Area Forecast Discussion
Issued by NWS Des Moines, IA

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000 FXUS63 KDMX 191114 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 614 AM CDT Mon Apr 19 2021 .DISCUSSION.../Today through Sunday/ Issued at 303 AM CDT Mon Apr 19 2021 Very little change made to the ongoing forecast early this morning. The well-advertised and much-anticipated cold front has moved southward over most of Iowa overnight, currently located in southern Iowa and expected to clear into northern Missouri in a few hours. Behind the front light rain/snow showers have affected parts of northern Iowa overnight, with more moving in from eastern Nebraska at this hour. However, precipitation amounts have been very light, which is expected to continue as the swath of light showers sags south across the remainder of our service area today. A mix of rain/snow should be the norm, but no real snow accumulations are anticipated...perhaps just a dusting in some of our western counties before sunrise this morning. An energetic mid-level trough will approach from the northwest late today and move across Iowa on Wednesday. On the leading flank of this system a broad area of forcing for vertical ascent will blossom over Kansas and northern Missouri tonight, producing a swath of snowfall with accumulations of a few inches likely. This will likely sneak up into our southern/southeastern counties, though considerable uncertainty remains as to just how far north it will get, with some models keeping it almost entirely in Missouri and others bringing it all the way up to near I-80. Have stuck close to consensus and previous forecasts in this regard, with the northern cutoff of accumulations roughly around the Highway 34 corridor, and calling for 1-3 inches of snowfall south of that line. However, much of the snow will come during the pre- dawn/early morning hours Tuesday, when traffic impacts will be mitigated, and it should accumulate more on grassy/elevated surfaces at any rate. With minimal hazardous potential, no headline has been issued at this time. As the aforementioned trough approaches late Tuesday and moves overhead early Wednesday, it will support weak elevated instability within the broad low-level cold air advection regime over Iowa, promoting the development of scattered, light showers from Tuesday afternoon into Wednesday afternoon. There has been a consistent signal for this for a couple days now, and it certainly fits with conceptual models. Therefore, have introduced low end POPs during this time, but with little to no accumulation expected. Aside from precipitation/snow potential, the cold front currently working through the region, along with the secondary trough approaching Tuesday/Wednesday, will support a prolonged period of temperatures well below seasonal normals. Estherville is already registering 29 degrees at this time, and sub-freezing temperatures are expected to spread across about the northwest half of our forecast area early Tuesday morning, and the entire area on Wednesday morning. Have issued a Freeze Watch for about the southeast half on Tuesday night/Wednesday morning, with some refinement anticipated later today/tomorrow as details of potential temperatures and impacts crystallize further. Once the second trough moves over on Wednesday, and off to the east by Wednesday night, brief ridging will allow temperatures to rebound on Thursday with highs near 60 predicted. Another, considerably weaker, trough will then move through on Thursday night bringing some light rain showers, then a longwave trough will approach Friday night pushing another cool front through the region. This will likely be accompanied by more precipitation chances, but the details of this scenario have been erratic and continue to be low-confidence. The best that can be said is light rain may be possible around the first half of next weekend, and any late-week warming trend will likely be held in check or somewhat reversed by the passage of that front. && .AVIATION.../For the 12Z TAFS through 12Z Tuesday morning/ Issued at 614 AM CDT Mon Apr 19 2021 Low MVFR ceilings will prevail at times, mainly this morning, lingering into the afternoon at OTM, then overnight tonight at OTM and perhaps DSM. Light rain/snow showers are also forecast concurrent with the lowest ceilings, but any reduced visibility should be brief and transient for the most part. && .DMX WATCHES/WARNINGS/ADVISORIES... Freeze Watch from Tuesday evening through Wednesday morning for IAZ049-050-059>062-070>075-081>086-092>097. && $$ DISCUSSION...Lee AVIATION...Lee

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