Extended Forecast Discussion NWS Weather Prediction Center College Park MD 206 AM EST Fri Feb 28 2020 Valid 12Z Mon Mar 02 2020 - 12Z Fri Mar 06 2020 ...Heavy rainfall threat over parts of the eastern half of the lower 48 next week... ...Overview... Medium range period begins with a deep closed upper low over the Southwest U.S. which progresses eastward reaching the Northeast U.S. by late next week. This continues to favor a potentially heavy rainfall event from parts of the Lower Mississippi Valley into the Eastern states next week. Meanwhile, additional shortwave energy should amplify somewhat across the Pacific Northwest behind this main feature, while a couple of weaker shortwaves work their way across the northern tier and southern Canada. Upper ridging from the east Pacific should build after mid-week across the West, in response to additional shortwave energy dropping southward out of the Gulf of Alaska. ...Guidance/Predictability Assessment... Regarding the upper low initially across the Southwest, the CMC continues to be a noticeably slower outlier, which also leads to a CMC surface low track to the west of most of the other guidance. Behind this, the CMC also remains the most aggressive with shortwave energy dropping from the Pacific Northwest bringing another deep low/shortwave into the Southwest by next Thursday, while the remainder of the guidance is much more suppressed with the energy and shows upper ridging by the same time period. Thus, the CMC was not included in the blend at all. The latest runs of the GFS and ECMWF, along with the ensemble means, showed fairly good agreement through much of the period with the progression of the closed low from the Southwest on Monday, eventually to off the East Coast by next Thursday-Friday. Out West, differences arise with regards to details of a shortwave dropping southward out of the Gulf of Alaska late in the period, so a blend of the ensemble means was preferred given the time range for this feature. This cycle of the WPC medium range progs consisted of a majority deterministic model blend (ECMWF/GFS) for days 3-4, with increasing weighting towards the ensemble means (ECENS/GEFS) by the end of the period to mitigate the detail and smaller scale differences. ...Weather/Hazard Highlights... Amidst the ongoing spread and variability for the details, confidence is increasing in the pattern evolution at the surface and aloft which continues to support the potential for a significant rainfall event over parts of the eastern half of the lower 48 next week. Strong low level flow of Gulf moisture should become established for 2-3 days--leading to anomalously high precipitable water values--while at least one leading surface wave lifts northeast from the Southern Plains along a slow moving front. Ejection of the upper trough/low expected to be near southern California as of early Mon should provide added focus/surface development by Tue-Wed. The best clustering of guidance continues to show the best potential for significant rainfall will be from the ArkLaTex region into the Tennessee Valley/lower Ohio Valley and possibly Appalachians. Some locations may see multi-inch accumulations with this event. Heaviest rainfall should occur to the north of areas that have had the most rain in the past couple weeks but this event could enhance/prolong flooding issues over and downstream from areas that see significant rainfall. The Storm Prediction Center continues to monitor severe weather potential, with the current outlook highlighting an area over and just west of the Lower Mississippi Valley for Tue-Tue night. Refer to latest SPC products for updated information. Continue to expect any winter weather effects to be confined to the far northern latitudes of the eastern states. Out west, the Northwest should see almost daily chances for rain/mountain snows associated with energy moving through in the flow aloft. Troughing building off the Pacific Northwest/British Columbia coast Thursday into Friday could bring some increased precipitation chances to coastal regions, though intensity and southward extent remains uncertain due to guidance spread for the details. Ahead of the developing mean trough aloft, above normal temperatures (some plus 10-20F anomalies) will progress into the East through midweek. Below normal temperatures can be expected from the Southwest to Intermountain West underneath the upper trough, though should moderate back towards normal by the time it reaches the Central U.S.. The West Coast states and eventually into the Great Basin should rebound to above normal temperatures after next Tuesday. Santorelli 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