Expires:No;;142254 FXUS63 KDMX 040546 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1146 PM CST Tue Dec 3 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Scattered snow showers possible (30-40% chance) across the north and northeast Wednesday. Low confidence (~20%) in visibility restrictions with snow. - Wind Advisory in effect across the northern half of the area from noon to 9pm Wednesday. Gusts up to 50 mph (locally 55 mph) likely (90% confidence) especially across the far north. - Cold Thursday morning with wind chills in the negative teens across the north. && .DISCUSSION... Issued at 218 PM CST Tue Dec 3 2024 A scattered deck of upper level clouds moved across the state this afternoon, primarily in the northern half. Southerly winds will work to recover temperatures slightly today with areas across the south just reaching above freezing. Tonight, a descending trough to the northeast will drag with it a front. The arrival of the fropa has trended slightly faster this forecast update which will limit highs across especially the north tomorrow. Have lowered highs, keeping northern Iowa right at freezing which it should reach in the morning hours just before the fropa. Soundings show the potential for some convective snow showers with steep lapse rates in the PBL. This potential will be across the north in the morning, focusing in the northeast through the daytime. Quick bursts of snow will be possible as mixing maximizes, but snow will be blown around enough in the wind to limit accumulation. One would be concerned that with expected gusts tomorrow (more on the winds shortly), bursts of snow could lead to visibility restrictions. For this area, the hi-res guidance does highlight narrow bands of vsby restrictions associated from simulated HCR snow showers, so reductions of 2sm or less cannot be completely ruled out. However, a limiting factor will be the lack of saturation in the DGZ, hindering the formation of more stellar dendrites, leaving a snow pallet consisting of smaller, less obstructive shapes. All this being said, confidence then becomes low (~20%) for significant visibility reductions in the north. Now, for the winds: have issued a Wind Advisory across the north for Wednesday afternoon and evening. It is likely (90% confidence) to see sustained winds of 25-30 mph with wind gusts up to 50 mph. It cannot be completely ruled out to see 55+ mph gusts in the peak mixing hours of the afternoon. This is supported by the magnitude of winds at the top of the mixed layer, which eased slightly this issuance, but still hit 50 kts for an hour or two in the far north. Pair this with steep PBL lapse rates, a tight pressure gradient, CAA, and subsidence from pronounced height rises, ingredients are certainly in place to maximize mixdown of higher wind speeds. Trends will be monitored to see what magnitude of winds will be realized. For now, the Wind Advisory is representative. CAA preserves mixing through the night, keeping gusty, but sub-advisory winds going until Thursday. Clearing skies will also work to plummet temperatures into the single digits for Thursday morning. The aforementioned winds will produce wind chills in the negative teens north of Highway 20. Highs will only warm to near 20 degrees. In the extended, an upper level trough will stall over the southwest CONUS and bring in a WAA regime for the weekend. A reinforcing open wave enhances this regime for Sunday, pushing highs in the 50s that day. The forecast for the following week remains uncertain as models diverge on how they handle the eastward evolution of these waves. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1147 PM CST Tue Dec 3 2024 Low level wind shear is coming to an end and concerns are shifting to ceiling restrictions, increasingly strong and gusty winds, and possible snow showers. Winds from the southwest will become from the northwest through the morning hours and increase in speed. Wind gusts have been increased to at least 40 knots at the northern sites of MCW, FOD, and ALO. It remains possible that a few wind gusts around 50 knots may occur in the afternoon hours over northern Iowa. Accompanying the increasing winds will be lowering ceilings into MVFR that will teeter around FL020 and may for a short time drop below this FL. Have now included a short period of MVFR stratus at DSM where confidence is above 50% in occurrence. Narrow snow shower bands will likely develop and could bring IFR restrictions to any terminal they pass over. For now, have advertised this as a PROB30 at both MCW and ALO late morning and early afternoon. Ceilings will improve late in the period into VFR with the strong winds very slowly decreasing into the end of the period. && .DMX WATCHES/WARNINGS/ADVISORIES... Wind Advisory from noon to 9 PM CST Wednesday for IAZ004>007- 015>017-023>028-033>039-044>050-057>061. && $$ DISCUSSION...Jimenez AVIATION...Ansorge