423
FXUS02 KWNH 290654
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Sat Jun 29 2024

Valid 12Z Tue Jul 02 2024 - 12Z Sat Jul 06 2024


***Hot and humid conditions for much of the Southern U.S., and heat
 increases across California and the Desert Southwest***


...General Overview...

Multiple shortwave passages across the northern tier of the nation
will fuel scattered to numerous showers and storms for much of next
week, particularly across the Midwest and portions of the Central
Plains where the heaviest rainfall is likely to be midweek. Heat
and humidity will continue to make weather headlines across much of
the southern tier states as a strong ridge of high pressure aloft
governs the overall weather pattern, and heat also expands across
much of California and the lower elevations of Arizona and southern
Nevada as the upper ridge builds across the West by the end of the
forecast period. There will also be copious moisture in place
across
much of the Southern Rockies that will fuel scattered storms.

...Guidance/Predictability Assessment...

The 00Z model guidance suite is in good synoptic scale agreement
for the beginning to middle of the week, and a general model
compromise suffices as a good starting point in the forecast
process. The NBM appeared a little too light with QPF across the
Four Corners region with respect to the monsoon, so these values
were raised roughly 20-30 percent. Forecast uncertainties increase
the most across the northwestern U.S. for the second half of the
week, with recent runs of the GFS/GEFS still at odds with the
ECMWF/CMC solutions regarding the upper ridge placement and the
downstream trough across the Northern Rockies and the Dakotas. The
GFS has been more progressive with that trough across the Northern
Plains, but the differences are smaller than they were yesterday at
this time. Upon examination of the machine learning guidance,
there was better support for the CMC/ECMWF solutions for Friday and
into next Saturday, so the 18Z GFS was tapered down by this time,
and there was more of the ECENS than the GEFS used as a result.

...Weather/Hazards Highlights...

It generally remains the case that widespread showers and storms
are expected to be ongoing across portions of the Upper Midwest
and western Great Lakes region on Tuesday ahead of a frontal
boundary and an upper level impulse moving through the region.
Although the overall forecast rainfall totals are currently
expected to be in the 1-2 inch range from central Iowa to southern
Wisconsin, this would be falling on highly saturated grounds in
many cases, which would be an aggravating factor when it comes to
flooding potential. Therefore, the Slight Risk remains valid for
the new Day 4 ERO across this region. Marginal and Slight Risk ERO
areas are planned for the new Day 5 outlook Wednesday as the
signal for a main axis of heavy convection drops southward to
include eastern Kansas, much of Missouri, and into central
Illinois.

Monsoonal flow into the Southwest states will continue the daily
threat for showers and storms through much of the period. Marginal
risks remain in place across parts of Arizona and New Mexico for
both the Day 4 and 5 EROs, with the potential for upgrades to a
Slight Risk in subsequent updates during the short range forecast
period. There may be some southern suppression of this moisture
going into the end of the week and confine the greatest coverage of
convection across southeast Arizona and southern New Mexico.

It will continue to remain hot and humid across the Southern U.S.
for much of next week, with the hottest conditions centered across
Texas and Oklahoma where triple digit high temperatures are likely.
Some of this heat likely reaches the Mid-Atlantic region after a
brief cool-down by the end of the week with highs returning to the
90s amid increasing humidity levels. It will also be getting
hotter for the inland lower elevations of California and into the
Arizona Deserts with widespread 100-110 degree readings likely, and
locally higher for the normally warmer locations.

Hamrick


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


















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