115
FXUS02 KWBC 131854
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
254 PM EDT Sun Jul 13 2025

Valid 12Z Wed Jul 16 2025 - 12Z Sun Jul 20 2025

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


...Overview...

A typical summertime pattern will be in place this week into next
weekend, with an expansive upper ridge stretched across the
Southern U.S. and progressive shallow troughs moving through the
northern stream flow. A shortwave over the northern Rockies at the
start of the period Wednesday will drift eastward with time,
sending a cold front through the northern and central lower 48.
Convection is likely along and ahead of the front with potential
for isolated flash flooding. Farther south, weak low pressure
meandering over the eastern Gulf will keep heavy rain threats over
the Sunshine State and toward the central Gulf Coast through the
latter part of the week. Meanwhile monsoonal moisture increases
through the period in the Four Corners states to south-central High
Plains. Upper ridging from the southern Plains to the East will
promote summer heat through late week into next weekend.


...Guidance/Predictability Assessment...

Model guidance has persistently shown agreement for a low
amplitude pattern, but with variability in the details and timing
of shallow shortwave and longwave troughs within it. Initial
shortwaves over the Upper Midwest and over the northern Rockies on
Wednesday continue to show better agreement compared to a day or
two ago, along with another shortwave tracking through southern
Canada Thursday-Friday. There are still minor model differences
that could affect frontal placement and QPF, but a general model
compromise worked well for the first part of the period to handle
these differences.

A more uncertain aspect of the forecast is the evolution of upper
energy over the northeast Pacific Thursday and where it tracks. The
00Z CMC was much less consolidated with the energy compared to the
ECMWF/GFS, and this led the CMC to be out of phase across the
northwestern and north-central U.S. by next weekend. Meanwhile the
00Z ECMWF and 00Z/06Z GFS were more agreeable with an upper low in
the Gulf of Alaska diving southeast late week and eventually
leading to troughing in the Northwest. These were also aligned well
with the ensemble means in their placement, though with the means
weaker as expected. Thus for the latter part of the period,
eliminated the CMC and gradually ramped up the proportion of GEFS
and EC ensemble means to around half Day 6 and more Day 7, but
maintaining the operational GFS and ECMWF in the blend. For the
newer 12Z guidance, the CMC still seems on the weak side but with
some improvement toward consensus, while the GFS is on the
stronger/slower side compared to the middle ground ECMWF and
ensemble means.


...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 into the Gulf by midweek after
crossing Florida, and potentially reaching the central Gulf Coast
Thursday-Friday. Moisture above the 90th percentile looks to remain
over western Florida and reach the central Gulf Coast by the
medium range, after a wet early part of the week in Florida. A
Marginal Risk is included on both the Day 4/Wednesday and Day
5/Thursday Excessive Rainfall Outlook (ERO) for those areas. Heavy
rain may linger in the Gulf Coast region into next weekend.

Much of the nation from the Rockies eastward will be active with
typical summertime convection in a warm and unstable airmass. A
cold front stretching from the Upper Midwest southwest into the
central Plains on Wednesday will support support showers and
thunderstorms with ample moisture and instability, resulting in a
heavy to excessive rainfall threat. Wednesday`s ERO shows a
Marginal Risk from the Midwest extending back into central Plains
near and ahead of the front, while also covering farther south and
east into the Appalachians where orographics could play a role in
forcing thunderstorms. Additionally, there may be convection with
moderate to heavy rain rates in the northern High Plains lingering
Wednesday morning after a wet Tuesday night, so a Marginal Risk is
in place there as well. By Thursday and the Day 5 ERO, the gradual
shift of the front toward the Northeast and south through the Ohio
Valley allows the Marginal Risk to shift more into the Ohio
Valley/Mid-Atlantic and Northeast. On both days, included the
central Rockies/Plains into the Marginal considering the front
stalling and possible west-east training of convection. Even by the
start of the period Wednesday there is considerable spread with
the model guidance regarding heavy rain amounts and placement, so
the Marginals are quite broad in order to cover the widespread
threat. Generally this is a low-end and isolated flash flooding
threat equating to a Marginal Risk, but some areas may eventually
need embedded Slight Risks in future cycles if models converge. The
East could continue to see scattered thunderstorms into late week,
while the front lifting north could lead to additional convection
in the north-central Plains and Midwest as well.

Farther south, monsoonal moisture will gradually increase in
coverage across the Southwest/Four Corners/southern Rockies region.
Marginal Risks are in place across much of Arizona and New Mexico
and stretching into Colorado for both Wednesday and Thursday. Areas
like burn scars and urban areas would be of greatest concern for
flash flooding. The monsoon pattern should continue into next
weekend.

Hot weather may linger in the Pacific Northwest through around
midweek, but temperatures in the northern High Plains will cool
dramatically by Wednesday with highs around 15 to 25 degrees below
normal. Temperatures there should slowly warm closer to average
late week. Temperatures look to be a few degrees cooler than
average for the south-central U.S. for much of the week as clouds
and rain hold temperatures down. The Great Lakes and Northeast will
see warmer than average temperatures Wednesday and Thursday under
an upper ridge, with somewhat widespread Major (level 3/4) HeatRisk
showing up in those areas and points southward mid-late week. In
the Northeast, a cold front will allow temperatures to cool toward
normal by next wekeend. Meanwhile the Southeast should be near
normal most days, 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


$$