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FXUS63 KLSX 092353 AFDLSX

Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 553 PM CST Sat Dec 9 2023

KEY MESSAGES

- While tomorrow will feature slightly below average temperatures, dry conditions and seasonable temperatures can be expected for much of the work week.

- A limited potential for precipitation exists over the weekend, but confidence remains low regarding timing and amounts.



SHORT TERM
(Through Late Sunday Night)
Issued at 209 PM CST Sat Dec 9 2023

Generally quiet conditions have developed across the area this afternoon as a cold front has completely moved to our southeast.
While severe thunderstorms are on going along and south of this boundary and out of this particular area, conditions behind the front are much more tranquil, with only gusty west to northwesterly winds reaching near 30 mph at times. Skies have also cleared in much of the area, although a shield of broken stratocumulus is gradually approaching from the northwest, and will keep much of the area under a broken ceiling for much of the night. Quiet conditions are also expected to persist through the night, with a slight reduction in wind gust speeds expected by morning.

Meanwhile, a broad upper trough will continue to dig southeastward tonight and into tomorrow, and this will reinforce a noticeably cooler airmass than what has been in place in recent days. In spite of this, significant cold anomalies are not expected, meaning that temperatures will likely settle only a few degrees below seasonal averages tomorrow afternoon...generally ranging from morning lows in the mid 20s to near the freezing mark, to afternoon maximums in the upper 30s to mid 40s. Dry conditions will also persist, and winds will become nearly calm by late afternoon/early evening as surface high pressure moves directly overhead.

BRC

LONG TERM
(Monday through Next Saturday)
Issued at 209 PM CST Sat Dec 9 2023

As we head into the work week, very few potential weather impacts and any real consequence can be expected thanks to a prolonged dry pattern. Dry northwesterly flow will remain in place Monday, and will gradually transition into a zonal flow. Meanwhile, a large area of surface high pressure will remain locked across the southeastern U.S. for most of the work week, keeping rich moisture and precipitation locked across the Gulf coast and farther south.

As a result, while there will be some minor temperature and sky cover variations from day-to-day, Monday through Friday will feature dry conditions and temperatures within a few degrees of seasonal averages. The resumption of southerly surface flow will allow temperatures to rebound to near average on Monday, but a backdoor cold front is likely to cool at least parts of the area Tuesday and possibly Wednesday as well. This feature is resulting in slightly reduced confidence in the temperature forecast around mid-week (and increasing spread among ensemble members), but overall, this is expected to amount to only a few degrees, and in the grand scheme of things is not particularly impactful either way.

The next opportunity for precipitation appears to arrive sometime over the weekend, potentially as early as Friday night. However, there is significantly reduced forecast confidence Saturday onward.
At issue here is the previously mentioned shortwave digging into the Mountain West, which is being depicted with a high degree of variability across ensemble members. This is not terribly surprising as this feature is dynamically weak, and may become almost completely cut off from the polar jet stream and undercut a building ridge. In short, what this means is that there is little confidence regarding exactly when this feature will move eastward and impact our local area, and exactly what track it will take. Not only this, but it remains to be seen whether this feature can tap into Gulf moisture, which may still be locked to our south by the weekend.

In spite of all of these mitigating factors, this still represents the next reasonable opportunity for our area to receive ANY measurable precipitation, even if the potential for meaningful amounts is low. NBM precipitation probabilities for Saturday and Sunday generally range from 20 to 30 percent, and considering all of the factors listed above, we do not see much evidence to support increasing those probabilities at this time. In fact, there is still a reasonable chance that much of the area will remain dry through the weekend as well. Meanwhile, current temperature projections suggest that frozen precipitation chances are also quite low.

BRC

AVIATION
(For the 00z TAFs through 00z Sunday Evening)
Issued at 550 PM CST Sat Dec 9 2023

An area of low range VFR clouds has moved out of IA and into much of MO and IL this evening. This will continue to rotate through our region overnight with conditions likely remaining VFR at most sites. More northern areas like Quincy have the best potential for high end MVFR conditions overnight. Clouds clear out from west to east during the morning hours on Sunday. Winds remain out of the northwest through the period, gradually decreasing in intensity especially by Sunday morning.

Kimble

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

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