Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 300951
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
251 AM PDT Thu Mar 30 2017

.SYNOPSIS...

A quick moving storm system will bring sharply colder conditions
today with strong winds and bands of rain, snow and pellet
showers. Dry and cool conditions are expected Friday, followed by
a return to warmer temperatures for much of this weekend. Another
quick moving low pressure may bring a round of showers and gusty
winds by Sunday night with cooler temperatures for Monday.

&&

.SHORT TERM...

Currently, some light showers have spread across areas near and
north of I-80 with snow levels still rather high (near 9000 feet).
The shower activity will increase during the early-mid morning as
the main low moves inland across northern CA-northwest NV, which
will drive a strong cold front southward across the region.
Forcing along this front could even be sufficient for a few
thunderstorms with short bursts of heavy rain or snow (with
graupel also possible), most likely affecting areas from
Susanville-Gerlach northward through 6 AM, then pushing southward
to I-80 and possibly US-50 between 5-9 AM. Snow levels could fall
all the way down to near 5000 feet with this cold front. The
majority of the precipitation associated with the front (totals
not expected to be very impressive despite the short convective
bursts) is likely to wrap up by late morning. By this afternoon,
most precip will be in the form of scattered showers, while near
and east of US-95 the air mass could be unstable enough for a few
thunderstorms containing graupel, even in lower elevations.

By this evening, most of the shower activity will push south of
US-50 and east of US-95, with a few light upslope snow showers
possibly continuing into early Friday morning over parts of Mono
County.

The greater overall impacts with this storm will be wind related,
as the impressive thermal gradient along with an upper level jet
streak will bring a period of strong winds to much of the region.
No major changes were made to the current wind forecast which
favors areas south of US-50 receiving the strongest winds from mid
morning through late this afternoon. For tonight, surface winds
will decrease, but north to northeast ridge top winds will remain
strong with gusts above 80 mph continuing into Friday. Anyone in
the back country near the Sierra tonight and Friday should be
extra cautious as this change in wind direction could produce some
increased risk of damage to trees.

The remainder of Friday will be dry with temperatures remaining a
few degrees below average--mainly in the 50s for lower elevations
and mid-upper 40s near the Sierra. While the winds will not be as
strong compared to today, there will be enough north to northeast
flow present to produce chilly conditions. MJD

.Long Term...Saturday through Wednesday...

The primary changes to the extended forecast this cycle were to
increase pops a bit for Sunday night into Monday morning, and to
increase the winds for Sunday afternoon and evening.

Medium range operational models are starting to come into better
agreement with the overall pattern for this weekend into early
next week...but there are still differences in some of the
details. The increasing agreement on the broad pattern helps
increase overall confidence in the forecast.

Brief ridging over the region Saturday gives way to an approaching
short wave trough by late Sunday. This will mean mild temperatures
both Saturday and Sunday and an increase in winds for late Sunday,
as winds aloft begin to increase and mix to the surface and the
surface gradient increases. A weak area of forcing ahead of the
trough may produce some isolated showers over the far northern and
northwest forecast area late Sunday afternoon...but the best
chance for precipitation looks to be overnight Sunday into Monday
morning when the primary upper trough and associated surface front
move through the region. This looks to be a fast moving system
with a limited amount of precipitation overall. Still...the
convective nature of the precipitation means some areas could see
brief moderate showers. Snow levels drop rather quickly on the
back side of this system...reaching down to 4500-5000 feet north
of Interstate 80. If the timing holds on this system holds...the
heaviest showers would be prior to sunrise Monday. Minor snow
accumulations may be possible above 5000 feet north of I-80.

The system exits as quickly as it moves in. A ridge builds briefly
again for Tuesday with a rebound in temperatures. This time of year
we can see fairly wide swings in temperatures from day to day in the
wake of a system like this. The lengthening days and higher sun
angles allow for ample heating even a day after cold air advection
affects the region.

The ridge slides east Wednesday and allows another fast moving
system to start impacting the area. A few showers are possible late
Wednesday over far western parts of the forecast area.


.Week 2 Outlook...Issued 3pm 3/29

The last few weeks the west coast has been in a fairly typical
spring weather pattern. The Pacific jet stream was retracted to the
west allowing weak fast moving low pressure systems to drop out of
the far eastern Gulf of Alaska with limited moisture potential.

This is expected to change next week as the jet strengthens and
moves into the eastern Pacific. Ensemble models are in good
agreement that a large area of low pressure will deepen along the
west coast. Atmospheric river (AR) detection tools show a strong
signal for an AR to impact the west coast in the 7-10 day time
period.

At this point, it is likely that an AR will reach the west coast by
the end of next week with with the current forecasts favoring the
Pacific Northwest; however, intensity and especially latitude are
still in the realm of low predictability. The deepening low pressure
and strengthening jet in the eastern Pacific, along with strong AR
signals for the west coast during the second half of next week
increase the chances for a return of stronger storms impacting the
Sierra and western Nevada. The main question is how far south will
the moisture and jet stream drop next week. Increased chances are
not a guarantee, but definitely worth keeping an eye on as a direct
hit from another AR would again increase flooding concerns in the
region. -Zach

* The Week 2 Outlook discussion is an experimental part of the Area
  Forecast Discussion. This product is designed to highlight the
  potential for significant pattern changes beyond day 7 and will
  not be issued on a daily basis.

&&

.AVIATION...

The big story today will be very strong gusty winds over the
forecast area. Ahead of a surface front passing through the region
this morning...west winds of 25-35 kt with gusts up to 45-50 kt
will be possible in many valley locations. By mid-late afternoon
the winds will shift to the northwest and may be even stronger
south of Highway 50 where northwest winds are more favorable for
gusts exceeding 50 kt. Ridge winds are likely to gust to 90+ kts
as well. This will lead to low level wind shear and turbulence
through a significant portion of the low to mid level atmosphere.
Winds will slowly subside tonight.

The other issue with the approaching system will be showers through
the day. Isolated to scattered showers early this morning will become
a bit more widespread by early afternoon...especially east of
Highway 95. The heaviest showers may produce brief periods of MVFR
conditions in the valleys with IFR conditions in the higher
elevations. Snow levels fall through the day so some brief snow/ice
pellets showers are possible by late morning. Given the spotty
nature of the showers and relative warm ground...any accumulations
should be confined to this morning at terminals in the Sierra
valleys. Even then...accumulations would be generally less than 2
inches and melt by afternoon.

A few stray thunderstorms are also possible today...mainly east of
Highway 95.

Ridging starts build for Friday and persists through Saturday. Gusty
northeast to east winds are possible over the Sierra late tonight
and early Friday. Another fast moving system Sunday night into
Monday could bring conditions similar to today.

&&


.REV Watches/Warnings/Advisories...
NV...Wind Advisory from 5 AM early this morning to 11 PM PDT this
     evening NVZ004-005.

     High Wind Warning from 8 AM this morning to 8 PM PDT this
     evening NVZ001.

     Wind Advisory from 5 AM early this morning to 8 PM PDT this
     evening NVZ002.

     Wind Advisory from 5 AM early this morning to 8 PM PDT this
     evening NVZ003.

CA...Wind Advisory from 5 AM early this morning to 11 PM PDT this
     evening CAZ070.

     High Wind Warning from 8 AM this morning to 8 PM PDT this
     evening CAZ073.

     Wind Advisory from 5 AM early this morning to 8 PM PDT this
     evening CAZ072.

&&

$$

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



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