Extended Forecast Discussion NWS Weather Prediction Center College Park MD 403 PM EDT Fri Mar 26 2021 Valid 12Z Mon Mar 29 2021 - 12Z Fri Apr 02 2021 ...Pattern Evolution and Guidance Assessment/Predictability... Models and ensembles agree that the upper level pattern over the continental U.S. will be amplified yet generally progressive next week, bolstering forecast confidence. A departing vigorous upper trough and deep low/cold front off the East Coast Monday will lay down a wavy trailing cold front over Florida and the Gulf of Mexico/Mexico. An early-mid week southern stream impulse will then track over the U.S. southern tier, but local convective focus remains uncertain in the wake of the lead system. Meanwhile, the next major northern stream storm system dig through the Intermountain West and Rockies early next week, and this storm system works across the central and eastern U.S. to induce lead return flow, reaching the East Coast into next Thursday/Friday. A large surface high then spreads over much of the lower 48 mid-later next week. Model and ensemble guidance is clustered much better than normal in a pattern with overall above normal predictability days 3-7. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of the 06 UTC GFS, the 00 UTC ECMWF/Canadian/UKMET and the 13 UTC National Blend of Models days 3-5 (Mon-Wed). Opted to only add modest inputs from the compatible 06 UTC GEFS mean and 00 UTC ECMWF ensemble mean days 7/8 considering slowly growing forecast spread. This plan along with manual edits provides excellent WPC continuity and is in line with newer 12 UTC guidance including the 12 UTC GFS that has trended more in line with the other models in the less certain southern stream days 3-5. ...Sensible weather and potential hazards... The strong East Coast storm system will be exiting the Northeast Monday morning, with strong and gusty winds and colder weather in its wake, and some snow showers for northern New England. The next system crosses the Intermountain West with a strong surface low trekking across southern Canada for the beginning of the week. This will bring another round of rain and mountain snow to the central and northern Rockies through Tuesday. As the cold front reaches the Central U.S. by Monday/Tuesday, it should advect enough Gulf moisture northward to produce showers and storms from Texas to the Deep South, and locally heavy rainfall is possible across the Appalachians by next midweek, although models differ on the axis of heaviest rainfall. Strong winds are also expected across the northern Plains and Upper Midwest through Tuesday owing to the strong pressure gradient that will be in place. Temperatures are expected to be well above average ahead of the cold front advancing across the Plains, especially on Monday when highs could be pushing 70 degrees as far north as the Canadian border. An abrupt return to reality ensues by the middle of the week as a much colder airmass advects into the region behind the front, with readings about 5-15+ degrees below average that could flirt with some local record values. Hamrick/Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy snow across the higher elevations of northwestern Montana, Mon, Mar 29. - Flooding possible across portions of the interior Southeast, the southern Appalachians, into the Ohio and Tennessee Valley, as well as northern New England. - Flooding occurring or imminent across portions of the lower Mississippi Valley. - High winds across much of the northern Rockies into the northern High Plains as well as much of New England, Mon, Mar 29. - Heavy precipitation across the Alaska Panhandle into the southern coastal ranges of mainland Alaska, Tue-Wed, Mar 30-Mar 31. 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