337
FXUS02 KWBC 090734
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
334 AM EDT Sat May 9 2026

Valid 12Z Tue May 12 2026 - 12Z Sat May 16 2026


...Guidance/Predictability Assessment...

Guidance solutions aloft seem reasonably well clustered with the
larger scale pattern develolpment and maintainance through early-
mid next week highlighted by a building/warming ridge over the
West, troughing over the East, and shortwaves dropping from the
Northern Plains/Great Lakes to reinforce troughing in the East. A
guidance composite offers a solid forecast basis in this time frame.

The greatest source of uncertainty next midweek and onward still
surrounds the well upstream evolution and timing of a main
shortwave that digs over the eastern Pacific before eventually
ejecting into the Northwest/West. Recent ECMWF/Canadian guidance
have been faster to bring system energies/precipitation inland
across the Northwest/West and into the north-central U.S.. In stark
contrast, recent GFS and GEFS members have consistently kept this
system offshore a day or more longer before working inland, with
slower downstream breakdown/eastward shifting of the downstream
warming ridge. ECMWF/GEFS AIFS runs offer middle of envelope
timing. Given unresolved uncertainty, WPC surface progs and
sensible weather grids tried to maintain continuity with this
weather-maker via a broad GEFS/ECMWF/Canadian ensemble mean blend
that also seems to handle other main systems fairly reasonably.

...Weather/Hazards Highlights...

An eastern Canadian closed upper-level low will continue to help
support a mean longwave trough down into the eastern U.S.. This
pattern will bring a persistent cyclonic circulation aloft and
multiple shortwave energies to approach the base of the mean trough
from upstream. Impulses will support progression of wavy front
systems to bring periods with showers/thunderstorms through the
eastern half of the country next week, each eventually working
downstream to the Atlantic to spawn moderate coastal cyclogenesis
with wrapping moisture feeds then lifing up/off the East Coast.

Upstream, an eastern Pacific closed trough uncertain ejection into
the West/Northwest mid-later next week will act to focus organized
light-moderate precipitation. A downstream frontal boundary will
form over the Northern Tier as a potential clipper system, bringing
chances for showers and thunderstorms across the northern Plains
into the Upper Midwest, and then the Great Lakes/East. Deep
boundary layer mixing may bring some gusty winds across the Rockies
and Plains with system passage. System progression to the western
Atlantic should support coastal cyclogenesis with inland wrapping
rains and unsettled weather mainly Wednesday into Friday. Later
next week trough/system ejection timing into the West/Northwest may
also spread some organized and terrain enhanced precipitation.

Temperatures will linger below average for the East. Across the
western U.S., a ridging pattern will bring well above normal highs
into mid-late week with pre-frontal warmth spreading into the
central U.S. to also include some record breaking high temperatures.


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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