Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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791 FXUS63 KLSX 071700 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1100 AM CST Fri Nov 7 2025 .KEY MESSAGES... - After another warm day temperatures will start to cool Saturday before dropping dramatically Sunday and Monday. && .SHORT TERM... (Through Late Saturday Afternoon) Issued at 312 AM CST Fri Nov 7 2025 Showers and a thunderstorm or two have exited the area ahead of a cold front pushing into the region this morning. Morning mid-level water vapor imagery shows a large trough stretching from the Rockies to the East Coast, with shortwave pushing through the area this morning. The shortwave will help push the cold front across the CWA this morning, clearing out the overnight cloud over as dry air surges into the region in its wake. The mild post frontal air will have no impact on temperatures today. In fact, the warm start thanks to overnight southwesterly flow and cloud cover combined with another day of full sunshine will result in temperatures up to 5 degrees warmer today than yesterday. By Saturday the mid-level trough will be centered over the Hudson Bay, but its influence will continue to extend across the eastern 2/3 of the CONUS. A shortwave within the cyclonic flow will push into the forecast area Saturday, bringing a surface low east along I- 70 into the mid-Mississippi Valley. Moisture return ahead of this system will be largely limited, and the best moisture will be north of the forecast area. Any rain that falls from this system is expected to be light across the CWA, and probabilities of exceeding 0.10" of rain peak around 35% across the far northern CWA. Delia && .LONG TERM... (Saturday Night through Thursday) Issued at 312 AM CST Fri Nov 7 2025 The low will push east out of the forecast area overnight Saturday into Sunday and a very strong Arctic airmass will storm into the region behind. This will pull 850 mb temperatures into the negative low teens, near the 2.5 climatological percentile for this time of year. Confidence is high both in the strength of this airmass and the resulting surface temperatures with only 3 degrees of interquartile spread for highs Sunday and Monday, peaking in the upper 30s to low 40s areawide. Overnight lows will plummet into the upper teens to mid 20s, the coolest night we`ve seen so far this side of summer. While the low will exit the region before most of this Arctic airmass has taken hold of the forecast area, the NBM is keeping a smattering of slight chance PoPs lingering through Sunday. This is due to uncertainty in the strength of the deformation zone and low-res grid spacing with some of the global models. While I cannot rule out a spot of light rain, perhaps mixed with a snowflake or two, on Sunday from the deformation zone, no accumulation is expected and most will remain dry. By Tuesday the strong mid-level trough will lift into Quebec, while a ridge will stall over the West Coast. Subsequent northwesterly flow will establish over the central CONUS, while in the low-levels southwesterly flow will establish, advecting warm and dry air into the region along a low-level jet. This is a classic fire weather set up that will need to be watched for increasing fire danger. The cluster analysis shows the northwest flow hanging on across the region as we remain stuck between the ridge to the west and the exiting and weakening trough to the east. This will continue to leave the region open to shortwaves sliding down from Canada, resulting in uncertainty surrounding the surface flow. So while there is a clear warming trend into next work week back to near to above normal temperatures, the details of how warm remain uncertain. Delia && .AVIATION... (For the 18z TAFs through 18z Saturday Afternoon) Issued at 1059 AM CST Fri Nov 7 2025 West/northwest winds around 10 knots are expected through the afternoon. A few gusts to near 20 knots are expected at KUIN. Winds will subside this evening. A clear sky tonight will gradually give way to increasing mid/high level clouds late tonight into Saturday morning, but VFR conditions should prevail. Some light rain may move into northeast Missouri late Saturday morning, but the better rain chances hold off at KUIN until the afternoon. Gosselin && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX