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FXUS63 KLSX 031943 AFDLSX

Area Forecast Discussion National Weather Service Saint Louis MO 243 PM CDT Tue Oct 3 2023

SHORT TERM
(Through Late Wednesday Night)
Issued at 236 PM CDT Tue Oct 3 2023

Key messages:

1) Confidence remains high (90-100%) for rain across the region late tonight through Thursday, with the best chances Wednesday night through Thursday. It will not be a complete washout as activity will be rather scattered for a majority of this period.

2) A secondary cold front will usher in much colder air Friday through Sunday. The coldest night will be Saturday night/Sunday morning with low-lying areas and small river valleys expecting low temperatures below 36F, so patchy frost is possible.

Tonight through Wednesday Night...

The upper level ridge overhead continues to weaken today as the deep trough over the western CONUS slowly slides to the east. The first in a series of shortwaves will lift northeast out of the base of the trough dragging a cold front towards the region. This front is associated with the main surface low centered over western Ontario.
In the meantime, southerly surface flow has picked up over the region with increasing low level moisture. Dewpoints will rise into the low to mid 60s ahead of the cold front. So with increasing moisture and cloud cover, lows tonight will be a bit milder, in the 60s, 10 to 20 degrees above normal for this time of year. As the shortwave approaches portions of central and northeast Missouri after 06z Wednesday, there will be enough moisture and lift for scattered showers to develop.

Through the day Wednesday, showers and storms will be on the increase as the cold front moves through. As for any severe chances Wednesday afternoon/evening, the latest HRRR is indicating mean CAPE values of around 500 J/kg over portions of central/northeast Missouri. However, mid level LRs are rather meager, between 5.5 and 6.5C/km as well as 0 to 6km bulk shear of 20 to 30 kts, so do not expect any severe weather at this time. When it comes to qpf amounts, despite PWs around 1.50 inches (90th climatological percentile), a majority of the forecast area will see less than half an inch of rain. Where storms develop, could see pockets of half inch or more per the latest LPMM.

Highs on Wednesday will remain above normal, but around 5 to 10 degrees lower than today's highs. Lows Wednesday night will be in the mid 50s to low 60s.

Byrd

LONG TERM
(Thursday through Next Tuesday)
Issued at 236 PM CDT Tue Oct 3 2023

Showers and storms will persist on Thursday, especially over portions of southeast Missouri and southwest/south central Illinois.
Localized rainfall totals up to 0.50 inches can be expected with this round of rain, but those who are not impacted by thunderstorms would see less.

As the cold front exits the region, the rain will taper off Thursday night. Since the CAA will lag behind the initial cold front, highs on Thursday will be in the 70s which is near normal for this time of year. Lows Thursday night will be in the upper 40s to mid 50s.

With strong cyclonic flow lingering across the central part of the country, a secondary cold front will slide south across the region on Friday. Even though moisture will be limited could see some spotty rain Friday afternoon through Friday night. Once this boundary moves through much colder air will filter in with temperatures well below normal through the weekend. The coldest night will be Saturday night with lows in the mid 30s to low 40s.
With a surface ridge building in across the region, expect clear skies and light winds, so with the cold temperatures, could see patchy frost, especially in low lying areas Saturday night/Sunday morning.

By early next week, surface ridge will begin to weaken and slide south, allowing moderating temperatures through the beginning of the work week. By Tuesday, highs will be near normal in the low to mid 70s.

Byrd

AVIATION
(For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1223 PM CDT Tue Oct 3 2023

Even with cold front approaching region by tonight, precipitation will hold off over central Missouri until 12z Wednesday. So VFR flight conditions through entire forecast period. Did add shower/vicinity shower mention after 12z Wednesday for KCOU, KJEF and KUIN. Otherwise, winds will remain around 10kts from the south, though should veer to the southwest at KUIN by 15z Wednesday.

Byrd

PRELIMINARY POINT TEMPS/POPS
Saint Louis 69 84 67 73 / 10 50 80 50 Quincy 68 79 62 75 / 20 50 50 20 Columbia 65 77 62 74 / 40 60 70 30 Jefferson City 66 78 63 75 / 40 70 70 30 Salem 64 84 64 71 / 0 30 80 70 Farmington 63 81 62 69 / 5 60 80 70

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

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