forecast
area.
Going forward for the rest of the afternoon and evening...this
boundary should shift slowly southeast with additional convection
likely to focus in its vicinity into the evening before diminishing.
Really hard to place much higher than chance pops over the southern
half of the forecast area as coverage is not expected to exceed
scattered in nature with much of the area remaining dry. However...
locations that can get underneath the broken line of convection will
get a respite from the heat (but not the humidity) and a nice drink
of water. Not out of the question to see isolated activity elsewhere
driven by heating and instability. As is typical with mid summer
pulse intensity convection...any stronger cells aloft will be
capable of producing localized damaging winds when their cores
collapse. We have not seen that to this point so far this afternoon
but enough DCAPE present that this remains a possibility.
ACARS soundings out of KIND have continued to show a shallow but
potent inversion present below 850mb for much of the day. While that
has not been enough to limit convection...it has led to a much more
extensive level of lower ceilings that have had some difficulty
mixing out. The bulk of the cloud cover will remain in the vicinity
of the boundary through the afternoon but in general skies should
trend towards mainly clear by mid to late evening as lingering
convection shifts into southern Indiana and eventually diminishes.
It still appears that Friday will be the hottest day of the summer
so far for the forecast area as the heat ridge anchored to our
southwest nudges into the Ohio Valley. That being said...there is a
wild card in play that may stunt temp rises initially in the
morning...and that is what remains of the expected robust convective
development later this evening over the upper Midwest. That complex
is expected to turn right and dive southeast around the ridge
periphery overnight and into Friday morning before weakening. Some
of the CAMs data attempts to pull that even more south into northern
Indiana around daybreak before completely diminishing. Confidence
remains low in that potential at this point but even if that did not
occur...remnant cloud debris could be drawn into the region during
the morning before scattering out for Friday afternoon. That could
also have a downstream impact on convective risks later Friday
afternoon and especially Friday night if any remnant boundaries
drift into the forecast area from earlier activity to our north.
More on this threat for Friday night in particular in the Long Term
section below.
Temps...most locations will make it or already have made it to 90
this afternoon except for those impacted by convection and the
clouds. Pulled high temps down for the remainder of the afternoon at
KIND because of this reason but increased sun is not that far to the
north and even a short period with more sun could help boost KIND
near 90 late. Overnight lows will only drop into the mid and upper
70s with heat indices likely lingering in the low 80s in many
locations all night.
Friday remains a bit of a challenge based on the points made above.
While morning cloud debris may limit temp rises initially...the
combination of increasing southwest flow and slightly lower
dewpoints in tandem with warmer boundary layer air should enable
temps to peak at higher levels than today. Still feel that the bulk
of the model guidance is too warm in general with highs especially
considering how temperatures have performed the last few days.
Nudged highs down a few degrees from the previous forecast but still
expect low to mid 90s for the entire area with some locations in
western counties into the upper 90s. Max heat indices will be
solidly in advisory criteria for Friday and those headlines will be
continued.
&&
.Long Term...(Friday night through Thursday)
Issued at 251 PM EDT Thu Jul 27 2023
Hot and humid conditions should persist into the long range as
surface ridging to our south remains. Upper-level ridging across the
southern Plains and Four Corners region is expected to amplify,
allowing a trough to dig across the northeastern US. The trough will
lead to a cold front sliding into Indiana from the north late
Saturday into early Sunday, which will bring cooler conditions
Sunday and early next week. Gradual warming is likely by late week,
with humid conditions returning along with a chance of storms.
Storm chances continue on and off Friday night through Saturday
night as some embedded disturbances in the flow aloft pass nearby.
These waves may trigger some upstream convection which may
consolidate into an MCS or loosely organized cluster. Flow aloft is
weak for the most part, but guidance does tend to increase winds
above 500mb later Friday into Saturday. Given the warm and humid air
ahead of the aforementioned cold front, plenty of instability will
exist through Saturday. In the lower levels, guidance shows a decent
low-level jet persisting through Saturday (20 to 30 kts at 850mb),
which may allow activity to sustain somewhat.
Any cluster or MCS approaching from the north will likely persist
where upper-flow is maximized. Though the system, if it develops,
could also propagate into the LLJ which would give it a slight
southwesterly component. However, by that point, the system would
probably be out of cold pool shear balance and enter into a
weakening phase. Convective redevelopment is again possible later
Saturday afternoon along any residual outflow boundaries. Given the
convective dependence on mesoscale forcing, convection-allowing
models will struggle with storm placement and propagation. Expect
wildly different solutions, particularly in simulated reflectivity,
depending on the model...even run-to-run with the same model.
By Sunday, the cold front should be through and cooler and drier air
(dew points into the 50s) will spread in from the north. 850mb temps
should fall by 10 to 15 degrees C, which will correspond to highs
only in the 80s Sunday through Tuesday. Northerly flow could persist
through mid-week as surface high pressure slides east over the Great
Lakes. Some slight airmass modification should allow temperatures to
rebound into the upper 80s by Thursday and Friday. Return flow on
the back side of the high brings southerly flow back by the end of
the week. Simultaneously, a system diving in from the north may
bring a renewed threat for showers and storms Thursday and Friday.
&&
.Aviation...(00Z TAF Issuance)
Issued at 700 PM EDT Thu Jul 27 2023
Impacts:
* Isolated convection possible this evening mainly at KHUF/KBMG
* Low confidence chance for convection north near sunrise
Discussion:
A few showers are near KBMG but at the moment most convection is
away from the TAF sites. Will watch some storms across central IL to
see if they can make it to KHUF between 00-02Z. For now will just
mention VCSH at KBMG and KHUF this evening. Can`t rule out
convection elsewhere, but odds are too low to mention.
Otherwise VFR conditions are expected. Some localized fog is
possible late tonight, but odds are too low to mention. Also, some
storms may move into northern Indiana toward sunrise. Confidence is
much too low to mention these at this time. Additional isolated
convection will fire after 18Z Friday, mainly east.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until midnight EDT Friday night for INZ021-028>031-
035>049-051>057-060>065-067>072.
&&
$$
Update...50
Short Term...Ryan
Long Term...Eckhoff
Aviation...50
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
816 PM CDT Thu Jul 27 2023
.UPDATE...
Issued at 816 PM CDT Thu Jul 27 2023
We are in a bit of a holding pattern this evening as we monitor
convective trends well to the N/NW and a mid-level wave in Iowa.
Both are in play for convection developing very late this evening
through daybreak.
A benign wave with generally warming cloud tops and very little
remaining mid-level reflectivity over the east half of Iowa
continues to drift east this evening, with a couple more embedded
subtle mid-level curls from Dubuque to Iowa City and west toward
Des Moines. Meanwhile, a WNW to ESE boundary well-defined along a
decent theta-e gradient is gradually lifting north across the far
southern CWA. A few attempts of convective initiation have been
observed along this boundary for the past several hours, but a
substantial layer of mid-level dry air evident per the 00Z KILX
RAOB and regional WV imagery have suppressed most activity in the
absence of more formidable forcing. Weak low-level isentropic
ascent will begin to align ahead of the approaching wave late this
evening beneath steep low to mid-level lapse rates. So while
saturation of LPL heights sufficient for more robust deep
convection remains in question, expectations are that some
isolated to scattered elevated storm activity may begin as early
as prior to midnight near the far western CWA. A gradually
eastward shift in activity is then expected by around daybreak
across the east half of the CWA as the parent wave exits east.
Modest effective shear of 20-25 knots combined with weak diurnal
stability and a reservoir of deeper drier air with DCAPE values
over 1000 J/kg will support locally damaging winds. Isolated
instances of large hail also cannot be ruled out.
Upstream convective trends in MN/WI are becoming more favorable
for a more robust cold pool to surge well south into the early
morning hours and perhaps reach the IL/WI state line by the 2-4am
window. This outflow could enhance any ongoing slightly elevated
convection with the wave to the west, reinforcing any stronger
outflow winds extending through northeast Illinois prior to
daybreak.
No additional changes were made beyond daybreak ahead of an
additional round of potentially severe convection late Friday
afternoon and evening. See the short-term discussion for more
details during this period.
Kluber
&&
.SHORT TERM...
Issued at 340 PM CDT Thu Jul 27 2023
Through Friday night...
Key Forecast Messages:
* Chance of thunderstorms overnight tonight-early Friday with a
level 1 severe threat and localized flash flooding threat
* Oppressive heat and humidity away from Lake Michigan shore
(especially IL shore) until cold front passage late Friday
* Thunderstorms developing near a southward sagging cold front
late Friday afternoon through Friday evening with an associated
level 2 of 5 severe threat (primarily damaging winds and hail)
and a level 2 of 4 flash flooding threat
...Thunderstorms and Associated Severe and Flooding Threats:
Highly uncertain convective forecast through tonight. A weakening
MCV and decaying convective footprint across central Iowa will
encounter a very dry mid-level air mass and strongly capped
conditions locally this evening. For now, no explicit precip.
mention for this, and would appear that at most spotty showers
clipping areas west of I-39 this evening.
Turning attention to overnight, strong to severe thunderstorms
have initiated across the Upper MS Valley/far northern Great Lakes
region near the cold front that will play a role in our weather
tomorrow. CAM solutions have ranged from little/no elevated
convection into our area, though outflow effects from the north,
to a strong/severe southeastward moving MCS and various
scenarios between these extremes. The global guidance,
particularly the ECMWF, has been quite consistent with a footprint
of storms in our area tonight. Continued with chance PoPs given
the uncertainty, highest I-80 and north, between roughly 1 AM and
6 AM, possibly hanging on as late as 7am-8am hour eastern CWA.
It`s unclear if upglide from strengthening low level jet will
result in elevated convection blossoming in addition to upstream
convection moving in, and certainly can`t rule out the "null"
scenario either. Conceptually an MCS would ride the thickness and
instability gradient southeast into the area, and mid-level lapse
rates will be steepening. On the other hand, there may be
lingering capping issues to elevated parcels from antecedent dry
air aloft and very warm EML base, plus effective bulk shear is
forecast to be on the marginal side at 25-35 kt. SPC included us
in a level 1 (marginal) risk for damaging winds, which appears
reasonable, and high PWAT regime could support pockets of heavy
rain/localized flooding *if* deep moist convection is widespread
enough. These next few to several hours well off to the northwest
will *hopefully* shed some light on how things will go.
Confidence is increasing that regardless of a decent overnight
convective footprint, extreme warmth at the 850 mb level should
cap things off and the balance of Friday will be dry. The steep
mid-level lapse rates, dew points pooling well into the 70s south
of southward sagging cold front, and temps into the 90s are
expected to contribute to very large (up to 3-4k J/kg MLCAPE).
Questions remain on exact timing of convective initiation, ranging
from mid-late afternoon across far northern Illinois to holding
off until the evening. MLCIN should erode with time and modest
height falls plus backdoor front shifting south late in the day
Friday point toward a decent chance of explosive convection
starting over far northern IL and then gradually expanding south
into or through the evening. This has been a scenario consistently
depicted by the ECMWF over recent days.
We`ll message a timing of 4pm-12am roughly for what will be a
fairly classic mid-summer severe and flooding threat. Sufficient
deep layer bulk shear up to 35-40 kt and large instability plus
steep low and mid-level lapse rates support damaging wind and hail
threats, with uncertainty regarding mode (surging bowing segments,
or more loosely organized clusters. Proximity of the cold front
boundary likely slowing its southward progress with inland extent
suggests that a brief tornado or two near the boundary can`t be
ruled out amidst favorable low-level CAPE. Finally, PWATs up to
2-2.25", basically top of the charts even for late July, and
likelihood of intense convection suggests pockets of excessive
rainfall are plausible, particularly if west-east training occurs
north of the sagging front and any outflows. For the reasons
above, collaborated with WPC for a level 2 (slight) risk in the
day 2 ERO. SPC maintained its level 2 of 5 (slight) severe risk in
its day 2 update, which is reasonable due to the overall
uncertainty in convective evolution.
...Oppressive Heat and Humidity:
No big changes in the thinking for the heat and high dew point
forecast, with main update to add northern and central Cook
(including Chicago) into the Heat Advisory on Friday. Thinking
most locales away from the lake will top out in the low-mid 90s,
with widespread mid 70s dew points common outside of the heart of
the Chicago urban heat island. Upper 70s to even 80F dew points
are a decent bet due to ET over farming areas. The extreme 100+F
temp scenarios appear to be strongly driven by over-mixing and
mixing out dew points well below what is likely to occur, though
ultimately ends up a wash when the oppressive dew points still
yield 105-110F to locally 115F degree heat index values, highest
southwest half of the CWA where no changes were made to the
Excessive Heat Warning.
As mentioned above, did add in northern and central Cook zones
into the advisory for Friday, but note that models have come into
better agreement on an earlier onshore wind shift prior to the
backdoor front arrival in the afternoon. This would entail Lake
County IL seeing onshore winds all day and the Chicago shore
seeing an earlier onshore wind shift and muting the heat there
somewhat. Given this, did not include Lake County IL in the
advisory and Heat Advisory text mentions inland of Lake Michigan
being in line for the peak heat indices near 105 degrees and we
did brief the city of Chicago on this element.
While debris clouds and stronger onshore winds may conceivably
start the day with north and eastward extent, the earlier
overnight convective timing (albeit with plenty of uncertainty)
and very potent air mass (mid 20s C at 850 mb) point toward us
being able to realize the forecast heat indices on Friday.
Castro
&&
.LONG TERM...
Issued at 258 PM CDT Thu Jul 27 2023
Saturday through Thursday...
Key Messages:
* Temperatures forecast to return to average for the weekend
* Dangerous swim conditions for Lake Michigan beaches Saturday and
possibly into Sunday
* Temperatures will warm again next week, but not expected to be as
hot as this week
Discussion:
As the storms move out of the area Friday night into Saturday
morning, a northerly wind will develop bringing some cold air
advection with it. The upper-level ridge will retreat back to the
west lowering heights and dropping 850-hPa temperatures below 20
degrees Celsius. Surface temperatures will follow suit and cool
back towards the seasonal average for both Saturday and Sunday
with highs expected to be in the low to mid 80s across much of the
area. Dew points will slowly drop throughout the day on Saturday
as well, decreasing into the low 60s and lowering further on
Sunday into the upper 50s.
The northerly winds helping to bring cooler temperatures for the
weekend will also help build wave heights along the southern Lake
Michigan shore resulting in dangerous swimming conditions Saturday
and possibly into Sunday morning.
Some models are showing the potential for showers and storms to
pass over the area on Saturday with a weak trough moving through,
but current thinking is that the front will pass with the storms
Friday night and will clear out of our area Saturday morning
leading the way for dry conditions for the day on Saturday. Any
showers or storms that do form will likely stay south of the CWA,
however a slight chance was left in the forecast just in case the
front is slower.
Moving into next week, model guidance is showing the ridge
rebuilding to the east bringing warmer temperatures with it. The
building of the ridge will be gradual with temperatures warming
slightly each day with the hottest temperatures not expected until
late in the week. Temperatures are not expected to be as hot as
this week, only reaching into the mid-to-upper 80s by Wednesday
and dew points will remain in the high 50s and low 60s through the
majority of the week making conditions much more seasonal. The
return of the ridge to the area will once again bring about a
northwest flow setup, with chances for storms returning.
Carothers
&&
.AVIATION...
For the 00Z TAFs...
* Two periods of TSRA possible, one late tonight and the second
late Friday afternoon/evening. Strong to severe storms possible
late Friday.
* Low confidence in southwest vs. some easterly component to wind
direction Friday morning.
* Northeast winds likely by Friday evening.
Early evening satellite/radar imagery depicts a well-defined mid-
level disturbance tracking east across central/eastern IA. AMDAR
aircraft soundings from KORD/KMDW late this afternoon indicate
considerable dry air above 850 mb (~5000 ft AGL), though modest
enhancement of southwesterly flow aloft ahead of approaching IA
wave will likely produce sufficient warm/moist advection into this
dry layer later tonight which will increase the potential for
elevated convective development across northern IL. Current
extrapolation suggests increasing ascent from this wave would
begin to increase TSRA potential for KRFD after 04Z or so, and
farther east into the Chicago terminals after 06Z. Most CAM
guidance does develop convection into the region, though may
perhaps be a little on the slow side given current position and
propagation of aforementioned wave. Convection potential would
likely linger through sunrise (for Chicago area) before easing as
the wave moves east of the region. Another round of convection is
then likely likely later Friday afternoon into Friday evening, in
association with a cold front which is expected to sag across the
area. Both periods of convection may feature some gusty outflow
winds, with activity late Friday likely to be stronger given
potential for greater low-level instability during diurnally
warmer afternoon/evening hours.
Wind wise, in the near term southeast winds across the Chicago
metro area due to the lake breeze off Lake Michigan will likely
veer light southerly this evening. Uncertainty in wind direction
develops later tonight into Friday morning associated with
expected convection and associated outflow. Some potential exists
for a period of easterly component winds by Friday morning, though
confidence is fairly low at this time. Winds should trend
southwest by afternoon and likely becoming breezy, prior to the
second round of strong storms. Combination of outflow with Friday
evening storms and the southward moving cold front should result
in a shift to northeast winds during the evening which would then
persist overnight and into Saturday. Can`t rule out some lower
(MVFR) clouds in the northeast wind regime later Friday evening.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Excessive Heat Warning...ILZ010-ILZ019-ILZ021-ILZ023-ILZ032-
ILZ033-ILZ039-ILZ107 until 9 PM Friday.
Heat Advisory...ILZ003-ILZ004-ILZ005-ILZ008-ILZ011-ILZ012-ILZ013-
ILZ020-ILZ105-ILZ106-ILZ108 until 9 PM Friday.
Heat Advisory...ILZ103-ILZ104...noon Friday to 9 PM Friday.
IN...Heat Advisory...INZ001-INZ002-INZ011 until 9 PM Friday.
Excessive Heat Warning...INZ010-INZ019 until 9 PM Friday.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Phoenix AZ
453 PM MST Thu Jul 27 2023
.UPDATE...00Z Aviation Discussion.
&&
.SYNOPSIS...
Strong high pressure will continue to hover over the region with
Excessive Heat persisting the next several days. Scattered afternoon
thunderstorm development will also continue over higher terrain
areas with the main impacts in lower elevation communities being
strong, gusty winds and blowing dust. However, an area of low
pressure will migrate northward out of Mexico over the weekend
bringing significantly increased chances of thunderstorms and cooler
temperatures to the entire area.
&&
.DISCUSSION...
Latest water vapor imagery reveals a southerly component to the
steering flow around the Monsoon High, which remains situated
across New Mexico. Dewpoints are running a few degrees higher than
at this time yesterday. However, ACARS sounding from KPHX
indicates that despite yesterday’s rainfall, conditions dry out
rapidly above the surface with mixing ratios falling below 10g/kg
between 850 mb and 700 mb. Temperatures are running 3-5 degrees
cooler than at this time yesterday, and forecast highs were
consequently lowered to 112-114 degrees for the Phoenix area.
Nevertheless, this still equates to a High Heat Risk and the
Excessive Heat Warning continues.
Latest mesoanalysis indicates abundant MLCIN across the lower
deserts, while conditions are less inhospitable further east
across the higher terrain. Latest HREF confirms the higher terrain
will be favored for convection this afternoon and this evening,
however even the ensemble max depicts reflectivities generally
below 50 dBZ. Severe storms are generally not expected and there
is less than a 10 percent chance of gusts above 57 mph. However,
there is a 30-50 percent chance gusts could reach 35 mph across
southern Gila and eastern Pinal Counties.
Latest models indicate similar conditions Friday with a
continuation of the well-above normal temperatures. However, the
record high will be well out of reach in Phoenix, with a daily
record of 121 degrees. Convection will again be most favored
across the higher terrain east of Phoenix. With the high lifting
northward, the HREF suggests somewhat higher probabilities of the
activity reaching the lower deserts, particularly across Pinal
County.
&&
.PREVIOUS DISCUSSION...
Confidence continues to increase that a significant pattern change
will materialize over the weekend as a classic late July inverted
trough propagates through northern Mexico concurrent to the
subtropical high shifting into the central/southern plains. Not only
will this pattern allow a deterioration in heights aloft by early
next week, but will also promote more pronounced moisture advection,
both of which should allow temperatures to fall closer to the
seasonal normal and away from excessive thresholds. The greatest
uncertainty appears to be the haste at which temperatures retreat,
and typically this occurs quite rapidly with the introduction of
expansive thunderstorm activity and convective overturning of the
environment. If not by Sunday, certainly by Monday the prospects for
110F high temperatures will have been exhausted - at least in the
short term.
Obviously, the increased thunderstorm and rainfall chances are most
notable with the incoming inverted trough. Model agreement is
excellent that enhanced ascent with seasonably strong easterly
mid/upper tropospheric winds will enter SE Arizona Saturday
supporting at least one regional convective complex. GEFS membership
continues to favor an intense complex over northern Sonora/southern
AZ Saturday evening thrusting deep outflow and well mixed moisture
northward. Despite forecast BUFR soundings indicating downstream
boundary layer mixing ratios in lower elevation communities only
hovering near 9 g/kg, the intensity of this outflow and incoming
wave could be sufficient to spark thunderstorms along and behind the
boundary with official NBM forecasts advertising POPs 30-60%.
However, the overwhelming signal still highlights Sunday as the most
substantial thunderstorm threat with many favorable conceptual
aspects present. The aforementioned Saturday outflows with deep
moisture advection should push mixing ratios of 10-11 g/kg
throughout the entire boundary layer such that lower elevation
afternoon MLCape and DCape both reach a "sweet spot" around 1500
J/kg in a strongly forced synoptic environment. With minimal
inhibition likely present, the enhanced easterly flow aloft will
result in effective deep layer shear 30-40kt juxtaposed over the
instability axis. This pattern certainly matches some of the more
significant historical monsoon severe events, and will continue to
amplify the messaging for the weekend time frame.
Not surprisingly, the official NBM spreads relatively high POPs over
a temporally extended range not very realistic of a typical monsoon
pattern. In reality, should a more active Sunday period come to
fruition, Monday would likely become more inactive with an
overturned atmosphere and subsident flow. There are some model
solutions that highlight Saturday and Monday versus Sunday, but
regardless having several consecutive days of expansive convective
activity is unlikely. Beyond Monday, forecast uncertainty grows as
some ensemble output suggests a measure of southwest flow partially
scouring moisture away from the forecast area, while other members
retrograde the center of the subtropical high back into central AZ.
Regardless, the preponderance of model evidence suggests some
semblance of a pattern revision back to mountain storms, but only
gusty winds in lower elevations.
&&
.AVIATION...Updated at 2350Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Breezy westerly winds will diminish tonight before switching to
favor an easterly component overnight. Slightly elevated winds
during the nighttime hours and varied timing on the east shift is
possible. While thunderstorms will form over higher terrain areas
north and east of the valley this afternoon, the potential for an
outflow to reach the valley is less than 20 percent. An early
west shift is expected tomorrow as winds increase in speed by the
afternoon. There is a better chance (30-50%) for outflows to reach
the TAF sites tomorrow afternoon through evening. Otherwise, FEW
to SCT cloud bases near 12-15 kft will prevail.
Southeast California/Southwest Arizona including KIPL and KBLH:
Overall tranquil weather is expected throughout the forecast
period. Elevated southerly winds will prevail through tonight,
with gusts between 20-25 kts at KBLH dropping off to sustained
speeds near 10 kts in the coming hours. Brief westerly sundowner
winds are possible at KIPL. Otherwise, FEW to SCT mid to high
level clouds will prevail.
&&
.FIRE WEATHER...
Well above normal temperatures will continue through the remainder
of the week as scattered thunderstorms commonly develop over higher
terrain locations in the eastern districts. While isolated areas of
wetting rainfall are likely with these storms, the greatest impacts
will be gusty and erratic winds as well as the potential for new
ignitions from lightning strikes. Afternoon minimum humidity levels
will continue to fall into a 10-20% range following fair to good
overnight recovery of 25-50%. Periods of afternoon upslope gustiness
will also be common across all districts. A pattern shift with a
marked increase in moisture and thunderstorm chances will sweep into
the region over the weekend. Outside of the far western districts,
widespread wetting rainfall will be possible with potentially
repeated rounds of storms. This pattern shift will allow humidity
levels to moisten substantially while also tempering much of the
recent excessive heat.
&&
.CLIMATE...
Record High Temperatures:
PHOENIX YUMA EL CENTRO
July 27 118 (1995) 118 (1998) 118 (1934)
July 28 121 (1995) 124 (1995) 121 (1995)
July 29 115 (2020) 118 (1878) 115 (1954)
Active Streaks:
PHOENIX
1. Consecutive days of high temperatures 110F or greater: longest
on record at 28 days (previous record: 18 days in June 1974)
2. Consecutive days of no measurable precipitation: 4th longest on
record at 126 days
YUMA
1. Consecutive days of low temperatures 85F or greater: tied 4th
longest on record at 16 days
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Saturday for AZZ530-532-
534-537-538-540>544-546-548>551.
Heat Advisory until 8 PM MST Friday for AZZ557-558-563.
Excessive Heat Warning until 8 PM MST Friday for AZZ531-533-535-
536-539-545-547-552>556-559>562.
CA...Excessive Heat Warning until 8 PM PDT Saturday for CAZ563-
565>567-569-570.
Excessive Heat Warning until 8 PM PDT Friday for CAZ560>562-564-
568.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...18
AVIATION...Leffel
FIRE WEATHER...18
CLIMATE...Young