Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
455 PM EDT Wed May 11 2022
Valid 12Z Sat May 14 2022 - 12Z Wed May 18 2022
...Developing heat threat for California and the Southwest from
the weekend into next week while persistent southern Plains heat
intensifies and expands eastward...
...Record warmth to continue over parts of New England into
Saturday...
...Overview...
A rapidly opening upper low over the East on Saturday (spreading
some rain across the region) will provide the last vestige of the
current blocky pattern over and near the lower 48. Guidance is
consistent in showing the upstream flow settling into a
trough-ridge-trough configuration soon thereafter, with the
eastern Pacific trough axis likely pushing into the West around
the middle of next week as the eastern trough nears the East
Coast. The combination of upper ridging that crosses the West,
persistence of a mean ridge over the southern Plains, and with
time rising heights over the Southeast, should lead to an
expanding area of unseasonably hot weather across the southern
U.S. This heat will challenge daily record highs for multiple days
at some locations. New England may see record heat extend into
Saturday as well. A series of fronts pushed along by the
developing central-eastern U.S. cyclonic flow and extending back
into the Plains will produce episodes of showers and thunderstorms
through the period. At the same time the mean trough eventually
reaching the West Coast should send multiple waves/fronts into
western North America, supporting periods of rain and perhaps very
high elevation snow over the Northwest.
...Guidance Evaluation/Preferences...
Model guidance remains consistent with the overall pattern during
the medium range period, which begins Saturday with a closed upper
low in south-central Canada and the opening low/trough centered to
its southeast, while ridging builds into the interior West and
southern Plains. These features all show good agreement in the
00Z/06Z and newer 12Z models. Somewhat more notable differences
arise as troughing develops across the east-central U.S. by Monday
from combining features. GFS runs remain flattest/less deep with
the northern stream part of the trough while CMC runs are deeper
and slower than consensus and almost every individual ensemble
member (though the newer 12Z run perhaps in better alignment than
the 00Z through Monday, but beyond Monday the 12Z CMC closes off
an upper low over the Northeast unlike other guidance). Preferred
a middle ground solution like the 00Z ECMWF along with the UKMET
for the depth/extent of the eastern trough on Monday, and the
ECMWF and GEFS and EC ensemble means Tuesday and Wednesday.
This blend of model guidance (00Z/06Z deterministic model
composite led by the EC early on, phasing in the GEFS/EC means and
phasing out the CMC by day 5) also worked well for ridging
building west of the eastern trough, as well as troughing upstream
of the ridging. An upper low offshore of British Columbia could
send several shortwaves through the West with overall low
amplitude troughing coming in, but with differences in the low
predictability details. The 00Z CMC once again appeared too
amplified compared to consensus.
...Weather/Threat Highlights...
The combination of initial southern Plains ridging plus the upper
ridge crossing the West and reaching the Plains, along with
eventually rising heights over the South will likely promote an
expanding area of heat across much of the southern U.S. during the
period. The primary focus of this heat during the weekend will be
over the southern Plains (persisting from the short range time
frame) and over the southern half or so of the West with highs
10-15F or so above normal. By Monday-Wednesday the gradual
progression of the upper pattern should lead to slow
intensification of the heat over the southern Plains as highs
could reach up to 15-20F above normal, while plus 10-15F anomalies
spread eastward across the South. The upper trough nearing the
West Coast may offer slight cooling over California after Sunday
and eventually trim the coverage of plus 10F anomalies farther
inland. Potential for daily record highs will be most persistent
through the period over parts of the southern Plains. Record highs
are most likely over southern parts of the West Sunday into early
next week and should steadily spread east into the Lower
Mississippi Valley and Southeast during the first half of next
week.
On the other hand, surface waves/fronts ahead of the approaching
eastern Pacific upper trough will tend to keep the Pacific
Northwest on the cool side with precipitation of varying
intensity. Snow levels should be quite high into early next week
and then may decline somewhat as the upper trough begins to move
inland. Individual supporting shortwaves have low predictability
so it will take additional time to resolve details of when/where
precipitation could be locally heavier.
Moisture ahead of a couple fronts could bring lingering moderate
to heavy showers and thunderstorms to the Mississippi Valley
region early in the weekend, with a consolidated front becoming
more progressive as upper troughing heads toward and into the
East. Some rainfall along the front could still be fairly intense
but the greater progression may temper maximum totals over the
East. Another trailing front could also support some
showers/thunderstorms, while the trailing part of each front
should stall over the Plains and could focus additional
convection. Currently there are at least vague signals for locally
enhanced rainfall potential within a broad area between the
eastern Plains and Ohio Valley/central Appalachians south to the
Lower Mississippi Valley. However disagreements in
shortwave/surface front details make it difficult to resolve any
defined areas of relatively greater potential. At this point
signals point to enhancement across parts of the Lower Mississippi
Valley/Mid-South on Saturday, which could cause localized flooding
especially over areas of training convection and/or wet soils.
Near the East Coast, record heat should continue into Saturday
over New England. The rapidly opening upper low lifting through
the East will produce some areas of rainfall farther south over
the Mid-Atlantic and vicinity.
Tate/Rausch
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:
- Flooding possible across portions of the Upper Mississippi
Valley and the Northern Plains.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley, the Upper
Mississippi Valley, and the Northern Plains.
- Flooding likely across portions of the Upper Mississippi Valley
and the Northern Plains.
- Excessive heat across portions of California and the Southwest,
Sun-Tue, May 15-May 17.
- Excessive heat across portions of the Central Plains and the
Southern Plains, Sat-Wed, May 14-May
18.
- Much above normal temperatures across portions of the Lower
Great Lakes, and the Northeast, Sat,
May 14.
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