Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1100 AM EST Mon Feb 25 2019 Valid 12Z Thu Feb 28 2019 - 12Z Mon Mar 04 2019 ...Pattern Overview... Expect progressive and broadly cyclonic mean flow aloft over the Lower 48. As an upper ridge initially extending from the Gulf of Alaska into the Arctic drifts into northwestern Canada, a deep south-central Canada upper low will descend toward the Upper Great Lakes region this weekend and continue rapidly eastward. Flow around this low may interact with energy from a Pacific Northwest coast upper low that opens up as it ejects inland. The combination of these features still offers some potential to produce an Ohio Valley/Great Lakes into Northeast storm system Fri into the weekend, but guidance has become more uncertain with this feature and latest WPC progs have backed off on system strength. Meanwhile another Pacific system will likely reach the West Coast by the weekend. Anticipate highest precipitation totals over favored terrain from CA to the central Rockies and with less certainty for the eastern third of the nation, while much below normal temperatures persist over the n-central U.S. ...Guidance Evaluation/Preferences... Models and ensembles offer reasonable forecast clustering for mid-larger scale systems effecting the nation, with a noticable exception mainly over the eastern third of the country. Guidance has increasingly broken into two forecast camps Friday into the weekend with the GFS/FV3 and GEFS members showing substantially more storm threat over the eastern third of country than the ECMWF/UKMET/Canadian or ECMWF ensembles. Recent storm history, WPC continuity, and consistent run-run GFS/FV3/GEFS guidance has become more suspect considering expected pattern transition/deamplification and ECMWF/UKMET/Canadian or ECMWF ensembles guidance that has strongly trended away from having short range closed low energy eject so bodily downstream. Given uncertainty, WPC progs have backed away somewhat from system development and associated heavier snow/rain threats. Overall, opted tp composite blend the 06 UTC GEFS mean with the 00 UTC ECMWF ensemble mean to create the WPC surface fronts/pressures and 500mb progs for the whole domain. ...Weather Highlights/Hazards... During Thu-Fri the initial flow of moisture over the West will bring areas of rain and higher elevation snow to about the northern 2/3 of the region with a brief drying trend progressing from west to east. The next Pacific system should start to bring moisture into California by the start of the weekend with rain/mountain snow then spreading eastward into the Rockies. For the 5-day period expect an area of enhanced precipitation from n-central California/southwest Oregon to the north-central/central Rockies with highest totals likely over windward terrain of the Sierra Nevada range. Late this week diffuse shortwave energy may assist in producing rainfall of varying intensity over the southern half of the East while the northern fringe of the moisture shield could contain a little light snow from the Mid Mississippi Valley into the northern Mid-Atlantic. The potential development of a organized low reaching the Northeast this weekend would initially spread snow across parts of the northern Plains late this week with precipitation coverage then expanding over the eastern states, but confidence in this system is reduced as guidance forecast spread increases. If deeper development occurs, best snowfall potential would extend from the Midwest through the Great Lakes to New England. Pockets of locally moderate-heavy rainfall may be possible over the South, but thus far with no coherent signal in the guidance for precise location/magnitude. This system may produce strong winds over some areas, but not to the magnitude of the system currently affecting the Great Lakes/Northeast. Expect a period of lake effect snow in the wake of this system while lingering moisture along southern latitudes may produce some rain near the Gulf Coast into early next week. In the wake of this system, a strong surge of very cold air will spread south and east across the central/eastern U.S. from late week onward, with the coldest anomalies spreading out from the northern Plains. Expect best potential for daily records to be for cold daytime highs over the northern-central Plains and Midwest during the weekend. Schichtel WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation and winter weather outlook probabilities are found 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