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Area forecast discussion 
National Weather Service Reno Nevada
323 PM PST Friday Nov 28 2014

Synopsis...

Low pressure moves into the West Coast with gusty winds through
tonight and periods of rain and snow through the weekend. Another
wet Pacific storm is expected Tuesday and Wednesday of next week.

&&

Short term...

A potent jet stream has pushed into our region today with strong
gusty winds and very dry conditions in the eastern Sierra and
western Nevada. Downsloping winds combined with a dry slot aloft
have decreased humidity in most locations to less than 5%, extremely
dry for this time of year. The strongest winds so far have been
along the Highway 395 corridor south of Reno and in Galena and
Washoe Valley where gusts have reached over 60 miles per hour. Elsewhere, gusts
have remained around 40-50 miles per hour for most of the day. See local storm
report for strongest wind reports. The wind advisories will continue
through Saturday morning as downsloping flow continues.

A frontal boundary is stretched from Modoc County to the northern California
coast this afternoon with an associated plume of moisture stretching
out in to the Pacific. This plume has precipitable waters over 1" and a couple of
shortwaves will move through the main flow, directing rain/snow into
the Sierra late tonight and again late Saturday night.

The latest runs of the NAM and European model (ecmwf) continue to show a bullseye of
precipitation over the Tahoe basin late tonight and early Saturday morning,
a trend that has held together for the last few days. This heavier
precipitation moving into the Tahoe basin after midnight will bring the
snow levels down to Lake Tahoe level by evaporative cooling (around
5500-6000 feet). The GFS, however, hangs the frontal boundary north
of Tahoe and brings much less precipitation for the Tahoe basin. This
discrepancy leads to uncertainty in the forecast, but we still have
high enough forecast confidence to issue a Winter Weather Advisory
for the Lake Tahoe basin due to the increased impacts to Holiday
travelers. We expect anywhere from 1 to 4 inches around Lake Tahoe
and Truckee by Saturday morning...with 4 to 8 inches above 7000
feet. Locally higher amounts are likely west of Highway 89. Anyone
traveling over the Sierra/Tahoe passes tonight or Saturday morning
should be prepared for slick winter driving conditions.

On Saturday, a back door cold front will drop into far northern
Nevada from the north as a surface high builds into the Pacific northwest. This
will setup a band of low level frontogenesis/precipitation north of
Susanville Saturday and Saturday night. There is much uncertainty
here, especially in location of the band and snow levels that could
be anywhere from 6000 to as low as valley floors north of Pyramid
Lake. It all depends on how far south the cold air pushes into
western Nevada. Anyway, there should be generally less than 0.25" of
precipitation in western Nevada through the weekend, but there is potential
some light snow accumulations north of Susanville and Gerlach
Saturday evening and Sunday morning. A second shortwave moving
through northern California will also bring additional snow to the
Sierra and rain in western Nevada by Saturday night and Sunday
morning.

Ridging builds back into California/Nevada Sunday night and Monday, bringing a
break in the action before the next Pacific storm moves into the
West Coast Tuesday. Hoon

Long term...Tuesday through Friday...

Some continuity was starting to show up with the timing of next
week's storm system. Precipitation is now projected to spread into
the region on Tuesday, with the best chances for rain and high
elevation snow continuing Tuesday night and Wednesday.

However, confidence is somewhat lower with snow levels and precipitation
amounts since the trajectory of the moisture feed and storm track
varies among the medium range guidance. Preliminary snow levels
generally range from 7000-8000 feet on Tuesday, then drop slowly to
between 6500-7000 feet on Wednesday, but could fluctuate by a few
hundred feet in either direction due to these storm track
uncertainties. A band of subtropical moisture may also be drawn into
the Sierra, which could push snow levels even higher, especially for
the first 6-12 hours of this event.

Model forecasts are suggesting between 1-2 inches of liquid precipitation
in the Sierra, which could yield up to 2 feet of snow above 7500
feet. Below this elevation, snowfall potential is much more
difficult to project due to the variance in snow levels, and would
also depend on time of day or night when heavier precipitation rates occur.
The location and duration of the heavier precipitation still remains
uncertain, so the rain and snow amounts are still subject to
change.

For western Nevada, rain will occasionally spill into lower
elevations from late Tuesday through Wednesday, but the location of
heavier rain bands still varies, so rough estimates for rain amounts
still vary widely from below 0.10 inch to around 0.50 inch.

By Wednesday night, overall precipitation is expected to wind down,
although moist upslope flow west of the Sierra crest could keep
showers going mainly near the Sierra from Tahoe northward to western
Lassen County. The 12z European model (ecmwf) favors a longer duration of this
upslope flow compared to the GFS, although the precipitation amounts have
come down compared to the previous run.

The drying trend should continue for the latter portion of next
week, with precipitation chances removed for all areas by Friday as
guidance rebuilds ridge into CA-NV.

Daytime temperatures should remain near or slightly above normal for
much of next week, with mild nights especially through Wednesday
night as cloud cover inhibits radiational cooling. Mjd

&&

Aviation...

Windy and turbulent conditions will continue across the region
through Saturday with strongest gusts 35-45 knots most likely through 03z
this evening. Some low level wind shear will be possible tonight for the Tahoe and
western Nevada terminals as some lulls in winds occur near the surface
while stronger winds persist a few hundred feet above the valleys
and at ridge level.

For precip, some MVFR ceilings/visibility from ksve northward slowly moves
south into the Tahoe basin between 08-12z Sat. Cooler air at
ktvl/ktrk could bring snow down to these sites with IFR conds and
possible light accumulations on runways mainly between 12-18z Sat.

For Saturday, precipitation shadowing should keep prevailing VFR ceilings/visibility
over western Nevada terminals, and at kmmh as the moisture band breaks
apart as it drifts south of Highway 50. Mjd

&&



Rev watches/warnings/advisories...
Nevada...Lake Wind Advisory until 6 PM PST this evening for Pyramid Lake
in nvz004.

Lake Wind Advisory until 10 PM PST this evening for Lake Tahoe
in nvz002.

Winter Weather Advisory from 10 PM this evening to 10 am PST
Saturday nvz002.

Wind Advisory until 7 am PST Saturday nvz003.

California...Wind Advisory until 10 am PST Saturday caz073.

Lake Wind Advisory until 10 PM PST this evening for Lake Tahoe
in caz072.

Winter Weather Advisory from 10 PM this evening to 10 am PST
Saturday caz072.

&&

$$

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