Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
209 PM EST Sat Mar 13 2021
Valid 12Z Tue Mar 16 2021 - 12Z Sat Mar 20 2021
...Bouts of heavy rainfall possible across the southeastern
quadrant of the CONUS next week...
...Overview...
A robust, upper low will track east from the Four Corners region
through the extended period; which will keep the potential for
widespread rainfall with embedded areas of locally heavy amounts
across the South and into the Tennessee Valley. Multiple weakening
low pressure systems will approach the West, keeping a majority of
the precipitation in British Columbia. Prior to the passage of the
cold front, most of the CONUS will experience near seasonal
average for mid-March.
...Model Guidance/Predictability Assessment...
The 6Z and 12Z model guidance was fairly clustered with respect to
the deep mid/upper low exiting the Four Corners region into the
central US. The GFS was more open and faster than the ECWMF, CMC
and UKMET solutions to track the front through the Plains-
especially in the initial and middle periods. Preferred a heavier
weighting to non-NCEP guidance for this issuance. The blend mainly
was nearly equal parts of the ECWMF/CMC/UKMET with light weighting
of the 00Z/06Z runs of the GFS increasing inclusion of the EC
ensemble means and the GEFS means by mid and late periods as there
is timing uncertainty as the low/front tracks through the eastern
U.S. and offshore.
...Weather/Threats Highlights...
The leading system will spread light to modest rain/snow over the
Central Rockies and into the adjacent Plains Tuesday while the
rainfall increases areal coverage over the Southeast along the
warm front. Areas north of the frontal boundary will have light
snow from the Corn Belt to points east into the higher terrain of
the Central Appalachians, spreading to the Northeast toward the
end of the forecast period. Rainfall could be heavy in some
locations in the warm air mass near and inland from the Gulf Coast
Tuesday through Thursday. Farther west, approaching Pacific system
will spread low elevation rain and higher elevation snow to the
West Coast (NorCal and northern Sierra into coastal OR/WA)
especially Wednesday onward.
The Southeast will have mild temperatures through Wednesday with
numerous locations in the 70s. Meanwhile, colder than average
temperatures will be ushered in by the cold front exiting the
Rockies. The daily high temperatures will average 5 to 15 degrees
colder across most of the the Interior West and into the High
Plains toward the end of the extended period. With ridging
expected to build back into the West, warmer temperatures will
slowly return.
Campbell
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