Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 111100

Area Forecast Discussion
National Weather Service Reno NV
300 AM PST Mon Dec 11 2017


High pressure will continue to bring dry conditions along with
valley inversions, cold nights, and light winds for the next
several days. Localized air quality issues are possible along the
Sierra Front due to the strong inversions. Inversions may ease by
the end of the week as a weak cold front brushes the Oregon border,
but no precipitation is expected.



Not much change to the forecast as the ridge of high pressure
hangs out over the Sierra and western Nevada for most of this
week. It does retrograde to just west of the California coast by
Thursday instead of being parked right over the Sierra and Great
Basin, but the effects will remain the same...dry weather, cold
nights, strong inversions, and hazy skies around the urban valleys.
Winds will also be on the light side with an east to southeast
flow for much of this week.

High temperatures will continue to be just above average topping
out in the lower 50s for valleys and upper 40s for higher
elevations. By Thursday afternoon, highs for most areas could
reach into the mid 50s due to the flattening of the ridge,
resulting in weaker inversions and a bit more mixing.

.LONG TERM...Friday onward...

For Friday-Saturday, the ridge is likely to continue flattening as
weak shortwaves move across the Pacific Northwest. The main effect
will be some cooling of mid level temperatures and increasing
areas of cirrus especially from US-50 northward. Winds on ridges
shift to west, but the surface winds are likely to remain light.
Model soundings show the inversion eroding during the afternoon,
but the increase in cloud cover may offset some of the potential
warming for valleys, resulting in only a modest warming for lower
elevations (highs mainly in the mid 50s) while mountain areas
begin to trend cooler. Haze around the urban areas will continue
through much of Friday, before having a chance to gradually
disperse by mid-late afternoon. For Saturday, a moderate inversion
may return behind a shallow back door cold front passage. This
should drop highs back to around 50 degrees for most valleys in
western NV and near the Sierra, and a bit cooler across northwest

By Sunday, flat ridging is likely to prevail, with areas of cirrus
retreating slowly northward. This should result in less of an
inversion, although mixing will still be limited with light
surface winds. Because of this limited mixing, we opted for a
more gradual warming into the lower-mid 50s, as opposed to some of
the guidance which is attempting to push highs to near 60

Beyond next weekend, there is still a mixed bag of potential
scenarios, although the consensus seems to favor the ridge
retrograding and rebuilding off the west coast. This reduces the
potential for any significant Pacific storm systems affecting the
region up to Christmas, but it could open the door to some
shortwave energy dropping in from the north. However, these types
of weather systems are unlikely to have much available moisture,
with the main effects being generally cool temperatures and
periods of light-moderate north or northeast winds. There is one
lower probability scenario for a wetter pattern--if the ridge
builds farther north, some moisture could undercut the ridge and
reach the Sierra (although this may be accompanied by higher snow
levels), possibly toward the start of the Christmas holiday
weekend. MJD



VFR with light winds continue through Thursday under the ridge.
Some shallow FZFG may form around KTRK each morning, but minimal
impacts are expected. The same goes for the haze along the Sierra
Front which is not expected to produce significant impacts to
aviation. MJD


.REV Watches/Warnings/Advisories...


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