Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Mon May 19 2025

Valid 12Z Thu May 22 2025 - 12Z Mon May 26 2025


...Overview...

Omega high pattern looks to set up across North America Thursday
night and then rebuild early next week, as ridging from the
Southwest amplifies as it shifts to the central U.S. and connects
to an upper high over Hudson Bay, while rounds of troughing move
through the Northwest and upper lows spin over the Great
Lakes/Northeast. The Great Lakes/Northeast upper low Thursday/
Friday will promote cooler than average temperatures and rain in
the Northeast, while the building ridge leads to warmer than
average temperatures over The West. Frontal systems emerging from
the West and stalling over the Plains along with Gulf-sourced moist
inflow ahead of them will allow for increasing rain and
thunderstorm chances in the central U.S. Friday through the
weekend.


...Guidance/Predictability Assessment...

Model agreement improves with upper low over the Great Lakes and
energy transferring toward a coastal surface low moving along the
New England Coast Thursday/Friday. This slow moving low, along with
Gulf-Stream sourced moisture sets up a potentially notable rainfall
case for southern/central New England as noted by consensus with
the 12Z global suite.

The upper ridge behind this troughing also seems well predicted by
the models, moving from the southwestern to south-central U.S.
through the lateweek. Uncertainty remains, however, upstream with
the flow pattern in the northeast Pacific and into The West through
this weekend. The 12Z GFS/EC are in decent agreement with a
Thursday night trough into northern CA that crosses the
Intermountain West through this weekend. The CMC has been much
more closed/north with the low which remains in the 12Z version
today. Further ridging spreading from the West Coast after this
trough sets up another omega high pattern over the western
U.S./Canada early next week.

The WPC forecast was based on a blend of the deterministic models
that increasingly depends on ensemble means by Day 5 given the
spread in The West. The transient nature of the shortwaves out west
should continue to lead to uncertainty as seen in the progress of
lows/troughs out west in 12Z guidance.


...Weather/Hazards Highlights...

Increased threat for flash flooding in the Northeast Thursday with
consensus in the 12Z global suite for 2-3" in southern New England.
Still, there are questions for instability, so a Day 4 Marginal
Risk remains in place for now, though an upgrade is possible.
Lighter rain lingers in the Northeast Friday and Saturday under the
slow moving upper low/trough.

A prolonged rainfall pattern over the central U.S. sets up ahead
of frontal systems on Friday with ample Gulf moisture streaming
north on return flow from high pressure over the Southeast. This
convection, likely initiating east of a southern high Plains
dryline should be organized at times starting Friday afternoon
over the south- central Plains to the Ozarks with potential for
heavy rain persisting through the weekend as frontal boundaries
linger. A Marginal Risk ERO was introduced from central KS to
central AR.

Precipitation, rain except for snow the highest peaks, is possible
across the northwestern U.S. underneath upper troughing Friday
night/Saturday and as frontal systems move through. The details
are uncertain based on the model spread with the supporting
energies.

Upper ridging will maintain Thursday max temperatures around 10
degrees above normal over California, the Central Great Basin, and
the Desert Southwest. A few additional daily max temperature
records are at risk in the LA metro on Thursday. The warmer than
normal temperatures will shift into the Four Corners states and the
southern Plains this weekend, with gradual moderating into early
next week while the Great Basin rises to a few degrees above
average. Meanwhile, cooler than normal temperatures will take hold
over the north-central to eastern U.S. late this week and into the
weekend underneath upper troughing. Highs of 10-20 degrees below
average will be common in the Appalachians to Northeast on Thursday
in particular before slowly moderating as the upper low drifts
northeast.


Jackson


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