…Heavy rain and flash flooding threat expands from Southern California
into the Desert Southwest Tuesday…
…Heavy Snow for the Intermountain West mountains through mid-week…
…Temperatures will continue to run above average from the Plains to the
Northeast with record breaking warmth for parts of the Upper Midwest…
Showers and thunderstorms will continue to linger for Southern California
while increasing across the Desert Southwest Tuesday as Pacific moisture
flows northward ahead of a slow moving deep upper-level trough/surface
frontal system. The anomalously high moisture as well as favorable upslope
flow along the higher terrain of the Transverse and Peninsula ranges in
Southern California and the Mogollon Rim in Arizona will lead to locally
heavy rainfall. Slight Risks of Excessive Rainfall (level 2/4) are in
effect for the threat of some scattered instances of flash flooding for
both portions of Southern California and the Colorado River Basin.
Although rain rates/totals will be trending downward across Southern
California compared to the last couple of days, the risk for flooding and
mud/debris flows remains given the very wet antecedent conditions. For
higher elevations, snowfall will be coming down for the Sierra Nevada
while remaining heavy for elevations above 7000 feet in the
Transverse/Peninsular ranges.
A continued influx of moisture from the Pacific as the upper-level trough
moves slowly eastward will bring heavy snowfall to the regional mountain
ranges of the Intermountain West over the next couple of days. Some
particularly high totals are expected for the Four Corners region, where
amounts of 2+ feet are currently forecast. Other ranges of the Great Basin
and Northern Rockies will see totals generally between 6-12″, with some
locally higher amounts possible. Lower elevation/valley locations across
the region will see a mix of moderate rain and snow showers, though any
snow accumulations are expected to remain limited. Height falls beginning
to overspread the Northern/Central High Plains will also lead to enhanced
lee cylogenisis and a developing low pressure/frontal system Wednesday.
This will bring increasing chances for wintry precipitation spreading
eastward across the Northern High Plains as the system strengthens. Some
freezing rain and sleet will be possible, as well as for a few inches of
snow, particularly for northeastern Montana.
Elsewhere, the Midwest, South, and East Coast will remain mostly dry
through mid-week. Upper-level ridging over the central/eastern U.S. will
also keep temperatures generally mild and above average from the Plains to
the Northeast/Appalachians, with below average temperatures along the
coastal Southeast and west of the Rockies. Highs across the Northern
Plains/Upper Midwest in particular continue to remain upwards of 20-30
degrees above average, with 40s and 50s forecast. Some daily
record-tying/breaking high temperatures will be possible for the Upper
Midwest Tuesday and Wednesday.
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