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Area forecast discussion 
National Weather Service Reno Nevada 
115 PM PDT sun Mar 21 2010 


Short term... 
only minor changes to forecast this afternoon including lower probability of precipitation tonight-Monday 
across northern zones...drier conds Monday night-Tuesday night...and an introduction of 
low probability of precipitation Wednesday night. Upper low moving into Pacific northwest will drop southeastward through Great 
Basin Monday followed by ridge Tue-Wed...and next syst brushing area late 
Wednesday night. 


Surface gradient between ksac-krno continued to increase this afternoon as short wave energy 
moved into pacnw and cooler air filtered into interior northern California. Rdgs 
were gusting to 70+ miles per hour with surface wind gusts now 30-35 miles per hour. Expect 
winds to remain gusty into early evening and will continue lake wind 
advisories until expiration. The air mass remained fairly dry ahead of this 
syst and showers were having a difficult time holding together as 
they moved across northern California and into parts of northestern California/northwestern Nevada. Satellite 
imagery showed enhanced band of clouds becoming quite narrow as 
well. So any showers are going to be isolated and produce meager quantitative precipitation forecast 
values. Lowered probability of precipitation overnight into Monday. Northerly winds will increase across the 
lower valleys of western Nevada on Monday as trough digs southeastward into the eastern part of 
the Great Basin and may result in a period of choppy lake waters 
again Monday afternoon for Pyramid Lake. 


A very dry air mass will once again follow this upper low Monday night-Tuesday and 
lowered dewpoints closer in line to MOS guidance which showed many 
locations in the teens and lower 20s. Area will be between incoming West 
Coast ridge and exiting trough. This will result in a cool Ely gradient 
with gust winds along the Sierra rdgs and possibly making Lake Tahoe 
choppy Monday ngt-Tue. Temperatures will be close to normal Tuesday. 


Upper ridge will begin to slide east on Wednesday with southwesterly flow returning ahead 
of next Pacific syst. Wednesday will be our warmest day and bumped temperatures up a 
few degrees. Strongest winds aloft and cooling air mass across California do not 
arrive until late in the day and thus gradient/winds will be slow to 
respond. So did not raise the winds too much as best gradient is 
expected to occur Wednesday evening-Thursday morning. The European model (ecmwf) has come more in line 
with the faster GFS and brushes short wave energy across northern areas Wednesday night 
and early Thursday. A slight chance of showers was introduced northern zones. 
Parent upper low is still well off pacnw coast (south of aleutians). 
This lends support to this more progressive flow with the best 
dynamics staying north of area. Hohmann 


Long term...Thursday through Sunday... 
progressive flow across the Pacific and North America for late next 
week...with systems moving into the West Coast. Pattern should 
amplify across the eastern Pacific for next weekend as a deep low 
moves into the Gulf of Alaska. Will give the European model (ecmwf) a bit more 
weight into the forecast for next weekend than the GFS due to its 
slower timing of systems in a higher amplitude flow. 


First trough will pass over northwest Nevada Thursday morning... 
with jet segment sitting over northern California Thursday 
afternoon. Low chance of showers across the far north...with breezy 
conditions possible along and south of I-80. 


Second trough on the heels of the Thursday system will affect the 
area Friday into Friday night. European model (ecmwf) track brings the system and 
cold pool overhead...while the GFS tracks the system through the 
northern rockies. Will follow the European model (ecmwf) here...European model (ecmwf) and GFS have 
same pattern on the jet...with segments over central Nevada and 
along the back side of the trough. Main issue with GFS is it does 
not put any energy over the forecast area between the jet segments 
where a low typically develops. Did lower temperatures/snow levels 
and increased wind and probability of precipitation for Friday and Friday night. Decent 
front ahead of the cold pool could bring a short period of heavy 
snow/rain to the northern Sierra. 


Ridge to build over the area Saturday...with energy nearing the 
Pacific coast late Sunday. Decreased highs for Saturday...with a 
cool and dry north flow behind Friday/S trough with a few degrees of 
additional warming Sunday with better mixing and dry southwest winds 
off the Sierra. Brong 
&& 


Aviation... 
low moving into British Columbia with high clouds and gusty winds 
across the Sierra and western Nevada through 06z. Ridge winds 40-60 
kts will decrease 00z-06z. North-northeast surface flow for Monday 
as surface high pressure moves into Oregon. 


For ktvl and ktrk...20-30kt gusts will continue through 03z then 
turn light as winds decouple and Sierra ridge winds drop below 30kts. 


For krno...southwest winds will turn to west-northwest at 20-30kts 
23z-03z. Gusts should dissipate after sunset...with 10-15kt 
west-northwest winds through 06z. North winds Monday afternoon 
with surface high building into Oregon...gusts should remain below 
25kts. Brong 
&& 




Rev watches/warnings/advisories... 
Nevada...Lake Wind Advisory until 8 PM PDT this evening for Pyramid Lake 
in nvz004. 


Lake Wind Advisory until 8 PM PDT this evening for Lake Tahoe 
in nvz002. 


California...Lake Wind Advisory until 8 PM PDT this evening for Lake Tahoe 
in caz072. 


&& 


$$ 


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