…Life-threatening, catastrophic, and potentially historic flash flood
event continues across the Lower Ohio Valley and Mid-South to Lower
Mississippi Valley…
…Additional episodes of significant severe weather expected from the
Southern Plains to the Ohio Valley…
…Moderate to locally heavy snow showers expected for the
Central/Southern Rockies through Saturday…
…Well above average warmth in the East; chilly temperatures in the
Central U.S….
Several developing waves of low pressure acting on a stalling frontal
boundary will continue to be the focus for the threat of life-threatening
flash flooding and significant severe weather from the Ohio Valley
west-southwest through the Middle/Lower Mississippi Valley, Mid-South, and
ArkLaTex through Saturday. Deep moisture pooling along the front combined
with impressive dynamics will set the stage for persistent rounds of
intense thunderstorms capable of producing torrential downpours throughout
the region. This will especially be the case for the Lower Ohio Valley
into the Mid-South and Lower Mississippi Valley, where the necessary
ingredients of moisture, instability, forcing, and wind shear best
overlap. Storm initiation and movement roughly parallel to the boundary
will lead to repeated rounds of heavy rainfall over the same areas,
leading to significant to extreme, potentially historic, rainfall totals
over increasingly saturated soils. High Risks (at least 70%) of Excessive
Rainfall remain in effect through Saturday, highlighting an increasingly
dangerous and life-threatening situation. Outside of the High Risk,
Moderate and Slight Risks also continue to be in place over broader areas
of the Ohio Valley into the south-central U.S. through Saturday where
scattered to numerous instances of flash flooding can be expected. As has
been said repeatedly for the last several days, this has the makings of a
catastrophic, potentially historic heavy rainfall and flash flood event,
with some locations potentially seeing rainfall amounts as high as 10-15″+
through the weekend. The repeating rounds of heavy rainfall each day will
also raise the risk of widespread significant river flooding, including
potentially catastrophic major flooding, in the Ozarks, portions of the
Middle Mississippi Valley, and much of the Ohio Valley. Thankfully, the
heaviest rainfall should ease somewhat for the hardest hit areas on Sunday
as the frontal boundary finally begins to push eastward into the Southeast
and Mid-Atlantic; however, major river flooding is likely to continue into
early next week. With the front on the move, the focus for heavy rainfall
shifts eastward into parts of the Carolinas southward to the Central Gulf
Coast to round out the weekend. A Slight Risk (at least 15%) remains in
effect as a result.
In addition to the flash flood threat, additional bouts of significant
severe weather will also be in play for many of the same locations through
the weekend. The same ingredients of moisture, instability, forcing, and
wind shear that are conducive to intense downpour producing thunderstorms
are also supportive of supercells and severe weather. The Storm Prediction
Center has issued a Moderate Risk (level 4/5) for tonight from the
ArkLaTex into southeast Missouri for strong tornadoes, very large hail,
and damaging winds. A broader Slight Risk is in place from Texas through
the Lower Ohio Valley. On Saturday, Slight to Enhanced Risks are
delineated for the Lower Mississippi Valley through the Mid-South and Ohio
Valley, with severe thunderstorms capable of producing strong tornadoes,
very large hail, and damaging wind gusts above 70 mph. Similar to the
flash flood threat, the severe weather risk shifts eastward into parts of
the Mid-Atlantic, Southeast, and southern Appalachians on Sunday, with the
Storm Prediction Center issuing a Slight Risk for the potential for
damaging winds and possibly a few tornadoes.
Farther west, a passing cold front will help support snow showers over the
Rockies as well as portions of the High Plains through Saturday.
Accumulations are expected to remain light. To the south, an area of low
pressure in the lee of the Rockies will help to focus upslope flow along
the mountains, resulting in moderate to locally heavy snows for the
regional mountain ranges on through this evening, with the potential for
some snow for portions of the High Plains along the Front Range. The cold
front to the north will also pass southward by late tonight and into the
day Saturday, bringing renewed post-frontal upslope flow and additional
heavy snow for the mountains of the Front Range. There is also an
increasing potential for accumulating snow to spread across portions of
New Mexico and into the southern High Plains into Saturday. Drier weather
returns on Sunday as high pressure settles over the Central U.S..
The highly amplified flow pattern will lead to well above average
temperatures across the Southeast as an upper-level ridge dominates the
region. Meanwhile, temperatures will remain much cooler and below average
under the upper-level trough over most of the Western/Central U.S. Highs
the next couple days across the Southeast are forecast to be in the 80s to
low 90s, with numerous record-tying/breaking highs possible. Farther
north, a cool surface high will take hold in the Northeast Saturday with
below normal highs in the 40s. Some wintry weather can’t be ruled out
across northern New England on Sunday either given persistently cool
temperatures on the north side of the front. Meanwhile, forecast highs
across the Plains into the Interior West will be mostly well below
average. Southern Rockies/High Plains can expect highs that are below
average by 20-25 degrees by Saturday with actual highs falling into the
40s. The West Coast can expect warmer, above average temperatures compared
to the rest of the West as a ridge builds northward over the region, with
highs in the 60s and 70s The West will continue to warm up on Sunday while
cooler air across the Plains spreads eastward into the Ohio Valley, the
Mid-South, and the Lower Mississippi Valley.
Kebede/Miller
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
