Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
305 AM EDT Fri Mar 18 2022
Valid 12Z Mon Mar 21 2022 - 12Z Fri Mar 25 2022
...Strong low pressure system will likely produce heavy
rain/severe storms across portions of the southern U.S. and heavy
central Rockies snow by early next week...
...Overview...
The main upper level feature of note during the medium range
period will be an initially closed low/trough tracking from the
Four Corners states Monday northeastward through the workweek with
an associated surface low pressure system. This will spread a
myriad of significant and hazardous weather to the U.S., including
potentially heavy snow over the central Rockies and vicinity,
heavy rain from the south-central U.S. to the Ohio/Tennessee
Valleys and Southeast, and severe thunderstorms from Texas through
the Deep South. Some precipitation in the northern fringe of the
moisture shield could be in the form of snow for the
central/eastern U.S. as well. Behind this system a strong upper
ridge will build into the West, bringing mostly dry and warm
weather to the region.
...Guidance Evaluation/Predictability Assessment...
Model guidance agrees that a well-defined upper low should be
closed with its centroid likely over New Mexico by Monday morning,
lifting into the southern half of the Plains by Tuesday. The
initial position of this upper low along with the associated
surface low on Day 3/Mon did have a bit of west-east spread in the
12/18Z (yesterday) model cycle, with the ECMWF the farthest west
and GFS runs a bit on the eastern side, but a compromise position
of deterministic guidance worked well early in the medium range
period and was consistent with ensemble mean guidance and
continuity. Guidance also agrees that strong ridging coming into
the West will serve to amplify the trough.
By Day 5/Wed and beyond, there is more notable spread in the
12/18Z cycle (and run to run of guidance cycles) with the
evolution of the upper low/trough, with questions about stream
separation, width of the trough, and trough axis/how much energy
is held back to the west. The 12Z ECMWF was particularly neutrally
tilted and narrow with its trough pattern with more phasing in
northern and southern streams for Day 6/Thu. GFS runs were
positively tilted and with more stream separation, with some
southern stream energy held back across the south-central
U.S./Mexico for late week. The 12Z CMC appeared to be a broad,
rounded outlier with its 500mb height pattern compared to other
deterministic guidance and ensemble members by Wednesday through
Friday, more separated from the polar jet and the slowest solution
for its track eastward. However, the newer 00Z model cycle appears
to be more agreeable, and actually trending overall toward the CMC
with a more rounded upper low especially Wed with more separation
from the polar jet, and a slower overall trough movement.
At the time of forecast creation, the latter part of the medium
range period went to an ensemble mean-heavy blend perhaps earlier
than average given these differences, with manual adjustments to
deepen surface lows. The 12Z EC ensemble mean was a good proxy for
the preferred consensus at least in terms of mass fields, and the
WPC forecast had good continuity with previous forecasts from this
approach. Future changes to the forecast remain likely given run
to run model differences, perhaps with a slower front track
especially by Day 7/Fri in the East.
...Weather Highlights/Threats...
Ample Gulf of Mexico moisture flowing into the surface/upper-level
lows tracking across the country will lead to widespread rain and
thunderstorms for the Southern Plains and Lower Mississippi Valley
early in the week, spreading eastward into the Ohio and Tennessee
Valleys and Southeast by around midweek. Per the Storm Prediction
Center, storms could be severe in eastern Texas Monday and across
the Gulf Coast states as the week progresses. Furthermore, heavy
rain is likely to cause areas of flash flooding particularly due
to heavy rain rates Monday into Wednesday, and Slight Risk areas
are indicated near the Ark-La-Tex/eastern Oklahoma and for the
Lower Mississippi Valley/Mid-South region for Days 4 and 5 in the
experimental WPC medium range Excessive Rainfall Outlook. Rain
should spread into the Eastern Seaboard around Thursday.
Additionally, heavy snow is increasingly likely for the central
Rockies Monday, with some potential for snow to spread into the
High Plains as well, along with an area of enhanced rainfall
totals likely near the Central Plains/Middle Mississippi Valley
(though with lesser rainfall amounts than farther southeast).
Precipitation coverage from the northern half of the Plains into
the Midwest and Northeast has much lower confidence, but if
moisture reaches that far north some precipitation could be in the
form of snow. In the West, mainly dry conditions are likely after
a period of precipitation in the Pacific Northwest on Monday.
Somewhat below normal temperatures are expected underneath the
upper level troughing, with particularly high temperatures 10-20F
below average across the Intermountain West Monday and
central/southern High Plains Tuesday and Wednesday. The cooler air
should moderate closer to normal by the latter part of next week.
Meanwhile, the Midwest will see warmer than average temperatures
by around 20F on Monday, and generally warmer than normal
conditions are forecast for the eastern third of the U.S. through
much of the week ahead of the main system. The West should also
see warmth build with the ridging, with temperatures 10-20F above
normal expanding from the West Coast inland through the workweek.
Daily record highs are possible particularly in California.
Tate
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
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