Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
118 AM EST Sun Feb 14 2021
Valid 12Z Wed Feb 17 2021 - 12Z Sun Feb 21 2021
...Well below normal temperatures expected to continue across much
of the central part of the nation into Friday...
...Stormy pattern with wintry precipitation events from coast to
coast and late week heavy rainfall potential across parts of the
East...
...Overview and Guidance Evaluation...
By the end of next week and weekend the models and ensembles are
still advertising a flattening trend for mean flow aloft across
the lower 48. This evolution would bring a drier period and more
moderate temperatures to areas east of the Rockies by the end of
the forecast, while primarily focusing rain/mountain snow from the
northern half of the West Coast into the Rockies. In the meantime,
the prevailing pattern with an amplified mean trough over the
central U.S. will feature upstream western energy digging into the
Plains/northern Mexico by Thursday and then progressing through
the eastern half of the country. The associated low
pressure/frontal system will emerge from the Gulf and continue
northeastward after midweek. With record cold air in place over
the Plains/Mississippi Valley at the end of the short range period
and only gradual moderation expected thereafter, a widespread area
of wintry weather is likely to extend from the Southern Plains
through the Northeast.
The guidance has come into better agreement on the late week
eastern system, though the ECMWF continues to be just a hair
faster and stronger than the GFS/CMC. This results in a little
flatter western-central U.S. flow late in the period from the
ECMWF, while the GFS/CMC continue to suggest some degree of mean
ridging ahead of the next shortwave expected to arrive into the
Pacific Northwest by day 6/Saturday. Of course, even small
differences in the details like this would have more meaningful
impacts to exact areas of heaviest rainfall and/or more
significant winter weather. The WPC progs reflect a blend of the
deterministic solutions early in the period, with some increasing
contributions from the means beyond day 5 to mitigate detail
differences, especially with the next PacNW shortwave next
weekend. This approach maintains good continuity with the previous
shift.
...Weather/Threats Highlights...
Precipitation over the Southern Plains/Lower Mississippi Valley
will be increasing in coverage by the start of the medium range
period, eventually reaching into the East by Thursday and Friday.
Moderate to heavy rainfall is likely from the Gulf Coast through
Tennessee Valley/southern Mid-Atlantic, with a broad area of
winter weather impacts on the northwest/northern side of the
precipitation shield from the ArkLaTex region northeastward into
the Northeast. Also to note, the Storm Prediction Center continues
to mention severe weather potential within the warm sector of this
system, with details to be better resolved over the coming days.
Behind this system, another couple fronts reaching the Northwest
between Thursday and Saturday should bring the potential for
additional focused rainfall along coastal portions of
Washington/Oregon with heavy mountain snows in the
Washington/Oregon Cascades and northern Rockies. Meaningful
rain/high elevation snow may extend into parts of northern
California as well.
In terms of temperatures, widespread record cold at the end of the
short range period should begin moderating somewhat by Wednesday,
though widespread 20-40F below normal is still expected across the
central/southern Plains and the Mississippi Valley into Friday
with some potential for more daily records across southern areas.
Upper ridging should finally allow for some recovery of
temperatures back closer to normal by next weekend across this
region. Given the less extreme anomalies over northern areas to
start with, the moderating trend over the Plains may be sufficient
to yield modestly above normal highs over parts of the Dakotas and
vicinity by next Saturday. Temperatures in the West will be near
to moderately below normal through midweek followed by a warming
trend, especially over the Southwest where highs may reach 5-10F
or so above normal Friday-Sunday. The extreme Southeast/Florida
will be the one area of persistent warmth through early Friday,
with morning lows in particular expected to be well above normal.
However, below normal temperatures should spread across the
Sunshine State by later Friday/Saturday after passage of the front
anchored by the system affecting much of the East.
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, 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