Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
312 AM EDT Fri Apr 19 2024

Valid 12Z Mon Apr 22 2024 - 12Z Fri Apr 26 2024


...General Overview...

The forecast period begins on Monday with an upper trough crossing
the Southeast U.S., and a second trough amplifying over the Great
Lakes and the Northeast U.S. going into Tuesday-Wednesday. This
will bring a strong cold front across the Eastern U.S. with colder
high pressure settling in behind it. A second trough likely
develops over the Western U.S. by the middle to end of the work
week, with a corresponding surface low expected to develop over the
western High Plains by Friday. This would probably be the next
best chance for potentially impactful weather in terms of rain,
thunderstorms, and wind across the Central U.S.


...Guidance/Predictability Assessment...

The 00Z model guidance suite indicated better than average
agreement
across the continental U.S. through the middle of next week on the
synoptic scale features. In terms of specific features, the
guidance is showing a stronger solution across the Northeast U.S.
for midweek as a potent disturbance drops south from the Hudson Bay
region and invigorates the shortwave approaching from the Great
Lakes region. The GFS is most amplified with this trough and has
the core of the upper low over northern New England. For the
Western U.S., the development of the broad upper trough by the end
of next week will be contingent on the level of phasing of two
separate shortwave troughs, with one originating west of
California, and the other dropping south from the Gulf of Alaska.
The GFS is quicker to bring the trough onshore across the
southwestern U.S, whereas the CMC is slowest with this, and the
GEFS mean serves as a reasonable middle ground solution. The WPC
fronts/pressures forecast was primarily derived from a
CMC/ECMWF/GFS consensus through Wednesday, and then increasing
contributions from the GEFS mean going into Thursday and Friday
while still using some previous WPC continuity.

...Weather/Hazards Highlights...

The shortwave crossing the Upper Midwest to the Great Lakes and
then the Northeast will be accompanied by some generally light to
moderate rain Monday into Tuesday, mainly ahead of and along the
cold front. Given the overall progressive nature of this storm
system, and the lack of appreciable instability and QPF, no flash
flood threat areas are currently warranted for the excessive
rainfall outlooks on both days 4 and 5. The next round of light
rain and mountain snow should arrive in the northwestern states by
next Wednesday ahead of the amplifying trough, and becoming heavier
going into Thursday across the Northern Rockies. More widespread
showers and storms are then expected to develop across the Plains
by the end of the week as moisture and instability increase in the
warm sector of a surface low pressure system, and the potential
exists for some strong storms ahead of the dryline in the Southern
Plains.

In terms of temperatures, there will likely be a modest warm up
expected from the Southern Plains to the Mid-Atlantic region on
Tuesday, but the next shortwave into the northern tier should keep
temperatures chilly for this time of year from the Rockies to the
Great Lakes and eventually into the Northeast for midweek. Initial
ridging out west should support above normal temperatures, but
temperatures are likely to fall to below normal levels along much
of the West Coast and inland by next Thursday. Warmer temperatures
and increasing humidity are forecast for the south-central U.S. by
next Friday as the upper ridge axis builds back, and southerly flow
from the western Gulf advects moisture northward ahead of a
developing surface low.

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 forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw