…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 into Friday night…
The mid- to upper level flow pattern will become increasingly amplified
over the next few days with an omega block forming, with upper lows
developing atop California and 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 through Friday night. The
boundary is becoming quasi-stationary in some areas and bringing repeated
rounds of convection, as storms should have a tendency to move generally
parallel to the front. 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 are possible
through this evening and tonight. 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 (SPC) 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. SPC has added a
Slight Risk of severe weather from portions of the Carolinas into the
Mid-Atlantic for wind and hail risks. Moderate to locally heavy rainfall
is expected with some additional isolated instances of flash flooding
possible.
To the West, some scattered showers and thunderstorms are occurring along
a lingering frontal boundary in Arizona/New Mexico Friday. Meanwhile a
cold front is forecast to slowly move through the West for precipitation
chances ahead of upper troughing that drops south to form the upper low to
solidify the omega block. Precipitation chances will first pick up over
the Pacific Northwest Friday evening before spreading into the Great Basin
and Rockies to High Plains this weekend. Some snow will be possible for
some of the higher mountain peaks, particularly in the Sierra Nevada and
San Juan Mountains. A few strong to severe storms are possible in the
Great Basin Saturday and the southern High Plains Sunday. Locally heavy
rain producing isolated flooding is also possible across the central Great
Basin and Four Corners states, particularly by Sunday.
The increasingly amplified pattern stretching west to east across the
CONUS will bring large temperature contrasts heading into the weekend.
Most of the eastern third of the lower 48 is seeing a warmer than average
Friday with temperatures rising into the 70s and 80s. 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. But highs along the immediate
East Coast will remain well above average and into the 70s north with 80s
further south. Meanwhile portions of the Great Lakes/Midwest and much of
the Plains should 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 is seeing above average temperatures
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. This will lead to highs in
the 70s and 80s across the northern Plains, northern/central Rockies, and
eastern portions of the Great Basin. But much cooler temperatures are
forecast for the West Coast under the influence of the trough this
weekend, with highs dropping into the 50s and 60s.
Tate/Putnam
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
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