Area Forecast Discussion
Issued by NWS Des Moines, IA

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342 FXUS63 KDMX 180754 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 254 AM CDT Sun Apr 18 2021 .DISCUSSION.../Today through Saturday/ Issued at 254 AM CDT Sun Apr 18 2021 The forecast remains on track with no major changes since previous updates. Highlights: - Partly cloudy and mild again today. - Much cooler Monday through Wednesday, with freezing temperatures possible on multiple mornings. - Light snowfall at times late tonight into Tuesday. Clouds have filled back in across much of Iowa overnight, but are slowly clearing out from northwest to southeast and should continue to do so through the morning, leading to mostly sunny skies by this afternoon. A few sprinkles may be possible at times, mainly over the southeastern half of Iowa, but would be so isolated and light that they are not included in the forecast. Meanwhile as winds turn to west and pick up this afternoon, concurrent with increasing insolation, temperatures should once again climb into the 60s across the area making for a beautiful spring day. Enjoy it while it lasts, because... By this evening a sharp cold front will be approaching from South Dakota and Minnesota, heralding a significant weather regime change as it ushers in several days of much cooler, and at times wet weather. As the surface boundary moves southward over Iowa tonight and early Monday it will be accompanied by light precipitation, mostly in the form of a cold rain but with forecast soundings and surface temperatures supporting potential for light snowfall, especially in our northern and northwestern counties where a dusting of accumulation is forecast, perhaps up to near an inch in a few spots. Monday will be a cool and dreary day, with temperatures steady or falling through the 40s in the afternoon, mostly cloudy skies, and areas of light rain. Things really get interesting from Monday night into Tuesday as an energetic mid- level trough rounds the base of cyclonic flow aloft, sharpening and deepening as it moves over Iowa by Tuesday. Along the leading flank of this trough, broad and strengthening forcing will promote the development of a swath of precipitation north of the old surface front, spreading across much of Kansas, Missouri and southern Iowa on Tuesday morning. Temperatures in our southern areas will have fallen to near or below freezing by late Monday night, with profiles supporting a change to all snow before sunrise and into late Tuesday morning. The primary uncertainties in this forecast are the northward extent of the precipitation, and the amount of QPF. Most of the prognostic models have been slowly trending southward with the northern edge of the precipitation shield, but still keep it within our service area and roughly between the Highway 34 and Interstate 80 corridors or so, with most snow accumulation south of that. The NAM is further north and paints light snow amounts all the way up to Highway 30 or so, but the farther south ECMWF/GEFS appear more likely at this time. While the highest QPF is over northern Missouri, it appears our southern counties, especially south of Highway 34, could receive perhaps 2-3 inches of snowfall on Tuesday morning, leading to minor travel impacts. The silver lining is that with temperatures warming into the lower 40s or so on Tuesday afternoon, any snow that does accumulate on roadways should melt fairly quickly. Nevertheless, it is possible a Winter Weather Advisory may become warranted for these areas in the next day or two. The precipitation will end by Tuesday afternoon/evening as the strong mid-level trough moves off to the east. A second impulse will move over the region Tuesday night and Wednesday however, providing an opportunity for perhaps a few light showers but also helping push temperatures down even further, with Wednesday morning lows forecast in the 20s across all of Iowa and making for a late season hard freeze in many areas. This will not last long however, as by Thursday morning deep layer ridging will be moving in quickly from the west, allowing for warm air advection and pushing temperatures up to near 60 degrees by Thursday afternoon. A weak impulse may then provide a chance for light rain or sprinkles from Thursday night into Friday, before another cold front approaches Iowa at the end of the week. && .AVIATION.../For the 06Z TAFS through 06Z Sunday night/ Issued at 1138 PM CDT Sat Apr 17 2021 Ceilings remain VFR for duration of the forecast with unrestricted visibilities. Surface winds will be northwest overnight becoming westerly on Sunday. A cold front enters northern Iowa on Sunday evening with winds becoming north behind the boundary across northern Iowa during the evening. Little threat of precipitation during the forecast period. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ DISCUSSION...Lee AVIATION...Cogil

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