…Continued rounds of heavy rain and mountain snow for the Pacific
Northwest and northern Great Basin/Rockies…
…Heavy rain and severe thunderstorms return for eastern Texas and the
ArkLaTex on Thursday…
…Relatively mild conditions across the majority of the country through
Friday…
Active storm tracks over the northwestern as well as south-central U.S.
will keep unsettled, impactful weather in the forecast over the next
couple of days. In the Northwest, multiple upper-level waves/Pacific
systems will pass over the region bringing rounds of moderate to heavy
lower elevation/coastal rain, an inland lower elevation rain/snow mix, and
very heavy snow to the area mountain ranges. One wave will pass through
the Pacific Northwest overnight Christmas and into the Great Basin and
northern/central Rockies Thursday followed quickly by a second wave into
the Pacific Northwest by Friday morning. A flow of plentiful moisture
from the Pacific/Atmospheric River will lead to several inches of rain
along favorable upslope regions of the coastal ranges of the Pacific
Northwest and northern California through Friday with the potential for
some isolated flooding. In the mountains, storm total snowfall of at least
8-12″ will be common, with locally higher amounts of 2+ feet possible,
especially for the Cascades and ranges of the northern Great
Basin/Rockies. In addition, strong, gusty winds are also expected, and
will lead to blowing snow and very dangerous travel conditions in the
mountains.
Scattered showers and thunderstorms will taper off through Christmas
evening for portions of the Middle/Lower Mississippi Valley and western
Gulf Coast along a lingering frontal boundary following the passage of an
upper-level wave. Another wave approaching from the west will lead to lee
cyclogenesis over the southern Plains, helping to reinforce the frontal
boundary and encourage very moist Gulf return flow northward over eastern
Texas and the ArkLaTex overnight. Storms will increase in coverage and
intensity through Thursday morning and into Thursday afternoon, with
sufficient CAPE and wind shear for some severe thunderstorms. The Storm
Prediction Center has included a Slight Risk (level 2/5) of severe weather
for the threat of large hail, damaging winds, and a few tornadoes. In
addition, the plentiful moisture and intense storms will lead to some
locally heavy downpours, with a Slight Risk of Excessive Rainfall (level
2/4) also in place for the threat of some scattered instances of flash
flooding. The system will continue northeastward Friday, bringing an
expanding area of showers and thunderstorms across the Mississippi and
Lower Ohio/Tennessee Valleys. A few isolated severe thunderstorms and
instances of flash flooding will remain possible, particularly from the
Lower Mississippi Valley into the Lower Tennessee Valley.
Elsewhere, conditions will be mostly dry except for some isolated storm
chances over Florida. Most of the country will continue to see relatively
mild conditions temperature-wise through Friday, with the greatest
anomalies of 10-15 degrees focused over the Plains and Mississippi Valley.
Forecast highs generally range from the 30s and 40s for the northern
Plains and Great Lakes; the 40s and 50s for the Pacific Northwest, Great
Basin, northern/central Rockies, central Plains, and Ohio Valley; the 50s
and 60s for California and the southern Rockies/Plains; and the 60s and
70s for the Desert Southwest, Texas, the Lower Mississippi Valley, and
Florida. One region that will see some cooler, more seasonable conditions
Thursday will be along the East Coast, with temperatures in the 20s and
30s in New England, the 30s and 40s in the Mid-Atlantic, and 50s and 60s
into the Southeast. Temperatures will begin to warm above average for many
locations here as well on Friday, with highs generally 5-10 degrees
warmer.
Putnam
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php