Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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
171 FXUS63 KDMX 231744 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1244 PM CDT Mon Sep 23 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Showers returning southeast today (25 to 40% chance) - Tuesday slight rain chances with no impacts - Lower confidence complex late week pattern with continued rather seasonal with showers possible (35 to 50% chance) && .DISCUSSION... Issued at 301 AM CDT Mon Sep 23 2024 Confidence: Medium to High Weak ridge of high pressure managed to sneak into the region late Sunday afternoon and provide for some clearing over the north and a bit of sunshine late afternoon in the south. Subjective surface analysis shows lee side trough forming over the High Plains while an H500 trough evident on water vapor imagery is moving into southeast Nebraska at 05z. This will eventually tap some of the moisture over the mid Mississippi River Valley, resulting in some showers in increasing PVA over the southeast as the trough swings east this afternoon and evening. The region will see a variety of sky conditions today with the north likely seeing a bit more sunshine than the south during the afternoon. Areas between I80 and US30 will see a sun cloud mix today. With that, highs will range from the lower 70s north to the upper 60s in the far south. This evening clouds will linger in the far southeast while most of the region clears out through 06z. The next upstream wave over southern Canada will dig south into Iowa by Tuesday morning with increasing clouds and shower chances returning over the northwest; gradually spreading south southeast into the afternoon hours. Slight rain chance to chance rain (15 to 30%) will cover the southwest third of the forecast area for Tuesday afternoon. Though CAPE is rather limited, there may be enough to hear a rumble of thunder over the far southeast Tuesday afternoon. The main ramifications of the digging trough over Canada will be to phase with the southern stream H500 trough, creating a more extensive trough from the Great Lakes southwest to the Southern Plains by late Tuesday evening. With the chances for showers tomorrow, highs will be milder over the east and far west in the lower 70s. Most areas will just top out over 70 for the day. .Long Term /Tuesday Night through Sunday/... Confidence: Medium As the trough swings southeast, any showers will come to an end by late afternoon with partly cloudy skies continuing into the evening hours. Most of the area will see decent radiational cooling Tuesday night which will bring overnight mins back down to the mid to upper 40s north and in the lower 50s south. There remains a fair amount of difference in the medium range models once again with the 00z packages. The EC is again slower with any eastward progression of the eventual H500 closed low over northern AR while the GFS initially begins to trek it east, then retrogresses the upper level closed low west southwestward into Friday evening. With the expectation of more significant tropical development in the Gulf by later Thursday into Friday, tracking into the eastern Gulf near Florida, the models continue to advertise the tropical and extra tropical systems phasing and eventually fully phasing into a rather unusual upper level system over the mid to southern Mississippi River Valley by later Friday and into the weekend. Though the timing and placement of the large gyre remains rather uncertain, it appears to impact our area with showers and some thunderstorms, beginning as early as Friday to beginning as late as Saturday afternoon. As might be expected, the blended approach we utilize in our extended stretches the timing from late Thursday all the way to Sunday night. This is not likely the best representation and we will need to revisit the timing again for most of this upcoming week. Given the tropical nature of the system, a large portion of the southeast into the Central US will see rainfall in excess of 3 to 5 inches. Specifically in our area, the risk of any significant rain will remain lower with a mean ensemble forecast by both the EPS and GEFs of about a half to 1.5 inches. Farther south from central/southern MO to the southeast states, a prolonged and more impactful rainfall and flooding event may unfold later this week and into the weekend. Prior the arrival of the unusual fall event this week, highs Wednesday and Friday will likely be the warmest with mid to upper 70s from central to northern areas; lower 70s south. Following that from Saturday through Sunday will be more range bound in the lower to mid 70s with shower chances for much of the period, provided the system wobbles back north and west far enough to impact the region for several days. Stay tuned for more forecast refinements as we move through the week. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1241 PM CDT Mon Sep 23 2024 VFR at all locations today outside of local MVFR potential near KOTM. Some patches of fog are also possible near KOTM late tonight into Tue morning with additional stratus arriving in southeast Iowa by late morning. Another system will reach northern Iowa by early Tue morning also with cigs dropping to near 5-6 kft and there is a chance for a few showers KFOD/KMCW but potential is low enough to exclude from the forecast. mainly light east/southeast wind today with some variable wind direction late tonight and thru 18z Tue. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...REV AVIATION...Donavon