942
FXUS02 KWNH 070734
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Sun Jul 7 2024

Valid 12Z Wed Jul 10 2024 - 12Z Sun Jul 14 2024


...Beryl`s moisture and energy will spread heavy rain into the Ohio
Valley/Great Lakes to Northeast by midweek, faster than previously
forecast...

...Dangerous heat wave in the West persists through the week...


...Overview...

The most prominent large scale features during the period will be
a persistent upper ridge over the West supporting a dangerous and
likely record-setting heat wave across much of the region through
the week, and a positively tilted Mississippi Valley/Great Lakes
mean trough in part comprised of energy from Beryl, which will be
post-tropical by midweek. Guidance continues to track
faster/farther northeast with Beryl`s low, making the northeastern
quadrant of the U.S. the primary area of concern for heavy rain
and flash flooding Wednesday-Thursday. A stalling front near the
Eastern Seaboard could promote additional thunderstorm chances
there into next weekend.


...Guidance/Predictability Assessment...

Model guidance has certainly struggled over the past several days
with the timing and track of Beryl even/especially as it becomes
post-tropical interacting and phasing with the northern stream.
Overall the trend has been for a faster/farther northeast track of
the low. In terms of the 12Z/18Z model cycle, the 12Z CMC, UKMET,
and GFS were slow compared to the faster trend of the 12Z ECMWF,
and then the 18Z GFS made a switch to an even faster/northeast
position. In terms of AI/ML models, all of them were faster than
the 12Z ECMWF even though it was on the faster side of the
operational models. The ICON model has also been maintaining a fast
track. So the early part of the WPC forecast, to support a faster
track for Beryl (but also worked well for other aspects of the
forecast), was comprised of a 12Z ECMWF/18Z GFS blend. This seems
to be a good way to go, as newer 00Z guidance maintains this
northeast trend, including the CMC and UKMET with a jump northeast.

There is some spread for the upper trough that lingers in the
Great Lakes/Northeast into late week/weekend. In varying ways, most
guidance suggests that Great Lakes into Plains/Mississippi Valley
upper troughing should persist into Sunday but with a gradual
weakening trend. This will occur as strong Atlantic ridging
(anchored by a 600+ dm high over 50-65W longitude by Friday-
Saturday) builds into parts of the East. A modest upper weakness
(with predictability low enough not to reflect yet in a
deterministic forecast by Saturday) could approach the East Coast
from the Atlantic on the western periphery of the ridge. A
composite of model/ensemble guidance appears reasonable for
aforementioned troughing and the retrograding Atlantic ridge.

Aside from typical detail differences, dynamical/ML guidance shows
good agreement with eastward drift of the western U.S. ridge from
California/Nevada into the Four Corners region over the course of
the period. However around the top of the ridge there has been a
fair amount of spread and run-to-run variability for Northeast
Pacific into western Canada dynamics, though recent guidance has
shown some convergence in solutions. A model/ensemble mean blend
worked to temper individual differences there as well.


...Weather/Hazards Highlights...

With Beryl trending much faster than previous forecasts indicated,
by midweek the tropical moisture and the post-tropical frontal low
is currently forecast to be pushing into the Ohio Valley and Great
Lakes region and streaming east into the Northeast. For the Day
4/Wednesday ERO, have introduced a Slight Risk for parts of
Indiana/Michigan near Post-Tropical Cyclone Beryl, and another into
the Northeast where precipitable water values will likely be above
the 90th percentile and west-east oriented fronts in the vicinity
may promote training. This is a significant change from the
previous ERO forecast, but necessary due to the model trends. By
Day 5/Thursday, above normal moisture and a front lingering across
the Eastern Seaboard could allow for more thunderstorms to develop,
and a Marginal Risk is delineated for potential for flash
flooding. Additional storms are possible there Friday and Saturday.
Farther west, some moisture may feed into the Four Corners states
in a monsoonal pattern. Marginal Risks are in place for Wednesday
and Thursday mainly for New Mexico--especially considering
sensitivities due to burn scars and areas that have seen ample
rainfall recently.

The West will continue to see a major to extreme and long-lived
heat wave through this week. Highs exceeding 110F should be
widespread in the Desert Southwest, with typically hotter locations
exceeding 120F. Farther north, highs into the 100s are forecast
into Oregon and Washington and east into the Intermountain West, as
temperatures soar 10-20F above normal with locally higher
anomalies. Numerous daily records are likely to be broken during
this heat wave, with monthly/all-time records not out of the
question. The prolonged nature of the heat wave and record warm
overnight temperatures will increase heat stress. The Pacific
Northwest looks to moderate closer to normal later week with
possible troughing aloft, but interior areas and expanding into the
north-central U.S. will be above normal. Meanwhile, slightly below
normal temperatures are possible Wednesday in parts of the central
U.S. with the rain/clouds from Beryl. These areas should moderate
to near normal, with near average temperatures for this time of
year likely across the Southeast as well--which is still hot and
humid. Near to a bit above average max/min temperatures are
forecast for the Northeast.


Tate/Rausch


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


$$