Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 AM EDT Fri Jun 28 2024

Valid 12Z Mon Jul 01 2024 - 12Z Fri Jul 05 2024


...General Overview...

The beginning of July will feature a high quality airmass across
much of the Eastern U.S. behind a departing cold front, with drier
and cooler conditions compared to the heat and humidity expected
over the weekend. Meanwhile, excessive heat will continue to make
weather headlines across the south-central U.S. where the upper
level ridge axis will be, and some of this heat reaches the East
Coast region in time for the Fourth of July holiday with the
surface high moving offshore. Rain and storms are likely across
the Midwest states for the first half of the week, and monsoonal
moisture across the Southwest will maintain scattered showers and
storms.

...Guidance/Predictability Assessment...

The 00Z model guidance suite is in good synoptic scale agreement
for the beginning 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 30
percent or so. Forecast uncertainties increase the most across the
northwestern U.S. for the second half of the week, with recent runs
of the GFS/GEFS becoming more at odds with the ECMWF/CMC solutions
regarding the upper ridge placement and the downstream trough
across the Northern Rockies and the Dakotas. Upon examination of
the machine learning guidance, there was better support for the
CMC/ECMWF solutions for the Fourth and into Friday, so the GFS was
tapered down by this time, and there was more of the ECENS than the
GEFS used as a result.


...Weather/Hazards Highlights...

Widespread showers and storms are expected to be ongoing across the
Upper Midwest on Monday 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, 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 much of Minnesota and portions of adjacent
states. Elsewhere, moisture pooling ahead of the cold front
approaching the Southeast U.S. coast may lead to some repeated
rounds of storms with high rainfall rates on Monday, where a Day 4
Marginal Risk area is planned.

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, New Mexico, and
southern Colorado for both the Day 4 and 5 EROs, with the
potential for upgrades to a Slight Risk in subsequent updates
depending on short range rainfall. This pattern is likely to
persist into next Wednesday as well given the lingering and
deepened moisture channel on the upper ridge western periphery.

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 by the
end of the week with highs in the middle to upper 90s. 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