Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
301 AM EDT Wed May 04 2022
Valid 12Z Sat May 07 2022 - 12Z Wed May 11 2022
...North-central Great Basin/Rockies cold heavy snow threat to
contrast emerging north-central U.S. convection and record
south-central U.S to Midwest heat pattern with Omega-style block
development this weekend into next week...
...Lead Mid-Atlantic rainfall threat into Saturday with the closed
low to settle over a blocked western Atlantic next week...
...Pattern Overview and Guidance Evaluation...
Model and ensemble solutions still offer pesky embedded system
timing and emphasis differences, but have overall converged upon a
better clustered mid-larger scale pattern evolution highlighted by
Omega-style block development over the lower 48 and vicinity. A
composite of the 18 UTC GFS/GEFS along with the 12 UTC
ECMWF/UKMET/Canadian, ECMWF ensemble mean and 01 UTC National
Blend of Models seems to present a reasonable forecast basis while
tending to mitigate embedded system variance consistent with a
pattern with near normal predictability Saturday into Monday. The
GFS/ECMWF and GEFS/ECMWF ensemble means remain best clustered and
in line with WPC continuity and the NBM Monday-next Wednesday.
Despite better similarities, recent run-run guidance continuity
issues offers caution with embedded feature details. Most of the
newer 00 UTC guidance maintain similar trends from earlier
guidance, but the Canadian is not as diggy over the western
Atlantic.
...Weather/Threat Highlights...
A leading closed upper trough and well organized surface
low/frontal system will track from the Ohio Valley through the
Appalachians/Mid-Atlantic this weekend. Some strong storms and
locally heavy downpours are possible considering slow system track
and pooled moisture/instability. The system will then stall and
retrograde over the western Atlantic next week as part of a
developing Omega-style block.
Robust digging of a series of dynamic upper systems will lead to a
dramactic change over much of the West later this week into next
week as an amplified mean upper trough and wavy frontal systems
become established over the region. This will support significant
cooling to include spotty record values along with a widespread
precipitation focus from the Northwest/Sierra through the
north-central Great Basin/Rockies. This will include a substantial
and lingering threat for widespread heavy snows as further
enhanced in favored terrain. Expect temperatures to range as much
as 10-20 degrees below normal.
Uncertain upper system ejections channeled between amplified
eastern Pacific upper ridging/upper troughing over the West and
amplified east-central U.S. upper ridging as part of the
aforementioned Omega-style block over the lower 48 will trap a
slow moving and wavy frontal zone over the north-central U.S. to
support an emerging convection/rainfall pattern. This offers a
runoff threat given moist ambient Northern Plains soil conditions.
The Storm Prediction Center also highlights a concern for severe
weather into the eastern Central Plains for at least Sunday and
Monday. The pattern meanwhile favors record high tempertures over
the south-central U.S., with pre-frontal warmth gradually building
northeastward next week through the MS/TN Valleys/Midwest under
the upper ridge, in stark contrast to the wintry conditions over
the West and moderated/cooled high pressure dammed airmass to
linger over the East on the backside of a difficult to dislodge
western Atlantic circulation.
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, experimental excessive rainfall
outlook, 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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml