Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
254 PM EDT Mon Mar 21 2022
Valid 12Z Thu Mar 24 2022 - 12Z Mon Mar 28 2022
...Overview...
Expect an amplified upper level pattern from late this week into
early next week, with some degree of progression. An eastern
Pacific trough should move into the West by around next Monday
while the mean ridge persisting over the West into the weekend
pushes into the central U.S. This gradual shift in the pattern
will eventually bring some moisture into the West and moderation
of potential record warmth over California and the Great
Basin/Southwest. Meanwhile the elongated upper low/trough over the
east-central U.S. as of early Thursday and the associated
precipitation will lift away fairly quickly but upstream
shortwaves will reinforce a fairly deep mean trough over the East,
producing chilly temperatures along with one or more episodes of
mostly light rain/snow over the northern half of the region.
...Guidance Evaluation/Predictability Assessment...
The latest cycle of guidance shows decent agreement with the large
scale pattern but there are persistent detail uncertainties. For
the system over the East as of early Thursday, consensus shows a
triple point wave over the Mid-Atlantic becoming the more dominant
feature Friday-Saturday as it tracks over/near New England and
into the Canadian Maritimes. Track differences are generally
within typical spread for a few days out in time. Into Saturday, a
faster trend in the 12Z CMC versus its questionably slow 00Z
version has improved clustering for the shortwave initially
rounding the western ridge and then digging into the eastern mean
trough. Thus far there is not much of a signal for flow to
separate within the trough as depicted in the new 12Z UKMET by
early Sunday. The reinforcing trough energy should support
offshore low pressure by early Sunday, most likely off the
Northeast and then tracking into/near the Canadian Maritimes per
the model and ensemble majority.
At least before today's 12Z cycle, over the past couple days the
ECMWF/ECMWF mean have generally been more consistent than the
GFS/GEFS with the handling of the eastern Pacific upper trough
moving into the West. The main adjustment in the ECMWF/ECMWF mean
has been a slightly faster trend. On the other hand GFS runs have
varied considerably for the handling of individual components of
the overall trough and upstream flow. 12Z/20 through 00Z/21 runs
were quick to separate flow within the trough, leading to an upper
low hanging back well offshore into early next week. More recent
06Z/12Z runs have adjusted faster and better fit within the
ECMWF-ECens/CMC-CMCens cluster. However the 06Z GFS differed from
most solutions in bringing enough southern stream energy into the
Plains late in the period to raise eastern U.S. heights more than
consensus (00Z and new 12Z runs appeared more reasonable). The
GEFS mean has trended a bit slower over the past day. Individual
ensemble member spread becomes very broad late in the period so
confidence in any particular solution is only moderate at best,
and now the 12Z ECMWF's change to more flow separation and slower
upper low further highlight the uncertainty here.
Review of 00Z/06Z guidance led to using the 06Z GFS/ECMWF and
lesser weight of the 00Z UKMET/CMC for the first half of the
forecast, and downplaying the slow CMC for the reinforcing eastern
U.S. trough. The rest of the period transitioned to a model/mean
blend and eventually split GFS input among the 00Z/06Z runs as one
run or the other had more or less appealing traits depending on
the region. The end result provided good continuity in principle.
...Weather Highlights/Threats...
An occluded low pressure system will be in place over the Upper
Great Lakes early Thursday, with lingering light precipitation
there but with heavier amounts possible along its associated cold
front near the East Coast. Expect mainly rain but snow will be
possible over northern New England, and the snow could linger into
Friday over Maine near a developing coastal low. Shortwave energy
and weak low pressure/frontal systems could lead to light
precipitation spreading from the northern Rockies/Plains Thursday
into the Great Lakes region to the central/northern Appalachians
and Northeast late week into the weekend. Some of this
precipitation may be in the form of snow over higher
elevations/northern latitudes. The central/eastern U.S. evolution
may lead to a period of brisk to strong winds from the northern
Plains late this week into the East during the weekend.
Precipitation ahead of the approaching eastern Pacific upper
trough will likely reach the Pacific Northwest around Friday and
then spread across more of the West thereafter. Most of this
activity should be in the light to moderate range but some locally
heavier totals could be possible depending on exact system
details. Coverage and intensity of this precipitation becomes
increasingly uncertain by late weekend into early next week.
Unseasonably warm temperatures will build and expand underneath
upper ridging from the western U.S. into the Plains. Highs that
are 10-20F above normal will be common over California and the
Central Great Basin/Southwest Thursday and Friday, with some plus
20-25F anomalies appearing in the Great Basin Saturday and moving
to the northern/central High Plains early next week as the upper
ridge axis shifts. Daily record temperatures could be tied or set
across California and eastward. The most likely scenario has an
increasing portion of the West seeing highs closer to normal by
next Monday but there is lower potential that above normal
readings could persist a little longer. Meanwhile, cooler air
underneath the upper trough/low over the central into eastern U.S.
should moderate as it moves eastward, with temperatures generally
10F or less below normal. However, additional cold fronts and
upper energy will bring below normal temperatures to parts of the
eastern third of the U.S. by Sunday, with the Great Lakes and
central Appalachians seeing 10-15F below normal highs.
Rausch/Tate
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
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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml