Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
151 AM EDT Fri Jun 04 2021
Valid 12Z Mon Jun 07 2021 - 12Z Fri Jun 11 2021
...Record Heat Threat from the Northern Plains to the Northeast....
...Multi-Day Heavy Rainfall Event For the Southern Plains and
Lower Mississippi Valley...
...Overview and Guidance Evaluation/Preferences...
The large scale pattern remains locked on the amplification and
persistence of a West Coast upper trough next week while
downstream ridging is forecast to build and anchor over much of
the Southeast to Mid-Atlantic. A weakness in the ridge over the
central U.S. and an associated surface boundary will be the
focus/lift for widespread precipitation, some of which could be
locally heavy and result in flash flooding over portions of Texas,
Louisiana, and the ArkLaTex region. With troughing established
over the West Coast, storm systems are expected to track along a
quasi-stationary boundary from the central/northern Rockies into
the northern Plains.
While the model guidance is reasonably clustered and agreeable for
days 3-5 (Mon-Wed), there is considerable uncertainty for the
Western U.S. with the evolution of shortwave energy coming out of
the Gulf of Alaska and Eastern Pacific. The ECMWF is actually fast
to eject energy out of the Gulf of Alaska through the base of the
trough into the Pacific Northwest by Friday while the GFS bottles
this energy back offshore into a closed low. By day 7, the
deterministic runs of the GFS/ECMWF are almost out of phase over
the Northwest. The ensembles (ECENS/GEFS) are a bit slower and
depict a solution toward the GFS idea instead of the faster ECMWF.
With this in mind, the WPC blend this cycle used mostly a
ECMWF/GFS/UKMET blend early on then mostly GEFS/ECENS blend for
day 6-7 to help offset some of the higher uncertainty for the
Pacific Northwest.
...Weather Highlights/Hazards...
The combination of deep flow from the Gulf of Moisture interacting
with a surface boundary along the western/central Gulf Coast will
continue to provide episodes of heavy rainfall and possible flash
flooding late this weekend into early next week from portions of
Texas, Louisiana, and gradually northward across the ArkLaTex and
Lower/Mid Mississippi River Valley where the greatest risk area
for several inches of rainfall totals exists. Over time next week,
the associated surface trough is forecast to weaken and lift
northward which will bring numerous to widespread showers and
thunderstorms to portions of the Ohio Valley and Great Lakes
regions, although with lighter rainfall amounts expected at this
time. Meanwhile, diurnally driven showers and storms will be
possible across the southern to central Appalachians and perhaps
into portions of the Mid-Atlantic with the flow around a strong
Bermuda high. The West will remain dry aside from some light
precipitation across the Pacific Northwest and far northern
Rockies.
The greatest temperature anomalies during the period are expected
to be across the northern tier of the CONUS where daytime highs
15F to 20F above normal. Record highs will be possible, especially
across the Northeast Monday and Tuesday. The South will see normal
to even slightly below normal temperatures thanks to increased
cloud cover and precipitation chances while the West Coast will
experience slightly below normal readings in response to the
troughing in place over the region.
Taylor
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