Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 101105

Area Forecast Discussion
National Weather Service Reno NV
305 AM PST Wed Jan 10 2018


A fast moving shortwave moves through the Great Basin today
bringing isolated to scattered light showers and breezy conditions
to the region. One last wave on Thursday will bring breezy
conditions, especially north of Interstate 80, and may bring
light precipitation to areas near the Oregon Border. Dry and warm
conditions will return for the weekend, with a return to wet
weather probable by late next week.



The upper low is currently centered between southern California and
western Arizona early this morning and continues to eject toward the
east. A fast moving shortwave and jet energy will move across
northern CA/NV today, and with lingering moisture it is likely to
trigger isolated-scattered showers across the region. This is a
situation where the showers will be very hit or miss and generally
short-lived with little in the way of additional total liquid.
With snow levels around 5500-6500 feet, even a quick shower may
result in very light snow accumulation on roads and periods of
slick conditions. Showers will taper into this evening as drier
air works into the region on the backside of the wave.

A secondary piece of shortwave energy moves through the Pacific
Northwest on Thursday into Thursday night which will bring
increasing winds, especially for areas north of a Portola-Pyramid
Lake-Lovelock line. A few light showers are possible near the Oregon
border as well, but the best moisture and dynamics remain north into
Oregon and Idaho.

Behind this feature, an upper level ridge builds over the west for
the end of the week and into the weekend bringing dry and mild
conditions. All this looks to change going into next week, please
see the long term section for additional details. -Dawn

.Long Term...Saturday into week 2...

Ridge of high pressure will be centered over the Sierra going into
this weekend bringing dry conditions along with high clouds,
light winds, and temperatures 10+ degrees above average. The ridge
of high pressure will amplify over the western U.S. during the
weekend with temperatures reaching into the mid to upper 50`s,
even in the Sierra, lasting into early next week.

There are strong signals that region will return to a wet, and
potentially colder, pattern by the end of next week. A large scale
low pressure anomaly is forecast to develop along the west coast
for the first time this winter. This is a very different pattern
than we have spent most of the 2017/18 winter season in, with most
of the winter so far dominated by a strong high pressure anomaly
along the west coast. Atmospheric River tools are forecasting high
likelihood of 1 or 2 ARs reaching the west coast in the 15-18th
time period with the highest chances from Northern California into
the Pacific Northwest. The best chance for winter weather to
return to the Sierra would most likely be near the end, or after
that. The strengthening jet stream along the west coast is
forecast to slide south by the end of the week, finally allowing
cold air to move into the Sierra.

By midweek there is a chance we could see an initial wave of
precipitation as the nose of the strengthening jet stream reaches
the west coast with the EC is much more bullish for midweek. This
will still be early in the evolution of the large scale pattern,
with the best chances to see storms making it into the Sierra
during the end of the week.

This is the best signal for a winter weather pattern setting up in
the long range forecast this season. Of course, that doesn`t
guarantee a wet, snowy pattern, but considering all the signals it
raises the possibility to "more likely than not". Or another way
way to put it is that at least 3 out of 5 times we see signals
this strong 7-10 days away, the Sierra will end up in a stormy
weather pattern. -Zach



Greatest concern early this morning is areas of fog and low stratus
impacting a few valleys bringing localized MVFR-IFR conditions
and terrain obscuration. Conditions will rapidly improve this
morning due to increasing winds.

Breezy southwest winds across Sierra ridges will transition to
westerly through the day and increase in strength. Sustained winds
around the 10k ft level around 40-55 kts will bring areas of
turbulence and mountain wave activity downwind of the Sierra.
Valleys are likely to see winds gusting 15-20 kts today.

A fast moving wave will bring isolated showers to the region today,
which may bring brief periods of MVFR-IFR conditions. Chances of a
shower impacting any terminal sites is around 30%. -Dawn


.REV Watches/Warnings/Advisories...


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