Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
301 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 remains to be favored
across 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 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.
Thus, half of WPC morning medium-range forecast was based on 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 impact 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 with widespread
light to moderate precipitation likely to impact the Eastern
states on Sunday. This system could undergo cyclogenesis on
Monday as it nears the New England coast. The trend should be
towards warmer and drier weather out West 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.
The eastern third of the country will start warm and above normal
through the weekend, with the greatest anomalies (+15 to +20F)
across the Mid-Atlantic and Northeast on Friday. 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. Out West, temperatures should trend warmer after this
week as upper level ridging builds across the region.
Kong
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