041
FXUS02 KWBC 071859
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Sun Jul 7 2024

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


...Beryl`s moisture and energy likely to spread heavy rain into
parts of the Great Lakes/Northeast by midweek...

...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. With some continued spread for specifics,
latest guidance is holding onto a progressive northeastward track
Beryl`s surface low with an overall evolution that would make the
northeastern quadrant of the U.S. the primary area of concern for
heavy rain and flash flooding Wednesday-Thursday. With a
strengthening western Atlantic upper ridge helping to stall a
front near the Eastern Seaboard later this week, that region should
see additional thunderstorm chances into next weekend.


...Guidance/Predictability Assessment...

The majority of dynamical guidance is finally settling into the
faster northeastward progression of post-tropical Beryl as
advertised earlier by the ICON model and machine learning (ML)
guidance. Per the 15 UTC National Hurricane Center advisory, this
would yield a track from southern Illinois early Wednesday through
the central Great Lakes and into southeastern Canada by Thursday-
Friday. There are lingering issues related to exact evolution of
upper dynamics from Beryl and interacting energy within the larger
scale upper trough incorporating Beryl. Specifically, somewhat
deeper and more closed upper level energy for a period of time would
yield a deeper/westward surface system versus an open upper trough
favoring a weaker/eastward surface reflection. A greater number of
00Z ECMWF-initialized machine learning (ML) models side with the
more closed evolution aloft and a western surface track that better
fits the 15 UTC official track. Among latest/recent runs, the 00Z
ECMWF/UKMET, 06Z GFS, and 12Z CMC cluster best among this scenario.
Latest ICON runs share a similar evolution but still with faster
timing. The 00Z CMC and 12Z GFS/UKMET are somewhat eastward.

Beyond this aspect of the forecast, there is continued spread for
exactly how this upper level energy ejects and specifics of
upstream energy that may filter into the overall Great
Lakes/Midwest mean trough. Regardless of the specifics, there is
agreement that this trough should steadily weaken through early
Saturday as strong Atlantic ridging (anchored by a 600+ dm high
near 60W longitude by Friday-Saturday) builds into parts of the
East. There is still a signal for some weak energy to approach the
East Coast from the Atlantic on the western periphery of the core
of strongest ridging with some potential influence on rainfall late
in the week. By Sunday, consensus suggests that shallow cyclonic
flow may expand into the Northeast while ridging persists over the
South. Low predictability for specific details mid-late period
would continue to favor a composite/mean approach to represent the
larger scale pattern for this part of the forecast.

Dynamical/ML guidance continues to agree fairly well for the
eastward drift of the western U.S. ridge from California and Nevada
into the Four Corners/Central Rockies region over the course of
the period. This drift should allow for weak troughing to develop
near the West Coast by next weekend. Around the top of the ridge,
there is improved agreement for the upper low/trough reaching
western Canada by early Friday, but increasing divergence
thereafter. There is also spread for low- predictability shortwave
details upstream. For now there is no well defined clustering for
specifics. Resolution of these issues would improve confidence for
surface front details over the far northern tier by next weekend.

The first half of the updated forecast based on 00Z/06Z guidance
primarily emphasized the 06Z GFS/00Z ECMWF/00Z UKMET to reflect the
official track for post-tropical Beryl. The blend added in some 06Z
GEFS/00Z ECens means for the latter time frames given the increase
in detail uncertainty within a generally agreeable large scale
pattern.


...Weather/Hazards Highlights...

While guidance still shows meaningful differences for the
evolution/track of post-tropical Beryl as the system most likely
continues northeastward through the Great Lakes, continuity
changes in the best clustering of guidance have at least become
less pronounced than in previous cycles. Based on the models
closest to the 15Z NHC track for Beryl, expect the flow of tropical
moisture to bring highest precipitable water (PWAT) anomalies into
the Lower Great Lakes and Northeast during the Wednesday-Wednesday
night period covered by the Day 4 Excessive Rainfall Outlook. Some
PWAT anomalies within this region will likely exceed the 90th
percentile and west-east oriented fronts north/east of post-
tropical Beryl may promote training. The general themes of the
favored guidance cluster allowed for incorporating the two separate
Slight Risk areas from continuity into a single broader Slight
Risk. Ongoing spread in the guidance certainly leaves the door
open for further changes though.

By Day 5/Thursday, above normal moisture and a front lingering
across the Eastern Seaboard could enhance thunderstorm development
within a broad north-south corridor. Some guidance suggests
sufficient moisture/instability for locally high rain rates as far
south as the Southeast Coast/north-central Florida, so the prior
Marginal Risk area has been extended south to include these
regions. Within this broad risk area there are various antecedent
ground conditions (such as drought over the Mid-Atlantic, wet
conditions over parts of the Northeast). Lack of agreement for best
heavy rain focus and relation to initial ground conditions
preclude introduction of any Slight Risk area at this time, but the
overall pattern supports the possibility once the details become
better refined. Additional storms are possible along the East Coast
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. These risk areas in the Days 4-5 EROs
remain close to continuity.

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 will remain above
normal and the heat will expand into the northern/central Plains by
late this week. Meanwhile, slightly below normal temperatures are
possible Wednesday in parts of the Midwest 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.


Rausch/Tate


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




$$