Reno Area Technical Forecast Discussion

Technical Forecast Discussion

FXUS65 KREV 202233

Area Forecast Discussion
National Weather Service Reno NV
233 PM PST Sat Jan 20 2018


Dry and cool conditions will prevail this weekend as weak high
pressure moves over the region. A weak disturbance may bring very
light snow for parts of eastern California Sunday night and Monday,
but this system is trending drier. A stronger, cold storm is
expected late Wednesday into Thursday, bringing more snow to the
Sierra and possibly to lower elevations.



Changes made to the existing forecast were modest and generally to
lessen overall QPF with the Sunday Night/Monday morning system.
Short range models continue to open up the already weak wave
projected to move into the region Sunday afternoon and evening.

Only up to 2 inches are now forecast for the higher Sierra around
the Tahoe Basin with up to an inch for the high Sierra in Mono
County and the Tahoe Basin below 7000 feet. Still, there could be
a few slick spots, so some caution is warranted for those heading
into and over the Sierra.

Otherwise, the biggest impact out of this system will be an
increase in area winds. Gusts are projected to only be 20 to 30
mph out of the south to southwest south of Susanville. Gusts could
reach 35 mph, and briefly 40 mph, north of a Susanville to
Gerlach line where valleys are more efficient in channeling
southerly flow.

Conditions improve Monday as we reload for a more significant
mid-week system. More on that system can be found below. Boyd

.LONG TERM...Tuesday through Friday...

Overall...the changes made in the extended part of the forecast
were geared toward increasing QPF for the mid-week system as the
GFS and ECMWF agree better in the overall evolution of the system.

Most of the region should be dry Tuesday...but some model solutions
do bring weak warm air advection type precipitation into the region
late in the day. Low end pops will remain in the forecast...mainly
north of account for this possibility.

The next significant winter storm should begin to affect the region
Wednesday night and last into Thursday. The forecast models continue
to show some slowing with this system. That has resulted in
increasing snow levels a little Wednesday and Wednesday night and
backing the low level winds. The backing of the winds results in
more southerly flow and less chance for immediate spill over into
western Nevada.

The system has been getting wetter over the last few runs; the
integrated vapor transport tools show increasing chances for more
significant moisture transport into the region. This leads to an
increase in QPF from northeast California south through the Sierra
and a slight increase in snowfall totals. This still does not look
like a blockbuster-type storm. Its progressive nature means the main
part of the storm is through the region late Thursday with lingering
showers into Friday.

Another warning sign with this storm is a recent development in a
few of the GEFS ensemble members to hint at the possibility of the
storm splitting by early Thursday. This is not supported by most
members...but we have seen multiple cases this winter where systems
look wetter days out then progress toward drier solutions.

Very low end pops were left in for Saturday near the Oregon border
as well. Both the GFS and ECMWF hint at another round of weak warm
air advection precipitation. XX



VFR conditions with few to scattered clouds low clouds will
prevail into the evening hours. Skies are expected to clear
further allowing for areas of freezing fog in Sierra Valleys. KTRK
can expect to be socked in until around 12Z when mid and high
clouds move into the region. It is likely that freezing fog will
lift into a IFR ceiling for an hour or so then mix out as ridge
winds increase.

Scattered snow showers will occur late Sunday into early Monday
morning for the Sierra with the potential for MVFR ceilings at TVL
and TRK. More isolated showers will be possible for the Sierra
Front, but conditions should remain VFR. There should not be much
in the way of snow accumulations for Sierra terminals since the
projected weak system continues to weaken with each model run.
Still, winds will increase with gusts to 25 kts and ridge gusts to
45 kts. Expect some moderate turbulence and mountain obscurations.

Flight conditions improve Monday, but a stronger, wetter system is
on tap for Wednesday/Thursday. Anticipate degrading conditions by
mid week as a moderate to strong winter storm moves into the
region. Boyd


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