Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/24/19
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
918 PM CDT Tue Jul 23 2019
.UPDATE...
913 PM CDT
Shortwave driving out of WI is now moving into a more capped
environment with loss of daytime heating, but the better
colocation of the wave and slightly better moisture remains off
to our west with water vapor satelitte very dry in the low levels
over NE Illinois and NW Indiana. Therefore any showers would be
minimal this evening.
With high pressure nosing in some patchy fog is possible out west
though guidance is generally not hitting it very hard.
KMD
&&
.SHORT TERM...
216 PM CDT
Through Wednesday night...
Really can`t ask for a much better early afternoon for the end of
July. Temperatures are in the upper 70s and lower 80s across the
region with dewpoints mainly in the mid to upper 50s with a light
northwesterly breeze. A lake breeze continues to push steadily
westward at this hour, and this will ensure that immediate lake
side locales remain in the lower to mid 70s today.
A couple radar blips have appeared out of an area of more
congested Cumulus which stretches more-or-less along I-57 along an
axis of enhanced low-level instability. Through about 5 PM or so,
diurnally-enhanced PBL circulations and enhanced convergence in
the vicinity of the aforementioned lake breeze will be the main
forcing mechanisms for spotty showers and thunderstorms. As a
result, have confined PoPs through this afternoon along and west
of the lake breeze and nudged them up a bit near I-55/57 near the
more developed Cu field. While mesoanalysis currently shows
equilibrium temperatures under -40 C which would support
more widespread storm electrification, AMDAR soundings reveal the
subsidence inversion noted on 12z soundings is still present, with
a relative maxima in the thermal profile around 600 mb. This
"CAPE" robber will tend to limit diurnal gains in instability, so
don`t think we`ll see quite as much lightning activity as is
occurring across Michigan (where mid-level temperatures are
colder).
After 5 PM or so, a shortwave which can be seen clearly in upper-
level water vapor imagery across northern Wisconsin will begin to
scrape our CWA. This should allow an additional area of isolated
to scattered showers and storms to develop near another axis of
relatively maximized instability which is progged to develop
across south central and southwestern Wisconsin. This activity
should drift southward into our CWA through the early to mid-
evening hours. Have nudged PoPs up in the vicinity of Rockford to
account for this additional activity. If instability/moisture were
in greater supply, we`d be talking about more of a strong-severe
thunderstorm threat given roughly 35-40 kts of flow at 500 mb.
Given the dearth of instability today, we`re not expecting severe
weather, but some gustier winds to 40-50 mph can`t be ruled out
with any of the taller storms. Activity should gradually cease
through the mid-late evening hours.
For tonight, there`s a low potential for some patchy light fog
across our western counties, but given the rather dry low-level
airmass in place, opted not to add a mention to the official
forecast at this point.
Wednesday is shaping up to be another nice day as dry air lingers
across the region. Prevailing northeasterly winds off the lake
will keep the lakeshore once again in the mid 70s, while lower to
possibly mid 80s prevail inland. There will be a very low chance
for some showers or storms across our northwest in the afternoon
in the vicinity of another instability axis, but coverage is not
expected to be more than 15-20%.
Carlaw
&&
.LONG TERM...
216 PM CDT
Thursday through Tuesday...
Generally quiescent conditions are expected to prevail through most
of the long term portion of the forecast as temperatures gradually
warm back to near and above normal values over the weekend and into
next week.
Surface high pressure will begin to slide east of the region on
Thursday, and this will allow light southwesterly flow to return.
Moisture will take some time to slosh back into the area, however,
so Thursday and Friday are still shaping up to be pretty comfortable
days with dewpoints in the lower 60s with highs in the upper 80s to
near 90 degrees. The low-level flow should remain light enough on
Thursday to allow a lake breeze to sneak inland during the afternoon
hours, so we`ve cooled highs just a tad along the immediate lake
shore. By Friday afternoon, 20-25 kt winds just off the surface and
a tightening pressure gradient should preclude any lake breeze push.
The GFS has been producing some light QPF across portions of the
area on Friday afternoon ahead of a sharp mid-level shortwave.
Forcing for ascent from this next feature looks to remain displaced
well to our north, however, with persistent height rises through the
day. Forecast soundings depict a dry and warm subsident 850-600 mb
layer overhead as well, so we`ll continue to discount guidance
producing precipitation at this time and message a continued dry
forecast into Friday evening.
Breezy and warm conditions will be the rule over the weekend with
negligible precipitation chances. The next appreciable chances for
showers and thunderstorms looks to move in sometime during the
Sunday night-Tuesday timeframe as the next cold front sweeps through
the area.
Carlaw
&&
.AVIATION...
For the 00Z TAFs...
638 PM...Only forecast concern this period is a chance of showers
and possibly thunder...mainly west of the Chicago terminals this
evening and again Wednesday afternoon.
Scattered showers and thunderstorms across southwest WI will
continue to move generally southerly this evening and slowly
weaken after sunset. This activity will remain well west of the
Chicago terminals and may remain west of rfd as well. A few
showers are possible across eastern IL...south of the terminals
through sunset. There is another chance of isolated showers and
possibly a thunderstorm Wednesday afternoon...mainly west of the
Chicago terminals. Confidence is too low for mention at rfd with
this forecast.
Northeast winds east of the lake breeze will become light
northwest later this evening with winds possibly going light and
variable or even calm overnight. Winds will turn northeasterly for
the Chicago terminals Wednesday with a possible early lake breeze
but only medium confidence for timing. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO
Area Forecast Discussion
National Weather Service Phoenix AZ
835 PM MST Tue Jul 23 2019
.SYNOPSIS...
Expect storm development to continue over higher terrain
locations this afternoon, with activity gradually spreading into
the lower deserts. Locally heavy rain and areas of blowing dust
are possible. A Flash Flood Watch is in effect from 3 PM till
midnight for Maricopa, Pinal, and southern Gila county. High
pressure will slowly become centered over Arizona for a downtrend
in storm chances starting Wednesday. High temperatures will also
increase...especially during the latter half of the week.
&&
.DISCUSSION...
Convection continued to diminish as of 8 pm this evening across the
area; IR imagery depicted far less of the cold cloud tops that
dominate eastern Arizona yesterday evening and the main strong MCS
remaining is well south of the border in Mexico. Latest SCP
mesoanalysis graphic shows the MLCAPE over the lower deserts is
somewhat diminished, mostly 500 j/kg or less and wind shear is also
less than 24 hours ago. Effective bulk shear is southeast 20kt or
less with southeast winds only 10kt as shown by the latest 00z
Phoenix sounding. Due to diminishing convection, and after
collaboration with Tucson, decided to cancel the Flash Flood Watch
for tonight. So far we haven`t received any flash flood reports from
south central Arizona and any storms that re-develop tonight should
not produce sufficient areal coverage of heavy rain to support the
watch. Otherwise expect lots of debris clouds and some lingering
showers across mainly south central Arizona rest of tonight with an
isolated embedded storm possible mainly during the rest of the
evening hours.
.PREVIOUS DISCUSSION...
High pressure is centered over northwest Utah, with
east/southeasterly flow over the region. Moisture values are
exceptionally high, with Phoenix`s PWATs above the 90th percent
moving average. Earlier today, we were really relying on cloud
cover to thin out to maximize daytime heating and instability,
especially over the lower deserts. Phoenix`s convective
temperature today was 105 degrees, and since clouds eventually
did thin out, we`ve had no trouble warming up to 107 degrees and
we could possibly warm up a little more. With the high being
further north today, it`s been evident, even by looking at
aircraft sounding, that mid-level temperatures have cooled off a
bit, which will also aid in storm development today. As a result,
we currently see thunderstorms favoring the high terrain in south-
central Arizona and even in southeast California. We can expect
this coverage to continue to fill in today and tonight, and
possibly even continue into the early morning hours tomorrow
(primarily across southwest Arizona and southeast California early
tomorrow morning). With significant moisture in place, and very
slow storm motion, flooding will be the biggest impact today. Thus
we have issued a Flash Flood Watch for Maricopa, southern Gila,
and Pinal county from 3 PM till midnight tonight. The Flash Flood
Watch may be expanded westward if warranted.
Wednesday through Monday...
There is general model agreement that the storm activity over the
lower deserts trends down beginning Wednesday. This is due in large
part to an increase in stability caused by the the high becoming
centered over Arizona. That also decreases steering flow which
makes it harder for storms to advect from higher terrain. There
also looks to be a west to east decline of moisture with time. The
moisture doesn`t drop to nothing. In fact, 1000-700mb mean mixing
ratios don`t drop dramatically over most of Arizona. Thus, there
will still be higher terrain storms (mainly outside of our CWA).
With less storms and clouds, and the location of the high, max
temps will climb. At this time, it looks like we will remain below
Excessive Heat thresholds. Over the weekend, there are some
indications that the high center may shift westward a little bit
which would make for somewhat more favorable steering flow. It
remains to be seen. For now, have temps trending closer to normal
with "low grade" monsoon PoPs.
&&
.AVIATION...Updated at 0520 UTC
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Potential continues for another round of gusty easterly outflow
winds into the greater Phoenix area this evening. For now,
atmosphere seems a bit less unstable as compared to yesterday and
thunderstorms east/southeast of Phoenix have been slower to develop.
Still, for now we will continue to call for east/southeast winds up
to 25kt to move in by 03z-04z for the TAF sites. Confidence is not
as high as yesterday for either timing or strength of the winds.
Otherwise, look for isolated showers or storms to accompany, or
develop slightly after, the main outflows move in. After 06z tonight
will continue with -SHRA through much of the night, as considerable
mid/high cloud will overspread the area in association with a weak
disturbance rotating around the high. Look for BKN-OVC decks aoa 10k
feet after 06z tonight. Clearing to occur during the morning hours
with SCT-BKN mid and high decks lingering into the afternoon.
Chances for storms are there for Wednesday late afternoon or evening
but they will likely be more isolated and confidence in their
occurrence or timing is too low to mention in the TAFs for now.
Southeast California/Southwest Arizona including KIPL and KBLH:
Isolated convection will occur over the western deserts this evening
but due to low areal coverage, confidence too low to mention thunder
in the TAF sites. Will just go with SCT-BKN decks 8-12k feet and BKN-
OVC mid/high level decks overnight into the day on Wednesday. Winds
will favor the south next 24 hours at KBLH, and favor the southeast
at KIPL. Winds this evening may initially favor the west before
turning to the southeast later tonight. Speeds mostly less than
12kt.
Aviation Discussion not updated for amended TAFs.
&&
.FIRE WEATHER...
Friday through Tuesday:
Expect thunderstorms to be limited to the higher terrain of south-
central AZ. Max temperatures will climb to several degrees above
normal Friday and Saturday before beginning to trend down. Any
thunderstorms that manage to form will be very effective at
producing strong winds but with little wetting rain. With the
rising temperatures, minimum humidities decline as well but are
expected to remain well into the teens. Overnight recovery
declines some but remains at least fair (better over higher
terrain).
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
PREVIOUS DISCUSSION...CB
DISCUSSION...Hernandez/AJ
AVIATION...CB
FIRE WEATHER...AJ