Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 241041
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
341 AM PDT Mon Apr 24 2017

.SYNOPSIS...

Several weak systems passing through the region throughout the work
week will bring chances for light showers in addition to breezy
conditions. Temperatures near to slightly below average for much
of the week will fall to well below average Friday. Drier conditions
with a warming trend are expected for the weekend.

&&

.SHORT TERM...

The main changes to the short term forecast include increasing
winds on Wednesday and restricting POP further Tuesday and Tuesday
night (to mainly well north of I-80).

Low pressure is approaching the Oregon coast this morning with an
associated upper jet in excess of 100 kts. The low is drawing in
a moisture plume with PWATs between 1" and 1.25" near and off the
northern CA coast. Rain, and snow above about 6000 feet, has
broken out in the northern Sierra and across northeast California
with the incoming plume and forcing.

The heaviest precipitation is expected this morning in the northern
Sierra and across northeast CA and far northwest NV, with rates
tapering off this afternoon once low pressure moves off into
eastern Oregon and Idaho. As far as impacts, while right now higher
Sierra roads just look wet (road temps above freezing) the heavier
rates could allow for light accumulations over Donner and Echo
Summits through mid-morning so be sure to check with CALTRANS
before traveling there.

For western NV and Mono County today, breezy conditions will be
the main story with fairly stout shadowing in the lee of the
Sierra expected due to weaker forcing farther from the upper low.
Temperatures will be 5-10 degrees cooler today as compared to
Sunday.

Late tonight through much of the day Tuesday, a shortwave ridge
will build over northeast CA and western NV for drier conditions
and lighter winds. Turning to Tuesday night and Wednesday,
simulations are focusing the main area of precipitation over
northwestern CA and southern Oregon as the upper jet re-focuses
farther north. Still, light to very light precipitation will be
possible, especially north of I-80, as moisture aloft remains
moderate to high. Snow levels are expected to rise Tuesday night
and Wednesday so pass impacts due to weather look minimal at this
time, especially given the light QPF.

Of more importance by Wednesday could be winds as MOS indicates
sustained winds of 20-32 knots for western NV. Some areas of the
western Great Basin may need a wind advisory by Wednesday afternoon,
although confidence is low due to extensive cloud cover and fairly
moist conditions in current simulations. In any case, it could be
the breeziest day of the short term. Snyder

.LONG TERM...Thursday through Sunday...
A backdoor cold front is expected to move through late Thursday into
Friday as the trough over the Intermountain West deepens. Below
average temperatures are expected both days with the coldest day
Friday. Highs in the 40s and 50s will feel even colder with a brisk
north wind. Any precipitation along the front would be very light
and looks isolated. Moisture is rather shallow and the best forcing
will be much further east. The flow eventually turns northeast
Friday night with good support for a gusty NE winds over the Sierra
Crest.

High pressure over the East Pacific will also amplify some and nudge
east this weekend. However, it does not appear that it will move
that far east as more short waves will drop down the east side into
early next week. These won`t be as cold, but they will prevent a
large warmup and it appears temperatures will likely be near average
instead of well above if the ridge were to move onshore. Wallmann


.Week 2 Outlook...May 1st-7th...Issued 3pm 4/23...

A ridge of high pressure, or upside down trough, is again forecast
for the far eastern Pacific during the first week of May. There is
still relatively high uncertainty on whether, or at least when, the
ridge axis will be able to progress over the western U.S. bringing
well above average temperatures to the region. Model simulations
during this very active winter and spring have been over predicting
ridging along the west coast. With the ridge building in the far
eastern Pacific shortwaves will continue to be able to dig into the
Great Basin keeping the ridge axis out to sea. This may keep the
ridge from creating significant amplification over the west coast
until near the end of, or past, the 2 week time period.

With the ridge continuing to strengthen in the eastern Pacific,
confidence is relatively high (for a week 2 outlook) that we won`t
see any strong atmospheric river induced storms for the beginning of
May. Fast moving cold fronts dropping in from the north with periods
of light precipitation will remain possible as long as the ridge
axis remains offshore.

So at this time, confidence is moderate that the first week of May
will remain below average for precipitation. Confidence remains
lower for how far inland (specifically in the Sierra), above average
temperatures will be felt and by when. With the near record snowpack
in the Sierra, any extended period of well above average
temperatures will remain a concern, and we will continue to keep a
close eye on that potential. -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...
Gusty winds expected today with a decent cold front moving through
this evening. SFC wind gusts to 35 kts are possible at all terminals
this afternoon into the early evening. Mtn wave turbulence will
occur as well with localized LLWS until 18Z. After 18Z, mixing
during the day will result in a deeper mixed layer with less shear,
but there could be a good shear layer at 10k MSL.

Aside form the winds, areas of MVFR west of a KSVE to KTVL line with
mtn obscn in -RA. Rain looks to end around 06Z tonight with
generally VFR conditions all areas after. Tuesday will see lighter
winds and VFR before winds increase again on Wednesday along with a
few more showers. Wallmann

&&

.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory from 11 AM this morning to 8 PM PDT this
     evening for Pyramid Lake in NVZ004.

     Lake Wind Advisory until 8 PM PDT this evening for Lake Tahoe in
     NVZ002.

CA...Lake Wind Advisory until 8 PM PDT this evening for Lake Tahoe in
     CAZ072.

&&

$$

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


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