Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 131746
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1246 PM CDT Sat Aug 13 2022

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 301 AM CDT Sat Aug 13 2022

We continue in a pattern of northwest flow aloft between a western
ridge and an eastern trough. At the surface, high pressure is
sliding east through the eastern Great Lakes with its axis
lingering through the Ohio Valley. Low pressure associated with an
initial shortwave trough within the northwesterly flow is located
in southern Minnesota with a cold front dragging behind it through
Nebraska. This low and cold front make slow progress southeast
today, with the low level flow in our area turning to the south
initially around the high, and then to the southwest as the front
approaches. We`ll see a return of much warmer and more humid air
moving into the area today on that southerly flow. Highs will
range from the mid 80s to the low 90s, with the hottest
temperatures expected in the west, closer to the upper ridge.
Moisture pools ahead of the front across northern Missouri into
western Illinois where dewpoints rise into the upper 60s. Although
we do develop some instability this afternoon, warm air aloft
pulled eastward ahead of the front will serve as an effective
cap, preventing any showers or thunderstorms from developing.

As the surface low tracks through central and northern Illinois
tonight into Sunday, the cold front will drop southeast behind it,
crossing through our area. There still remains some disagreement
in the models on the timing of this front, with the GFS the
slowest. But even the slow GFS has trended toward the faster
solutions. This faster front will bring in the cooler air quicker,
with less of our area experiencing the warm sector heat again on
Sunday. Again we`ll see some moderate to strong instability ahead
of the front, but warm air aloft will cap any attempts at shower
or thunderstorm development. This will be a dry frontal passage.

Kimble

.LONG TERM...  (Sunday Night through Friday)
Issued at 301 AM CDT Sat Aug 13 2022

While the front continues pushing south behind the departing low,
its progress will slow on the western side as southerly flow
strengthens in the plains ahead of the next developing low in the
lee of the Colorado Rockies. It will settle into a position
roughly from eastern Kansas to southeast Arkansas by late Monday,
leaving our area fully in the cooler air mass. With a fair amount
of mid and high level clouds as well, we`ll see a somewhat cool
late summer day with highs only in the mid 80s.

This next low will nudge southeastward Monday night into Tuesday
in response to the next shortwave trough aloft dropping through
the northwesterly flow. A low level jet develops ahead of it,
pushing a moist low level flow toward and over the boundary.
Showers and possibly some thunderstorms initially develop over
Nebraska and northwest Missouri, tracking southeast into central
and southern Missouri Tuesday morning. This will be our best
chance of rain this week, and it could be a beneficial soaking for
areas still plagued by drought. The axis of precipitation lines
up roughly along the 850MB front which will be displaced into the
cool side of the boundary. An axis of 0.5 to 2.0 inches is likely
to fall in about 12 or so hours. More would be possible if there
were better instability available. Although there is good
agreement among the models, there is still some uncertainty on
where the axis of heaviest precipitation will fall. The GFS is the
furthest east with it in part because of the lingering effects of
its slower frontal push on Sunday. Overall confidence has
increased that rain will occur, but we`ve shifted the axis of
heaviest rainfall a bit to the west in line with the blend of
available guidance. Our westernmost forecast area has the best
chance to see substantial rainfall on Tuesday. With clouds and
rain around, temperatures will be cool by late summer standards,
topping out only in the mid to upper 70s depending on whether the
sun comes out at all.

Another round of convection is expected to develop Tuesday evening
as the low level jet ramps up again. This time, the convection is
expected to begin in southeast Kansas or southwest Missouri,
tracking southeast from there. Our area is less likely to be
affected by this as the steering flow should push this southeast
into Arkansas through Wednesday morning. We still have some PoP
extending into the western part of our area during this time
period in case this axis shifts east, but the trend is further
southwest.

Broad high pressure builds in from the north Wednesday and
Thursday bringing a couple of nice weather days. With the cooler
air mass, we`ll see highs only in the low 80s even with a good
amount of sunshine.

Beyond this, there`s still a lot of uncertainty on the strength
and track of the next trough dropping southeast through the
northwest flow. Depending on how this evolves, it could send the
next cold front through our area as early as Friday, although
again there`s a good deal of uncertainty on the timing of this.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1241 PM CDT Sat Aug 13 2022

A low impact, VFR forecast will persist through the period. The
only item to note is a cold front that will drift into the region
from the north tonight. The front arrives at KUIN around 03z-04z,
slowly moving through the remainder of the terminals Sunday
morning between 12z and 16z. Other than and occasional gust at
KUIN this afternoon, winds remain light as they veer behind the
front tonight into Sunday.

Maples

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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