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
43
067 FXUS63 KDMX 012321 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 621 PM CDT Sat Jun 1 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Fog likely east overnight - Several periods of convection expected Sun-Tue although confidence in details is low. Severe weather possible at times with damaging wind the primary concern. - Mainly dry from midweek into the start of next weekend with seasonal temperatures && .DISCUSSION... Issued at 305 PM CDT Sat Jun 1 2024 Our weather pattern will be active later this weekend and into early in the next work week as our progressive, low amplitude flow persists and eventually evolves into a stronger MO Valley upper trough late Tuesday. Although confidence in the details is low due to varied model solutions, this will overall keep the potential for thunderstorms of varied strength and severity in the forecast off and on until the middle of next week when less active northwest flow returns. In the meantime, Iowa is in generally subsident flow behind the mid level OH Valley short wave, and a lower level circulation quite evident in visible satellite imagery across eastern MO. There are still low chances for showers and a few storms central and east early this evening however, with a few weak showers already evident on radar. The airmass is generally uncapped with little CINH, but some weak convergence has aided the spotty showers east, with the latest GOES Cloud Phase Distinction images also noting some enhancement farther west into central IA. A few convection allowing models /CAMs/ do suggest very isolated development, so have kept a token mention in these areas until shortly after sunset. Effective shear is weak, so there is little severe potential outside of a brief funnel cloud with steep low level lapse rates generating 100+ J/kg 0-3km MLCAPEs. Even if anything matures further, it should dissipate with the loss of insolation leading to dry conditions through at least the start of the early morning hours. There is little upstream at the moment, but some CAMs suggest lingering Plains peak heating convection could drift into western sections toward daybreak and then dissipate with the loss of instability. Much of the model guidance also continues to suggest some radiational fog development east overnight, which matches pattern recognition with light winds following lingering low level moisture and cloudiness. Confidence decreases later in the day tomorrow however, as is often the case with warm season convection in these weakly forced initiation mechanisms. ARW based HRRR and HRW ARW solutions, as well GFS and EC parameterized solutions, suggest peak heating development northwest with some low end severe potential in fairly seasonal instability and shear parameter space, while the NamNest, FV3, and other ARW NSSL WRF solutions hold off until latest in the evening. Confidence increases in that regard however with more uniform guidance agreement, with an increasing potential for upstream peak heating development maturing into a severe MCS with wind being the primary threat. Although it would likely be elevated and rooted around 0.5-1km per forecast soundings, 12Z HRRR across western IA approaching daybreak depicts ESRH 500+ m2/s2 and effective shear 50+ kts suggesting an organized MCS being maintained with that and other CAMs noting quasi-linear structure reinforcing the wind potential. This is also corroborated by elevated NCAR HRRR neural network severe wind probabilities. The complex should be weakening in time as it crosses the MO River and moves east, but may still be capable of damaging winds west, and even a few brief QLCS tornadoes depending on its maturity. Some convection may linger into day, as the forecast becomes more nebulous with nondescript forcing, but broad but weak moisture transport could maintain anything that lingers into the night to some degree. Confidence increases again around Tuesday when a maturing long wave trough brings a lobe of larger scale synoptic lift coincident with its associated frontal passage. This will bring one last higher chance for convection until the pattern becomes less active later into the week and to start the weekend with mainly dry continues in persistent northwest flow aloft behind the Ontario/Great Lakes closed upper low. The severe potential around Tuesday is undefined for the time being, with GEFS based CSU machine learning solutions suggesting some severe potential, while the deterministic GFS keeps MLCAPEs <2000 J/kg and 0-6km shear <40kts. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 621 PM CDT Sat Jun 1 2024 VFR conditions will prevail for most of the TAF period, excepting a period during the early morning hours Sunday when fog will develop over about the eastern half of Iowa. The most dense fog should remain just east of our area, but may encroach on MCW/ALO and perhaps OTM toward sunrise, primarily between about 09Z and 13Z. Have included this in the 00Z TAFs, and will examine short-term forecast trends to refine details for 06Z update. && .DMX WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...Small AVIATION...Lee