Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Fri Apr 19 2024

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


...General Overview...

A southern stream upper trough will cross and move offshore the
Southeast U.S. Monday into Tuesday. This will lead to maritime low
development over the western Atlantic and will leave a trailing
front back through the Gulf of Mexico. Northern stream upper
troughing meanwhile over eastern Canada and the Northeast early
next week will exit as upstream/amplified northern stream upper
troughing works through the north-central U.S. prior to feeding
into the East mid-later next week as new trough energies work
through the Northwest. In this pattern a strong cold front will dig
across the Central and Eastern U.S., with colder high pressure
settling in behind it, including some post-frontal uptick in
Rockies winds Monday. Ample digging of Pacific energies next week
into the southern stream seems likely to then bring an amplified
upper trough inland to the Southwest later next week, with a
corresponding surface low expected to develop downstream over the
south-central Plains Friday. This would probably offer the next
best chance for potentially impactful weather in terms of rain,
strong thunderstorms, and wind across the Central U.S. to monitor
as advertised by the WPC Hazards Outlook and CPC week 2 guidance.

...Guidance/Predictability Assessment...

A composite of reasonably clustered mid-larger scale guidance from
the models and ensembles seems to provide a good forecast basis
along with the National Blend of Models and WPC continuity for
early-mid next week in a pattern with slightly above normal
predictability overall. Forecast spread and uncertainties increase
into later next week, lending more preference toward an ensemble
mean approach. The 00 UTC Canadian ensemble mean may be on the
best track given recent guidance trends toward a bit more stream
separation and slower southern stream progression inland from the
Pacific compared to recent GEFS means. ECMWF ensembles were not
available. Accordingly weighted the Canadian mean more than the
GEFS and the ECMWF/Canadian models at these longer time frames.

...Weather/Hazards Highlights...

Upper trough and frontal passages through the Midwest/Great Lakes
and then the Northeast will be accompanied by some widespread
moderate
rains early-mid next week. Given the overall progressive nature of
this storm system, and the lack of appreciable instability and
QPF most places in this period, no flash flood threat areas seem
currently warranted for the WPC Excessive Rainfall Outlooks for
Monday
or Tuesday. The next round of generally light rain and mountain
snow should arrive in the northwestern states by next midweek ahead
of an amplified trough, and then into Thursday across the Northern
Rockies. More widespread showers and storms are then expected to
develop across the Plains and Mississippi Valley states into later
next week as moisture and instability increase with surface low
pressure system deveopment, 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 starting 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/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 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