Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM 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 heat 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 contiguous U.S. 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 to the east, 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...
12Z/18Z models and ensemble means (serving as the basis for the
updated forecast) along with the new 00Z runs continue to agree
for the overall pattern evolution but exhibit some
spread/variability with details. Among the 12Z/18Z solutions the
most notable issue involved the GFS, especially the 18Z run,
straying faster and deeper than most other guidance with the
shortwave reaching the Northwest around Sunday and the larger
scale trough pushing into the West Tuesday-Wednesday. This in turn
led to the 18Z GFS becoming faster with the eastern trough. The
12Z GFS was closer to consensus during the latter half of the
period in particular. The 12Z CMC became slower/more amplified
with the Pacific trough late in the period and has adjusted that
feature favorably in the 00Z run. However the new CMC has become a
lot more amplified with the eastern trough, which has been its
tendency in a number of earlier runs. Multi-day trends have
generally been toward slightly less amplitude with this trough but
consecutive model runs are still oscillating, causing shifts in
southward extent of the surface front reaching the East. Based on
the guidance comparisons through 18Z, the updated forecast started
with a blend of operational models early (GFS split between
12Z/18Z runs) followed by some incorporation of the 18Z GEFS/12Z
ECMWF means along with the 12Z GFS/ECMWF/CMC (but low enough CMC
weight to downplay its Pacific trough late in the period).
...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 of the southern Plains
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 shortwave/surface front details
are not sufficiently agreeable to resolve any defined areas of
relatively greater potential. 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.
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
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