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Area forecast discussion 
National Weather Service Reno Nevada 
243 PM PDT Friday Jul 18 2008 


Short term... 
significant middle to upper level dry air remains over the region today 
with a low amplitude trough well off shore near 140w. Strength of 
the dry air aloft will result in poor overnight humidity 
recoveries again tonight. Short range models in fair agreement 
with overall pattern evolution this forecast as GFS...European model (ecmwf) and 
NAM all indicate trough pushing slowly east and closed low 
developing by Monday just off shore California coast. This low may slowly 
eject by early Tuesday but models typically have difficulties this 
time of year with ejecting weak lows. European model (ecmwf) is a bit deeper with 
the low by Monday morning than either GFS or NAM...but not by much. 
With the low remaining west of the region through the forecast and 
limited moisture returning around high to the southeast...set up is not as 
favorable as previously thought for convection Saturday. 


Still models indicate minimal instability...especially over southern 
portions where moisture will be most readily available by Sat afternoon for 
high based convection as weak vorticity lobe lifts north across the region. 
Any storms that develop will be moving around 20 miles per hour and combined 
with dry sub cloud layers this should limit any quantitative precipitation forecast...resulting 
in mainly dry thunderstorms. Coverage should be no better than isolated 
late afternoon then expand a bit northward well east of the Sierra by 
the early evening. GFS shows significant dry air aloft punching 
into the northern portions of the County Warning Area by early Saturday evening which 
should end any convective potential as middle/upper layers become 
more stable. Thus will remove much of the probability of precipitation from the far northern 
and western portions of the County Warning Area. With jet streak aloft winds could 
become a factor Saturday afternoon but current thinking is 
strongest gusts will be across the northern sections...25 to 30 
miles per hour...with an occasional higher gust in the windiest areas. Do not 
feel this will be widespread enough to warrant any headlines at 
this time but relative humidity levels will be quite low again during the 
afternoon. 


Best instability and moisture should remain east of the County Warning Area on Sunday 
but once again daytime relative humidity levels will be low with gusty winds in 
the 20 to 25 miles per hour range by afternoon. Will keep Sunday dry given 
fairly dry/stable middle/upper levels. Temperatures not likely to cool much Sunday 
as low remains off shore and heights do not see much of a fall 
yet. Change begins for Monday as models try to push the closed low 
closer to California. This should lower heights and cool daytime highs a 
few degrees and also result in slightly more instability. Moisture 
appears somewhat limited but will continue idea of isolated 
convection far southern County Warning Area for late Monday afternoon. All models indicating a 
jet streak rounding the low and nosing into the western County Warning Area by late 
Monday afternoon/early Monday evening. With this little boost will spread 
isolated convection a bit further north Monday evening although 
confidence is low with this solution. 


Smoke has thinned considerably over most of the County Warning Area with only 
portions of NE California and far northwest Nevada seeing any effects from the California 
fires. Will confine mention of haze to caz071 and nvz005 and far 
western portions of nvz004. Will have to monitor though as gusty winds 
this weekend could result in increased fire activity a more smoke 
for the region. Mlf 


Long term...Monday through Thursday... 
no changes were made to ongoing forecast. Large scale pattern will 
feature weak trough along the West Coast with upper ridge over The 
Rockies/plains. Any convection associated with shortwave energy just 
prior to this period should be ending as jet dynamics/large scale 
forcing shift east and north of the area. However both the GFS/European model (ecmwf) 
continue to show some instability hanging back into Mono/Mineral 
County where the ongoing slight chance of thunder seems reasonable 
for diurnally driven activity. Models diverge some middle to late week 
as the GFS maintains a slightly stronger southwest flow and the most 
stable conditions. It shows little 500mb relative humidity response to convection 
even across southern areas where it would be typical under lighter 
flow regimes. The European model (ecmwf) maintains this weaker pattern and shows 
some middle level response. Ensemble data shows no strong signal to 
make a choice with any confidence either way. So will keep both 
Wednesday Thursday dry with an introduction of probability of precipitation south Friday as 
already advertised. Temperatures will remain slightly above normal. 
Hohmann 
&& 


Aviation... 
no significant issues. Terrain driven winds will gust to 25kt at 
times through early evening. Otherwise light winds overnight and 
into the morning Saturday. Hohmann 
&& 


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


$$ 


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