882
FXUS02 KWNH 210659
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Sat Sep 21 2024

Valid 12Z Tue Sep 24 2024 - 12Z Sat Sep 28 2024

...Eyes to the Carribean for next week...


...Guidance/Predictability Assessment...

The WPC medium range product suite was primarily derived from a
composite blend of the 18 UTC GEFS mean, the 12 UTC ECMWF mean and
WPC continuity. These guidance solutions are reasonably well
clustered and compatible through medium range time scales and best
fits latest NHC guidance on a possible formation and northward
track of a tropical system into the Gulf of Mexico late next week
to monitor. Recent model runs suffer from greater than normal cycle
to cycle continuity, both with interacting flow evolution over the
lower 48 and with any tropical development. However, it should be
noted that latest NHC system evolution is now on the slower side
of newer 18 UTC and 00 UTC model solutions, pending potential
formation and impacts for the western Carribean earlier next week.

...Weather/Hazards Highlights...

Energy digging southward over the Rockies/High Plains in uncertain
separating flow may offer a period favorable for enhanced rainfall
over the southern High Plains under upper diffluent flow and with
frontal proximity. A WPC Marginal Risk area remains in place on the
WPC Day 4/Tuesday Excessive Rainfall Outlook (ERO).

Meanwhile, upper trough energy and wavy frontal systems will be
kicked slowly into the Midwest/East early next week along with an
associated threat of showers/thunderstorms with some local runoff
issues given motion. WPC (ERO) Marginal Risk areas are depicted to
shift eastward Day4/Tuesday and Day/5 Wednesday across the Upper
Ohio Valley and northern Mid-Atlantic. Upper trough reinforcement
may support additional rainfall potential to monitor over the
East-Central U.S. mid-later next week in amplified but uncertain
flow. The eastward progression occuring remains contingent of far
upstream development of a potent and slowly progressive upper
trough from the northeast Pacific early next week that provokes
downstream upper ridge amplification, with possible shift of the
warming ridge from the West Coast to mid-continent over next week.

Meanwhile NHC and WPC will continue to monitor possible tropical
development in the Caribbean that may slowly lift northward into
the Gulf of Mexico to threaten the Gulf Coast late next week. The
ultimate position and southward breath of the upper trough over the
lower 48 will determine extent of northward lifting. Given some of
the latest guidance trends, there is potential that heavy rainfall
may begin impacting parts of the Gulf Coast by late next week. The
timing and exact location of impacts is uncertain at this time.

Out West, most areas should stay dry. The Washington coastal
ranges/Cascades will be an exception with growing daily enhanced
rain potential with Pacific system energy and moisture approaches.

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










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