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fxus66 kotx 231149 
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Area forecast discussion 
National Weather Service Spokane Washington 
350 am PST Monday Nov 23 2009 


Synopsis... 
weak high pressure over the region will promote dry but mostly 
cloudy conditions today. A weak Pacific warm front will bring a 
possibility of very light precipitation tonight...with generally 
dry but cloudy weather returning Tuesday and through Thanksgiving. 
On Friday a cold front will pass through with another reasonable 
chance of mountain snow and valley rain or snow. Conditions will 
remain cloudy and unsettled into next weekend. 


&& 


Discussion... 
today through Tuesday...after yesterday's trough 
passage...satellite indicates a weak upper level ridge building 
over the forecast area today ahead of the next storm system which 
is approaching the Pacific coast. It will take much of the day for 
this next wave to reach the forecast area...thus a mainly dry but 
variably cloudy day is on tap for the inland northwest. The moist 
low level air mass from yesterdays precipitation will promote 
areas of morning low clouds and patchy fog across the eastern 
basin...with dense middle and high clouds elsewhere. High 
temperatures will crest at about seasonal normals today with 
decreasing winds. 


Model agreement is reasonable with the evolution of the incoming 
storm system. Most of the dynamic energy associated with the 
parent trough will swing north into British Columbia...however a 
strong and favorably directed fetch of Pacific moisture will 
enhance along a weak warm front tonight and likely produce some 
light precipitation across the northern and eastern zones. 
Precipitation type will be mountain snow...but over the valleys 
and basin p-type will be more ambiguous. A nigh time passage and 
wet bulb cooling as the air mass moistens up argues for light 
snow...however the magnitude of the precipitable water fetch 
suggest a low level air mass too warm for snow. Either the model 
fetch magnitude is being over forecast...or the precipitation over 
the basin and the lower northern valleys will be either rain or a 
non-accumulating mix of rain and a few sopping wet snow flakes 
which will melt upon contact with the ground. The AMSU 
precipitable water satellite suggest the models are initializing 
the magnitude of this fetch well...thus will bet on the latter 
reasoning and expect mountain snow and valley/basin rain or non- 
accumulating mix with this next wave. In any event amounts will be 
light...and pretty much pass out of the region by Tuesday morning. 


On Tuesday the ridge builds back with surface high pressure 
becoming established over the region once again for another dry 
but mostly cloudy and seasonably cool day. /Fugazzi 


Tuesday night through Thursday...the inland northwest briefly transitions 
to a drier pattern as a warm front lifts through and a short-wave 
ridge builds in. Weak but moist isentropic ascent will provide 
middle/higher clouds for much of the region and risk for precipitation over 
the Cascades and northern mountain zones through Wednesday. A near 
isothermal profile in the surface-800 mb layer supports either rain or 
wet snow or a mix. Either way precipitation amounts look light. The middle 
and higher clouds and precipitation risk retreat to the Canadian border 
and Cascades by Wednesday night...as the short-wave ridge 
continues to build. At most other times of the year the building 
ridge would support warming temperatures. Yet the ridging will 
favor stratus/fog in the valleys...inhibiting temperatures from 
warming. Thus confidence in precise numbers is low. At this time values 
lay slightly above normal. However stratus/fog is more persistent 
..values could be lower. In fact it is possible mountains will 
see warmer temperatures than the valleys...especially away from 
the southeast County Warning Area. The southeast County Warning Area will be most apt to mix out 
with a southeast wind...and so see better warming. 


Thursday night into Friday...the precipitation risk increases and 
expands east from the Cascades into Idaho as the next cold front 
passes. Right now it does not look like a significant snow 
producer...but rather a rain or a rain/snow mix threat with 
precipitation tied more to the front. The system begins to move 
east Friday night into Saturday. The northwest flow behind it pushes the 
primary precipitation chances to the Idaho Panhandle and far southeast 
zones. Thereafter model consistency falters. Current runs suggest 
a warm front skims by and a short-wave ridge builds in Saturday 
night into Sunday...supporting some low precipitation risk over the far 
northern and eastern mountains. Yet previous runs were a bit wetter. Until 
better agreement is established some low-grade probability of precipitation are warranted 
..though at this point they remain below climatology. /Jcote 




&& 


Aviation... 
a shortwave ridge will move overhead today resulting in weakening 
winds and largely VFR conditions area wide. Main forecast challenge 
in the short term will be whether or not low stratus will develop 
along the kgeg-kcoe corridor. Between the 12z kotx sounding 
displaying a shallow moist layer approx 800ft above ground level...winds backing to 
a more favorable SW upslope flow...and the 06z NAM model suggesting 
a slight increase in the 925-850mb relative humidity this morning...believe there 
is a 50:50 chance of stratus developing briefly at kgeg-kcoe. Other 
than that...a weak warm front will move into northern Washington and the Idaho 
Panhandle tonight resulting in rain and snow showers. However...some 
uncertainty exists on whether or not precipitation...and subsequent MVFR 
ceilings...will reach the kgeg-kcoe corridor late tonight. /Neuman 






&& 


Preliminary point temps/pops... 
Spokane 38 33 39 31 41 31 / 10 50 10 10 0 0 
Coeur D'Alene 38 33 39 31 41 31 / 10 50 10 10 0 0 
Pullman 39 34 41 29 43 32 / 10 50 30 0 0 0 
Lewiston 45 34 45 34 45 34 / 10 30 20 0 0 0 
Colville 39 34 40 29 40 27 / 30 70 10 20 20 10 
Sandpoint 37 30 35 27 36 26 / 20 60 10 20 20 10 
Kellogg 34 28 37 28 40 29 / 20 60 30 10 10 0 
Moses Lake 43 28 44 31 44 30 / 10 10 10 0 0 0 
Wenatchee 42 31 43 32 43 32 / 10 20 10 10 10 0 
Omak 40 27 43 29 43 29 / 50 60 10 20 10 10 


&& 


Otx watches/warnings/advisories... 
Idaho...none. 
Washington...none. 
&& 


$$ 

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