Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Reno Nevada
315 am PDT Wednesday Apr 23 2014

Synopsis...
high pressure will build over the eastern Sierra and western
Nevada today for warmer temperatures and much lighter winds.
Friday, another strong cold front will move through for well
below average temperatures and the chance for rain and snow as
well as higher elevation travel impacts. High pressure returns
early next week for much warmer and drier conditions.

&&

Short term...
a secondary upper disturbance behind yesterday's cold trough is
currently moving overhead. This has brought a middle and upper level
cloud deck to eastern California and western Nevada (but no
precip) resulting in a slow cool down this morning. As the clouds
exit in the next few hours, temperatures will be allowed to drop
off into the middle 20s to middle 30s for the lower valleys. Today will
feature warmer temperatures and generally light winds as an upper
ridge builds in behind the exiting upper impulse. Tonight, low
temperatures look considerably warmer for many areas as cloud
cover beefs up ahead of a Pacific trough.

Friday, the far eastern Pacific trough elongates north-south as a
disturbance moves into California. The approaching low will push a
surface cold front through northeast California and western
Nevada. The front looks to hold together decently per model forecasts
of tight thermal packing and a modest jet streak moving into the
northern or central Sierra so I have bumped up pop more on Friday,
especially in the Sierra. As far as impacts, timing of heaviest
snowfall in the northern Sierra currently looks to be during the
day Friday which would limit overall travel impacts. However, with
fairly cold temperatures aloft (falling to -8c to -10c at 700 mb),
if precipitation can become heavy for a time there could still be
some periodic slushy passes especially above 8000 feet. Also, if
the system slows down some and snow continues to fall into early
evening there could be more widespread travel impacts in the
northern Sierra. For alpine and Mono counties, there is a better
shot at higher elevation travel impacts as the heaviest precipitation
comes in later in the day. With all this in mind, at least winter
weather advisories are possible for the Sierra Friday and Friday
night.

Another feature for Friday/Friday night will be a possible
band of precipitation extending from around Mono County northeast
into central Nevada in the afternoon and evening. The precipitation
is prognosticated to be focused around and to the north (some overrunning
with southwest flow aloft) of the surface cold front which could
stall temporarily as the system's upper disturbance begins to drop
more south than east late Friday. The NAM, GFS, European model (ecmwf) and sref all
indicate the precipitation band which increases confidence in the
formation of the band. The only issue is where exactly the band
forms as it could affect travel in the higher elevations of
Mono/western Mineral counties by Friday evening in the deformation
zone of the upper low. Snyder

Long term...Saturday through Wednesday...
this period will feature a transition to a warmer and drier
pattern as a ridge builds along the West Coast by Monday. Models
are holding onto a system moving into the Pacific northwest
Saturday night and Sunday. With the bulk of the energy well to the
north, only light precipitation amounts will occur over the
northern Sierra and northeast California. As the ridge builds,
afternoon highs will warm back into the middle 70s to near 80 for
western Nevada with 60s to low 70s for the Sierra for Monday to
Wednesday. Brong

&&

Aviation...
VFR conditions today with light winds. Next system will being to
impact the area on Thursday with increasing winds in the afternoon
and rain/snow moving into areas north of Susanville- Gerlach. Peak
gusts of 30-40kts are possible with mountain waves and turbulent
approaches to the Sierra and western Nevada terminals.

This system will track south for Friday with a period of moderate to
heavy snow likely in the Sierra. At trk and tvl, snow should easily
accumulate on air frames and elevated surfaces with an inch or two
possible on runways. Rain/snow will also spread into western Nevada
Friday though accumulations are unlikely at this time. Brong

&&

Rev watches/warnings/advisories...
Nevada...none.
California...none.
&&

$$

For more information from the National Weather Service visit...
http://weather.Gov/Reno (all lower case)