Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
248 AM EDT Wed May 26 2021
Valid 12Z Sat May 29 2021 - 12Z Wed Jun 02 2021
...Record highs possible in the Pacific Northwest next week...
...Heavy rain potential over portions of the Plains...
...Overview...
Upper ridging will likely build into the Pacific Northwest early
next week while a trough takes shape over the Great
Basin/Southwest. Farther east, Upper Midwest shortwave energy will
push along eastern U.S. low pressure Friday into Saturday with the
trailing front sinking well southward over the eastern half of the
country into the northern Gulf of Mexico. The western end of the
front should linger over the Plains while another front moves in
from the west/northwest, helping to promote episodes of showers
and storms which may contain locally heavy rainfall. After a
recent spell of warm weather in the East and cool temperatures in
the West/Northwest, the opposite will manifest itself through the
weekend into next week.
...Guidance Evaluation and Preferences...
Through the 12Z/18Z cycle, deterministic models offered reasonable
clustering for the first two days of the period this weekend as a
wave of low pressure exits the southern Mid-Atlantic but lingers
along a frontal boundary just off the East Coast. For the Mon-Wed
period, models diverge in the East and West with the handling of
both troughs/upper lows, so a trend toward the ensemble means was
prudent. In the East, 18Z GFS was on the slower/southwest side
with its low pressure near the New York Bight Sunday evening while
the ongoing preference/consensus has been near or just outside the
40/70 benchmark. In the West, 12Z ECMWF became quicker with the
trough (like the 12Z GFS) as it released the northern part of the
trough but allowed the southern part to close off over the Baja.
For now, preferred a simplified progression of the upper trough
via the pace of the ensemble means (18Z GEFS and 12Z ECMWF
ensemble mean) which was near the 18Z GFS. Upstream ridging into
the Pac NW (at least +2 sigma) may be squeezed by next Wednesday
as a Pacific front edges into Washington.
...Weather Highlights/Hazards...
The main focus for rainfall during the period will be over the
central/southern Plains along the west end of the wavy frontal
boundary and ahead of a weaker northern stream cold front. High
pressure that builds in behind the latter front could lead to some
areas of low level upslope flow that would help to enhance
convective development over the High Plains. It will take
additional time to monitor potential overlap of heavy rainfall
potential with areas that have seen above normal rainfall over the
past week or so. The West Coast will see little to no
precipitation but areas near and east of the Great Basin to the
Divide may see at least scattered showers as the upper trough
moves in. Along the East Coast, offshore frontal boundary and low
pressure may only bring light showers to coastal areas but this
will depend on how the system evolves and how close it may be to
the coast. Again kept the heaviest rain offshore for now.
Temperatures will be cool in the Great
Lakes/Northeast/Mid-Atlantic Saturday with northeast winds over
most areas. Expect readings to be 10-15F below normal in general
(many areas only in the 60s). Though the cold front may dip into
the Gulf of Mexico by Sunday, this may only cool temperatures in
the Southeast to a few degrees below normal (low 80s but dew
points in the 50s to low 60s). The Pacific Northwest will see a
warming trend with temperatures 10-25F above normal by Memorial
Day into next Tue-Wed. This could approach or exceed record levels
for parts of WA/OR/ID and northern CA. On the other hand the
cloudy/stormy pattern setting up over the central/southern Plains
and eastern slopes of the Rockies will bring highs down to 10-15F
below normal by next Mon-Wed.
Fracasso
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