Area Forecast Discussion
Issued by NWS Reno, NV

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863
FXUS65 KREV 222153 AAA
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
252 PM PDT Mon Apr 22 2019

.SYNOPSIS...

Warm days, cool to chilly nights, and drier conditions are expected
this week for northeast California and western Nevada. The warmer
temperatures will lead to increases in cold and swift flows for area
streams. Breezier conditions along with a few showers are possible
for Thursday and Friday afternoon and evening.

&&

.SHORT TERM...

Not much change to the forecast through Thursday night. Above to well
above average temperatures are expected this week for northeast
California, the Sierra, and western Nevada as a ridge of high pressure
builds overhead. There will be moderate northeast to east flow over
Sierra ridges through Tuesday morning (gusts generally 40-70 mph) as
a gradient persists between the ridge building into northern California
and low pressure slowly exiting from the Colorado River Valley. Winds
will wane Tuesday afternoon and Tuesday night as the ridge moves
overhead.

As far as precipitation/convection, little or no afternoon cumulus
development is expected through tomorrow. However, by Wednesday
and Thursday, simulations indicate increasing chances for cumulus
development as afternoon temperatures rise to well above average
(more typical of late May/early June) and a westerly, zephyr-like
flow develops to aid low level focus for convection. We have left
a general 5-10% chance for Wednesday afternoon/evening for eastern
CA and far western NV with no showers mentioned as deeper cumulus
development is still expected to be very isolated with a very low
chance for measurable rain. By Thursday afternoon, the flow is
expected to increase further for better low-level convergence;
therefore, showers remain in the forecast for northeast CA, eastern
Mono County, and Mineral County (the typically-favored convergence
areas in west flow). As far as thunderstorm potential Wednesday
or Thursday, it cannot be ruled out between about 3 and 7 PM given
temperatures more common of late May or early June (when storms
can form just from terrain heating); however, as with showers, it
will be a very low chance so have left out for now. -Snyder

.LONG TERM...Friday and beyond...

The high pressure ridge over much of the U.S. Southwest begins to
flatten by the end of next week as a broad area of low pressure in
the Pacific NW region interacts with a weak, cut-off low off the
southern coast of California. This will lead to more of a zonal flow
pattern over northern California and Nevada for Friday into much of
the weekend yielding gusty west winds, decreasing temperatures, and
partly cloudy skies.

On Friday morning, there is a chance for some light rain showers for
northern portions of Lassen and Washoe counties as a cold frontal
boundary sets up over the CA/NV/OR border. Once the weak boundary
drifts off to the east by the afternoon hours, westerly winds look
to increase as the pressure gradient tightens to the north. Nothing
too strong, but at this time gusts of 20-30 mph are possible for the
western Nevada valleys. During this time, temperatures are forecast
to still be quite warm with highs 10-15 degrees above normal, but
not as warm as Thursday.

As we enter into the weekend, similar conditions look to stick
around for Saturday with gusty afternoon westerly winds, clouds, and
above average temperatures. Even though the weather pattern will be
active, chances for precipitation look minimal at this time depending
on when the weak, cut-off low off the southern California coast moves
inland. As of now, the deterministic models have it moving onshore by
Sunday afternoon/evening, developing showers for southern Mono and
Mineral counties during this time.

Once the weak low moves onshore by Sunday into Monday, it looks to
get absorbed by the broader trough to the north. As they phase
together, temperatures become cooler (closer to average) and the
pressure gradient weakens resulting in a decrease in winds (but
still breezy).

The forecast after next Monday and into the beginning of May looks
interesting as multiple long range guidance tools suggest a continuation
of an active weather period. Both the EC and GFS ensembles show a
broad trough over much of the West Coast with the Climate Prediction
Center`s 3-4 week outlook indicating above average precipitation
and cooler temperatures. Nothing set in stone, but something to think
about for long term planning purposes. -LaGuardia

&&

.AVIATION...

Gusty east winds (60-65 knots) are possible over the Sierra
ridgetops again this tonight which may result in areas of turbulence
along and west of the range. Otherwise VFR conditions with lighter
winds are expected through midweek as high pressure builds across
the Sierra and western Nevada. -Fuentes/Hoon

&&

.HYDROLOGY...

Temperatures rise starting today with the warmest temperatures of
the season by Wednesday and Thursday. Highs Wednesday could reach
the lower to mid 80s in the lower valleys with upper 60s to lower
70s in the Sierra valleys. Overnight lows should remain mild in the
higher elevations as well. These warm temperatures are likely to
persist through the weekend as high pressure holds on a bit longer
and a trough meanders off the Pacific coast.

These warm highs and mild overnight lows will result in increased
snowmelt this week. The current forecast for the West Carson at
Woodfords pushes the river near flood stage by late Thursday night.
Some minor impacts could be possible in Douglas County by late
Thursday Night into the early morning hours Friday morning.

The East Carson and West Walker are also forecast to rise well above
current levels...but not approach flood stage. The next river
forecast will be available at 9am today, so check cnrfc.noaa.gov for
the update.

If the average temperatures in the West Carson basin were to rise 2-
3 degrees above current projections, it is probable that the river
would rise above flood stage. The West Carson is a smaller
contributor to the mainstem Carson than the East Carson, but even a
slight rise above flood stage may be cause for concern in the
southern part of the Carson Valley.

Main change: Current forecast temperatures for the weekend are
warmer than yesterday`s forecast. While latest crests from snowmelt
are forecast to peak on Friday, the snowmelt will likely not slow
over the weekend since temperatures will remain warm.

Remember: snowmelt peaks typically occur in the evening and
overnight hours in the higher portions of the basin while peaks are
more likely in the early morning hours in the lower portions of the
basin, so the highest flows may be at night.

&&

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

$$

For more information from the National Weather Service visit...
http://weather.gov/reno



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