342
FXUS02 KWBC 121858
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Sat Jul 12 2025

Valid 12Z Tue Jul 15 2025 - 12Z Sat Jul 19 2025

...Florida to the central Gulf Coast could see heavy rain next
week...


...Overview...

A typical summertime pattern will be in place much of the medium
range period next week with an expansive upper ridge stretched
across the Southern U.S. and progressive shallow troughs moving
through the northern stream flow. A shortwave will amplify over the
northern Rockies by the start of the period Tuesday, drifting east
through the northern tier through the rest of the week. This
trough will send a cold front through the northern and central U.S.
aiding convection over much of the country from the Rockies and
eastward. Farther south, weak low pressure near/over Florida
drifting west into the Gulf will keep heavy rain threats over the
Sunshine State and toward the central Gulf Coast through the latter
part of next week. Meanwhile monsoonal moisture increases
throughout the week in the Four Corners states to south-central
High Plains. Heat in the West early to midweek should lessen by
later next week, while warmer than average temperatures affect the
Ohio Valley to Northeast Tuesday onward.


...Guidance/Predictability Assessment...

Model guidance continues to struggle with the details and timing
of shortwaves through the northern stream flow within the low
amplitude pattern. The first shortwave digging into the interior
Northwest Tuesday showed reasonably good agreement on timing, aside
from the 00Z GFS that was slower. This will push eastward across
the northern tier through the rest of the week, but there is
uncertainty with upstream energy and whether it pushes east to
reinforce this trough, or dive a bit south to create a Northwest
trough around Thursday. Deterministic and ensemble and AI guidance
are all quite variable with this, so started leaning toward the
ensemble means. An Alaska/northeastern Pacific upper low or trough
will also wreak havoc on the pattern as it moves southeast without
much model agreement. The 06Z GFS was quite strong with this upper
low late week while the 00Z ECMWF was so weak/shunted east into
Canada that there was ridging around Vancouver Island. Ensemble
means were at least somewhat agreeable on a British
Columbia/Northwest U.S. trough by Friday-next Saturday, so leaned
toward the means. The newer 12Z ECMWF and GFS fortunately seem to
have some consensus on a trough there.

The WPC forecast used a multi-model deterministic blend early in
the period. But with the increasing model spread, quickly ramped up
the proportion of GEFS and EC ensemble means to almost the total
blend by the late period. Maintained relatively good agreement with
the previous WPC forecast as well.


...Weather/Hazards Highlights...

A surface low pressure system (which the National Hurricane Center
is now monitoring with low probabilities of tropical cyclone
development) will be retrograding across Florida into the Gulf on
Tuesday. Moisture above the 90th percentile is likely to be in
place and promote multiple inches of rain in the Florida Peninsula
from Monday (short range/Day 3 period) into Tuesday and Wednesday.
There was sufficient model agreement in heavy rain amounts to add a
Slight Risk of excessive rainfall to the Day 4/Tuesday ERO. By
Wednesday/Day 5, the low should be pulling west into the Gulf.
Enhanced moisture will remain in place though, and spread into the
central Gulf Coast. A Marginal Risk was maintained in the Day 5 ERO
for those areas. Heavy rain could linger in the Gulf Coast region
into later week as well.

Much of the nation from the Rockies eastward will be active with
typical summertime convection in a warm and unstable airmass.
Enhanced moisture stretching toward a lingering front in the
Southeast will maintain convective threats there on Tuesday.
Farther north, a cold front moving through the northern/central
Plains and eastward will support showers and thunderstorms with
ample moisture and instability, resulting in a heavy to excessive
rainfall threat. Both EROs on Tuesday and Wednesday feature broad
Marginal Risk areas from the northern High Plains eastward into the
Upper Midwest and southward towards the Middle Mississippi
Valley/Ohio Valley. This issuance also stretched the Marginal into
the Appalachians midweek with orographic enhancement of storms in a
moist environment. Model guidance varies considerably with
placement of heavy rain amounts, so the Marginals are quite broad
in order to cover the widespread but low-end threat. In areas like
Montana, rain amounts of a couple of inches are reasonably rare (as
indicated by Extreme Forecast Index shift of tails and other
measures), but the character of the rain looks to be moderate rates
for multiple hours rather than very high rain rates, so held off
on a Slight Risk there. Other areas may eventually need embedded
Slight Risks in future cycles if models converge on placement and
amounts of heavy rain.

Elsewhere, monsoonal moisture will gradually increase in coverage
across the Southwest/Four Corners/southern Rockies region. For
Tuesday, continued a Marginal Risk in far western Texas and the
Sacramento Mountains (particularly over very sensitive burn scars),
with the Marginal Risk expanding westward into southern Arizona by
Wednesday. More widespread monsoonal moisture will continue making
its way northward in this region later in the week.

Hot weather may linger in the Pacific Northwest through around
midweek, but temperatures in the northern High Plains will cool
dramatically into Tuesday-Wednesday with highs around 15 to 25
degrees below normal. Temperatures look to be a few degrees cooler
than average for the south-central U.S. for much of next week as
clouds and rain hold temperatures down. The Great Lakes and
Northeast will see a return to above normal temperatures on
Tuesday, with somewhat widespread Major (level 3/4) HeatRisk
showing up in those areas by midweek. Meanwhile the Southeast
should be near normal to a few degrees above, for typical summer
heat and humidity.


Tate/Santorelli


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


$$