FXUS63 KFGF 030521 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 1121 PM CST Sun Feb 2 2025 .KEY MESSAGES... - Period of heavy snow late tonight into Monday morning will impact travel conditions in southeast North Dakota and west- central Minnesota. Expect sharply reduced visibility and quick accumulation of snow between 2 to 4 inches, with locally higher amounts. - Hazardous wind chills Monday through Tuesday morning. Wind chills as low as 30 below zero are expected. Additional periods of hazardous wind chills through next week. - Additional opportunities for winter impacts next week. Medium chance (60%) for impactful accumulating snow and blowing snow between Wednesday into Thursday. && .UPDATE... Issued at 1002 PM CST Sun Feb 2 2025 Some snow is finally starting to reach the surface through the sub cloud dry layer, however accumulations haven't started in our area yet and may not start until after midnight. SLR based on soundings (after saturation occurs) should still support average ranges during the first half of this event in the 13-15 to 1 range, with highest ratios after any more substantial banding exits. This still favors a Swath of 1-5" in our south, with the embedded/narrower mesoscale banding where 6" may occur. I made some adjustments to timing, otherwise forecast remains on track. UPDATE Issued at 705 PM CST Sun Feb 2 2025 Returns on radar that have been filling in ahead of the main wave yet to move into the region are predominantly virga in proximity of our CWA with some reports of snow reaching the surface farther west from automated stations. Very dry air highlighted by Td depressions at the surface near 20F and close to 50F in the 7-10ft agl layer will continue to limit the onset of snowfall until later tonight, though a few flurries/reports of lighter snow can't be ruled out before midnight. For now this even seems to be on track, with mesoscale banding leading to highly variable accumulations in the southern Red River Valley late tonight through Monday morning. && .DISCUSSION... Issued at 207 PM CST Sun Feb 2 2025 ...Synopsis... Strong zonal upper jet is observed over the Pacific Northwest nosing through the Northern Rockies into the Northern Plains. This is sandwiched between a stalled upper trough over the Pacific maritime of Canada into the Pacific Northwest and upper ridging over the Southwest. This jet is helping tap into deep moisture from interior Pacific; with a portion of this moisture expected to spill through the Northern Rockies into the Northern Plains and Upper Midwest through the majority of this week. The first batch of this mid/upper moisture moves through the Dakotas into Minnesota tonight into Monday. This along with a weak shortwave trough aloft and strong low/mid level mesoscale forcing will generate banded snow near the South Dakota border/tri-state area into central Minnesota, leading to travel impacts from snowfall. More details on this below. As this week progresses, the current upper trough over the Canadian maritime is forecast to elongate deeper into the Pacific Northwest while remaining stalled or even retrograde. This will help continue to migrate several shortwave trough/s moving through the flow aloft, while continuing to tap into residual Pacific moisture exiting the atmospheric river into Sierra/Great Basin. This will serve to bring several opportunities for impactful winter weather from accumulating snow and gusty winds. More details on these potential impacts found below. The synoptic setup this week will promote modified polar, continental air mass to filter into our area from Canada. This will trend temperatures toward average to slightly below average. Periods of breezy winds combine with these temperatures bringing a chance for hazardous wind chills this week. More on this also found below. ...Snow impacts late tonight into Monday morning ... There remains a strong signal for banded snow to move west to east along/near the ND/SD border into central Minnesota late tonight into Monday morning. This is mainly driven by subtle, progressive midlevel wave moving through the zonal jet, along with strong convergence in the low level to increase frontogenesis through the low and mid layers in a transient manner. In addition to the strong signal of frontogenesis, there is decent agreement in weak instability feeding into this circulation. This addition of instability tends to thin/sharpen the snow band while slightly increasing amounts. The vast majority of latest guidance continues to show an interquartile range of snow accumulation between 2 to 4 inches of snow near the tri-state area of SD/ND/MN. While most guidance depicts this scenario/location, because of the mesoscale nature of forcing, there is still some opportunity for this band of snow to be displaced from the expected location of SD/ND/MN, with the band of snow possibly staying mostly south of the SD border or as far north as between I-94 and Highway 200 (10% chance of this occurring). Given the likely presence of instability feeding into the frontal circulation, localized bands of 4-7 inches are possible (40% chance), with some potential to overperform on snow ratios closer to 20:1 rather than 15:1 as well. Coverage of warning- criteria snow is not expected to be large enough to warrant an upgrade in headlines. Additionally, strong indication of low level dry air feeding into the frontal circulation from the north should serve to limit how far north snow can reach and/or sharpen snow gradient on its northern flank. This also has influence start time of snow into our area, and thus decided to push start time of the Winter Weather Advisory from 6 PM to 9 PM, although impactful snow could start as late Midnight - 3 AM timeframe. With the presence of strong, but transient frontogenesis as well as instability, heavy snow rates are expected for a 2-5 hour period. Because of the expected period of heavy snow rates of 1" or more per hour, significantly reduced visibility less than quarter mile and quickly accumulating snow will contribute to travel impacts. This will impact the Monday morning commute. This time around, winds are not anticipated to be a main driver of impacts, staying less than 25 mph. Drifting snow should still be anticipated, and any wind will only compound reduction in visibility, however. ...Hazardous wind chills this week... Colder, modified polar air will continue to filter into the area from the north. With periods of breezy winds in the forecast, there is potential for hazardous wind chills around 30 to 40 below zero several nights/early mornings this upcoming week. The first instance where this threshold is met comes Monday, lasting into Tuesday within the Devils Lake basin. Relatively highest chance for seeing wind chills 30 below zero or colder exists in northeast North Dakota. This is true almost every night/early morning next week, generally ranging between 20%-50% of meeting this threshold occurring between Wednesday and Saturday. Coldest conditions may come Thursday when winds are forecast to be at their strongest over 25 mph. Uncertainty still exists in magnitude of wind and how this combines with expected temperatures. Chance for dangerously cold wind chills 40 below zero or colder remains low, less than 10%. ...Additional opportunities for winter impacts later this week... Majority of ensembles now depict a synoptic scenario where a larger branch of energy emanates out of the Pacific Northwest upper trough into the Northern Plains and Upper Midwest Wednesday/Thursday. This branch of energy accompanied with relative increase in moisture will bring potential for winter impacts from accumulating snow. There is currently a 60% chance for advisory-type impacts from accumulating snow over much of the area. However, much uncertainty continues within ensembles, particularly with respect to amount of moisture, magnitude and track of forcing, as well as wind potential that could drive blowing snow impacts. At this time, chance for warning-type impacts remains less than 10%. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1121 PM CST Sun Feb 2 2025 Accumulating snow is expected to overspread southeast ND and west central MN during the first 6hr of the TAF period and where this tracks IFR vis and MVFR ceilings should occur. Brief areas of LIFR vis may occur where moderate to heavy snow tracks, however so far confidence remains low in this at KFAR. Flurries or dry/VFR conditions are favored in northeast ND and farther north in northwest MN. Eventually this system transitions east and while there may be some lingering pockets of stratus in the 2500-3500 range early the trend should be towards VFR conditions at KFAR during the daytime period Monday. North-northwest winds 10-12kt increase from the west-northwest behind this system during the day Monday with gusts 18-25kt in eastern ND and parts of northwest MN. Winds should decrease some (at least loosing the gusts) Monday evening as low levels stabilize and gradient weakens. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...Winter Weather Advisory until noon CST Monday for NDZ038-039- 049-052-053. Cold Weather Advisory until 9 AM CST Tuesday for NDZ006>008- 014-015-024-026-028-054. MN...Winter Weather Advisory until noon CST Monday for MNZ003- 029>031-040. && $$ UPDATE...DJR DISCUSSION...CJ AVIATION...DJR