Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EDT Wed Apr 13 2022
Valid 12Z Sat Apr 16 2022 - 12Z Wed Apr 20 2022
...Overview...
Lower amplitude mean flow aloft should prevail over the lower 48
at least through the weekend, behind a departing deep upper low
which may take its time drifting across eastern Canada into next
week. Guidance generally shows a shortwave and associated
rain/snow progressing into and through the West during the weekend
then into the Plains/Mississippi Valley by early next week.
Meanwhile, an upper trough reaching the eastern Pacific by Monday
may serve to amplify the overall flow with potential for a closed
low over the Great Lakes/Midwest around next Monday-Tuesday and
into the Northeast by Wednesday. Within what has been a decently
agreeable forecast of the large scale pattern, persistent
significant detail differences at the surface and aloft keep
confidence lower than desired for coverage and intensity of
precipitation--especially over the eastern half of the country
from Sunday onward but also to some degree over the West.
...Guidance Evaluation/Predictability Assessment...
The first half of the period started with a composite of latest
operational runs. This part of the forecast involved primarily
timing issues, with the GFS beginning to stray a bit faster than
most other guidance for the surface front and supporting dynamics
crossing New England during the weekend. There's also some initial
spread/variability persisting for the system reaching the West by
Saturday. The western system has some degree of complexity,
involving potential interaction of a trough/upper low off the
Pacific Northwest/Vancouver Island and separate shortwave just to
the south. The 18z GFS and 12z UKMET both were faster than the
ECMWF and CMC. The UKMET is also the quickest/farthest south to
close off a low over the Ohio Valley and was not included in the
blend for tonight. By days 6-7, the ECMWF and the ECENS mean both
become noticeably slower with the upper system through the
Northeast, with the CMC continuing to be a nice middle ground
(along with the NAEFS mean). The new 00z runs actually look a
little more agreeable, with the GFS slowing a bit and the ECMWF a
little faster than the previous run. The 00z UKMET remains a
fast/south outlier. The next system enters the West Coast early
next week with again, the GFS a fast/stronger outlier and wanting
to close off an upper low over the Northern Plains/Upper
Mississippi Valley next Wednesday. Prefer a blend towards the
slower ECMWF/CMC along with modest inclusion of the NAEFS/ECENS
ensemble means for the later periods.
...Weather Highlights/Threats...
The departing low pressure system north of the Great Lakes should
continue to produce some generally light to moderate precipitation
across the Great Lakes/Northeast as a secondary surface low lifts
off the coast. Moisture and instability interacting with a warm
front lifting through the Southeast and Lower Mississippi Valley
this weekend and approach of a cold front from the north should
bring areas of moderate to locally heavy rainfall to parts of
those areas, but for now with low confidence in exact placement of
heaviest totals. Farther west, a system forecast to reach the West
by Saturday should continue to focus rain/mountain snow over the
central and northern West Coast into the northern Rockies late
this week into the weekend. Moisture should spread east beyond the
Rockies Sunday onward as low pressure/fronts reach the
central/eastern U.S.. At least some precipitation across the
northern tier may be in the form of snow while rainfall
coverage/intensity over the East will depend on currently
uncertain system details. The central Rockies/High Plains could
see a brief period of strong winds around Sunday with system
passage. Expect another episode of precipitation from the Pacific
Northwest/northern California into the northern Rockies early next
week, with some enhanced totals possible over favored
coastal/terrain areas.
The core of below normal temperatures across the northern High
Plains will likely persist into early next week, with daytime
highs generally 20-30F below normal, and moderating slowly with
time. Over the West, temperatures should moderate in between
systems as a period of upper ridging moves through. Saturday will
feature chilly readings over the northern half of the region
(minus 10-15F anomalies for highs) and closer to normal
temperatures farther south. As the upper ridge builds over the
region by the start of next week, northern locations should trend
toward normal and southern areas above normal. The Great Basin and
Southwest could see highs as warm as 10-15F above normal. The East
should stay near normal on Saturday, but the system potentially
reaching the Midwest/East early next week could draw some of the
chilly northern Plains air southward and eastward behind it, with
expanding coverage of minus 10-20F anomalies. The southern Plains
will see highs 10-15F above normal next weekend followed by a
cooling trend.
Santorelli/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