Extended Forecast Discussion NWS Weather Prediction Center College Park MD 133 PM EDT Mon Mar 09 2020 Valid 12Z Thu Mar 12 2020 - 12Z Mon Mar 16 2020 ...Southwest heavy rain threat to redevelop over the Southern Plains to lower MS Valley and TN Valley later this week and weekend... ...Guidance/Predictability Assessment... The northern stream trough starting in the northern Plains Wed night is progressive, moving steadily across the Great Lakes Day 4 and off the northeast coast Day 5. Heights recover quickly, so the post frontal cold wave is expected to be short lived. The models were agreeable on the timing and amplitude, lending the situation to a consensus based approach. The Day 3 southwest closed low is forecast to slowly eject east northeast across the southwest on Day 4/Fri. The models agree the low shears out into an open wave Sat Day 5 as it moves on the central and southern Plains. The wave continues to decay Sat as it ejects into confluent flow. Model consensus on timing of this feature has continued to improve, with the ECMWF, Canadian, and their ensemble means clustering well. Consequently, a blend of these solutions was used for the forecast. The 12z UKMET marks the slowest solution. A trailing cold front associated with this wave is forecast to linger across the Southern Plains Fri-Sat before moving south into the Gulf of Mexico by Sun-Mon as a relatively strong polar surface high moves from central Canada into the Great Lakes. On Fri 13 Mar-Sat 14 Mar, models continue to show an amplifying shortwave diving southward across western Canada toward the northwestern U.S. A complex interaction with additional northern stream energy across western Canada continues to result in model spread as to the specific evolution of this feature. The ECMWF has been fairly consistent in showing a relatively deep cutoff low developing across the Pacific Northwest by early Sat, which then slowly drifts southward along the West Coast through Sun and finally inland by Mon. The 00z ECMWF, Canadian, ECMWF Ensemble Mean, and 12z UKMET cluster well on the track of the 500 mb low. A blend of these solutions was used. The GFS was further east on the low track, which was least preferred as the upstream high amplitude ridge over the northern Pacific to southern AK favors a more slowly moving cutoff further west. ...Weather/Hazard Highlights... Moderate to heavy precipitation is expected in advance of the closed low as it ejects across the southwest Thu, with showers and thunderstorms expected to become more widespread from the Southern Plains northeastward to the lower MS Valley Valley and TN Valley Fri. Locally heavy rain is expected. Snows are expected in the higher elevations of the southern CO and NM Rockies. As the mid level wave ejects from the central Rockies to the central Plains, an area of snow is possible across the plains of Colorado and Nebraska Fri-Sat. The Northwest should see an increase in valley rain/mountain snow heading into the weekend as the aforementioned trough and frontal system affect the region. Snow is expected in the higher elevations of the Pacific northwest to northern Rockies Fri and early Sat, sinking south into northern CA and the northern Great Basin Sat into Sat night. The Canadian and ECMWF show potential for snow in the northern Plains as a wave ejects, creating a frontogenesis max and lift for snow to occur on the high Plains. The system drops slowly south, bringing snow into the CA Sierra Nevada Mountains/ranges of southern CA and across the mountains of NV/UT/southern WY Sun-Mon. With the front drifting south across the southern Plains to the southeast, showers and storms are expected near the low level front Sunday into Monday 16 Mar. The system drifting south across the Pacific Northwest into the northern Rockies allows an arctic front to drift south early next week. Strong high pressure up in Canada favors cold air draining south across the Plains of MT and the Dakotas over the weekend and south into the Great Basin and central Rockies next Sun-Mon. The biggest cold temperature anomalies are expected in MT. Persistent above normal temperatures are expected from the central to southern Plains across the lower MS Valley and Gulf coast. Strong high pressure over the northeast to mid Atlantic may produce cold air damming and below normal temps in the mid Atlantic east of the central Appalachians Sun 15 Mar and Mon 16 Mar. Petersen/Ryan 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