Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
359 PM EST Tue Jan 12 2021
Valid 12Z Fri Jan 15 2021 - 12Z Tue Jan 19 2021
...Overview and Guidance/Predictability Assessment...
The Pacific Northwest should catch a break in the prolonged heavy
precipitation event this Saturday before additional plumes of
moisture reach the region on Sunday and early next week. Farther
east, a low pressure system should be near its peak intensity
Friday morning as it tracks across the upper Great Lakes with
wintry precipitation gradually tapering off from west to east.
There has been a general model trend of delaying the eastward
progression of the weakening cyclone into southeastern Canada
during the weekend. In addition, the slower and more amplified
pattern also encourages a wave of low pressure to form along the
trailing cold front off the northern Mid-Atlantic coast on
Saturday and then rapidly lifts northward across New England.
This would increase the chance of heavy rain spreading into
interior New England during the day on Saturday after a period of
wintry precipitation most likely in the morning. The
precipitation should change back to a period of wet snow Saturday
night as the system lifts further northward into southeastern
Canada by Sunday morning.
Near the western Gulf Coast, a couple of upper-level troughs
sliding southeast across the southern Plains will help develop a
couple of low pressure waves just off the Texas coast. The first
wave should be more subtle as it moves across the region on
Sunday. By next Tuesday, a more vigorous wave appears to be
moving toward the region. The GFS shows a faster progression of
the associated rainfall across the Texas Gulf Coast region on both
days compared with the ECMWF.
The WPC morning forecast package was derived based on a consensus
of the 00Z ECMWF/00Z EC mean together with the 06Z GFS/06Z GEFS.
The CMC has not been included as its synoptic evolution appears
noticeably different from the ECMWF and the GFS.
...Weather/Threats Highlights...
Leading closed low energy into the Great Lakes would support a
combination of synoptic and lake effect/enhanced snows from the
Great Lakes into the northern/central Appalachians, with
precipitation also extending into parts of the Northeast. Heavy
rain could lead to snow melt issues on Saturday over interior New
England on Saturday. Expect rain in the southern part of the
moisture shield along the leading cold front into the East as
well. In the West, some light precipitation is expected along and
over favored terrain as various shortwaves move through. As
troughing again deepens over the Rockies/Plains this weekend,
precipitation may begin to push out of the mountains and expand
into parts of Texas and the lower Mississippi Valley early next
week.
Above normal temperatures should be fairly widespread across much
of the northern half and southwestern portions of the lower 48 on
Thursday, though temperatures +5-10 degrees should persist across
California and the Desert Southwest through the period. In the
East, the mild temperatures on Friday into Saturday will be
replaced by more typical mid-January values by early next week,
while parts of the Southeast and Rockies will see near to below
normal temperatures by about 5 degrees. Another round of above
normal temperatures should also move into the Northern Plains by
next week, with daytime highs 10 to 15 degrees above normal.
Kong/Santorelli/Fracasso
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
Hazards:
- Flooding occurring or imminent across portions of the Southeast,
the Mid-Atlantic, and the
Pacific Northwest.
- Flooding likely across portions of the Pacific Northwest and the
Northern Great Basin.
- High winds across portions of the Northern/Central Plains, Fri,
Jan 15.
- Heavy precipitation across portions of the Northeast, Fri-Sat,
Jan 15-Jan 16.
- Much above normal temperatures across portions of the Northeast,
Fri-Sat, Jan 15-Jan 16.
- Heavy rain across portions of the Lower Mississippi Valley and
the Southern Plains, Tue, Jan 19.
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