426
FXUS02 KWBC 120738
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
338 AM EDT Tue May 12 2026

Valid 12Z Fri May 15 2026 - 12Z Tue May 19 2026


...Guidance/Predictability Assessment...

Guidance forecast clustering has improved across much of the lower
48 valid Friday into Sunday, bolstering confidence in a
GFS/ECMWF/UKMET/Canadian model composite blend that is well
supported by ensembles. Model forecast clustering is not as
stellar with details and system/stream interactions heading into
next week as upstream energies work into the western to central
U.S., but a more compatible GEFS/ECMWF/Canadian ensemble means and
machine learning guidance composite blend seems to provide a decent
forecast basis and product continuity given growing uncertainties.

...Weather/Hazards Highlights...

Amplified upper troughing will persist over the East into Friday.
System progression to the Atlantic will spawn moderate coastal
cyclogenesis with moderate wrapping moisture/rains/winds lifting
into New England while acting as a maritime threat.

Upstream guidance finally agrees to progress a current main eastern
Pacific upper level closed low/trough bodily inland to the north-
central U.S./south-central Canada by Friday to spawn surface
cyclogenesis and focus light-moderate Midwest/Great Lakes trailing
frontal QPF. Activity diminishes with weekend downstream system
progression over eastern Canada and the Northeast.

Farther upstream system energies subsequently work into the West
and downstream up across the central U.S. with less certainty this
weekend into early next week. However, there is am emerging signal
that weekend upper trough passage over the West will focus some
organized precipitation chances broadly over the Northwest and
north-central Intermountain West/Rockies. Wavy downstream frontal
genesis and lead Gulf return flow of moisture and instability may
set the stage to fuel an emerging later weekend/early next week
enhanced central U.S. convective rainfall pattern to monitor.

Meanwhile, an eastward spreading upper ridge will spread well
above normal pre-frontal temperatures across the Central to Eastern
U.S. this period that may support local high temperature values.
To the south, low level onshore flow will bring shower into Florida
in proximity to upper low development near/east of the Bahamas.

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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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/#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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