028 FXUS63 KDMX 121728 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1128 AM CST Tue Feb 12 2019 .SHORT TERM.../Today through Tonight/ Issued at 323 AM CST Tue Feb 12 2019 Upper trough lifting across the Upper Midwest today will push the surface low into the Ohio Valley. Still some decent low level forcing to come across Iowa this morning...mainly across the east. Sufficient moisture remains so we still could see some light snow lingering across the northeast half or so of the state. However any additional snowfall will be an inch or less and that would mainly be from Forest City to Waterloo. The bigger concern today will be the wind. Currently winds are 10 mph or less and they will remain relatively light through 8 or 9 AM but will pick up from mid to late morning through mid evening. Soundings show the strongest winds from late afternoon through mid evening with 20 to 25 mph sustained and 35 to 40 mph gusts. This will likely cause blowing and drifting snow and issues especially for the evening commute. The gap between the snow and the increasing wind is somewhat problematic for headlines...especially since we have headlines in effect. For this mornings forecast package, I have trimmed headlines from the southwest, where snowfall was generally light and winds will not be quite as strong later on. Adjustments were also made to the winter storm warning in the western/southern end where lower snowfall amounts will not produce the kind of blowing snow we will see further north. Locations that saw 5+ inches of snow were kept in the warning and even though there will be a lull this morning between the snow diminishing and the wind increasing, for simplicity the warning was kept going and will stress the blowing snow and reduced visibility especially this afternoon and evening. For this reason the warning was extended through 13/03Z. After that time, winds will begin to diminish and visibilities will be less of a problem. High pressure will build into the region tonight and Wednesday for clearing skies and diminishing wind on Wednesday. Lows tonight will be rather cold as clearing is expected to occur northwest by mid to late evening and with lighter winds, lows in the single digits below zero seem likely. Further south we will be above zero...but not by much. Wednesday highs will be somewhat tricky but I went colder than guidance. The surface high will shift east across the state Wendesday switching winds around from the northwest to the west by early Wednesday then to the south or southeast by late morning but they will be generally light and with fresh snow on the ground, temps will not recover as quickly as models want to push them. Plus clouds will be increasing in the afternoon which will also negatively impact the temps. Temps were taken down 3 to 5 degrees most locations on Wednesday. .LONG TERM.../Wednesday through Monday/ Issued at 323 AM CST Tue Feb 12 2019 Confidence: Medium A trough of low pressure is expected to quickly develop over the southern Plains by Wednesday evening. The trough will extend north into southern Canada to a weak area of low pressure which will be pulling an Arctic front south with time. Much warmer air will be streaming northeast into Iowa ahead of the southern stream trough/low pressure. Clouds associated with the warmer air will move over the region Wednesday night into Thursday. Along with the push of H850 temperatures of 5 to 7C during the overnight into midday Thursday, temperatures will be warming overnight and most of Thursday over southern Iowa to the lower to mid 30s. By midday to late afternoon the trough will pass east of the area with the secondary trailing Arctic front moving into northern Iowa. Strong cold air advection, subsidence and increasing winds at H850 will result in a quickly increasing sfc gradient with northwest winds increasing to 15 to 20 mph and gusts likely over 30 mph once again as high pressure over North Dakota begins a push south into Thursday night. Though the overall system is moisture starved, there may be a flurry or two that accompanies the colder air. The cold air will quickly settle southeast into the region by Friday morning with overnight lows dropping below zero northwest to the single digits southeast. Some clouds will return to the area with light snow over the southwest as isentropic lift in combination with a very weak wave at H500 develops in return flow aloft. Another piece of energy upstream in the Northern Rockies will drop southeast Saturday night into Sunday. There are some differences between the GFS/Euro with regard to strength and amount of available moisture. The GFS is hinting at a stronger system with possibly more snowfall. Given the uncertainty, will not be able to say too much at this time other than that the system may produce at least light accumulating snowfall. Temperatures through the weekend remain cold with H850 temps at -10C to -15C in either model. This will keep highs in the freezer with mid teens northwest to the lower to mid 20s southeast. There remains no real change in the pattern through Monday. A large southwest trough will keep some energy focused toward the Midwest to Southern Plains going forward. We remain cold with the northern branch of the jet stream continuing to phase enough to maintain a general below normal bias over much of the Northern Plains and Great Lakes into early to middle next week. After the Sunday storm exits, Monday is at least looking quiet right now. && .AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/ Issued at 1128 AM CST Tue Feb 12 2019 Low clouds will be slow to rise/clear out this afternoon and evening, with prevailing MVFR ceilings lingering at DSM for the next couple hours and at MCW/ALO all the way into the evening or possibly beyond. Meanwhile, increasing northwest winds will cause BLSN problems into the evening as well, with scattered light snow showers also expected, resulting in periods of MVFR visibility and possibly brief IFR visibility especially at MCW/ALO. Amendments are anticipated as the BLSN develops this afternoon. Conditions should improve rapidly between 00Z and 06Z tonight as winds die off and clouds likely move out, with VFR conditions expected on Wednesday. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 9 PM CST this evening for IAZ017- 026>028-037>039-048>050-060>062-073>075-084>086. Winter Weather Advisory until 9 PM CST this evening for IAZ004>007-015-016-023>025-033>036-045>047-058-059-072-083- 095>097. && $$ SHORT TERM...FAB LONG TERM...REV AVIATION...Lee