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
884 FXUS63 KDMX 051147 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 647 AM CDT Wed Jun 5 2024 ...Updated for the 12z Aviation Discussion... .KEY MESSAGES... - Few showers or storms possible this afternoon into evening but may end up being more vigorous virga with low level dry air. - Breezy to gusty conditions also expected today, especially north, with some strong gust potential near showers/storms (virga). Wind Advisory in place mid afternoon into early evening for northern Iowa. - Breezy to windy again Thursday. && .DISCUSSION... Issued at 352 AM CDT Wed Jun 5 2024 The front that helped kick off our storms yesterday has since moved through the area with the rain exiting our far southeast around 330 AM. Initially this morning we`ll be in for a quiet morning, though mixing will start to increase by 15-16Z which in turn will help increase our winds. Another shortwave and associated cold front will move into northern Iowa by roughly mid afternoon with the front pushing through the state into this evening. Model reflectivity in both CAMs and the deterministic models are littered with precipitation this afternoon into evening and although a few showers or storms could be possible north or northeast with lower chances central and south as the boundary pushes through the area, forecast soundings paint a different picture. Moisture is going to be a limiting factor, as mentioned in the previous discussion, with LCLs looking to be near to over 6000ft and any moisture limited to the mid levels with significant dry air (inverted-V soundings) in the lower levels. Mixed layer winds at the bottom of the mixed layer are around 35 knots up north with 20-25 knots towards central Iowa providing a floor for potential wind gusts alone today. At the top of the mixed layer, some soundings at locations like KMCW or KEST indicate some gusts near 50 or even 60 knots. Although it is generally unlikely we`ll mix all the way to 700 mb or more even with our steep lapse rates, the potential is definitely there for gusts over 39 knots and as such have issued a Wind Advisory for the northern two tiers of counties to cover this higher wind gust potential. The caveat to this is some of the higher wind gusts are likely to be associated with the shower activity which given the dry air may be more like vigorous virga or rain that evaporates before it reaches the surface. Even if the rain doesn`t reach the ground, it could help get some of the stronger wind gusts aloft down to the surface. Can`t rule out some severe gusts up north, and some strong gusts outside of the advisory slightly further south of the northern two tiers of counties, but most likely area in soundings and HREF probabilities for the higher gusts are covered in the wind headline. The departing upper low will keep hold of our flow for the next several days as it moves into the eastern CONUS with various waves at times moving through the otherwise northwest flow. After today, our next chance for precipitation may not be until Friday night into early Saturday but uncertainty remains in eastern extent of moisture return with a high pressure in place earlier Friday. One thing we will have to watch for is another potential day of wind headlines Thursday as the upper low moves out increasing the pressure gradient and in turn winds/gusts. LREF probabilities for wind gusts over advisory criteria (39 knots/45 mph) are 40-60% in northeast Iowa with HREF mean gusts around 30-40 mph through much of the area on Thursday afternoon, the highest gusts in the north. Temperatures remain pleasant for early June in the 70s to low 80s with notably less humidity into the weekend. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 639 AM CDT Wed Jun 5 2024 Widespread VFR conditions ongoing early this morning with VFR conditions expected to continue through the period despite increasing scattered to broken cloud cover this afternoon into early evening with some chances for showers or a few storms. Northern sites most likely to see any activity today, but may end up being more virga and not precipitation reaching the ground and as such, have continued with only VCSH mentions as confidence in direct impact to TAF sites remains low. Refinements may still be needed in timing. Winds also pick up today by about 15-16Z becoming quite gusty at times through the afternoon. Higher gusts than included are possible around showers. && .DMX WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 2 PM this afternoon to 7 PM CDT this evening for IAZ004>007-015>017. && $$ DISCUSSION...KCM AVIATION...KCM