Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
218 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
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