Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
239 AM EDT Mon May 03 2021
Valid 12Z Thu May 06 2021 - 12Z Mon May 10 2021
...Weather Pattern and Model Guidance...
An amplified upper level pattern will be in place across the
nation through Saturday with well developed troughs near the West
Coast and East Coast, with an upper ridge over the Rockies that
weakens with time as it emerges over the Plains. As the trough
over the Northeast lifts out, a more quasi-zonal pattern is
expected by Sunday and Monday, with a second trough building
across the West by next Monday.
Models and ensembles remain in above average agreement through the
end of the week and offer good run to run continuity. There is
some variance with the timing and strength of smaller scale
systems, but guidance composites tend to mitigate these
differences that is consistent with predictability. The GFS
remains stronger and farther west with the coastal low near New
England Friday night compared to the other guidance, including the
GEFS mean, so a more offshore solution is being favored at this
time. The greatest model spread resides across the Great Lakes
and Ohio Valley region by early next week, so more of the ensemble
means were incorporated for the Sunday through Monday time period.
...Weather/Hazards Highlights...
Residual showers and some thunderstorms remain likely from the
central Gulf Coast into the southeast Wednesday into Thursday,
with additional enhanced activity up across the East near a wavy
front. A developing coastal low Friday and Saturday along a
trailing front with renewed upper trough support should produce
unsettled coastal conditions to include some moderate rains for
the Mid-Atlantic and Northeast, but the worst weather conditions
are expected to remain offshore. By Sunday, another area of
enhanced rainfall is becoming more likely across portions of the
middle Mississippi River valley as deep Gulf moisture intersects a
stationary front, with locally 1-2 inches of rain possible.
Upstream over the western U.S., above normal temperatures are
likely from the Desert Southwest to the Intermountain West through
Friday, which will equate to some 100+ degree high temperatures
for the lower elevations of eastern California and southern
Arizona on Thursday. With the passage of the cold front on
Saturday with emergence of an upper trough over the West, seasonal
to below normal temperatures are expected for the weekend. Trough
amplification offers the potential for some moderate precipitation
from the Pacific Northwest to the Northern Rockies, where terrain
enhanced snows are possible.
Hamrick
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