Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1256 PM EDT Tue Jun 08 2021
Valid 12Z Fri Jun 11 2021 - 12Z Tue Jun 15 2021
...Locally heavy rainfall threat Friday across central
Appalachians/Mid-Atlantic...
...Much above normal temperatures and record heat this weekend
into early next week across much of the interior West/Northern
Plains....
...Overview...
Upper pattern is forecast to amplify along 105W this weekend into
early next week, promoting warm/hot temperatures over much of the
West and northern High Plains that may near or break daily
records. Troughing will exit but then build back into the East
where rainfall will focus over the Mid-Atlantic into the
Southeast. A Pacific front will push into WA/OR early next week.
...Guidance/Predictability Evaluation...
The latest model guidance offers average to above average
predictability for the Nation during the medium range period
(Friday-Tuesday) and will be driven by a strong upper ridge or
closed high over New Mexico (500mb height anomalies at least +2 to
+3 sigma). Weaker ridging across the southern to central U.S. will
erode as troughing becoming established over the Northeast this
weekend an reinforced early next week. 00Z ECMWF and its ensembles
were more bullish in troughing over the Great Lakes than the
GFS/GEFS and CMC/CMC ensembles, but such a strong upstream ridge
could support this deeper troughing in the ECMWF guidance. For
now, opted to split the difference via a multi-model/ensemble mean
blend (GFS/GEFS and ECMWF/ECMWF ensemble mean) as the lead-in
evolution across the Upper Midwest will be sensitive to how some
smaller-scale features track.
...Weather Highlights/Hazards...
The amplification of the upper ridge over the central U.S. is
expected to bring another round of much above normal to possibly
record warm/hot temperatures to the northern Rockies and northern
Plains late this weekend and early next week. Temperatures may be
10-25F above normal with some triple-digit readings possible
across central/eastern Montana Monday and Tuesday. Nighttime lows
will also remain warm for the region and likely stay 10F to 15F
above normal for middle of June. Elsewhere across the CONUS,
temperature anomalies are expected to be near to slightly above
normal.
The threat of locally heavy rainfall capable of producing flash
flooding will linger on Friday across portions of the central
Appalachians and Mid-Atlantic as higher moisture interacts with a
southward-dropping cold front. For the weekend and early next
week, the dominant upper ridge over the central CONUS will keep
much of the area on the drier side with any substantial
precipitation confined to the Pacific Northwest as well as
portions of the Southeast and Florida along a residual frontal
boundary.
Fracasso/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