Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
519 PM EDT Tue Mar 23 2021
Valid 12Z Fri Mar 26 2021 - 12Z Tue Mar 30 2021
...Heavy rain possible across parts of the interior Deep
South/Tennessee Valley on Saturday...
...Overview...
An unsettled and active weather pattern is forecast for the
eastern two-thirds of the country through this weekend into early
next week, as shortwaves/troughs from both the northern and
southern streams tend to interact/merge across the region. A
compact and possibly intense low pressure system is forecast to
track through the Great Lakes and New England Friday to Saturday
before another developing system tracking across the same regions
Sunday into Monday with cyclogenesis possible near the New England
coast. A swath of moderate to heavy rain is forecast for parts of
the Deep South to the Tennessee Valley on Saturday under this
pattern. Meanwhile, much of the West should trend warmer/drier as
upper ridging builds into the weekend before the next system
enters the Pacific Northwest and brings another round of rain and
mountain snows to the region.
...Model Guidance/Predictability Assessment...
Among all of the model guidance, the ECMWF has been showing the
best level of consistency for the past few runs although it has
been generally the slowest piece of the guidance through the
medium-range period. The GFS has been on the fast side while the
CMC has been somewhere in between through Day 5 and then closer to
the fast solution through Day 7 for the Pacific Northwest system.
The preference for this morning's WPC medium-range forecast was to
use 50% 00Z ECMWF/EC mean. The 06Z GFS/06Z GEFS, and the 00Z
CMC/CMC mean made up the second half. More of the ensemble means
were incorporated for Days 5-7 to account for the increasing
uncertainty. Very good WPC continuity was maintained with a
slightly faster eastward progression of each system than the
previous forecast.
...Weather/Threats Highlights...
There is increasing model signals for a compact and possibly quite
intense low pressure system to track through the Great Lakes and
New England Friday to Saturday, bringing the potential for strong
and very gusty winds to the Northeast. Some heavy wet snow could
fall across northern Maine Saturday morning as the low pressure
center likely passes to the south. The trailing frontal boundary
in the Gulf of Mexico should lift northward as a warm front
focusing another round of moderate to heavy rainfall across parts
of the Deep South to the Tennessee Valley on Saturday. The next
system sends another cold front into the East on Sunday with
widespread light to moderate precipitation likely to impact the
Eastern states. This system could undergo cyclogenesis on Monday
as the center nears the New England coast, and could bring another
round of wintry precipitation for northern New England. Out West,
the trend should be towards warmer and drier weather this weekend,
ahead of the next system into the Pacific Northwest which should
bring another round of rain and mountain snow to the region early
next week with a return to cooler than normal temperatures.
The eastern third of the country will start out very warm Friday
afternoon with the greatest anomalies (+15 to +20F) across the
Mid-Atlantic and Northeast, and will remain warmer than normal
through the weekend. Morning lows will be even more so
anomalously warm, with several record high minimum temperatures
possible late this week stretching from Florida to the Northeast.
Troughing entering the region early next week should bring
temperatures back down towards normal next Monday and Tuesday.
Kong/Santorelli
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:
- Heavy precipitation across portions of the Northeast, Fri, Mar
26 and Sun, Mar 28.
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, the Southern
Appalachians, and the Tennessee Valley, Sat, Mar 27.
- Heavy snow across portions of the Pacific Northwest and the
Northern Great Basin, Sun, Mar 28.
- Heavy snow across portions of the Southern Rockies, the Central
Rockies, the Central Great Basin,
and the Southwest, Fri, Mar 26.
- Flooding possible across portions of the Central Plains, the
Middle/Lower Mississippi Valley, the
Tennessee Valley, the Southeast, and the Ohio Valley.
- Flooding occurring or imminent across portions of the Middle
Mississippi Valley and the Ohio
Valley.
- Flooding likely across portions of the Central Plains.
- High winds across portions of the Great Lakes, the Mid-Atlantic,
the Northeast, the Central
Appalachians, and the Ohio Valley, Fri, Mar 26.
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