012 FXUS63 KDMX 162331 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 631 PM CDT Thu Apr 16 2020 .DISCUSSION.../Tonight through Thursday/ Issued at 346 PM CDT Thu Apr 16 2020 Early afternoon GOES East upper level water vapor imagery shows the potent shortwave trough diving through Utah into northern Colorado with a broad cloud and precipitation shield eastward into our area. Surge of 925mb and 850mb theta-e advection has pushed precipitation back into southwest and south central Iowa. Temperatures did not recover much in these areas from the first round of snow overnight and this morning with midday temperatures in the low or middle 30s over parts of south central Iowa. There could be a brief period of rain to start over our southeast where temperatures are closer to 40 degrees. However, dewpoints in the upper teens or low 20s suggest temperatures will quickly go toward the wet bulb. Further, high resolution model cross sections show moderate to strong lift moving in with saturation in the dendritic growth zone leading to moderate to heavy snow and dynamic cooling. Thus, forecast over southern Iowa remains mostly all snow. The cross sections also show weak static stability and have noted GLM showing lightning over northeastern Kansas indicating convective instability potential over northern Missouri and southern Iowa later today into tonight. As was the case yesterday and last night, 3z/9z SREF and 12z HREF have high probabilities of 1"/hr rates with even 20 to 40% probability of 2"/hr snow rates. While the snow that fell early today melted on roadways quickly, these types of rates will easily allow for accumulation late this afternoon and particularly tonight with loss of insolation. These rates will also drive visibilities under a mile and often less than that. The snow rate probabilities, peak omega in the cross sections, and the HREF snow band would support the general time of peak intensity from 21z (e.g. now) through about 6z tonight. For areas farther north over central Iowa along I-80, cross sections show drier air so the snow intensity will not be as high as over southern Iowa until perhaps mid-evening when deeper saturation arrives. Further, a tight gradient is still likely along the I-80 counties, though northerly winds are not as strong as some events so the gradient may not be as razor sharp. Overall, the heaviest QPF has shifted slightly southward as discussed earlier this afternoon. 12z HREF probability matched mean (PMM) and mean shows a band of a foot or a bit more from Decatur to Davis Counties into adjacent tier of northern Missouri counties. The HRRRv3 snow band is farther south, but the experimental HRRRv4 remains along the border. Frontogenesis in the 850 to 700mb layer looks to be focused along and just south of the border this evening leading to banded snowfall. So, have tried to tighten up the gradient a bit in southern Iowa and also raised amounts slightly above previous forecast where HREF PMM snowfall has been fairly consistent last 3 runs. While the southern portion of the third tier of counties is around warning criteria (6"/12 hr), the southward trend in QPF has led to the decision to keep headlines unchanged at this time. Snow ratios will favor a wetter snow that could lead to tree damage and isolated power outages. As low level thermal advection and frontogenesis push eastward overnight, will see the snow come to an end. As with the previous forecast cycle, have slowed down the departure time a little bit more again, but most of the snow should still be out of our forecast area by sunrise Friday. Cross sections do show a little bit of saturation and weak omega across northern and more so northeastern Iowa tomorrow afternoon. High resolution models do point to nebulous, generally less than token PoPs. This may end up being some cumulus and perhaps a few sprinkles or flurries. Heights will rise this weekend as flow aloft becomes more westerly. A front will pass through the area Saturday night into Sunday with the best forcing northeast of the state. Temperatures will trend upward and closer to normal over the weekend and will be above normal early next week. A shortwave passing south of the state toward midweek will spread the next chance for showers and thunderstorms with the highest chances over southern Iowa later Tuesday night into Wednesday. && .AVIATION.../For the 00Z TAFS through 00Z Friday evening/ Issued at 631 PM CDT Thu Apr 16 2020 Low ceilings and visibilities will produce widespread IFR to LIFR conditions across the southern third of Iowa tonight in moderate to heavy falling snow. The northern half of the state will side widespread VFR conditions with ceilings remaining at or above 4kft. By Friday, VFR conditions will become widespread statewide as the snow ends by daybreak in most areas. Surface winds will become northwest to west and increase into the afternoon. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 7 AM CDT Friday for IAZ057>062- 070>075. Winter Storm Warning until 7 AM CDT Friday for IAZ081>086- 092>097. && $$ DISCUSSION...Ansorge AVIATION...Cogil