Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Reno Nevada
316 am PDT Thursday Oct 30 2014
winds will start to increase Thursday night over the higher terrain
with gusty winds for Friday as low pressure approaches the West
Coast. The storm will move into the Sierra Friday afternoon with
a period of moderate to heavy snow through Friday night. The
system will bring a period of rain for western Nevada valleys
Friday night, with rain and snow showers on Saturday. Warmer and
drier weather will return next week.
the main change to the short term forecast was to slow the arrival
of colder air/lower snow levels Friday-Friday night. The 00z
GFS/ec/Gem models have come into decent agreement regarding timing
and general features with this weekend's storm system. The 00z NAM
was a bit slower than the other models but has come more in line
with its 06z run.
High clouds will be on the increase today as an upper ridge axis
shifts off to The Rockies and low pressure over the Pacific slowly
advances eastward. Temperatures will be quite mild once again today
with highs 10-15 degrees above average. Late tonight, winds increase
mainly over the ridges as the thermal gradient aloft tightens
between the Pacific trough and exiting ridge.
On Friday, winds increase area-wide as the incoming low's cold
front moves into California. Winds do not look like anything
special but they will be gusty and could cause issues for high
profile vehicles, especially in areas susceptible to southerly
flow. Regarding the front, the flow aloft will be rather parallel
to the low level boundary for much of Friday as the front awaits
a forward push from upper energy off the California coast. With
the front slowing somewhat, I have pushed back the lowering of
snow levels and, in some areas, the arrival of precipitation.
Still, the front looks to hold together well as it moves into
western Nevada as a jet maximum noses into the state and keeps the
front intact. Given the more southerly flow aloft, I did raise
precipitation near Mammoth Mountain as the orientation of the Sierra
there aids orographic forcing in southerly flow. For most other
areas, forecast precipitation totals have not changed much so we
are on track with the Winter Storm Watch.
Saturday, precipitation becomes showery under the cold pool aloft.
Given the convective nature of saturday's precipitation, snow or
ice pellets could mix in with rain down to all but the lowest
valleys (under 4000 feet). However, daytime temperatures will be
plenty warm to prohibit snowfall accumulations outside of the
Long term...Sunday through Wednesday...
few changes made to the long term this morning as the models all
agree on the transition to a moderate amplitude ridge for midweek.
The biggest differences in the models occur on Sunday with the ec
slower to move the trough out of the Great Basin. It drops another
weak short wave or inside slider on the back side of the trough. The
GFS and its ensemble is much weaker with that wave and thus more
progressive with the trough. The ec ensemble shows higher than
average uncertainty with the western portion of the trough so this
wave should not be dismissed. That said, only lowered temperatures Sunday
and kept forecast dry. The ec does show precipitation and temperatures a good 5-10
degrees colder than I have. At this point, the ec is on the western
edge so will just trend that way since sliders do have a tendency to
come further west than advertised.
Once that weak wave GOES through, the trough progresses east and the
models all show a moderate amplitude ridge by Wednesday for a
consistent warming trend. The trend will be faster in the mountains
while the lower valleys in northeast California and western Nevada are slower to
warm due to moderate inversions and light surface winds. Still,
expect temperatures to warm a little above average by Wednesday. Wallmann
VFR with winds aloft increasing today with peak surface gusts 20-25
kts near and just east of the Sierra by middle-late afternoon.
Storm still expected for late Friday through Saturday morning.
Periods of IFR/LIFR ceilings/visible in the Sierra as rain changes to snow
by Friday evening, with some snow accumulating on runways above 6000
feet. Moderate to high confidence now in MVFR ceilings/visible in -ra for
western Nevada valleys Friday night/Saturday morning as surface low
develops over central Nevada. Mjd/wallmann
Nevada...Winter Storm Watch from Friday afternoon through Saturday
California...Winter Storm Watch from Friday afternoon through Saturday
Winter Storm Watch from Friday afternoon through Saturday
For more information from the National Weather Service visit...
http://weather.Gov/Reno (all lower case)