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Displaying AFOS PIL: AFDDMX Received: 2022-01-21 05:48 UTC
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190 FXUS63 KDMX 210548 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1148 PM CST Thu Jan 20 2022 ...Updated for the 06z Aviation Discussion... .DISCUSSION.../Tonight through Thursday/ Issued at 225 PM CST Thu Jan 20 2022 Key Messages: - Very cold tonight with overnight lows approaching 20 below over parts of northern Iowa. Wind chill values of 20 to 35 below will be common. - Several chances for light snow from Friday night into early Monday. Arctic high pressure is centered over western Iowa this afternoon with temperatures currently ranging from the single digits above and below zero. With the very light wind, the wind chill values have risen above headline criteria for the time being. The forecast challenge for tonight is how far temperatures will plummet as the high moves east across the state and the timing of weak warm advection on the backside of the system. Outside of some eroding stratus over southwest Nebraska, widespread clear skies are in place across a large portion of the region. The Arctic high will be moving over a relatively new and deep snow pack over central Iowa and this is all leading to peak radiational cooling conditions setting up overnight. Temperatures should plummet this evening and the radiational cooling conditions will persist the longest over the east. Guidance temperatures continue to initialize too warm with current temperatures and routinely do not do well with the setup for tonight, therefore have continued overnight lows below the NBM 25th percentile which drops lows to near 20 below at both Waterloo and Mason City with most of that drop occurring this evening before some warm advection arrives late. Despite the overall light wind expected, the wind will increase some with the switch to more southerly wind overnight and with wind chill values in the 20 to 35 below range, have issued another Wind Chill advisory for parts of central and northern Iowa through noon on Friday. Expect that southwestern parts of the advisory will be canceled prior to that time. Temperatures Friday will remain well below normal despite the warm advection, with highs in the teens to low 20s. An short wave trough will arrive by the evening and will bring a chance for some light snow as warm advection aloft increases ahead of the system. The band of moisture associated with the system is relatively narrow so any light snow duration will be short but some minor accumulations could occur, especially over northern Iowa Friday evening. Not expecting any freezing drizzle on the back side as the mid-level moisture clears out with the passage of the upper level short wave as only subsidence will remain in any residual stratus field. The upper northwest flow will remain active into this weekend with once disturbance expected to arrive Saturday night followed by another Sunday night/Monday. The overall northerly trend with these clippers continues but the potential for some light snow accumulations remains over mainly northern Iowa. The Saturday night clipper could bring one to two inches of snow over parts of northeast Iowa but little to no snow into central Iowa. Will continue to fine tune the track of the surface low as any snow will be relegated to the northeast quad of that system. The Sunday night into Monday system is stronger but Minnesota and Wisconsin likely will take the brunt of that systems. This low pressure will drag another Arctic cold front through Iowa sometime Monday. While Monday could have temperatures above freezing in the morning, falling temperatures and some wrap around light snow could arrive already by the afternoon. Cold temperatures will follow for Tuesday and Wednesday with Arctic high pressure on track to arrive Tuesday night and bring another round of well below zero temperatures. && .AVIATION.../For the 06Z TAFS through 06Z Friday night/ Issued at 1147 PM CST Thu Jan 20 2022 Expectations have changed little since 00z with VFR conditions through 00z. High and eventually mid level cloudiness will spread west to east by the evening hours however, with MVFR ceilings possible north. There may also be a period of MVFR visibilities in light snow in these locations. The one low confidence VFR exception into early this morning is that some guidance is suggesting patchy visibility restrictions northeast, in what would likely be MVFR IC versus BR considering the temperatures. Confidence isn't there to include at the moment, but trends will have to be watched in the coming hours. Winds will remain light and variable into the morning, but then increase from the south with some gusts, especially north and west. && .DMX WATCHES/WARNINGS/ADVISORIES... Wind Chill Advisory until noon CST Friday for IAZ004>007-015>017- 023>028-033>039-044>050-057>062-070>074. && $$ DISCUSSION...Donavon AVIATION...Small