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FXUS63 KLSX 291134 AFDLSX

Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 534 AM CST Wed Nov 29 2023

KEY MESSAGES

- A big temperature rebound will occur today with highs some 5 to 10+ degrees above normal.

- Widespread beneficial rainfall is still on track to impact the area Thursday into Friday morning. The potential for rainfall amounts of 1 inch or greater remains high (60-90%) across the southeast and east-central Missouri and southern Illinois.

- Periodic low rain chances (20-30%) persist from Saturday Night through Monday however confidence is low in anything actually occurring



SHORT TERM
(Through Tonight)
Issued at 157 AM CST Wed Nov 29 2023

Hang on because we are in store for a big temperature warm-up today. Heights aloft will be rising as the axis of the eastern U.S. long wave trof shifts further east over the Atlantic, and as short-wave ridging moves into the area from the Plains attendant with the upper low/trof digging into the West Coast. The passage of a surface trof to our east early this morning will result in deep west-southwesterly lower tropospheric flow and pronounced WAA. There will be an increase in high clouds later this afternoon, but the combo of the rising heights and a favorable WAA regime should result in highs some 5 to 10+ degrees above normal. Enjoy as this will be the last day with this degree of warmth for awhile (maybe late next week).

There have been only minor changes for our upcoming storm system and a widespread beneficial rain still is on track to impact the area Thursday through Friday morning. In general all of the guidance has shifted slightly further north with the surface low track, but there remains north-south spread in the position and track through northeast MO vs southeast MO.

Low level moisture return will commence tonight as a southwesterly LLJ takes shape, with the initial thrust of moisture through daybreak Thursday to our southwest centered across eastern OK/western AR into southeast KS and southwest MO.

Glass

LONG TERM
(Thursday through Next Tuesday)
Issued at 157 AM CST Wed Nov 29 2023

Rain is still expected to develop from SW-NE on Thursday morning in the vicinity of the I-44 corridor in response to increasing moisture transport and lift via the southwesterly LLJ. The coverage of rain should ramp-up during the afternoon along/south of I-70 as the low-mid level flow backs in response to the progression of the upper trof into the southern High Plains, resulting in strengthening and elongating low-level moisture convergence and forcing.

Widespread rain including bouts of moderate rainfall will be centered on Thursday night when forcing is greatest resulting from a well-developed warm conveyor belt (WCB), the translating mid- upper trof, and coupled ULJs. There may be just enough elevated instability for a rumble or two of thunder across the far southern CWA on Thursday night. The upper trof will deamplify and eject rapidly out of the area and into the Ohio Valley on Friday morning taking the forcing and rain shield with it, and thus by Friday afternoon the only lingering precipitation should be very light rain or drizzle. The low signal for any snowfall across northeast MO late Thursday night-Friday morning is even lower with this forecast cycle. The more northward track of the system has further diminished enough cold air, and now only 5% or so of the NBM membership has any accumulating snow and what is present is very light.

Southwest flow will persist Friday-Friday night and there is potential albeit low (20-30 percent) for some light precipitation Friday night across the far northern CWA with a weak fast-moving low-amplitude short wave. For the remainder of the weekend and into the first part of next week there is considerable deterministic model and ensemble variability with the position/timing and depth of a series of progressive upper trofs that could impact the area. This results in low predictability and low confidence in forecast details and any rain chances. The NBM probabilistic temperature data has the entire interquartile range above normal through the weekend, however the spread in the range increases early next week with the lower quartile near or slightly below normal.

Glass

AVIATION
(For the 12z TAFs through 12z Thursday Morning)
Issued at 531 AM CST Wed Nov 29 2023

VFR flight conditions are expected through the forecast period.

Glass

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

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