Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
217 AM EDT Mon Jun 21 2021
Valid 12Z Thu Jun 24 2021 - 12Z Mon Jun 28 2021
...Heat intensifies late week over the interior Northwest/West
toward record levels...
...Heavy rain threat for the mid-section of the country late this
week...
...Guidance/Predictability Evaluation...
The WPC medium range product suite was derived from a composite of
best clustered solutions of the 18 UTC GFS/GEFS mean, 12 UTC
ECMWF/UKMET and NAEFS/ECENS means along with the 01 UTC National
Blend of Models days 3-4 (Thu-Fri) in a pattern with above average
continuity and predictability. Prefer a solution more in line with
the still compatible GEFS/NAEFS/ECENS means starting next weekend
amid growing forecast spread. Developing differences include hot
ridge transitions over the West, but especially with longitudinal
focus of downstream trough amplification over the central U.S. as
energies dig lee of Rex blocking. 00 UTC model guidance does not
seem to clarify the differences.
...Weather Highlights/Hazards...
An upper low just off northern California is forecast to meander
offshore later this week as a hot ridge builds inland through the
Northwest. This will allow temperatures to climb to 15-25+ degrees
above normal from Washington/Oregon to the northern Rockies, and
more generally 5-15 degrees above normal along and west of the
Rockies. Record highs are likely from the Pacific Northwest to the
northern Rockies, with afternoon temperatures peaking well over
100F are forecast for the interior sections of the West. Little to
no rainfall is expected to ease the high heat throughout the broad
region.
Downstream, robust upper trough digging from south-central Canada
will solidify a wavy and fortified cold front to move steadily
over the central to eastern U.S., inviting moisture return by
later week. Well organized showers and storms will significantly
increase rainfall/runoff potential along and ahead of the front
from the Midwest to the Mid-South, Southern Plains and across the
Ohio Valley and Appalachians to the Northeast.
Schichtel
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