Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
914 FXUS63 KLSX 290954 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 454 AM CDT Wed May 29 2024 .KEY MESSAGES... - Mild and dry conditions will persist today and tomorrow. - Widespread showers and a few thunderstorms are expected sometime between Friday afternoon and Saturday evening. Some showers may produce locally heavy rain. - Additional waves of showers and thunderstorms will be possible Sunday onward, with warmer temperatures expected. && .SHORT TERM... (Through Late Thursday Afternoon) Issued at 315 AM CDT Wed May 29 2024 Quiet conditions have settled into the area this morning behind yesterday`s cold front, thanks to high pressure and a dry airmass. While a few mid level clouds continue to percolate across the southern half of Missouri and far southern Illinois, possibly even producing a few instances of virga, this activity will continue to move south through the morning, and measurable precipitation is not expected. Otherwise, while surface winds have weakened, the presence of this mid-level cloud cover is likely to limit fog formation early this morning across Ozark valleys, and as a result we do not expect this to be as widespread in these areas as it was yesterday. During the day, high pressure and dry northwest flow will persist, leading to a mild day with plenty of sun. Temperatures this afternoon are likely to reach only the mid 70s to perhaps near 80 degrees in the southern Ozarks, with light winds as well. This will continue into Thursday as well, with a chilly morning followed by a barely noticeable warmup as a transient ridge aloft builds overhead. This slight boost in temperatures will likely bring afternoon temperatures closer to 80 degrees, but easterly low level flow will prevent most areas from climbing much higher than this. Meanwhile, the potential for precipitation overnight Thursday has diminished, which will be discussed in greater detail in the following Long Term discussion. BRC && .LONG TERM... (Thursday Night through Tuesday) Issued at 315 AM CDT Wed May 29 2024 Attention turns to the arrival of a shortwave/vorticity maximum Friday and Saturday, which continues to trend a bit slower in recent model projections. This is the primary reason that precipitation chances have waned overnight Thursday, although a few ensemble members and the deterministic GFS continue to produce a few elevated showers very late at night, likely due to modest mid-level warm air advection and isentropic ascent ahead of the main wave. This possibility is now within the minority of possible solutions, though. Rather, the best chances for precipitation have shifted to sometime between Friday afternoon and Saturday evening, although enough timing variance remains among ensemble members to preclude increasing precipitation chances to greater than 60% at any specific time. However, at least some rain is expected to fall at some point in that time window in most areas. As for the potential for thunderstorms, instability projections continue to be rather marginal ahead of this wave (~250-750 J/kg MUCAPE) due to very poor mid-level lapse rates, and forecast profiles appear almost tropical in nature with high humidity throughout the column. Bulk shear parameters are also marginal overall owing to weak mid-upper flow and a displacement from the primary polar jet to the north. However, there will likely be an enhanced low level jet, which may lead to locally higher low-level wind shear but is not expected to significantly increase severe weather chances given the other factors. As such, the potential for strong or severe storms remains rather low, although some convective cells could be reasonably efficient rain producers, with precipitable water projections ranging from roughly the 75th to 90th percentile and some outliers exceeding this range as well. From Sunday onward, weak zonal flow aloft will develop across the CONUS, with additional weak shortwaves/vorticity maxima passing through it. There remains very little specificity regarding the timing of these waves, but this will maintain an unsettled pattern heading into next week with multiple opportunities for showers/thunderstorms. While these features may have some similarities to this weekend`s system, it does appear that temperatures and moisture will be steadily rise early next week, along with instability, which increases the potential for thunderstorms whenever precipitation does develop. However, the persistence of modest mid and upper level flow will continue to limit the ceiling of severe weather overall. BRC && .AVIATION... (For the 12z TAFs through 12z Thursday Morning) Issued at 451 AM CDT Wed May 29 2024 VFR conditions are expected throughout the 12Z TAF cycle. Very light north winds will gradually veer to easterly tomorrow morning, with minimal cloud cover aside from a few mid level clouds lingering near I-70 terminals. Otherwise, no weather hazards are expected. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX