Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 071004

Area Forecast Discussion
National Weather Service Reno NV
204 AM PST Thu Dec 7 2017


A persistent high pressure ridge will bring dry conditions with
valley inversions, cold nights, light winds, and periods of
reduced air quality for northeast California and western Nevada
valleys through at least mid-December.



Sierra crest ridge winds are still gusting around 50 mph while on
Lake Tahoe, buoys are reporting sustained 15-20 mph with gusts to
25 mph. These winds are projected to subside as the upper ridge
axis edges closer to the Sierra, but we ramped speeds down a bit
more slowly through today based on the current conditions and
continued east flow (although weaker) over the region. This ridge
then settles over the eastern Sierra and western NV tonight and
remains overhead through Saturday. This will keep dry conditions
and mainly light winds in place. Stronger subsidence and higher
500 mb heights/700 mb temps under the ridge center should allow
for daytime temperatures to edge upward by a degree or two each
day, but inversion conditions will still prevail with highs in
Sierra valleys equal to or a bit warmer than lower elevation
valleys of western NV. Chilly nights with lows mainly in the
single digits and teens will continue, with mountain areas
relatively mild with lows mainly in the 20s.

Air quality issues are still possible in urban valleys, but this
threat does not appear to be as serious compared to inversion
patterns of past winters. There is still projected to be some
lifting of the inversion to about 1200-1500 feet AGL each
afternoon, with about 5-10 kt of east flow, which should help to
limit the extent of haze at least through Friday, although some
light haze will probably be present each day. MJD

.LONG TERM...Sunday onward...

A rather depressing sight for anyone wishing for rain and snow, with
a strong ridge of high pressure remaining firmly in place over the
west. This means that the forecast remains dry with light winds and
inversions in place. The stagnant conditions under the inversion
will keep haze in place with possible air quality concerns.
Temperatures will continue to gradually warm through the period with
seasonably mild days and cool nights.

Longer range operational EC guidance suggests a wave moving in
from the northwest will help to retrograde the ridge westward
around mid-month. However, looking at ensemble guidance there is
a significant amount of spread and the overall pattern would not
favor the ridge breaking down this early with a deep trough in
the east. Extended GFS guidance is showing potential for the
ridge weakening and shifting eastward around the start of the
third week of December. There is still significant spread in
ensemble guidance, however the longwave height anomaly pattern
would at least make more sense in this case. This is due to the
eastern trough shifting east toward Nova Scotia and Greenland,
and ridging downstream of a possible western CONUS trough. -Dawn



An extended period of high pressure will produce light surface winds
and valley inversions this week. Inversions will lead to hazy
conditions and possible reductions in slantwise visibility by the
upcoming weekend.

Easterly ridge winds are starting to weaken across Sierra ridges,
however localized light turbulence and mountain wave activity
remain possible through this morning with sustained winds of
30-40 kts. Winds will continue to lighten through the day as the
ridge axis shifts over CA/NV. -Dawn


.REV Watches/Warnings/Advisories...


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