Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
408 PM EDT Wed May 05 2021
Valid 00Z Thu May 06 2021 - 00Z Sat May 08 2021
...Lingering showers and thunderstorms expected across the Mid Atlantic
and Southeast this evening as a cold front continues to push through the
...Unsettled weather enters the Pacific Northwest and Northern Great Basin
...Unseasonably warm temperatures continue in the West as cooler
temperatures spread through the East...
After an active stretch of weather in the central and eastern U.S.,
relatively quieter conditions are expected across much of the Lower 48
through for the latter half of the week.
As an area of low pressure tracks northeast along the coast, rain is
expected to continue into the evening hours across the Northeast. Showers
and thunderstorms are forecast to develop along the low's trailing cold
front at pushes east across the Mid-Atlantic, while sagging south from the
Southeast and Gulf coasts this evening. Some of the storms developing
over the Mid Atlantic region may become strong to severe, producing
strong, gusty winds. On Thursday, shower and storms are forecast to
continue across the Florida Peninsula as the front drops slowly south
across the region. Some of these storms may become strong to severe as
well, producing hail and strong, gusty winds. Behind the front,
seasonable to below-normal temperatures will spread across much of the
eastern U.S. on Thursday, with average to below average temperature
continuing through Friday.
Father west, a weak upper disturbance is expected to support shower and
thunderstorm development over the central and southern High Plains through
this evening. There is an isolated threat for severe wind gusts and
large hail with these storms. Then on Thursday, a system moving east
across the mid Mississippi Valley into the Ohio Valley is expected to
produce showers and thunderstorms across the region, with some potential
for strong, gusty winds and large hail along its advancing cold front.
In the West, a well-defined cold front is forecast to move into the
Northwest on Thursday. Widespread precipitation, including some
high-elevation mixed precipitation, is expected as the system pushes
across the Northwest into the northern Rockies late Thursday and Friday.
Ahead of the front, above normal temperatures are forecast to continue
across much of the West through Thursday. Much cooler temperature will
spread across the Northwest on Friday, as above normal temperatures
continue across much of the Great Basin and Southwest, while spreading
east from the Rockies into the High Plains.
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
410 PM EDT Wed May 05 2021
Valid 12Z Sat May 08 2021 - 12Z Wed May 12 2021
...Heavy rain possible for portions of the central U.S. this
weekend and early next week...
The 00Z/06Z guidance mostly maintained good continuity from the
overnight progs. Uncertainty remains over the West/Rockies early
next week with the speed of the upper trough. The 00Z
ECMWF/Canadian and their ensembles were displaced a bit farther
northeast than the GFS/GEFS, resulting in a bit quicker pace
toward the Plains/Midwest of the former compared to the latter.
With continued wavering in some GEFS cycles and no clear trend,
opted to split the difference with a blended solution. Lead-in
setup still suggests a multi-day heavy rainfall pattern east of
the Plains though perhaps not in the same place each day as the
frontal zone slowly sinks toward the Gulf Coast. The previous
discussion from 07Z is below for reference.
...Weather Pattern and Model Guidance...
The amplified upper level flow pattern during the short range
period is expected to become more quasi-zonal by this weekend as
the trough over the Northeast lifts out, and the central U.S.
ridge flattens out. At the surface, a meandering frontal boundary
with multiple waves of low pressure along it will be the main
weather maker during the medium range period across the central
and southern tier states.
Models and ensembles are in relatively good agreement going into
the weekend, although there is some variance with the timing and
strength of smaller scale systems. The GFS is more progressive
with the surface low crossing the Ohio Valley and Mid-Atlantic
region through Monday morning, and the CMC is slower than the
model consensus. The GFS is also stronger with the upper trough
across the western U.S. The WPC fronts/pressures forecast was
based on a CMC/ECMWF/GFS blend along with some of the ensemble
means through Day 5, and then primarily ECMWF/EC mean/GEFS means
by days 6 and 7.
The best rainfall prospects will likely be from the Central Plains
to the Ohio Valley, where multiple convective complexes are likely
in the vicinity of a stationary front and a wave of low pressure.
The potential exists for 2 to 4 inches of rain, with locally
higher amounts, from eastern Kansas to Kentucky. Another zone of
heavy rain is also probable across portions of Arkansas,
Mississippi, and Tennessee for next Tuesday and Wednesday with
similar rainfall totals possible. Some training of thunderstorms
may lead to instances of flooding, and this is something that will
continue to be monitored in the days ahead. Widespread moderate
to locally heavy rain can also be expected from eastern Colorado
to central Montana as the upper trough/closed low builds in
overhead combined with moist upslope flow. Dry conditions should
persist across most of the Intermountain West and the Desert
Southwest, as well as the northern Great Lakes.
Temperatures will likely be more reminiscent of March across the
central and western High Plains, and adjacent portions of the
northern Rockies for the Sunday to Tuesday time period, with highs
up to 20 degrees below early May averages. This equates to
readings maxing out in the mid 40s to mid 50s for many of those
areas, and the higher elevations of Wyoming, Montana, and northern
Colorado can expect some late season accumulating snow, perhaps
exceeding six inches for some of the higher ranges. Some of these
cooler temperatures should also be realized across Great Lakes and
Northeast U.S. courtesy of the upper trough and Canadian surface
high in place, although not as anomalous.