Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 121122

Area Forecast Discussion
National Weather Service Reno NV
322 AM PST Tue Dec 12 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 due to the
strong inversions. Inversions should ease by the end of the week
as a weak cold front brushes the Oregon border, but no
precipitation is expected.



The strong, amplified ridge that we have been discussing for over
a week now will continue to bring dry weather, mild days, and
cold nights through the middle of the week. Inversions will still
be in place through Thursday due to radiational cooling at night.
That is why haze will be kept in the forecast for most valleys in
the western Great Basin.

By Friday, the retrograding ridge just off the US west coast
starts to flatten out due to a shortwave moving through the
Pacific Northwest. Winds will shift and pick up a bit to 5-10 mph
from a southeast flow Friday morning, to a west to northwest flow
by Friday afternoon in response to the passing shortwave.
Precipitation is not expected for Friday through Friday night for
most of the area, except possibly for a few sprinkles of rain
near the NV/OR border.

Temperatures for Friday will be on the warmer side with highs in
the upper 50s, with a few sites possibly reaching 60 degrees!
Lows Friday night will not be as cold compared to recent nights...
mainly in the 20s to near 30 degrees. This is a result of the
ridge flattening and allowing more mixing to occur, with less
influence from the inversions. -LaGuardia

.LONG TERM...Saturday onward...

Behind Friday`s shortwave passage, the ridge retrogrades offshore
from the CA coast, with cool northwest to north flow and areas of
cloud cover over the region dropping max temps a few degrees from
Friday. This pattern would also favor a period of stronger Sierra
ridge gusts over the Sierra Saturday which may continue into
Saturday night.

For Sunday through Tuesday, flat ridging returns to CA-NV with
some inversion conditions returning, but the inversions are not
expected to be as strong compared to this week. As a result, max
temps should be able to edge upward a few more degrees into the
50s for most valleys in western NV and near the Sierra. Areas of
cirrus are probable especially north of I-80, but no precip is

After next Tuesday, there may be a change to a more active
weather pattern as stronger shortwave energy is poised to drop in
from the north. While there have been fluctuations among medium
range guidance runs, for several days the overall trend seemed to
be targeting the time frame around the 20th for this change to
occur. The scenarios are generally divided among two

(1) A dynamic cold front passage accompanied by a short period of
precip (mainly snow) possible by the middle of next week, followed
by most energy shearing off to the east with cold dry air
prevailing into the start of the Christmas weekend.

(2) An upper low closes off over California, which would draw in
more Pacific moisture and bring a better chance for mountain snow
with a snow-rain mix in lower elevations. Depending on where this
low sets up, these precip chances could be short lived or
continue for a couple of days into the later portions of next

Because there is a nearly equal split among the ensemble guidance
for these possible scenarios, we are not yet ready to lean toward
one or the other. However, it does appear that temperatures are
more likely to drop later next week, and anyone planning travel
around Christmas should prepare in advance for possible winter
driving conditions, and have their emergency kit and alternate
travel plans handy. MJD



Minimal weather impacts for aviation this week with VFR conditions
and light winds prevailing. Valley inversions at KRNO, KCXP with
haze could produce some minor reductions in slantwise visibility
for the next few days. MJD


.REV Watches/Warnings/Advisories...


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