Scientific Forecaster Discussion
fxus65 krev 201118
Area forecast discussion
National Weather Service Reno Nevada
418 am PDT Fri Sep 20 2019
Areas of frost are expected this morning in the Sierra valleys,
western Nevada and northeast California. Dry and tranquil
conditions return for the remainder of today and into the weekend
with a warming trend before increasing winds and shower chances
return by late Sunday into Monday. The active fall pattern looks
to continue through late next week.
Not many changes were made to the inherited short term forecast. The
main story for early this morning is the chilly temperatures region
wide. Many areas are already 5-10 degrees cooler compared to last
night's temperatures at this time mainly due to clearing cloud
cover as the current low pressure trough centered over eastern
Nevada shifts to the east.
Weather conditions improve throughout the day today with partly
cloudy skies, a light north-north easterly wind, and slightly warmer
temperatures. Overnight lows are still expected to be below normal,
but a few degrees warmer compared to this morning's. As we begin the
weekend, a shortwave ridge builds over the west leading to a brief
time of tranquil weather. Expect clear skies, light winds, and high
temps in the 70s across the Sierra and western Nevada for Saturday.
By Sunday afternoon, cloud cover increases and southwest winds pick
up as a short wave trough from the northwest pushes the ridge off to
the east. Temperatures will increase as well with highs in low to
mid 70s for the Sierra and upper 70s, low 80s for western Nevada.
Winds are forecast to be in the 10-20 mph range with gusts up to 30
mph for most areas. Not too concerned for heightened fire weather
conditions at this time as winds do not look overly strong and min
relative humidity values look to be above 15-20% across most of the region.
As the trough slides into Nevada, temperatures decrease once again
and winds shift from the southwest to a northerly direction by
Monday morning. Rain showers will also be possible Sunday night into
Monday morning mainly focused for areas north of I-80. Left
slight chances in the forecast for areas south of US-50 at this
time. This will depend on the interaction of the trough with
atmospheric moisture over southern Nevada and Arizona. -LaGuardia
Long term...Monday night through Thursday...
There were not many changes in the long term portion of the
forecast...at least not through the daytime hours of Thursday.
Beyond Thursday the forecast starts to get more interesting.
A trough of low pressure exits to the east Monday night and brings
some clearing. A ridge develops in the eastern Pacific with
weakening northwest flow aloft. This is likely to allow temperatures
to rebound for Tuesday and Wednesday. Highs could reach above normal
with readings in the lower to mid 80s in some lower valleys by
Wednesday. Overnight lows should remain seasonal for late September.
The model solutions are a bit at odds by Thursday. The operational
GFS and a few of its ensemble members are more aggressive in trying
to drop a shortwave trough down into northern Nevada. This solution
has less support from the European model (ecmwf) and many ensemble members. This
solution would produce a lowering of temperatures over the northern
third of the forecast area along with an increase in wind. We will
allow the winds to increase a little...but not buy completely into
this solution just yet.
It is beyond the forecast period where the forecast starts to get
more interesting. There is fairly good consensus between the model
solutions that a deeper trough will drop into the region for Friday
into next weekend. Timing differences remain so exact details are
hard to pin down. This trough would bring much cooler temperatures
and fairly widespread precipitation if it develops as outlined in
the current model solutions.
Weather conditions have improved across the region overnight with
leftover scattered clouds as the low pressure trough moves off to the
east. Fzfg is currently impacting ktrk and should continue until
~16z this morning.
For the remainder of today, expect VFR conditions with mostly clear
skies and a light north-northeasterly wind. Tranquil conditions
continue into Saturday before another trough moves into the region
by Sunday afternoon increasing southwest winds and cloud cover.