Scientific Forecaster Discussion

000 fxus63 kgrb 221210 aaa afdgrb Area forecast discussion...updated National Weather Service Green Bay WI 610 am CST Fri Feb 22 2019 Updated to add short term portion for morning forecast issuance Synopsis... issued at 606 am CST Fri Feb 22 2019 A major winter storm this weekend, then colder next week. The large scale pattern with high upper heights over the northeast Pacific and split flow downstream over noam will undergo a transition during the period. The positive anomaly over the Pacific will shift north-northeast into Alaska and strengthen. That will cause the negative anomaly with the downstream trough to reform in the Lake Winnipeg region, resulting in a consolidation of the flow across noam. The large scale changes will result in a transition from the active southwest flow regime to a much colder but more tranquil northwest flow. Temperatures will remain at or above seasonal normals through the weekend, then drop below normal next week. The intense storm crossing the area this weekend will bring heavy precipitation, resulting in above normal amounts for the period. && Short term...today...tonight...and Saturday issued at 606 am CST Fri Feb 22 2019 The bulk of the work in the short-term part of the forecast was in trying to work out the details of the wintry precipitation expected tonight into Saturday morning. Models have not been very consistent with the event. They were more aggressive with the precipitation a couple days ago (especially for east-central wisconsin), drier yesterday, and now flopped back to having more precipitation again. They are a little colder today as well, which would suggest mainly snow until daybreak before warmer air aloft starts to arrive in east-central Wisconsin. That should limit the freezing precipitation potential some, as surface temperatures will also be warming as the warm layer advances into the region aloft. Snowfall totals alone were not sufficient to warrant a Winter Weather Advisory. One may be needed for freezing precipitation, but confidence that we've got this totally figured out yet isn't great given the changes over the past 2 days. So will defer to the day shift to make the final call after reviewing the 12z dataset. Long term...Saturday night through Thursday issued at 344 am CST Fri Feb 22 2019 Main story for this period will be strong winter storm moving across the region Saturday night and Sunday, and then the cold next week. A strong low pressure system is expected to move from the Central Plains Saturday afternoon into northeast Wisconsin late Saturday night, and then into Canada on Sunday. The models are all in good agreement, except the WRF in the placement of the axis of heavy precipitation north and west of the Fox Valley Saturday night and Sunday. This scenario will lead to a heavy band of snow north of a Wausau to Wausaukee line where the precipitation should be mainly in the form of snow. Snowfall totals of 8 to 14 inches are expected with only a minor glaze possible. Just to the south, which is in the southern part of the watch area, snowfall totals of 3 to 7 inches are expected with ice accumulations under a quarter of an inch. Snow fall totals of a couple inches are possible across the Fox Valley with less than an inch is expected at Manitowoc. Behind the departing system, wind gusts over 40 mph are expected at times late Saturday night and Sunday. The strong winds will create areas of blowing and drifting snow and may cause damage to trees resulting in sporadic power outages. The snow will gradually taper off during the Sunday, except across the far north where lake effect snow showers will linger through much of Sunday night. Colder weather will work into the region Sunday night. Wind chill readings to around 20 below zero are expected across central and north-central Wisconsin late Sunday night into Monday morning. It will be cold on Monday with highs from 5 to 12 above zero. Confidence is low with the next system for Monday night and Tuesday. The GFS has been consistent with this feature, while the 00z European model (ecmwf) tonight did not have any precipitation for the first half of next week. Stay tuned! It will be cold through next week, with high temperatures some 5 to 15 degrees below normal. No signs of Spring into the first week of March. && Aviation...for 12z taf issuance issued at 606 am CST Fri Feb 22 2019 A strong low-level inversion was resulting in MVFR fog across much of the area this morning. Suspect the visibility will edge down a little more around daybreak, then improve. Otherwise, good flying conditions are expected until precipitation develops tonight. && Grb watches/warnings/advisories... Winter Storm Watch from Saturday evening through Sunday afternoon for wiz005-010>013-018>021-030-031-035>037-073-074. && $$

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