Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
201 AM EST Thu Jan 07 2021
Valid 12Z Sun Jan 10 2021 - 12Z Thu Jan 14 2021
...Overview...
Trend in the upper pattern next week will favor western ridging
and eastern troughing, but with an uncertain evolution of the
embedded smaller-scale features. Split flow out of the Pacific
will take a southern system across the Gulf and off the Southeast
coast, then perhaps just offshore the Mid-Atlantic and Northeast
by the middle of the week. The Pacific Northwest will continue
their recent active pattern with several systems tied to the Gulf
of Alaska that maintains WSW flow into coastal Washington and
Oregon. Cooler than normal temperatures are forecast for the
southern tier with milder than normal temperatures for the
northern tier.
...Guidance/Predictability Assessment...
Consensus blend approach served well for only the start of the
period Sun-Mon with the developing system in the Gulf and frontal
approach in the Pacific Northwest. Thereafter, GFS/ECMWF were
closer in agreement with their ensembles and to each other in the
West (until next Thu) as heights rise, but diverged markedly in
the Southeast in timing/track of the southern system. Overall
trend has been unsteadily slower but that still depends on
difficult-to-predict smaller-scale shortwaves out of the northern
stream, leaving a broad consensus or middle ground an attractive
starting point. However, with a preference to nudge a bit slower
only the 12Z ECMWF ensemble mean was near this middle ground as
the GFS runs remained quickest and ECMWF slowest. Confidence
remained low with this system as it would not take much to trend
quicker again with a more sheared system that ejected in pieces.
...Weather/Threats Highlights...
The Pacific Northwest will continue to see rounds of precipitation
with few breaks during the period. Low confidence in details of
shortwaves carried by fast flow aloft will temper confidence for
precise intensity and southward extent at any particular time.
Still the overall guidance signal is for heaviest rain/high
elevation snow to be during the first part of next week (Mon-Tue)
and especially over Washington. The system emerging into the
western Gulf Sunday may access enough Gulf moisture to produce
some locally enhanced rainfall along and just offshore from the
Texas coast. Farther east, light to moderate rainfall is possible
across the Deep South with enhancement near the area of low
pressure should it maintain itself or deepen. Some snow will be
possible over parts of the southern Plains/lower Mississippi
Valley well inland. Confidence remains low for precipitation
coverage and type over the East during the early/middle part of
next week. Amounts could trend lower or slightly higher depending
on future shifts in the track/speed/intensity.
Expect locations from Montana into Minnesota to be in the core of
warmest temperature anomalies through the period, with some
coverage of plus 10F or greater anomalies each day. Morning lows
should generally be farther above normal than the daytime highs
with plus 20F or greater anomalies for lows most likely next
Wed-Thu. Strengthening upper ridge should lead to more widespread
plus 5-10F or so anomalies over the West Coast states into Nevada
heading into midweek. Within a cool pattern for the southern tier,
the best potential for highs more than 10F below normal will
extend between the southern Plains and Lower Mississippi Valley
from Sunday into the start of next week. Readings across the South
should moderate gradually by midweek.
Fracasso/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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml