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FXUS63 KLSX 301141 AFDLSX

Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 541 AM CST Thu Nov 30 2023

KEY MESSAGES

- Widespread beneficial rain remains on track starting this morning and ending on Friday morning. Everyone should see storm totals from 0.75 to 1.00 inches, and there is high potential (50-90%) for amounts in excess of one inch for all but northeast Missouri.

- There remains a good deal of forecast uncertainty this weekend into the first part of next week. There could be a couple of light precipitation events during this time frame but the pattern features low predictability. There is greater confidence that temperatures during this time frame will be near to above normal.



SHORT TERM
(Through Late Friday Afternoon)
Issued at 222 AM CST Thu Nov 30 2023

Our anticipated widespread beneficial rainfall event remains on track and overall there have been only minor changes to the previous forecast.

The southern stream upper low/trof was located near the Four Corners early this morning with lead vort max just south of Wichita, and a series of attendant surface lows strung out from southeast KS into northern NM. Moisture return is underway across TX into southern OK and the latest SPC mesoanalysis has 850 mb dew points of 6-8 degC into south central OK within the axis of the LLJ. Rain/showers are still on track to develop later this morning, generally centered along or just south of the I-44 corridor, in response to the increasing southwesterly LLJ and the associated lift and northeastward moisture transport, and also ascent with the aforementioned migratory vort max. The rain coverage will ramp-up during the afternoon from the I-70 corridor southward in response to backing low-mid level flow and attendant strengthening and elongating low-level moisture convergence and forcing.

Rain will advance northward this evening and become widespread across the entire CWA as forcing maximizes in association with the northeastward ejecting upper low/trof, a well-developed warm conveyor belt (WCB), and coupled ULJs. At times this afternoon and tonight, there are hints at some weak elevated instability with 800 mb and 750 mb LI's flirting near zero, thus an occasional rumble of thunder is certainly possible but the probability and longevity is not great enough to include within the forecast. The weakening southern stream upper low is forecast to be in the vicinity of SE IA/NE MO by 12z Friday with the negatively tilted trof axis along or east of the MS River, with the upper trof weakening significantly as it ejects northeastward into the lower Great Lakes/Ohio Valley region by midday. This progression will quickly shift any residual forcing and more continuous rain out of the area during the morning. Pockets of light rain/drizzle could persist into the afternoon and actually increase during the later part of the afternoon in association with another trailing compact vort max tracking through northeast MO in the southwest flow aloft.

One of the trends in the latest guidance is more clustering around a northern surface/850 mb low track from central through northeast MO, which also keeps temperatures warmer across northeast MO where we have been eyeing any potential for wintry precipitation late Thursday night/Friday morning. Present indications are temps of 32F or less will remain well north of the CWA and thus there is no longer any mention of light snow or freezing rain. The already low NBM probabilities of the last few days are even lower this cycle with no membership showing any potential within the CWA.

Rainfall potential with this system is solidly showing the entire area will see from 0.75 to 1.00 inches and there is a 50-90% chance of greater than 1 inch. The highest probabilities for 1+ inches is centered in a zone from Columbia/Jefferson City through Troy MO to near Taylorville IL, and the HRRR PPM/LPPM data suggests there could be some local totals of 1.5-2.00 inches in this area. This evening and into the first part of the overnight period could feature periods of moderate-heavy rain.

Glass

LONG TERM
(Friday Night through Wednesday)
Issued at 222 AM CST Thu Nov 30 2023

The aforementioned compact vort max across northeast MO will quickly exit during Friday evening, but could bring some light precipitation to the northern CWA where we have low POPs (20-30 percent). We will have to watch the availability of cold air during the evening to support some light snow but currently the NBM probabilities are below 10% for anything.

While there is general agreement in the ensembles in the evolution of the large scale pattern this weekend into next week, there remain some notable enough differences in the depth/timing of a progressive upper trof late Saturday night into Sunday, and another Sunday night into early Monday. These differences signal low predictability in the pattern, and as a result its debatable whether we will see any light precipitation as well as the ptype due to differences in position of deeper cold air. The NBM probabilistic temperature data indicate the interquartile spread is near to above normal for the period from the weekend through next Wednesday.

Glass

AVIATION
(For the 12z TAFs through 12z Friday Morning)
Issued at 535 AM CST Thu Nov 30 2023

Stratus currently across NE OK/SE KS/SW MO will spread to the northeast this morning resulting in first VFR cigs from 4000-6000 FT, with cigs lowering to MVFR late morning-early afternoon, and then IFR this evening. Rain/showers will develop across southern MO and into southwest Illinois this morning, spreading north and northeast this afternoon and then becoming widespread this evening. The TAFS reflect these trends with deteriorating flight conditions this afternoon and evening.

Glass

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

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