…Widespread heavy rain threat emerging across the central to eastern
Gulf Coast region today will spread rapidly up the entire East Coast on
Wednesday…
…Active Lake effect snows to begin Wednesday and continue through
Thursday downwind of the Lakes…
…Record warm morning lows likely along the east coast Wednesday
morning…
…Arctic air to surge south into the Northern Plains/Upper Mississippi
Valley region late Tuesday into Wednesday…
…Santa Ana winds along with critical to extreme fire weather danger
across portions of southern California…
The upper-level flow pattern across much of North America will undergo
significant amplification over the next few days, producing various types
of impactful weather across mainland U.S. The most active weather in
terms of precipitation and winds will be the primary focus along the East
Coast through the next couple of days. Precipitation currently falling
across portions of the Southeast is in its organizing stage ahead of a
developing low pressure wave over the Mid-South along a cold front. As
the cold air behind the front interacts with a rapidly amplifying upper
trough, rain and embedded thunderstorms will rapidly expand northeastward
during the day Wednesday and up the entire East Coast, producing a period
of widespread heavy rainfall from the central to eastern Gulf coast,
across the Southeast, Mid-Atlantic, Northeast and New England. With much
of these areas currently in moderate to extreme drought conditions, this
rainfall will be beneficial. Still, given the potential for periods of
heavy rains over a short period, there will be a threat of localized flash
flooding, especially in more urbanized regions.
The cold front associated with this rapidly intensifying system will
become rather potent as it sweeps across the East Coast during the day on
Wednesday. There is potential for some very strong thunderstorms to form
ahead of the front together with heavy downpours. Meanwhile, drastically
colder air behind the front is forecast to produce accumulating snowfall
up the western slopes of the Appalachians on Wednesday together with
blustery northwesterly winds. The snow will then sweep across interior
New England through Wednesday night into Thursday morning as a potent
elongated low pressure system races northward into southeastern Canada.
With a warm southerly flow strengthening ahead of this potent front, there
is the potential for widespread record high morning low temperatures on
Wednesday across the southern Mid-Atlantic, Mid-Atlantic and portions of
the Northeast. In the wake of this front, much colder air will stream
across the Great Lakes from west to east beginning on Wednesday. This will
ignite active lake-effect snows, initially downwind of Lakes Superior and
Michigan on Wednesday and then downwind of Lakes Erie and Ontario
Wednesday night into early Thursday. Before these lake-effect snows
diminish by early Friday, snowfall totals of 1 to 2 feet are possible in
the favored Snow Belt across portions of northwest and western New York
State, far northwest Pennsylvania, far northeastern Ohio, the Upper
Peninsula of Michigan and the western portions of the Lower Peninsula of
Michigan.
The above-mentioned lake-effect snows will be driven by arctic air that
will be first surging east southeastward late Tuesday into early Wednesday
across the Northern Plains into the Upper Mississippi Valley and then
eastward trough the Great Lakes into the Ohio Valley on Wednesday. While
there are not expected to be any records with this arctic outbreak,
temperatures will be much below average on Wednesday across the Northern
Plains into the Upper Mississippi Valley. These much below average
temperatures will then push farther southeast into the Great Lakes and
Ohio Valley region on Thursday. Across these regions, high temperatures
will be 10 to 25 degrees below average during the height of the cold
temperatures during Wednesday and Thursday.
In contrast to the wet and cold conditions across portions of the
north-central to eastern U.S., dry condition and milder temperatures are
in store across the West coast, Great Basin and Rockies region. The dry
air, low relative humidities together with the latest episode of Santa Ana
winds across southern California will produce critical to locally extreme
fire weather danger. These fire weather conditions will be most prominent
in the higher terrain areas to the north and east of the Los Angeles to
San Diego region. Winds of 35 to 45 mph in the valleys and gusts of 50 to
65 mph in the mountains will help fan any fires that do develop quickly
and may reduce visibility with blowing smoke and dust adding to travel
concerns in the region. Across these areas, red flag warnings are
currently in effect, affecting nearly 13 million people.
By early on Thursday, the next round of coastal rain and mountain snow is
forecast to reach northern California as the next Pacific cyclone arrives.
Kong/Oravec
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php