Weather Service Report


085 
FXUS65 KREV 222046
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
146 PM PDT Wed Sep 22 2021

.SYNOPSIS...

A slight cooling trend starts overnight into tomorrow with daytime 
highs hovering just below seasonal averages.  Temperatures rebound 
slightly by Friday and continue with slightly above average values 
through the weekend. Areas of haze and smoke should be fairly 
transient as winds diminish this evening before turning mostly to 
the north and east Thursday morning through Friday.

&&

.DISCUSSION...

The main weather highlights this first day of Fall through this 
weekend will be an increasing easterly low and mid-level flow and 
reduction in smoke and haze across most areas of the eastern Sierra 
and far western NV.  Slightly cooler temperatures tomorrow but 
rebounding going into the weekend.

High pressure will nose east into the Sierra and western NV this 
evening into tomorrow as a weak cold frontal boundary exits east 
into the Rockies.  The resulting west-east orientated upper ridge 
axis will push over across central OR into southern ID. This will
result in a mostly northeasterly flow sitting up across western NV
and the Sierra that continues into northern and central CA. As 
this flow pattern continues into Friday, smoke and haze from 
regional fires will decrease sharply and be directed mostly east 
of the Sierra Crest. Hi-Res HRRR simulations complement this
forecast outcome for the near-term forecast into Friday.

By this weekend, the ridge axis will gradually weaken and sag south 
thus allowing a more westerly mid and upper flow to increase across 
the region.  The resulting upper height falls will steepen thermal 
gradients across western NV Basins that translate to a return of the 
typical afternoon zephyr breezes with gusts to 25 mph over the 
eastern Sierra and far western NV. Unfortunately periods of haze and 
smoke will once again begin to filter east of the Sierra crest into 
western NV. But this is all contingent upon regional fire activity. 
As the upper ridge recedes westward, warm and dry conditions will 
continue influence the region through this forecast period.

Highs tomorrow will be cooler and only rise into the 70s to lower 
80s for valleys as cooler air spreads south and southeast over the 
region in an increasing easterly wind regime. Highs on Friday will 
rebound several degrees into mostly 80s across western NV valleys 
with higher Sierra valleys edging up into the upper 70s.

EXTENDED OUTLOOK through the middle of next week...

* CHANGES: Another cooling trend for next Tuesday-Wednesday with 
  possible precipitation over northern portions of CA/NV. 

Ensemble cluster and extended model guidance are beginning to show a 
pattern change by mid-week next week. Any precipitation that 
results from this anticipated pattern change will be mostly light 
and confined to the northern Sierra. But it is worth noting that  
the second week of the autumn season has a long-wave trough 
pattern digging south across the West Coast before surging bursts
of short wave energy into the region. The only nexus will be a 
split trough pattern separating upper dynamics and moisture into a
cooler more dynamic northern branch and a much drier southern 
extension into the Sierra and Northern NV. Therefore, it is safe 
to say that forecast confidence is split between a higher much 
cooler outcome that is accompanied by a drier, more uncertain 
rainfall prediction over the forecast region. The best bet lies in
the increasing probability of gusty conditions Monday-Tuesday as 
both European and GEFS ensemble guidance show tightening gradients
as the upper trough deepens over the western US. One thing is for
sure, the upcoming pattern change could reflect in today's season
change.

-Amanda

&&

.AVIATION...

For today, gusty southwest winds to 20-25 kts, locally to 30 kts, 
are likely in the afternoon and evening mainly north of US-50. Light 
to moderate turbulence is expected to increase along and east of the 
northern Sierra crest due to the increased airflow. Increasing winds 
this afternoon should mix out most smoke affecting area terminals.

Winds turn to easterly Thursday for a shift of any turbulence to 
over and west of the Sierra Crest. Lighter winds and dry conditions 
expected through the weekend, until the next low pressure system 
moves into the region Monday with increasing winds and chances for 
showers. -Hoon

&&

.FIRE WEATHER...

* Breezy winds today may lead to localized areas of critical fire 
  weather conditions.

Breezy winds remain on track as a system passes to our north today. 
Expect gusts in the 25-35 mph range during the afternoon and evening 
hours. In the higher elevations of the Sierra and northeast 
California, peak ridge level winds may touch 45 mph. The combination 
of the wind with dry conditions may produce localized areas of 
critical fire weather conditions especially the Sierra Front for a 
couple hours. 

After today, winds switch out of the north and east. Winds will be 
lighter for most areas, but some areas over the Sierra Crest along 
the western slopes will become breezy early Thursday morning and 
again Thursday night into Friday morning.  -Hoon

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

$$

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http://weather.gov/reno

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Western Regional Climate Center, wrcc@dri.edu