Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Wed Feb 26 2020 Valid 12Z Sat Feb 29 2020 - 12Z Wed Mar 04 2020 ...Overview... Upper pattern over the weekend will see increasing troughing into the West coincident with the slow exit of the upper low in the St. Lawrence River Valley. This will be forced by upstream ridging to the north/northeast of Hawai'i and south of the Gulf of Alaska Sun-Mon and rebuilding of the subtropical ridge over the western Caribbean next week. ...Guidance/Predictability Assessment... Though the models mostly clustered near the ensemble consensus, all but the 12Z ECMWF showed varying degrees of plausibility with the embedded features. The 12Z/18Z GFS runs were quicker than the rest with the incoming system on Sat into BC, though the 12Z Canadian was slower and farther southwest. The 12Z UKMET became quicker with the front through the Plains Sun-Mon compared to the consensus which is not necessarily unreasonable given the quasi-zonal northern stream flow as the western system splits into two. With the southern portion, speed differences were more pronounced than amplitude/depth differences as the trough closes off briefly and the opens up again out of Arizona late Mon/early Tue. Trend has been slower but this may be contingent another trough out of the northeast Pacific that has rather low predictability. The 12Z ECMWF/Canadian and their ensembles favored this second reinforcing trough (albeit through the Great Basin vs through CA) while the GFS and GEFS members mostly shear this system through the Gulf of Alaska. Either way, broad consensus agrees on Plains cyclogenesis extending toward the Great Lakes next Tue/Wed. Forecast preferences through the 18Z cycle led to a starting blend that consisted of mostly the 12Z ECMWF/UKMET with minority weighting of the GFS/CMC and the ensemble means early in the period. Trended to a model-mean blend by the latter part of the period, favoring the ECMWF for some details to the forecast. ...Weather/Hazard Highlights... The North Pacific energy digging into the western U.S. will initially bring rain and high elevation snow into the Northwest in the late week/early weekend time frame with a fairly broad moisture shield spreading south-southeast over the West into early next week. Most activity should be light to moderate though with some terrain enhancement possible. Expect another precipitation episode over the northwestern states next Mon-Wed that has the potential for heavier amounts (coastal areas and Cascades) but with lower confidence in details. To the east of the Rockies precipitation should be limited in coverage Saturday outside lingering lake-effect snow. Parts of the Plains and east-central U.S. should see increasing coverage/intensity of precipitation starting late Sunday and especially by next Mon/Tue due to the combination of upper trough with possible embedded low approaching from the southern portions of the West and strengthening low level flow of moisture from the Gulf. Currently expect highest totals within an area between the southern half of the Plains and Tennessee-Ohio Valleys/Lower Great Lakes by Tue into Wed. Any snow will likely be confined to fairly northern latitudes. Areas of above/below normal temperatures will follow system progression during the period. The East will see highs 10-15F below normal on Saturday before trending back toward and then above normal next week. Above normal readings over the West (some 10F or greater anomalies) this weekend will push eastward into the Plains by Sat-Sun and expand toward the East thereafter. Min temperatures may be as high as 15-20F above normal from the Southern Plains northeastward into the Ohio Valley by next Mon-Wed ahead of the cold front. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml