…Upper-level omega block to form across the CONUS, leading to periods of
unsettled weather and large temperatures contrasts heading into the
weekend…
…Heavy rain, flooding, and severe weather threats to stretch from the
Southern Plains northeast into the Ohio Valley Friday…
The mid- to upper level flow pattern will become increasingly amplified
over the next few days with an omega block forming from California,
eastward into the Ohio Valley. This pattern will bring periods of
unsettled weather first to portions of the eastern and southern U.S., and
eventually to the western U.S. heading into the weekend. Southerly flow
supporting a moist airmass along a cold front stretching from the Lower
Great Lakes southwestward through the Ohio Valley, Middle/Lower
Mississippi Valley, and southern Plains will help to focus the first area
of showers and thunderstorms. The boundary is forecast to slow through
Friday and become quasi-stationary in some areas, bringing repeated rounds
of storms as storms will have a tendency to move generally parallel to the
boundary. The plentiful moisture will lead to locally heavy downpours, and
there is a Slight Risk of Excessive Rainfall (level 2/4) across portions
of the Lower Mississippi Valley/Mid-South, ArkLaTex, and southern Plains
where scattered instances of flash flooding will be possible. In addition,
increasing upper-level winds as an upper-level trough drops southward over
the very moist, buoyant airmass will lead to some more intense clusters of
thunderstorms. The Storm Prediction Center has outlined an Enhanced Risk
of severe weather (level 3/5) stretching from the Ohio Valley
southwestward through the Tennessee Valley, the Lower Mississippi Valley,
and into portions of Texas for the threat of damaging winds, large hail
(especially in Texas), and perhaps a tornado or two. The front will make
some progress south and eastward into Saturday, bringing shower and
thunderstorm chances to the Northeast, Mid-Atlantic, Appalachians, and
Southeast. Moderate to locally heavy rainfall is expected with some
additional isolated instances of flash flooding possible.
To the West, some scattered showers and thunderstorms will be possible
along a lingering frontal boundary through the Four Corners region
Saturday before a second upper-level trough solidifying the omega block
drops southward from the northeastern Pacific and over the West Coast by
late Friday/early Saturday. Precipitation chances will first pick up over
the Pacific Northwest Friday evening before spreading into the Great Basin
and northern Rockies Saturday. Some snow will be possible for some of the
higher mountain peaks, particularly in the Sierra Nevada.
The increasingly amplified pattern stretching west to east across the
CONUS will bring large temperatures contrasts heading into the weekend.
Forecast highs from the Ohio/Tennessee Valleys east to the East Coast will
remain above average Friday, with the greatest anomalies focused across
portions of the Mid-Atlantic. Forecast highs generally range in the 70s
across the Northeast and Ohio Valley with 80s for the Mid-Atlantic and the
Tennessee Valley/broader Southeast. The cold front will bring cooler
temperatures to the Ohio Valley and much of the Southeast Saturday as
highs fall into the 60s and 70s. Highs along the immediate East Coast will
remain well above average and into the 70s north with 80s further south.
Portions of the Great Lakes/Midwest and much of the Plains will be well
below average the next couple of days under the eastern trough, with highs
generally in the 50s and 60s for the Great Lakes/Midwest and 60s and 70s
for the central/southern Plains outside of southern Texas. Much of the
West will be well above average Friday, especially across the northern
Great Basin/Rockies, as highs rise into the 70s and 80s for most
locations. The well above average temperatures will shift eastward on
Saturday as the second upper-level trough drops southward along the West
Coast. Highs across the northern Plains, northern/central Rockies, and
eastern portions of the Great Basin will remain and rise into the 70s and
80s. Much cooler temperatures will come to the West Coast under the
influence of the trough with highs dropping into the 50s and 60s.
Putnam
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php