Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Reno Nevada
239 PM PST Thursday Dec 25 2014
below normal temperatures with a cold northerly flow will
continue into the middle of next week. Light snow is possible late
this weekend as another cold front nears the region. Cold
temperatures will prevail through early next week with a
very cold low pressure system developing across the western U.S.
clouds continue over most of the region this afternoon under cold NE
flow. Daytime instability under cold air aloft generating a few light
snow showers from Pyramid Lake to Yerington/Fallon. These should
continue through Sundown with localized light accumulations
possible. Further south - upslope component may generate some light
snow showers near the Sierra crest in Mono/alpine counties through
early evening. Per NAM/hrrr guidance, clouds should largely clear
out by midnight leaving a cold night ahead. With cold air banked up
against Sierra, associated pressure gradient, and upper jet nearby -
strong gusty winds will likely continue through daybreak Friday
along the ridges above 8000 feet. Cs
Short term...Friday through Sunday
cold, below seasonal average temperatures will prevail with north
to northeast winds continuing behind the departed cold front. High
temperatures Friday will largely remain in the 30s region wide
with frigid overnight lows expected into early Saturday.
Decreasing clouds and winds should allow lows to fall into the
single digits across many Sierra valleys with teens widespread
across western Nevada.
By Saturday, an upper level ridge across the eastern Pacific slides
eastward which will result in warming temperatures aloft with winds
veering to the south-southwest. Only a few degrees of warming is
expected along valley locations with as much as 10-15 degrees of
warming expected across higher terrain as the ridge builds. This
will result in enhancement of valley inversions and reduced
dispersion of air pollutants. Inversions should weaken by Sunday as
a shortwave trough quickly dives south from the Pacific northwest.
This will result in cooling temperatures aloft and will send a
backdoor cold front across northern Nevada Sunday afternoon. A
period of light snowfall is possible with the front across northern
Washoe and Pershing County Sunday afternoon with chances spreading
south of Pyramid Lake by early Monday morning. Fuentes
Long term...Monday through New Years Day...
Next week, a very cold low pressure center will drop over the
western United States. This will be right over the Great Basin with
good model agreement that -18c 700mb temperatures will settle in
over Nevada. There is a clear downward trend in the 500mb heights in
the models over the western states over the last couple days.
Forecast confidence is high that next week's temperatures will be
well below normal with high temperatures in the 30s for the basin
valleys and 20s for the Sierra valleys. Low temperatures will also
be very cold with single digits for many locations. There is also a
slight chance of snow showers on Monday and Tuesday as the cold pool
drops overhead, but confidence in the precipitation is very low.
Another impact that we will see next week is much stronger east
winds as a strong 1055dm surface high pressure builds into the
northern rockies. On Tuesday into Wednesday we will see winds
increase at 700mb, approaching 50kt. That is a 3 Standard deviation
anomaly...pretty uncommon to see that magnitude of east flow. We'll
have to keep a close eye on this as we get closer, as this could be
a significant east wind event around new years evening. Hoon
Forecast confidence in the tafs today is medium to high. Main
uncertainties are timing cloud clearing across the region and
potential fog at trk.
Following NAM guidance scattered-broken clouds and isolated -shsn should
dissipate after 3z for rno,trk,tvl,cxp as drier air moves in.
Mountain obscuration is expected along the entire Sierra through at
least early evening. Clouds likely to hang on longer at mmh due to
upslope flow nearby. Shsn is possible at mmh but predictability is
low. Assuming skies clear as forecast, recent moisture from light
snow may be enough to generate fog at trk after 8z tonight.
Confidence is less than 50% however so have just mentioned shallow
fog in the taf. Cs
For more information from the National Weather Service visit...
http://weather.Gov/Reno (all lower case)