Scientific Forecaster Discussion

000 fxus63 kdlh 191122 afddlh Area forecast discussion National Weather Service Duluth Minnesota 522 am CST Tue Feb 19 2019 Short term...(today through Wednesday night) issued at 442 am CST Tue Feb 19 2019 Two starkly different days expected for the short term with high pressure and sunny skies today before a winter storm moves in for Wednesday. High pressure was located from the Red River valley of the north into Iowa early this morning. This will lead to mainly clear skies today with highs in the upper teens and lower 20s. The high will move off to the east this evening as an upper level low emerges from The Rockies and begins to move into the plains. Surface low pressure will develop over the Central Plains in response and begin to move northeast late tonight. Clouds will begin to increase ahead of the low tonight, which will help keep lows above zero. There will be a brief window in the Iron County area where skies may remain clear after sunset and result in a brief period of good radiational cooling before the clouds move in. Have dropped lows a few degrees here as a result. Snowfall will spread across the Northland from south to north through the morning Wednesday as the low moves into Iowa. Models continue to differ with the onset timing of snowfall with the GFS now being the quickest and furthest north, followed the European model (ecmwf) and the NAM now being the slowest. All models have shifted to the north and bring an inverted trough through as well heading into Wednesday evening. Additionally, the European model (ecmwf) and NAM thaler qg progs bring a Stout area of lift through much of the region with the strongest being seen across northwest Wisconsin. The GFS shows this as well, but not to the same magnitude. As such, have slowed down the onset a bit and increased snowfall amounts. Snowfall amounts of 2-6 inches will be seen across northeast Minnesota with 4-7 inches for much of northwest Wisconsin. Another factor in play is lake enhancement along both the north and south shores of Lake Superior. Winds will turn northeasterly across Lake Superior Wednesday morning and provide some additional moisture for the system to work with. Areas from roughly Silver Bay to the twin ports and then over to Ashland may see some locally heavier amounts as a result. Confidence on this was a bit lower on this, so opted to treat with a Winter Storm Watch for now. Confidence was higher for warning level snow across Pine, Burnett, Washburn and Sawyer counties, so have issued a warning for those with a watch surrounding. Will leave to later shifts for advisory considerations elsewhere across the County Warning Area. Snowfall will diminish from southwest to northeast Wednesday evening with mainly dry conditions expected after midnight. Highs Wednesday will be in the 20s with lows Wednesday night in the teens. Long term...(thursday through monday) issued at 442 am CST Tue Feb 19 2019 After the Wednesday snow, a brief break in precipitation with perhaps a chance for seeing some sunshine on Thursday before chances for snowfall return Friday and through the weekend. There is a chance for a few rounds of light to moderate snowfall Friday and Saturday, then a chance for a high impact snow storm Saturday night into Sunday. There remains considerable uncertainty for the late- weekend storm. Temperatures will be near to even slightly above normal late-week, then seasonable to slightly below normal temperatures late-weekend into early next week. On the synoptic scale a longwave mid/upper level trough will deepen over the southwest and slowly eject into the Southern Plains late- week, lifting northeast towards the Great Lakes and causing a resultant surface low to deepen over the Midwest. Unlike the Wednesday storm, this low will take a more southerly and slightly slower track to start off, which will allow for much more low level warm air and moisture advection, aiding in the large-scale lift and contributing to a more moisture-rich environment when the low deepens and lifts towards the Great Lakes. There remains significant spread in model solutions with regards to the track of the low and associated precipitation, with a chance for the Northland (highest chance in northwest wisconsin) to see snowfall rates in excess of two inches per hour at times Saturday night and winds gusting to 20- 30 mph. However, it is also just as possible that the storm tracks off further to the east and the region sees little to no significant snowfall accumulation. In terms of snowfall for the Northland, the European model (ecmwf) has had the most aggressive tendencies over the past few days while the Canadian has had solutions too far east to produce any significant precip. The GFS and its ensemble has been more of a middle ground, and recent trends with the 00z guidance suite continue this trend, with 00z European model (ecmwf) also coming in more in line with the GFS in a solution that would produce some snow in northern Wisconsin, but with a sharp gradient towards little to no snow for the twin ports and northeast Minnesota. (This is in contrast to the 12z European model (ecmwf) which produced some unspeakably high snowfall amounts for the twin ports.) While there is overall good agreement in the 00z ECMWF, GFS, and Canadian deterministic models, there still remains the same amount of spread across ensembles, so while there is high confidence that a powerful low pressure system will produce significant snowfall across the Great Lakes Saturday night into Sunday, the confidence that the storm track will be far enough west to cause significant impacts to the Northland is low, with the best chance for measurable snowfall in northwest Wisconsin. Ahead of this weekend storm, a warm front lifts north into the upper Midwest on Friday into Saturday, producing a broad area of light to moderate snowfall Friday into Friday night. Typically this kind of a pattern would lead to around 1 to 3 inches of snowfall with some locally higher amounts, but the GFS deterministic is on the high end compared to other guidance and the gefs ensemble producing amounts more like 3-6 inches, which would be impressive considering the forcing mechanisms in place. Generally think the GFS is being a bit too aggressive with widespread higher amounts. A break in the snow expected Saturday afternoon as the main low pressure deepens and approaches the Great Lakes. && Aviation...(for the 12z tafs through 12z Wednesday morning) issued at 522 am CST Tue Feb 19 2019 VFR conditions will prevail today at all sites under clear skies and a light southwest wind around 5-10 knots. Increasing clouds overnight, with MVFR ceilings developing at brd and hyr before daybreak Wednesday morning. Snowfall will develop from south to north Wednesday morning causing widespread MVFR conditions to develop. && Preliminary point temps/pops... dlh 18 5 21 13 / 0 10 80 80 inl 16 1 23 12 / 0 10 80 80 brd 15 4 23 9 / 0 40 80 50 hyr 22 8 27 15 / 0 30 90 70 asx 22 7 25 16 / 0 10 90 80 && Dlh watches/warnings/advisories... WI...Winter Storm Warning from 6 am Wednesday to midnight CST Wednesday night for wiz006>008. Winter Storm Watch from Wednesday morning through Wednesday evening for wiz001>004-009. Minnesota...Winter Storm Warning from 6 am Wednesday to midnight CST Wednesday night for mnz038. Winter Storm Watch from Wednesday morning through Wednesday evening for mnz020-034-036-037. Ls...none. &&

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