Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 AM EDT Wed Apr 28 2021
Valid 12Z Sat May 01 2021 - 12Z Wed May 05 2021
...Weekend south-central U.S. heavy rainfall/convection threat...
...North-central to east-central heavy rainfall/convection threat
early next week...
...Guidance/Predictability Assessment and Preferences...
Models and ensembles may have converged upon a more well clustered
solution through much of the medium range period, bolstering
forecast confidence to average or better levels. The WPC product
suite was primarily derived from a composite blend of the 12 UTC
ECMWF/UKMET/Canadian and ECMWF ensembles. Recent GFS/GEFS runs
trended in this direction, but were more progressive overall until
finally the latest 00 UTC runs.
...Weather/Hazards Highlights...
A storm over the Canadian Maritimes Saturday will support strong
winds back over the Northeast as an amplified northern stream
upper troughing working over the region. A wavy trailing front
will stall down across Florida and the Gulf of Mexico and may
focus some locally enhanced weekend rainfall, but guidance has
backed off on amounts.
Meanwhile, slow moving southern stream troughing over the southern
Plains this weekend best favors a threat of heavy rainfall and
strong convection from Texas to the lower MS Valley as fueled by
deepening Gulf of Mexico moisture and instability. The system is
expected to shear northeastward into early next week along with a
waning rainfall focus across the east-central then eastern U.S.
with lead return flow.
Upstream, an approaching Pacific trough aloft and leading cold
front will start a pronounced cooling trend by the weekend and
focus generally modest Pacific Northwest to north-central Rockies
precipitation, albeit with a threat of terrain enhanced spring
snows. Steady system progression and lead impulse ejections may
combine with measured north-central Plains
cyclogenesis/frontogenesis and TX dryline formation to favor an
emerging pattern for ample Plains convection by early next week
that shifts eastward near an increasingly sharp and wavy front
from the east-central U.S. to the Northeast. Expect above normal
warm sector temperatures for the East and the South.
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