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
379 FXUS63 KDMX 092329 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 629 PM CDT Sun Jun 9 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Breezy winds decreasing this evening - Pleasant conditions continue into Monday - Seasonal warm summertime temperature begins Tuesday - More active pattern with storm chances at times Tuesday through Thursday && .DISCUSSION... Issued at 225 PM CDT Sun Jun 9 2024 The breakdown in the sprawling, broad trough over southern Canada into the Northeastern US is in progress as one longwave trough is now being carved out over northeastern North America with its center along the Quebec/Ontario province border. Of first influence, this has kept the overnight and morning convection well south of Iowa with heavy rainfall and flash flooding over southern Missouri. Secondly, the resulting surface pressure gradient has been tight over the Great Lakes stretching into the northeastern third to half of Iowa this afternoon. This has resulted in breezy to gusty winds there with winds gusts of 35 to around 40 mph. With the potential for blowing dust as shown on the Iowa DOT Plainfield camera, did issue an SPS for these winds and potential, localized visibility impacts. Temperatures near to below normal and low humidity will prevail today and Monday as high pressure passes through the region making for comfortable June conditions. Tuesday will mark the transition towards a warmer and more active pattern for the remainder of the work week. The longwave trough over northeastern North America will depart and at the same time a ridge will build over the Desert Southwest. This will push higher heights over Iowa Tuesday through the end of week and perhaps into next weekend. High temperatures will be above normal reaching well into the 80s to around 90 degrees during this period. This heat will be nothing unusual for June with nothing of note on the ECMWF extreme forecast index or shift of tails. Latest NBM maintains a 70% chance of reaching or exceeding 90 degrees Thursday afternoon along and south of Highway 30 across much of Iowa. Now, the ridging would push farther northward allowing for more heat, but a parade of shortwave troughs passing over the southern Canadian prairies will keep the ridge depressed. These shortwaves will bring several storm opportunities through the week with the first being early Tuesday with a lead shortwave. These could bring a few showers or storms to northern Iowa, but time of the day does not lend itself to an apparent severe risk. As the high departs to the east, near surface flow will become from the southwest allowing for the return of richer boundary layer moisture. A cold front tied to a surface low associated with a northern stream shortwave will be brought into the area later Tuesday. Appreciable instability and shear may be along this boundary for a strong storm, but the shortwave energy is making a glancing pass that may limit widespread thunderstorm chances or severe weather. Another shortwave moves into the region later Wednesday and with more instability and higher deep shear, this could result in organized thunderstorm development. This seems most likely over northern Iowa closer to the forcing with the SPC day 4 outlook as well as the Colorado State University`s (CSU) machine learning random forest outlook placing higher probabilities over some or all of northwestern or western Iowa. Thursday will bring a final round of storms and possible severe risk with this parade of shortwaves, though how much of the state may have storms will depend on the speed of the cold front. Mid-level lapse rates, instability, and deep layer shear all look favorable for a severe risk and here too, SPC and CSU show the highest probabilities over southern and/or central Iowa. This cold front is currently forecast to push south of the state Thursday night into Friday and give a short break from the active pattern. However, waiting off the southern California and Baja California coast most of the week will be an upper level closed low, which will finally eject towards the region late in the week. This could bring a better chance of thunderstorms on or around Saturday with the shortwave energy moving closer to or over the state. Looking at hydrology concerns, while the warm cloud depths and precipitable water values look to be seasonal to perhaps seasonally high, QPF amounts at this time horizon do not look concerning looking at the 100 member ensemble data. Also, with agricultural crops established with last week`s USDA crop progress showing nearly all corn planted and 80% emerged with soybeans lagged being about 20%, this will help to absorb and mitigate heavy rainfall concerns. Rivers are also trending downward allow for some capacity as well. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 629 PM CDT Sun Jun 9 2024 VFR conditions will prevail through the period. Breezy northwest winds continue to gust 20-30+ kts but will diminishing after sunset this evening. On Monday winds will shift to out of the northeast, becoming southerly beyond the current period. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Ansorge AVIATION...Hagenhoff