Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
435 PM EDT Tue Apr 12 2022
Valid 12Z Fri Apr 15 2022 - 12Z Tue Apr 19 2022
...Overview...
Lower amplitude mean flow aloft should prevail over the lower 48
at least from Friday 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. By early next week an upper trough reaching the eastern
Pacific early next week may serve to amplify the downstream ridge
crossing the West and trough heading into the East, with the
Pacific trough likely entering the West next Tuesday and bringing
another episode of precipitation to the region. Within what has
been an 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 and 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. Through the 06Z cycle the GFS was on the faster side of the
spread but the new 12Z UKMET has adjusted closer to the GFS,
leaving the 00Z ECMWF/ECMWF mean a little on the slower side and
the 12Z CMC essentially a compromise. The new 12Z ECMWF has nudged
to a middle ground as well.
By the first part of next week, detail issues with the incoming
western system lead to additional divergence of solutions at the
surface and aloft over the East. The ECMWF through 00Z continued
to be the most consistent model in principle with development of
an embedded closed low along with surface system whose track is
over the mid-latitudes of the East, with its mean and the CMC/CMC
mean favoring similar timing which is slower than the GFS/GEFS
mean. The new 12Z GFS/CMC keep the core of the upper trough
farther north which leads to a much farther north surface low
track than what other guidance had been showing through the
00Z/06Z cycles. The 12Z GEFS mean has adjusted the surface track
at least partially in the 12Z GFS/CMC direction. Meanwhile the new
12Z UKMET becomes a fast extreme with greater strength than
consensus. The 12Z ECMWF has adjusted its upper system northward
somewhat but not to the extent of the GFS/CMC. The upper trough
reaching the West by Tuesday was closer to consensus in the 00Z
GFS versus the faster 06Z run, while the 12Z version has reverted
back to the majority. The new CMC/ECMWF are fairly consistent. The
early-period blend based on 00Z-06Z based guidance transitioned to
a model/mean mix tilted somewhat more toward the ECMWF/ECMWF mean
relative to the GFS/GEFS, with 06Z GFS input switching to the 00Z
run late.
...Weather Highlights/Threats...
The departing low pressure system north of the Great Lakes will
likely continue to bring gusty winds into Friday across the
northern tier, resulting in blowing a drifting of snow and
possible hazardous travel conditions in regions that received
heavy snowfall in prior days. This system may also produce some
generally light precipitation across the Great Lakes/Northeast.
Moisture and instability interacting with a warm front lifting
through the Southeast and Lower Mississippi Valley next 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 focus rain/mountain snow over the central and northern West
Coast into the northern Rockies late this week into the weekend.
Currently the best signal for heaviest totals is from southwest
Oregon into northern California but still with some uncertainty
over exact location and magnitude. 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. Locally colder readings
(especially for daytime highs) are possible late this week into
the weekend with some lingering daily records for lows/cold highs
possible mainly on Friday. Over the West, temperatures should
moderate in between systems as a period of upper ridging moves
through. Friday-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 this
weekend, 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 Friday-Sunday followed by a cooling trend.
Rausch/Santorelli
Hazards:
- Heavy precipitation across portions of northern California into
southwestern Oregon, Fri-Sat, Apr 15-Apr 16.
- Heavy precipitation across portions of northern California into
southwestern Oregon, Mon-Tue, Apr 18-Apr 19.
- Heavy rain across portions of the interior Deep South to the
Southeast, Sun-Mon, Apr 17-Apr 18.
- Heavy rain across portions of the New England coast, Tue, Apr 19.
- Flooding possible across portions of the upper Great Lakes to
the northern Plains.
- Flooding occurring or imminent across portions of the Southeast
and the mid-Mississippi Valley.
- Flooding likely across portions of the Red River near the
Canadian border.
- High winds across portions of the central Rockies and into the
central High Plains, Sun, Apr 17.
- Much below normal temperatures across portions of the interior
Pacific Northwest, Fri, Apr 15.
- Much below normal temperatures across portions of the northern
Rockies to the northern High Plains, Fri-Sun, Apr 15-Apr 17.
- Much below normal temperatures across portions of the northern
Plains, Fri-Tue, Apr 15-Apr 19.
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