Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/23/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 847 PM CDT Fri Jul 22 2022

.UPDATE...
Issued at 847 PM CDT Fri Jul 22 2022

No changes planned to tonight`s forecast with the evening update.
Fairly widespread coverage of showers and thunderstorms still
expected across the CWA overnight with threat of locally heavy
rainfall and perhaps a localized flash flood threat, with a lesser
threat of strong to severe thunderstorms.

GOES-16 simple water vapor RGB early this evening nicely depicts
shortwave trough moving across northern Nebraska/southern South
Dakota. Ahead of this trough, evening soundings from ILX and DVN
confirm the SPC mesoanalysis depiction of a large reservoir of
steep lapse rates aloft across the Cornbelt and mid-Mississippi
Valley. Already saw some widely scattered highly elevated
convection develop across northern IL earlier this evening on the
periphery of this pool of very steep lapse rates. Significant
north-south oriented low level moisture gradient exists between
our CWA and central IA. Very dry low levels locally, with recent
ACARS soundings showing 925mb and 850mb dewpoints in the single
digits, while upstream evening RAOBs at DVN, OAX, and MPX showing
substantially more moist low level air mass.

As shortwave trough over the central Plains tracks east toward the
region tonight, should see 35-45kt west southwesterly low level
jet develop from the central plains east across Iowa and pointed
into northern IL/southern WI by later tonight. While the magnitude
of the low level jet is not expected to be off the charts, it will
be blowing orthogonal to the very sharp low level
moisture/theta-e gradient resulting in strong low level theta-e
advection overnight into northern IL and southern WI. This will be
taking place beneath the plume of steep lapse rates aloft, with
MUCAPE values near or just above 2000 j/kg overnight.

Forecast soundings generally show fairly modest shear in the cloud
bearing layer. Given the steep lapse rates, would anticipate a
threat for marginally severe hail with the initial convective
development tonight. Anticipate that the coverage of convection
will ramp up pretty quickly late this evening into the early
portions of the overnight hours. Dry air aloft and resultant DCAPE
should result in cold pool development as convective coverage
increases. Would anticipate MCS to become cold pool dominant given
the modest shear and with forward propogating Corfidi vectors
generally 20-25kt, a widespread damaging wind threat appears
unlikely. Certainly with the high DCAPE, more robust updraft could
produce some wet microbursts and perhaps isolated wind damage
threat. Overall severe threat overnight appears on the low end of
the spectrum, in line with SPC marginal (level 1 of 5) risk.

Finally, potential does exist for locally heavy rainfall and
perhaps some flash flooding later tonight especially as MCS likely
becomes more organized and low level jet veers more westerly and
resulting in shrinking Corfidi vectors and potential for upwind
development/propagation and perhaps some training, particularly
given the upstream moisture/instability that the low level jet
should continue to feed into the western flanks of the MCS. While
moisture and forcing appear sufficient to support a heavy
rainfall/local flash flood threat, none of the parameters are
really maxing out on the high end of the spectrum. PWATS are
forecast to reach 1.5-1.7 inches by late tonight, which is
sufficient for heavy rainfall, but not particularly noteworthy
for July in the Midwest. Given somewhat modest parameter space
we`re in for heavy rainfall, not planning a flash flood watch
tonight, despite some risk for heavy and potentially excessive
rainfall.

Biggest uncertainty at this point is exactly when and where
exactly convection will develop. Not surprisingly given its
elevated convection, there is some spread in the CAMs. At this
point, it will turn to more of a nowcasting issues and will be
closely monitoring satellite imagery this evening for signs of
blossoming ACCAS field. Given the expected orientation of the low
level jet and current satellite imagery, NE Iowa/southwest WI area
seems like a prime candidate for area of initial develop later
this evening, but confidence on precisely when/where is low. Once
convection develops and congeals into an MCS, would anticipate a
southeastward motion given the orientation of the instability
gradient.

Will freshen up forecast products, but no big changes anticipated
at this point.

- Izzi

&&

.SHORT TERM...
Issued at 254 PM CDT Fri Jul 22 2022

Through Saturday...

The main weather bullet points through Saturday afternoon consist
of:

* Increasing likelihood of shower and thunderstorm development
  tonight into Saturday morning.

* Associated threat of at least a localized flash flood and strong
  to severe wind gust threat overnight.

* Uncertain coverage of morning showers and embedded storms and
  subsequent impact on afternoon heat indices. Some potential for
  peak heat index readings near or in excess of 105 degrees during
  the afternoon.

Conditions are relatively tranquil across our forecast area early
this afternoon, and notably more comfortable than yesterday as
dewpoints have managed to mix out into the mid 50s and lower 60s.
Upstream, a very weak/subtle shortwave is translating across Iowa
along the northern periphery of an appreciably-steep zone of mid-
level lapse rates. This feature will push into northern Illinois
through late this afternoon and early evening. A dearth of low-
level moisture means we`re not expecting much in the way of
precipitation, but the presence of a little instability aloft
suggests there`s some potential for a few spits of light rain.
Can`t entirely discount a stray lightning strike if this activity
materializes, but thunder chances overall appear quite low.

Things should stay pretty quiet during the mid to late evening
across our forecast area, but attention will quickly be turning to
eastern Iowa as a stronger shortwave--currently pivoting out of
South Dakota--encourages an increase in the low-level mass
response. A 30-40 kt west to southwesterly low-level jet is
forecast to impinge upon the aforementioned lapse rate plume after
10-11 PM. While atmospheric moisture from an absolute perspective
isn`t terribly high with PWATs initially in the 1.5-1.7 inch
range, guidance does suggest these will climb more notably towards
2 inches late tonight and early Saturday morning. The character
of ascent via isentropic upglide is broad and at least modestly
strong--at times very strong--especially above the 305-310 K
theta surfaces. This suggests at least scattered convection should
have no trouble initiating to our north and west late this
evening before meandering east and southward within the mean flow.
The degree of initial sub-cloud dry air suggests at least some
propensity for any loosely-organized complex to attempt to develop
gusty outflow and surge a bit south and eastward which could help
limit the potential for net stationary/upwind propagating cells.
However, given the orientation of and persistence of warm and
moist upglide through the night, still concerned that regenerative
development will occur, leading to cells potentially tracking
over the same areas repeatedly leading rain totals stacking up
quickly.

In typical fashion, confidence in placing these mesoscale features
and any favored training zone is much too low to warrant hoisting
a flood watch, and it`s possible this threat remains somewhat
localized. As such, we will be highlighting the flooding potential
within graphics and our HWO.

Of additional note is the potential for some of these storms to
pose a localized damaging wind potential. Given the elevated
nature of convection, effective deep shear isn`t terribly high
(near 25-30 kts), but MUCAPE increasing to 2000-2500 J/kg and the
increasingly moist airmass indicates a potential for strong
precip-loaded downdrafts. Whether damaging gusts will be able to
make it through the stabilizing nocturnal boundary layer remains
to be seen, but with high-res guidance explicitly modeling severe
or near-severe wind gusts, think the potential for at least
isolated pockets of damaging winds exists even with the typically
unfavorable time of night.

How expansive rain and storms are into Saturday morning is a big
wildcard, with guidance that develops more expansive cold pools
shoving outflow well south and helping to scour things out a bit
more quickly. For some of the reasons indicated above, however, am
skeptical of the solutions that are totally dry as WAA/upglide
is forecast to persist through the morning hours and even into the
early-afternoon. For now, have smeared some low-end PoPs across
the forecast area through mid-afternoon. Deep layer shear will be
weakening (briefly) during the afternoon, but with additional
arriving boundary layer moisture, MUCAPE will build, so if
activity does indeed continue to fester Saturday afternoon, it`ll
need to be monitored for a gusty wind and continued flooding
threat.

Finally, while high temperatures remain a big wild card on
Saturday owing to the potential for expansive stratus and
rain/storms into the morning, there`s higher confidence in deeper
surface moisture arriving during the afternoon. If things scour
out more quickly than currently anticipated allowing air
temperatures to rise faster, heat indices will jump above 105
degrees, especially south of I-80. However, given the current
expectations of greatly delayed insolation, confidence is simply
too low to justify the issuance of a Heat Advisory. The current
gridded guidance will reflect a very brief period of 100-104
degree heat indices south and west of a Rockford to Joliet to
Rensselaer line for now.

Carlaw

&&

.LONG TERM...
Issued at 349 PM CDT Fri Jul 22 2022

Saturday night through Friday...

The primary concern beyond Saturday afternoon is the potential for
severe weather and flooding Saturday evening into Sunday. Thereafter,
additional rain and thunderstorms are expected to arrive towards the
middle of the upcoming workweek.

Saturday`s synoptic setup will initially feature a region of surface
low pressure over the Dakotas that will track northeastward into
Minnesota by Saturday afternoon and eventually reach the western
Great Lakes sometime Saturday evening. A cold front extending to the
southwest of the surface low will push eastward in tandem with the
low while a warm front will be draped off to its southeast, likely
moving northeastward through our CWA sometime around the early
evening after convection from earlier in the day staved off its
earlier attempted northeastward advances. An upper shortwave
trough currently located over the Pacific Northwest will zip
eastward into the Upper Midwest during the day on Saturday and
help foster convective development along the cold front. This
convection is expected to grow upscale into an MCS that will track
eastward and/or southeastward towards our longitude with a fair
likelihood that it could at least clip a portion of our CWA before
it weakens later in the night.

The main uncertainties with this probable MCS at this point revolve
around the exact track that it will take and where/when it will
start to weaken. While deep layer shear vectors will be oriented in
a more west-east direction where the core of the MCS is likely to
materialize and track through, Corfidi downshear propagation
vectors, cloud layer thickness gradient orientation, and the
presence of a northwest-southeast oriented warm front for convection
to ride along lead to concerns that at least part of the MCS will
take a more southeasterly path that will send it into at least
the northern portions of our CWA with an inherent damaging wind
threat. If the MCS does impact our CWA, it would likely not be
until after sunset, by which point, nocturnal stabilization will
be in the process of introducing an increasing amount of convective
inhibition with time that would be expected to weaken the MCS as
it progresses farther east and south into our CWA. However, a
burgeoning low-level jet could help offset the increasing
stability and allow for the severe thunderstorm threat to continue
deeper into the night given the continued presence of a robust
cold pool. All in all, the SPC`s Day 2 Convective Outlook is an
excellent reflection of our current overall thoughts on Saturday
night`s severe potential with the brunt of the severe threat
likely to remain to our north and northwest, the best chances for
severe weather to occur in our CWA being located in our
northernmost tier of counties along the Illinois-Wisconsin
stateline (where a Slight (level 2/5) Risk has been introduced
with the most recent outlook), and increasing uncertainty with
the sustainment of severe convection further south in our CWA
where the Marginal (level 1/5) Risk is present.

On top of the severe thunderstorm potential, there will also a
threat for at least localized flash flooding Saturday night into
Sunday. PWATs will be pushing 2 inches out ahead of the incoming
cold front and will support efficient downpours within any
thunderstorm that moves through our forecast area. General storm
motion is expected to be easterly or east-southeasterly beneath a
west-southwesterly low-level jet, so if the composite outflow
laid out by the MCS or other nocturnal convection in the area
takes on at least a somewhat west-east orientation, there is
concern that training convection could occur and lead to at least
localized flash flooding as the low-level jet continues to
regenerate convection overnight across our forecast area. This
would especially be true if storms train over wherever heavy rain
fell Friday night/Saturday morning. This flooding threat could
then persist into the daytime on Sunday, though would continue to
shift southward with time as the composite outflow boundary
continues to sink farther south. There is also a low potential for
a renewed severe weather threat Sunday afternoon with our
southeastern counties being most favored for that, though the
expected ongoing convection and associated cloud cover casts some
doubts as to whether we`ll be able to destabilize enough to get
robust convection to develop either along the leading outflow
boundary or the trailing cold front.

By Monday, the cold front should have sagged far enough south
where any precipitation traversing the frontal zone should remain
south of our CWA while high pressure moves over the Great Lakes. The
next shot at precipitation is expected to come towards the middle of
the week as a low pressure system deepens across southern Canada and
thrusts a cold front through the Midwest while also forcing the
baroclinic zone associated with the aforementioned front back
northward. The NBM currently advertises daily PoPs in at least
part of our CWA from Tuesday onward with the best precipitation
chances coming on Wednesday before things dry out behind the cold
front by the end of the week. While it`s plausible that rain
could be seen somewhere in our CWA each day during this period,
there is still a non-trivial spread amongst long range forecast
guidance regarding the exact timing of the mid-week cold frontal
passage and whether the baroclinic zone to our south will lift
into our CWA prior to the arrival of the cold front. Thus, refinements
to the going precipitation forecast for this upcoming week will
likely need to be made in the coming days as forecast trends
pertaining to the placement and timing of these frontal boundaries
become clearer.

Ogorek

&&

.AVIATION...
For the 00Z TAFs...

709 PM...Forecast concerns include...

Isolated thunderstorms early this evening.
Scattered thunderstorms early Saturday morning.
Chance of thunderstorms Saturday night.

Scattered showers and isolated thunderstorms have developed late
this afternoon as a weak upper wave moves across the area. This
activity is high based, 10kft or higher and moving along quickly.
Thunder is expected to stay isolated but opted to carry vicinity
thunder through 02z for the Chicago terminals. Possible this
activity will end prior to 02z.

Additional thunderstorms are expected to develop over eastern IA
and northwest IL late this evening and then spread southeast
across northern IL and the terminals during the early morning
hours on Saturday. Guidance remains in reasonable agreement for
thunderstorms to become fairly widespread for a few hours and
current timing seems on track. Some of this activity may be
strong, with wind gusts into the 30-40kt range along with very
heavy rain. Possible for both ifr vis and cigs where heavy rain
persists. There is some potential for scattered thunderstorms to
continue through mid morning Saturday but confidence remains low.
Maintained prob mention for now but its possible this time period
may end up being dry.

Saturday afternoon is looking mainly dry with additional
thunderstorm development possible mid/late Saturday evening.
Confidence is low for how much coverage and how strong this
activity will end up being. Added prob mention for later Saturday
evening in the ord/mdw tafs for now.

Generally south/southwest winds through the period, but there
could be short periods of southeast winds behind thunderstorms,
particularly Saturday morning. Some gusts into the 15-20kt range
are possible early this evening and again on Saturday. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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Area Forecast Discussion

National Weather Service Phoenix AZ

 440 PM MST Fri Jul 22 2022

.UPDATE...
Updated Aviation

.SYNOPSIS...
Chances for thunderstorms will be largely confined to higher terrain
areas of north/east/southeast Arizona today. Well above normal
temperatures will continue today with highs of 110 to 115 degrees
in Phoenix and the lower deserts along with moderate to high heat
risk. Moisture will begin to increase across the region this
weekend leading to slightly cooler temperatures as storm chances
gradually increase. Storm chances dramatically increase Sunday
into early next week with the potential for locally heavy
rainfall amounts across the area.

&&

.DISCUSSION...
Abnormally warm temperatures are in place, with the center of a
594 dm ridge over northwest Arizona. Highs today will have no
trouble rising into the 110-115 degree range, with widespread
moderate to high HeatRisk. Great moisture still remains in place
across the region, with spc mesoscale analysis showing
precipitable water values ranging from 1.2-1.8 inches. Latest
ACARS soundings still show a pretty capped environment due to
very warm temperatures aloft. Hi-res guidance still suggests
isolated to scattered storms will have no trouble developing
across the high terrain in north/east/southeast Arizona. DCAPE
values in these areas are still high, ranging around 1500-1800
J/kg. Thus, strong thunderstorm downbursts will be possible with
storms, especially across southern Gila county in our forecast
area, where there is a 50-70% chance of wind speeds exceeding 35
mph. Outflows from these high terrain storms will approach lower
deserts this evening, with indication that the southerly outflow
that moves in from southern Arizona would be the stronger one.
Thus blowing dust will also be a concern, especially across Pinal
county. There is about a 10-20% chance of storms redeveloping in
the Phoenix area, with higher amounts (20-30%), across northwest
Pinal and southern Maricopa counties. Any storm that develops
will be capable of producing heavy rainfall, with a 10% chance of
accumulations exceeding an inch in a 3-hour period across
southern Gila county. In addition, there is also at least a 5%
chance of rainfall exceeding flash flood guidance in southern Gila
county this afternoon and evening. As we’ve seen the past few
nights, there may be some lingering precipitation overnight into
tomorrow morning, mainly across western Maricopa county and
southwest Arizona.

High shifts east of the four corners region by tomorrow
afternoon, with south-southeast flow across our forecast area.
PWATS will be closer to 1.5-2.0 inches tomorrow and a little
better instability will develop across the lower deserts. It will
also help that heights aloft will be slightly cooler, so it
won’t take as much to get storms going in the lower deserts
tomorrow. The only wildcard will be the leftover cloud cover and
activity overnight into tomorrow morning and how quickly that will
be able to clear out. It still appears that we will have better
coverage of storms tomorrow across the high terrain
north/east/southeast of Phoenix. HREF showing outflows from all
directions intercepting somewhere around western Maricopa county.
This could be the area that see’s the best potential for storm
redevelopment in the lower deserts. However, if this interaction
occurs a little further to the east, the Phoenix area could have
the better potential. It will definitely be something we keep
assessing as we get closer to the event. Currently, the Phoenix
area has a 30-50% chance of seeing thunderstorm winds exceeding 35
mph, areas in northwest Pinal county have about a 50-70% chance.
Thus, blowing dust will also be more likely tomorrow. With better
moisture in place tomorrow, the HREF has about a 10-20% chance of
some of these cells producing over an inch of rain in an hour.
There is also the potential for activity to continue into the
overnight hours and last into the morning on Sunday. WPC has all
of Arizona at least under a marginal risk of flash flooding, with
southeast Arizona having a slight risk.

.PREVIOUS DISCUSSION...
Ensembles are bullish on an even more pronounced increase in
moisture for Sun and the early week period with PW forecast to
increase to ~1.9-2.1" during that period. The corresponding
chances of precipitation for Phoenix and the lower deserts will
increase from 30% on Sun to 60% for Monday, and up to 70% for the
high country. Even SE CA and SW AZ will see POPs of 20-40% through
that period. The favored WPC multiday QPF for the Phoenix metro
and the lower deserts from Sun night through Wed is ~0.75-1.15",
and near 1.4" for Globe. Locally heavy rainfall during the period
will increase the chances for at least some high country/burn scar
and urban flash flooding, especially for flash flood prone areas
such as low water crossings, underpasses and high country burn
scars.

With the increased moisture and storm chances, much cooler
temperatures are forecast for the region by Sun with below normal
highs of 100-101 degrees likely for Phoenix. Then for Mon-Wed
below normal highs will continue with mere double digit highs of
97-100 degrees for Phoenix on Mon and Tue. The chance of a high of
99 degrees or less for Phoenix by Mon is 47%. Clusters favor a
slight downtick in storm chances for the second half of the week
however the preferred NBM solution still maintains 20-30% chances
for Phoenix and the lower deserts during that time which is still
higher than both today`s and tomorrow`s chances of rain.

&&

.AVIATION...Updated 2339Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Timing wind shifts and issues from distant traveling outflow
boundaries will be the primary weather issues through Saturday
afternoon. Mid and high clouds decks will be common resulting from
leftover debris of storms. High confidence that west winds will
prevail thru the evening rush (04Z) with a few gusts as high as 20
kts possible as well thru 02Z. Confidence is low to moderate that at
least one outflow boundary will advance into the Phoenix area later
this evening/shortly after midnight, with the most likely direction
being from the south-southeast. At this point, wind gusts are
expected to be less then 25 kts. Chances of an actual storm
impacting any given aerodrome is less than 10%. Odds are around 25%
that multiple wind shifts between SE and SW could occur through the
late evening hours before settling on the typical easterly drainage
component later in the overnight hours.

As far as Saturday is concerned, a earlier-than-usual switch to
westerly is anticipated during the late morning hours with some
gustiness in the afternoon. Chances for convective activity look
better for Saturday evening, with chances of an actual storm
impacting any given aerodrome is rising up into the 30-40% range,
giving enough confidence to include VCTS in the KPHX TAF at this
time. Timing/strength of outflows still looks uncertain, with the
mid-evening (03-04Z) looking to be the most likely time for a wind
shift. CIGS on Saturday to remain mainly in the SCT-BKN range with
bases likely lowering into the 9-10k ft range during the
afternoonn/evening hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
Little to no weather issues will exist through the TAF period under
frequent periods of high cirrus cigs. Winds will be very similar to
the past couple days where S-SE directions are favored during the
day, then veering SW during the evening and overnight hours. Once
again, extended hours of light and variable winds will be likely
during the morning time frame.

&&

.FIRE WEATHER...
An upper level high pressure system and drier air will continue to
linger over AZ today and should limit storm chances to the eastern
Arizona high terrain well into Sat. Expect shower and thunderstorm
chances over the next couple of days to generally favor the E AZ
high terrain with up to a 40% CWR across far eastern Gila Cty by Sat
evening. Primary threats with thunderstorms will be lightning,
strong erratic outflow winds, and heavy downpours. Very warm
conditions will also persist with temperatures 4-9 degrees above
normal today. Expect minRH values of 12-17% across the lower deserts
to 19-24% over the high terrain today to improve to 18-24% and 24-
30% respectively by Sat. Starting late this weekend a dramatic
increase in moisture and in turn much better chances for showers and
thunderstorms, potentially widespread by Sun. Gusty winds, heavy
rainfall, and flooding will all become possible by Sunday across S-
Cent AZ and also extending into SW AZ and SE CA during Sun and Mon.
Temperatures will also trend lower starting tomorrow and RH levels
improve significantly starting Sun.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST this evening for
     AZZ530>544-546-548>551-553>555-559.

CA...Excessive Heat Warning until 8 PM PDT this evening for
     CAZ562>570.

&&

$$

DISCUSSION...Feldkircher
PREVIOUS DISCUSSION...Sawtelle
AVIATION...Percha/18
FIRE WEATHER...Sawtelle/Kuhlman