668 FXUS63 KLSX 051731 AFDLSXArea Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1231 PM CDT Fri Sep 5 2025
.KEY MESSAGES...
- Cloudy and mild conditions can be expected today as a cold front moves through the area, with intermittent light rain possible.
- Mild and dry conditions will persist through Monday, with a steady warm up expected through the work week.
- Very little opportunity for meaningful rain exists for the next week.
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.SHORT TERM... (Through Late Saturday Afternoon) Issued at 318 AM CDT Fri Sep 5 2025
The primary item of interest today and tomorrow continues to be a slowly progressing cold front, which will usher in both cooler temperatures and a limited opportunity for some light rain.
As we start the morning, the aforementioned cold front is located across northwest Missouri and southern Iowa, with a more diffuse remnant surface front much farther south across Arkansas. Over the course of the morning, a subtle shortwave will pivot around the base of a much larger synoptic trough across the upper great lakes and Ontario, which will both add some mid and upper level frontogenesis and help to drive the cold front south through the morning. While forcing will increase through the day today, precipitation will be battling progressively drier air in the low levels, so much so that any precipitation that does manage to work it`s way through this layer is likely to be very light. We will likely see steady cloud cover through the day and plenty of virga, but with 6-8k ft cloud bases and very little elevated instability, it will be difficult to produce accumulating rain aside from a few pockets here and there.
Later in the evening, another shortwave will pivot around the base of the trough, and we`ll also likely see a resurgence of mid-level moisture ahead of this feature. As this shortwave moves through, a reinforcing shot of cooler air will finally drive the surface front completely through the area this evening overnight, producing an increase in low-level convergence as it does so. The combination of these factors should help to push more precipitation through the dry low levels and to the surface later in the evening, but mainly across southeast Missouri and southwest Illinois.
Given all of the above, it`s difficult to see a scenario that results in widespread accumulating precipitation. What`s more likely is that most areas will see a cloudy day, with perhaps a few brief periods of light rain that doesn`t amount to much more than a few hundredths of an inch. This is most likely along and south of I-70. Meanwhile, temperatures will be highly variable, with highs only likely to reach the upper 60s to mid 70s along and north of the I-44 corridor, to perhaps near 80 degrees across southeast Missouri and southwest Illinois.
BRC
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.LONG TERM... (Saturday Night through Thursday) Issued at 318 AM CDT Fri Sep 5 2025
Behind today`s cold front, a large surface high will steadily build into the region and remain in the area through the weekend and into early next week. This will lead to a rather non-descript period featuring mild temperatures and minimal chances for precipitation. From Saturday through Monday, confidence is quite high that we will see afternoon temperatures topping out in the mid 70s to near 80 degrees, with a slight upward turn as early as Monday. This is roughly 5 to 10 degrees below seasonal averages for early September, and these comfortable temperatures will also be accompanied by low humidity. In other words, it should be a great weekend to head outside.
Over the course of the work week, mid and long range ensemble guidance continues to project that an upper level ridge will steadily build and southerly flow will resume across the central Plains. Both of these factors will almost certainly lead to a steady warming trend across our area, in spite of the fact that the the axis of the upper ridge will likely remain to our west throughout the forecast period. While confidence is high that a warming trend is on the way, there remains some uncertainty regarding both how quickly we will warm up and the upper-end potential, primarily due to continued variance in the upper flow pattern evolution among ensemble members. In spite of this, NBM guidance suggests that there is a greater than 50% chance that we will climb back above normal (roughly 85 degrees) by Wednesday, increasing to 70+% by the end of the work week, and maximum temperature forecast spreads have shrunk to 5 degrees or less throughout this period.
Meanwhile, precipitation chances remain rather low throughout the extended period. We do see a very slight increase in precipitation- producing members late Tuesday through the end of the week as more moisture-rich southerly flow inches eastward, but these solutions remain firmly in the minority. As such, our extended stretch of mostly dry weather appears much more likely than not to continue for the next week.
BRC
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.AVIATION... (For the 18z TAFs through 18z Saturday Afternoon) Issued at 1225 PM CDT Fri Sep 5 2025
VFR flight conditions are expected to prevail through Saturday morning. Intermittent light rain will be possible along and south of I-70 mainly late this afternoon and this evening. Rain is not expected to be heavy enough to affect flight conditions, but could reduce braking action at times. Rain will likely linger across the eastern Ozarks overnight, and could become heavy enough to impact ceilings/visibilities intermittently.
Carney
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.LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. &&
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WFO LSX
NWS LSX Office Area Forecast Discussion