Heavy Snow in Nevada, April 6 to 7, 2020

Area Forecast Discussion
National Weather Service Las Vegas NV
159 PM PDT Mon Apr 6 2020

.SYNOPSIS...Active weather pattern is underway as a strong low
pressure system lingers over the region for much of the week.
Periods of heavy rainfall, and significant mountain snow are
expected. Improving conditions are anticipated over the weekend.

&&

.SHORT TERM...through Friday.

Impressive, late season low pressure system will be the main
driver the weather details for the coming days. It remains on
track to very slowly dip southward along the SoCal coast before
meandering inland by midweek. Thus far, precipitation has been
fairly light and sporadic, mainly focused across our western
zones, though some of the mountain terrain has squeezed out over a
quarter of an inch since this morning. This frontal band will very
slowly work eastward this afternoon and overnight, sparing Las
Vegas the Colorado River Valley much precipitation during the
daylight hours today. As the band of precipitation moves through
tonight, expect mostly light precipitation totals of 0.10-0.25
inches across the desert valleys, with precip totals dwindling
with eastward extent.

Tomorrow, the aforementioned frontal band will tend to wash out
across southern Nevada with gloomy and damp conditions but
generally only light precipitation lingering. Then by late in the
day, the low off the coast of San Diego will begin to make its
approach into the deserts, with strong forcing and anomalous
moisture combining for a significant precipitation event across
much of the Mojave Desert region. Strongest forcing is expected
during the overnight hours Tuesday night into Wednesday morning,
with a band of heavy rainfall stretching central San Bernardino
County northward into eastern Inyo county. Rainfall totals of 1-2
inches will be possible with this activity, much of which could
fall in a 6-12 hour window. With these kind of rates and the
already very sensitive soils of the Mojave, went ahead with a
Flash Flood Watch for much of Inyo and San Bernardino counties
from Tuesday into Wednesday afternoon.

Further east, second round of rainfall will likely hold off until
Wednesday afternoon for Las Vegas and points north and east as the
low creeps closer. While overall rainfall totals will be a little
less than Inyo and San Bernardino counties, there will still be a
marginal risk of excessive rainfall, especially with any
thunderstorm activity that may occur Wednesday afternoon. Rainfall
totals of 0.50-1" remain likely for most desert valleys along and
west of the Colorado River Valley, with amounts tempering downward
across Mohave County.

By Thursday, confidence decreases slightly as there are
discrepancies in the exact location of the low. Favored slower
solutions given that the low is pretty well cut off from the mean
flow, which would keep conditions rather unsettled into Thursday.
Should the ECMWF solution verify, the cold core aloft would be
still parked over Southern NV, likely resulting in widespread
showers and afternoon thunderstorms. The low should finally start
pushing eastward with conditions drying out by Friday. By the time
all is said and done, The Spring and Sheep Range, as well as the
Sierra should have a healthy new coat of 1-3 feet of snow above
6500 feet.

.LONG TERM...Saturday into early next week.

Confidence in the longer term is fairly low and a lot hinges on
details still being resolved in the shorter term period.
Nonetheless, still anticipate the low pressure system which
brought so much disturbed weather for the past week to be filling
and pushing eastward, with heights rebounding and conditions
drying out. Temperatures should also return to mid April normals.
Thereafter, longer ranger solutions favor a more northwesterly
flow pattern which would resume our typical dry conditions but
could result in occasional bouts of gusty winds.

&&

.AVIATION...For McCarran...South-southeasterly winds with
occasional gusts to 20 knots will remain possible for another hour
or two before shifting to a more southerly direction. A stray
shower is possible late this afternoon, but better chances of
light rain at the terminal will hold off until after 3z, along
with CIGs gradually lowering below 5kft AGL. By dawn Tuesday, CIGs
may decline as low as 2kft AGL with light showers lingering into
the morning. Slight improvements expected during the day but CIGs
will struggle to rise above 5kft through Tuesday afternoon.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light rain and reduced ceilings will continue to
impact TAF sites DAG and BIH through this evening, with CIGs at
times falling to between 3-6kft AGL. Shower activity will develop
eastward tonight, but tend to stay west of the Colorado River
through sunrise Wednesday. Another round of heavier precipitation
will develop Tuesday afternoon and spread across the Mojave
Desert Tuesday evening with low CIGs and mountain obscuration
likely.

&&

.CLIMATE...
A late-season storm looks to break daily precipitation records
across the region.

DAILY RECORD RAINFALL TOTALS

               MON 4/6      TUE 4/7      WED 4/8      THU 4/9
Las Vegas, NV  0.10 (1986)  0.35 (1958)  0.28 (1943)  0.81 (2016)
Bishop, CA     0.41 (1986)  0.90 (2017)  0.21 (2016)  0.71 (2016)
Barstow, CA    0.07 (1986)  0.27 (1958)  0.34 (2016)  0.43 (1975)
Needles, CA    0.50 (1906)  0.35 (1978)  0.67 (2016)  0.13 (1978)
Kingman, AZ    0.35 (1906)  0.43 (1943)  0.48 (2016)  0.71 (1965)

&&

.SPOTTER INFORMATION STATEMENT...An unusually potent late-season
storm system will bring gusty winds, desert rain, and mountain
snow to the region for much of the upcoming week. Embedded
thunderstorms are possible through the week, especially Wednesday.
Though spotter activation is not anticipated at this time,
spotters are encouraged to report any wind impacts or
precipitation amounts according to standard operating procedures.

&&

DISCUSSION/AVIATION...Outler

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