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-- Discussion containing changed information from previous version are highlighted. --
577
FXUS65 KREV 190931
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
231 AM PDT Mon Apr 19 2021

.SYNOPSIS...

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Dry and warm spring conditions continue today. A low pressure
system will then drop into the area Tuesday and Wednesday with
cooler temperatures, increased winds and chances for showers. A
few thunderstorms are also possible. Drier and warmer conditions
return later this week, with a wetter storm is possible by late
next weekend.
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&&

.DISCUSSION...

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Another day like Sunday is in store today with the main difference
being a turn to a more west-northwest wind this afternoon and high
temperatures about 5 degrees warmer (upper 60s Sierra valleys to
mid-upper 70s in warmer lower elevations).

Model consensus is reasonably good in dropping a compact upper low
into northeast CA Tuesday, with the system moving south
along/just west of the Sierra early Tuesday night before turning
east across southern NV Wednesday. Marginal instability and
forcing will be sufficient for scattered showers/isolated
thunderstorms along its track with some of the scenarios still
painting some locally stronger cells and decent QPF signatures
over northeast CA, from about Truckee northward into Lassen
County. While overall QPF amounts will be 0.20" or less and in
many cases just a few hundredths, amounts may exceed 0.50" with
stronger clusters of storms. Showers will likely decrease going
into the late evening and overnight hours Tuesday night as forcing
and heating wane. On Wednesday, north winds will be advecting
drier and more stable air into western NV and northeast CA. This
will limit shower/storm potential mainly to the Sierra south of
Lake Tahoe, with northeast steering currents favoring the west
slopes. However, outflow could still force a few storms east of
the crest into the Highway 395 corridor of Mono County.

Surface pressure/thermal gradients tighten ahead of this low in
the eastern Sierra Tuesday afternoon. Wind gusts approaching 35
mph and dry air will bring elevated fire weather concerns,
especially to southern Mono/Mineral counties (see fire weather
discussion for more information). Otherwise, expect cooler and
more seasonal temperatures both Tuesday and Wednesday.

A few showers may linger in the Sierra close to Mammoth Lakes
Thursday, otherwise a shortwave ridge will build into the region
Thu-Fri for warmer and drier conditions. West winds will begin to
increase Friday afternoon as surface thermal gradients begin to
increase again with the warmer afternoon temperatures.

A couple of the ensemble clusters continue to favor a trough over
the eastern Pacific this weekend with the GFS ensemble IVT
probabilities indicating plenty of moisture available, although it
points the main plume between 40-45N. The national blend of
models was increasingly wet for the Sierra, and the forecast
maintained chance POPs and light-moderate QPF. However, there is
at least one cluster that is drier and a lot still depends on how
the tropics (specifically Typhoon Surigae east of the
Philippines) phase with the progressive westerly flow into North
America. Definitely worth watching as we could use the
precipitation! Hohmann
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&&

.AVIATION...

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VFR conditions today with late day west winds 10-15 kts along the
eastern Sierra slopes to about Hwy 95. Elsewhere, winds will be
more northwest to north, also 10-15 kts.

A compact low pressure system will drop through the area Tuesday-
Tuesday evening for a chance of showers and slight chance of a
thunderstorm. The chances for a thunderstorm at KTVL-KTRK-KRNO-
KCXP-KMEV late Tuesday afternoon-early Tuesday evening is around
15%. West winds 15-20 kts with gusts to 30 kts will be possible
along the eastern Sierra Tuesday afternoon, including KMMH.
Hohmann
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&&

.FIRE WEATHER...

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A weak area of low pressure will drop into the region Tuesday into
Wednesday, bringing showers and isolated thunder to parts of
eastern CA and western NV. Humidity values will be relatively high
so if any lightning strikes occur they are unlikely to ignite any
significant fires.

Farther south in Mineral and southern Mono counties, wind gusts
could reach 30-35 mph Tuesday afternoon. These gusty west to
northwest winds combined with very dry conditions (RH 5-15%)
will create localized critical fire weather conditions in areas
with dry carry-over fuels from prior years. The main areas of
concern include the US-95 corridor near and south of Walker
Lake, and across Long/Chalfant/Round valleys and Swall Meadows in
southern Mono County. Breezy north winds will continue for these
areas into Wednesday, but temperatures will cool with humidity
increasing, along with a chance of showers especially for Mono
County. MJD
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&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

$$

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