Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 AM EDT Wed Jun 02 2021
Valid 12Z Sat Jun 05 2021 - 12Z Wed Jun 09 2021
...Record Heat possible from parts of the Northern Plains into the
Northeast....
...Multiple Day Heavy Rainfall Event Likely For Parts of Southern
Plains and Lower Mississippi Valley...
...Overview and Guidance Evaluation/Preferences...
A large scale trough entering the Northwest U.S. at the start of
the period (Saturday) should finally suppress the strong Western
U.S. ridge that will be anchored over the region during the now
short range period. Settling and amplification of this trough
across the West into early next week will result in rising heights
for the East and a shift of much above normal
temperatures/possible record heat across much of the northern
tier. Meanwhile, in between, lagging/residual troughing in place
over the Southern Plains and Lower Mississippi Valley will promote
unsettled weather and potentially heavy rainfall over an already
overly saturated region through the weekend.
Overall, the guidance shows reasonable agreement to warrant a
general model blend for days 3 and 4. After this, more significant
and typical differences in the details of individual systems
begins to increase. While all of the guidance suggests
amplification of the Western U.S. troughing through the period
(and resulting build of the East ridge), there are some timing and
intensity differences regarding individual systems dropping into
the mean trough which translates to greater structure
uncertainties late period. As such, a quick increase towards the
ensemble means for days 6-7 was imperative to help mitigate the
differences. Farther east, the models show fairly good agreement
with the presence of the Southern Plains low/trough, but placement
and timing (the ECMWF is a bit west/south, and the CMC farther
east) remain in question. These smaller scale details seem to be
driving some fairly large QPF differences across parts of Texas
into the Lower Mississippi Valley regarding placement and
intensity of the heaviest rainfall axis, details of which are
difficult to resolve this far out. Thus, prefer a blend towards
the ensemble means at this point which represent a good middle
ground solution.
...Weather Highlights/Hazards...
A multi-day heavy rainfall event is looking more likely across
portions of Texas, Louisiana, and into the ArkLaTex region with
the persistent source of deeper Gulf moisture interacting with a
Southern Plains upper level trough and frontal boundary reflected
at the surface. Models continue to suggest the potential for
several inches of rain, or more, within a region which has seen
well above normal precipitation over recent weeks. Elsewhere, much
of the East should remain dry although showers may linger over
parts of the Southeast. Out West, a gradual increase in moisture
over the Pacific Northwest is expected, with some activity
reaching into the northern Rockies and eventually the northern
Plains and Upper Mississippi Valley.
For temperatures across the CONUS, much above normal temperatures
will shift from the Great Basin/northern Plains this weekend, into
the Upper Great Lakes and Northeast early next week. Daytime highs
15 to 20 degrees, locally higher, above the average may approach
or exceed both daytime high and warm overnight low records for a
number of locations across the northern tier. Farther south, below
normal highs are likely the first half of the period, at least,
across much of Texas and Louisiana due to continued unsettled
weather and clouds. The West Coast should trend cooler through the
period as amplified troughing becomes established over the region.
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, winter weather outlook probabilities
and heat indices are at:
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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml