Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/02/22

Area Forecast Discussion...Updated Aviation

National Weather Service Saint Louis MO

 1055 PM CDT Mon Aug 1 2022

.UPDATE...
Issued at 917 PM CDT Mon Aug 1 2022

I have done some refinement on POPs for the remainder of the night
and into the first part of Tuesday morning. A weak quasi-
stationary frontal boundary stretched from southwest IA across
northeast MO through west-central IL into south-central IL at 02z.
There hasn`t been much movement in the boundary this evening,
although it`s forecast to move northward overnight. Overall the
convergence along this stretch of the boundary is weak. That
seems to be a good part of the reason we can`t really get any
sustained convection despite an axis of 3500+ MLCAPE spanning the
frontal zone and weak capping. Across our far eastern CWA we are
getting some westward moving outflow from the storms to our east
and that has resulted in a few short-lived cells across Marion
County IL. I think this boundary will continue to be the focus
the rest of tonight. The severe threat, while not zero, appears
rather low. There would be a better threat of isolated heavy rain
if the aforementioned outflow in south-central IL could enhance
convergence and possibly promote some back-building.

I didn`t touch POPs much on Tuesday. Those were a reflection of a
potential remnant convective boundary from tonight and/or diurnal
heating.

Glass

&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 252 PM CDT Mon Aug 1 2022

Regional surface analysis drapes a cold front across the far
northern tier of Missouri counties and up through northern Illinois.
Ahead of it along the I-70 corridor, a remnant outflow boundary from
convection this morning is discernible but quite diffuse as
compared to earlier in the day. Dewpoints across the region are
uniformly in the low/mid-70s, with some pooling evident near the
baroclinic zone. The hot and humid conditions in the boundary
layer resulted in MLCAPE around 4000J/kg near the front, with
lower but still impressive values to the south across the CWA.
Aloft, northwest flow across the Mid-Mississippi Valley is
allowing for subtle shortwave impulses to enter the bi-state area.

As low-level lapse rates steepen, it is expected that the weakening
inversion currently in place will erode to some extent. This is
already evident in latest ACARS soundings from KSTL, but recently
MLCIN was observed to be increasing (perhaps a function of height
rises/thermal ridge building). The question of how much the
inversion erodes is still uncertain, and will have impacts on the
extent of CI and longevity of the threat for strong to severe storms
this afternoon and evening. Some CAMs depict an uncapped atmosphere
with robust convection by 22-23Z along the MLCAPE gradient near the
Mississippi River, others only have isolated convection developing
amidst a stronger inversion. Given the strength of the inversion
currently in place and the lack of appreciable upper-level
support, this forecast favors the less-robust solution. However,
if convection can escape the inversion, it will be in a favorable
environment for strong/low-end severe wind damage. The most likely
timeframe for this would be from roughly 22Z-04Z. Again, the
coverage of such storms would be widely-scattered at the worst and
with deep-layer shear values of roughly 30kts, organized long-
lived thunderstorms are unlikely.

Convective activity will likely wane overnight with the loss of
mixed-layer/surface-based instability, though an MCS looks poised to
develop overnight in Iowa on the nose of a strengthening low-level
jet across the Great Plains. While this convection will likely miss
us to the northeast, an outflow boundary that lays across the region
during the morning will serve as a potential focal point for
thunderstorms to redevelop Tuesday afternoon. The predominant threat
will likely be along and south of I-70, but that can change if the
boundary`s location shifts. While instability will still be more
than sufficient for thunderstorms to develop, shear will be weaker
than it will be this evening which should preclude severe
thunderstorms in our CWA. The SPC Day 2 Marginal Risk does clip our
southeast counties, but we are opting not to message this given the
uncertain severe potential and very limited spatial extent.

Finally, regarding the ongoing Heat Advisory: heat index values
reached or exceeded 105F for most within the current product mainly
due to higher humidity. The trick for Tuesday will be how much cloud
cover and convection will occur, which will impact temperatures and
may preclude us from reaching dangerous heat and humidity tomorrow.
However, there is not enough evidence to suggest canceling the
Heat Advisory, especially in the face of higher probabilities of
seeing dangerous heat and humidity Wednesday.

MRB

.LONG TERM...  (Wednesday through Next Monday)
Issued at 252 PM CDT Mon Aug 1 2022

Attention in the extended forecast surrounds the dangerous heat and
humidity likely on Wednesday, though there is some lingering
potential that convective activity will act to limit temperatures
during the day on Wednesday. Rain appears likely along a cold front
late Wednesday through Thursday, which will usher in a break in the
heat to end the work week. Temperatures are on the rise for the
weekend, but there is some question into how hot we get.

Cluster analysis of the ensemble guidance members shows uniform
agreement on an amplified low-level thermal ridge impinging on the
Mid-Mississippi Valley on Wednesday, particularly across western and
central Missouri. However, it also shows a more muted upper-level
ridge with shortwaves propagating around the feature. Those impulses
may act to stimulate some convection ahead of an advancing cold
front during the day on Wednesday, but looking at ensemble QPF
probabilities and the synoptic pattern it appears that most
precipitation will be tied closer to the front itself. Nevertheless,
any cloud cover from precipitation ongoing north of the region may
act to keep temperatures in the mid-90s as opposed to the upper 90s.
Even a more conservative forecast for temperatures, coupled with dew
points forecast to exceed the mid-70s, would bring heat index values
over 105F. As such, the going Heat Advisory that is set to expire
Wednesday evening appears on track.

Widespread rain is still forecast to impact the region later
Wednesday into Thursday. Ensemble and deterministic guidance shows a
trough drop south through the Ohio River Valley, with the resultant
PVA being sufficient to force precipitation along a surface cold
front. NAEFS precipitable water values fall within the 97th
climatological percentile, indicating a notable amount of moisture
available to the forcing. However, the precipitation should be
fairly progressive given Corfidi vectors perpendicular to the
forcing. While there is some indication in the ensemble guidance of
upwards of 1.50in of rain over a 6-hour period. Even so, the
progressive nature of the storms will likely keep flooding concerns
minimal.

The front that drops across the region will suppress temperatures
notably (mid/upper 80s for highs across most of the area) Thursday
and Friday, but the humidity will stay elevated and keep conditions
rather uncomfortable but not dangerous. By the weekend, the ridge
across the western CONUS builds back into the center of the nation.
However, subtle differences in the strength and location of the
ridge are evident in the cluster analyses that bring some
uncertainty to how hot we will get. Like this week, the hottest
temperatures appear more likely across the northern Great Plains and
Upper Mississippi Valley where a more intense low-level thermal
ridge is forecast. For us, if a less-amplified ridge ends up
developing, our 850mb temperatures (and thus surface temperatures)
will be slightly closer to normal (low 90s). If a stronger, more
amplified ridge develops we could see temperatures 5-10F above
normal. The heat may break to start the next work week, but stark
differences in the upper-level flow pattern are evident in the
guidance that leaves the door open for the hot weather to persist.

MRB

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1051 PM CDT Mon Aug 1 2022

A weak front remains draped across northeast MO and west central
and south central IL. I still think if we see storms overnight
then they should be focused in the vicinity of the boundary. The
only terminal then that could be impacted would be KUIN. However
confidence is low on the coverage or even occurence of any storms.
With this in mind I have kept the new KUIN TAF free of any
mention of SHRA or TSRA. Elsewhere predominately VFR flight
conditions are expected through the forecast period.

Glass

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 8 PM CDT Wednesday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Pike MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

IL...Heat Advisory until 8 PM CDT Wednesday for Bond IL-Calhoun IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Randolph IL-
     Saint Clair-Washington IL.

&&

$$

WFO LSX