Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Sun May 02 2021
Valid 12Z Wed May 05 2021 - 12Z Sun May 09 2021
...Weather Pattern and Model Guidance...
Models and ensembles remain in above average agreement days 3-7
and offer good run to run continuity. This bolsters forecast
confidence in a pattern expected to significantly amplify over
medium range time scales as upper troughs work into the West and
the East to sandwich a warming west-central U.S. upper ridge.
Variance remains with the timing and strength of smaller scale
systems, but guidance composites tend to mitigate these
differences consistent with predictability. Accordingly, the WPC
medium range product suite was primarily derived from a blend of
best clustered guidance of the 06 UTC GFS/GEFS mean, the 00 UTC
ECMWF/ECMWF ensemble mean and the 13 UTC National Blend of Models.
The latest 12 UTC models and ensembles remain very much in line
with this forecast strategy.
...Weather/Hazards Highlights...
Heavy showers and storms 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.
Upstream over the western U.S., heat is expected to build in
response to the upper level ridge, with highs 10-20 degrees above
normal possible Wednesday-Friday. This will equate to some 100+
degree high temperatures for the lower elevations of eastern
California and southern Arizona. 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 potential for some moderate
precipitation from the Pacific Northwest to the cooling Northern
Rockies where terrain enhanced snows are possible. Meanwhile, an
emerging downstream return flow pattern over the south-central
U.S. may set the stage for an expanding rainfall/strong convection
threat with deepening Gulf moisture and instability.
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