Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
329 PM 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...
Upper trough in the East will move offshore, close off and linger
off the Southeast coast through the medium range. There was plenty
of spread in the guidance, particularly with the 00z
CMC/CMCE/UKMET 06z GEFS, with respect to the intensity of the
closed low in the Atlantic beginning on Sunday and continuing
through Wednesday. The 00z EC appears to best capture the pattern
across the CONUS. There's notable spread in the 00z EC ensemble
members with respect to the upper-trough in the west by next
Tuesday and Wednesday. Thus, a blend of majority deterministic 00z
EC and 06z GFS was utilized through day 6. A more even combination
of deterministic and ensemble guidance was blended for day 7.
...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
dramatic 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 temperatures 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.
Kebede/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
Hazards:
- Heavy precipitation across portions of the Pacific Northwest and
the Northern Great Basin, Sat,
May 7.
- Heavy precipitation across portions of the Pacific Northwest,
Sat-Sun, May 7-May 8.
- Heavy snow across portions of the Central Rockies, the Northern
Plains, the Northern Rockies, and
the Northern Great Basin, Sat-Tue, May 7-May 10.
- Severe weather across portions of the Central Plains, the Middle
Mississippi Valley, the Upper
Mississippi Valley, and the Northern Plains, Mon, May 9.
- Severe weather across portions of the Central Plains, Sat, May 7.
- Severe weather across portions of the Central Plains, the Middle
Mississippi Valley, and the
Upper Mississippi Valley, Sun, May 8.
- Flooding possible across portions of the Central Plains, the
Lower Mississippi Valley, the
Northern Plains, the Southern Plains, the Middle Mississippi
Valley, and the Great Lakes.
- Flooding occurring or imminent across portions of the Upper
Mississippi Valley and the Northern
Plains.
- Flooding likely across portions of the Middle Mississippi Valley
and the Northern Plains.
- Excessive heat across portions of the Lower Mississippi Valley
and the Southern Plains, Sat-Tue,
May 7-May 10.
- High winds across portions of the Central Plains, the Central
Rockies, the Central Great Basin,
the Southern Rockies, California, the Southern Plains, and the
Southwest, Sun-Mon, May 8-May 9.
- High winds across portions of the Mid-Atlantic, Sat-Tue, May
7-May 10.
- Enhanced wildfire risk across portions of the Southern Rockies,
the Southern Plains, and the
Southwest, Sun, May 8.
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