Sunrise 6:07 AM   Sunset 7:49 PM Moonrise 9:00 PM   Moonset 5:48 AM

  Print   HELP   Reset   Save   Recall

FXUS63 KLSX 250259 AFDLSX

Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 959 PM CDT Wed Apr 24 2024

KEY MESSAGES

-Multiple rounds of showers and thunderstorms can be expected between late Thursday and late Sunday, with widespread rainfall expected and at least some potential for strong/severe storms.

-Strong/severe thunderstorms will also be possible at various times within this timeframe, with a slight preference for Friday afternoon/evening, late Saturday night, and Sunday/afternoon evening. Confidence remains low regarding this potential.

-Well above normal temperatures can be expected Friday through Sunday.



SHORT TERM
(Through Late Thursday Night)
Issued at 235 PM CDT Wed Apr 24 2024

Quiet conditions have returned to the region in the wake of yesterday's cold front and associated round of showers, with temperatures rising into the mid 60s to near 70 degrees this afternoon and only some scattered afternoon cumulus standing in the way of clear skies. This will largely continue through the overnight hours, with perhaps some increasing cirrus cover towards daybreak.
Patchy fog is also likely to redevelop in Ozark valleys that can remain sheltered from the wind, but this is not expected to be particularly widespread.

By tomorrow morning, winds will switch to the southeast and steadily increase in response to lee cyclogenesis across the central High Plains. While this will be discussed in greater detail during the long term discussion to follow, the effect on local sensible weather during the day tomorrow will simply be slightly increasing breezy southeast winds. Temperatures tomorrow are also expected to be rather similar to today, ranging from the mid 60s to near 70.

BRC

LONG TERM
(Friday through Next Wednesday)
Issued at 235 PM CDT Wed Apr 24 2024

While benign conditions will persist through at least tomorrow afternoon, a major pattern change will bring significant changes to the area between late tomorrow and late Sunday.

The primary driver of this change will be the development of a longwave trough across the western U.S. Thursday, which in itself will be constructed of two distinct shortwaves that will pivot into the central plains one after the other between late Thursday and Sunday. These waves will each drive lee cyclogenesis across the high plains, and the resulting low pressure systems will each move from southwest to northeast and into the upper Midwest, the first between Thursday night and Friday, and the second between Saturday night and Sunday. Meanwhile, persistent southerly flow with a largely uninterrupted trajectory from the Gulf of Mexico will transport an increasingly moist and unstable airmass into the central plains, setting the stage for several rounds of showers and thunderstorms across the region.

While confidence is high that this pattern will surely produce multiple rounds of showers and thunderstorms locally, with at least some potential for strong or severe storms at times, confidence remains low regarding the latter potential. On a regional scale this pattern is almost certain to produce severe thunderstorms, but the St. Louis forecast area remains slightly removed from what appears to be the greatest threat area for the majority of the Thursday/Sunday timeframe, with considerable timing uncertainties and additional complexities inherent with multi-day events that complicate this forecast. At this stage, it remains a bit early to get into too much detail regarding the timing of each individual round, but they can be roughly separated into five semi-coherent rounds:

1. Remnant showers and a few thunderstorms traversing a stalled front Thursday evening across the Ozarks.

2. Redeveloping showers as the stalled front lifts northward across the area overnight Thursday and early Friday.

3. Potentially stronger surface-based thunderstorms developing Friday afternoon and persisting through the evening and overnight hours.

4. Additional thunderstorms late Saturday and Sunday morning, again with the potential to be strong or severe.

5. The final round of showers and storms potentially along an advancing cold front sometime between Sunday afternoon and evening, again with the potential for strong or severe storms.

Each successive round will be impacted by how its predecessor evolves, and as such, confidence in the potential for each round steadily decreases. Specifically regarding the potential for strong or severe storms, strong southwesterly flow aloft will maintain a sufficiently sheared environment to produce organized thunderstorms, particularly as stronger jet streaks move through the area. What is less certain will be the available day-to-day instability, as the deepest moisture will likely remain to our west until Sunday, and highly variable cloud cover and morning showers will have a significant impact on daytime destabilization. However, there is a slight preference for Friday afternoon/evening and Sunday afternoon/ evening, due to the presence of stronger southwesterly flow aloft as the primary jet streaks traverse the area. This increases the potential ceiling during these timeframes, should we achieve sufficient destabilization. In addition, all severe hazards will be in play at various times, including wind, hail, and tornadoes. Not to mention, widespread soaking rainfall can be expected between Thursday and Sunday, regardless of whether severe thunderstorms materialize.

Meanwhile, persistent southerly flow will maintain well above average temperatures between Friday and Sunday, with only a modest cold front serving as a brief speed-bump Monday before temperatures rebound to well, above average values Tuesday onward.

BRC

AVIATION
(For the 06z TAFs through 06z Thursday Night)
Issued at 954 PM CDT Wed Apr 24 2024

VFR flight conditions are expected to prevail at least through early to mid afternoon on Wednesday across the area. Lower clouds will build into central and parts of northeast Missouri late Wednesday afternoon and evening, along with widely scattered showers, and perhaps a thunderstorm or two. Additionally, southeast flow will likely become gusty in central and northeast Missouri during the afternoon and evening. The rest of the area should remain in VFR category through the remainder of the period.

Carney

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

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

St. Louis, MO,