Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
240 AM EDT Thu May 27 2021
Valid 12Z Sun May 30 2021 - 12Z Thu Jun 03 2021
...Record highs likely in parts of the West next week...
...Heavy rain potential over portions of the Plains...
...Overview...
Upper troughing initially in the Southwest will slowly shear
eastward into Texas/lower Mississippi Valley while ridging asserts
itself into the Northwest. A system in the Atlantic will lift
northeastward and spread some rain over parts of the Northeast
Sun-Mon before exiting on Tuesday. Temperatures will be cool in
much of the East to start before moderating, but very warm/hot in
the Northwest into the Great Basin where record heat is likely for
some locations. Areas in the central and southern Plains will see
several chances of rain and cooler than normal temperatures with
abundant cloud cover.
...Guidance Evaluation and Preferences...
Through the 12Z/18Z guidance cycle, the 18Z GFS and 12Z
ECMWF/Canadian were in generally good agreement through the period
with the GEFS/ECMWF ensemble means. This maintained an area of low
pressure along the frontal boundary just off the East Coast late
Sun into early Mon, not as far west as some earlier GFS runs and
not as far east as the ensembles were several cycles ago. In the
Northwest, GFS and Canadian were a bit quicker to bring in
troughing compared to the ECMWF and most ensembles, but upstream
pattern of a modest jet across the northern Pacific certainly
deems that plausible. For now, consensus solution toward the
ensemble means kept good continuity. Over the Plains, somewhat
messy upper pattern with lower amplitude waves interacting with
the stationary frontal boundary (initially two, then focusing
around one) that should trend toward a less active period later in
the week next week. Again a consensus served well due to lower
predictability of the smaller wavelength features, contingent
partially on how the southwestern extension of the Southwest upper
low evolves.
...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. Some areas could see
several inches of rainfall over the multi-day period, perhaps
adding to flooding concerns over areas that have seen above normal
rainfall recently. Others may welcome at least some of the
rainfall as little has been observed in the past week for some
areas.
The West Coast should see little to no precipitation given the
ridge, but coastal Washington may see at least some scattered
showers as the upper trough and cold front move in next Wednesday.
Along the East Coast, the offshore frontal boundary and low
pressure is likely to bring showers to the region. Rainfall
amounts will depend on the evolution of the system, but the
heaviest rain amounts still look to be offshore. Nevertheless, at
least some light rainfall is forecast for areas east of the
Appalachians with higher chances along I-95 from NJ into New
England.
Cool temperatures in the Northeast/Mid-Atlantic Sunday will
moderate through the rest of the week as skies clear and high
pressure moves offshore. The Pacific Northwest can expect
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. As the cold front comes ashore, the warm
temperatures will push through the Great Basin to the Divide. The
cloudy/stormy pattern setting up over the central/southern Plains
and eastern slopes of the Rockies should bring highs down to
10-15F below normal by next Mon-Wed, sinking into Texas by next
Thursday while moderating.
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
- Much
above normal temperatures across portions of California, the Great
Basin, the Pacific Northwest, and the Northern Rockies , Mon-Wed,
May 31-Jun 2.
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