Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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168 FXUS63 KDMX 240732 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 232 AM CDT Tue Sep 24 2024 .KEY MESSAGES... - Today slight rain chances with no impacts - Milder temperatures return Wednesday through Monday; especially northwest/north - Lower confidence complex late week pattern with continued rather seasonal with showers possible (35 to 50% chance) - Late week rainfall amounts greater than 1/2 inch mainly far southeast && .DISCUSSION... Issued at 232 AM CDT Tue Sep 24 2024 .Short Term /Today through Wednesday/... Confidence: High Forecast progressing as expected. Trough over the Northern Plains already producing an area of light showers over western MN as well as far northwest IA into northeast NE early this morning. Yesterday afternoons southern stream wave departing, with a few lingering showers now near Burlington. Most of our area is currently between systems, with clear skies and patchy fog expected through early morning. Subjective H850 analysis shows moisture return has been weak overall through the Central Plains, with dry conditions aloft over Iowa, but there is a pocket of 5C dew points from the Dakotas north to southern Manitoba. HIRES models and synoptic, too, are in generally good agreement with the a trough/trailing cool front associated with the long wave trough in the Northern Plains to move east today across the region. This will bring very light showers/sprinkles into central Iowa through 15z. In the afternoon, some isolated showers/brief thunder will still be possible in the south/southeast through around 00z. Chances today will be (15-30%) with rainfall totals of a couple hundredths expected. With clouds being the main temperature restraint today, highs are likely to top out in the lower 70s most areas with a few upper 60s in the southwest. Tonight will see clearing with lows in a seasonal range of the upper 40s to lower 50s. Tomorrow, high pressure will arrive with weak flow both at the surface and aloft. This will result in a very pleasant day as H850 temperatures recover to the lower to mid teens from east to west by afternoon. Highs will warm to the mid to upper 70s over the region. .Long Term /Wednesday Night through Monday/... Confidence: Medium Confidence this period remains medium with still some timing issues to iron out regarding the beginning time of the showers as well as the ending time of the precipitation early next week. The overall evolution of the rather complex, but anomalous pattern we continue to anticipate affecting the central and eastern CONUS through late week is still intact. There remains uncertainty in the exact details, but there has been slightly better consensus between the medium range models GFS/EC regarding the overall impact to our area and Iowa in general. The exiting southern stream trough is still expected to phase with the digging northern stream wave we are experiencing today and this a closed low process will occur over southeast MO or northern AR by late tonight/early Thursday. Looking farther south into the Gulf, the expected TS or hurricane reaching the western or northwest coast of FL by Thursday afternoon will begin to phase with the closed off H500 low near Arkansas. As the two systems phase further, a Fujiwara dance will commence with the entire system swinging back west toward Iowa by Saturday. Remarkably the GFS/EC suites are in rather similar agreement for now, with most of the remainder of the week still dry in our area until Saturday afternoon. For the remainder of the weekend into Monday, the H500 low just parks itself and will likely fill/weaken into early next week. This will then keep clouds and perhaps some showers over the southeast two thirds of our forecast area during that time. With our area being on the north/back side of the upper level low through the evolution, we will not see much in terms of moisture/rainfall compared to the folks in the southeast/mid Atlantic and lower Ohio River Valleys. Though the ensemble mean precipitation in both the EPS/GEFs suites suggest up to 1/2 inch in the far southeast at most, the current 00z deterministic suites have backed off to one to two tenths of an inch. Contrast that to the deluge expected from southern MO to the lower Ohio River Valley and areas south and southeast which may end up with widespread 5 to 9 inch amounts. Through the period we will see a variety of temperatures with precipitation chances/cloud cover higher in the south and southeast. This area will see lower highs Friday through Monday with lower to mid 70s common. The north/northwest will be slightly warmer with readings closer to the mid to upper 70s. Mins will be milder southeast and cooler northwest for similar reasons. Looking out beyond Monday, ridging high pressure should replace the old filling H500 system. This will bring the region more sunshine and back to pleasant conditions. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1104 PM CDT Mon Sep 23 2024 Expectations haven`t changed much since 00z. Conditions approaching 06z vary from mostly clear/VFR northwest to overcast VFR/MVFR conditions southeast with spotty IFR already in place as well. Confidence in how these trends evolve is low, but generally conditions should worsen along the northwestern edge of the current VFR/MVFR ceilings during the overnight hours with fog and/or stratus development. Current expectations are for MVFR/IFR at KDSM/KOTM/KMCW, but lower LIFR conditions are possible, with restrictions at other sites possible as well. Confidence increases that VFR conditions will return later in the morning and through the day with varied ceilings and cloud heights. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...REV AVIATION...Small