517 
fxus65 krev 221017 
afdrev 


Area forecast discussion 
National Weather Service Reno Nevada 
317 am PDT Monday Mar 22 2010 


Short term... 
shortwave that moved through the area yesterday evening did bring 
isolated showers to the Sierra north of I-80...however with such 
little moisture and extremely dry low levels...there was not much 
in the way of quantitative precipitation forecast. Broad upper level trough axis remains over the 
County Warning Area...but the moisture and middle level cloud deck have pushed 
eastward. Any lingering showers are across northeast Nevada and 
southern Idaho early this morning. 


Surface gradient has relaxed this morning and light winds are 
being reported through all valleys. Ridges...however...continue to 
be gusty with gusts up to 70 miles per hour being reported as of 2 am this 
morning. Ridge winds should begin to subside later today as the 
upper level trough moves out of the area. Northerly winds will 
increase this afternoon and evening on the back side of the 
trough. A period of choppy lake waters on Pyramid Lake is possible 
late this afternoon...though it should be less than it was Sunday. 


Very dry air mass to return to the area today and Tuesday with poor 
relative humidity recoveries once again expected and large diurnal temperature 
swings. Winds will generally be light with an easterly gradient. 
Secondary cool shot of air Tuesday will drop temperatures down to 
normal before a ridge builds into the west on Wednesday... 
returning temperatures 5 to 8 degrees above normal. 


Upper level ridge slides eastward Wednesday night with southwest 
flow returning and winds becoming gusty by Thursday morning ahead 
of the next Pacific system. System will mainly stay north of the 
County Warning Area...but have continued the trend of slight chance to chance probability of precipitation 
across the Sierra north of I-80. Df 


Long term...Thursday through Sunday... 


Thursday will feature a negative-tilt system brushing by to the 
north. With all the forcing/instability north...it will be hard to 
get much precipitation past the crest from about Tahoe north with an 
increase in wind and a cool down the main feature for most of the 
area. 


Friday...another system will jam through the region. This system 
will bring additional cooling to the region with a -30c cold pool 
aloft. It will also feature a better shot at precipitation thanks to the 
ridge weakening provided by the Thursday system. As with the 
previous shift...I am feeling the slightly deeper European model (ecmwf) solution 
with the strength of the backside-of-the-low jet streak and the fact 
that the GFS ensemble has a Standard deviation bulls eye (hinting at 
a deeper solution than the GFS mean depicts) at the base of the 
disturbance as it digs into Nevada on Friday. With the European model (ecmwf) in 
mind...I lowered highs a bit Friday and raised probability of precipitation slightly 
(especially north of I-80). I also tailored Friday night's probability of precipitation with 
the idea of the exiting cold pool Friday evening...which implies 
possible showers in the basin more than in the Sierra. 


Beyond Friday...we will have a warm up to near or slightly above 
average highs as a ridge settles in aloft. After next weekend...the 
attention turns to the day 8-10 period. The ensembles show a 
definite trend for lowering heights and troughiness in the eastern 
Pacific beginning to affect the region next week. It is too early 
for details...but a colder and wetter pattern seems to be in the 
offing for next week per the European model (ecmwf)...GFS...and Canadian ensembles. 
Snyder 




&& 


Aviation... 


A dry cold front will bring a wind shift to NE-east winds this 
afternoon and overnight. Ridge winds gusting to around 45 kts this 
morning will diminish this morning (northern sierra) and afternoon 
(mono County sierra) as the front moves through...which should 
decrease/end potential turbulence in the Lee of the Sierra. 
Snyder 




&& 


Rev watches/warnings/advisories... 
Nevada...none. 
California...none. 
&& 


$$ 


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