Weather

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afdotx 


Area forecast discussion...updated 
National Weather Service Spokane Washington 
955 PM PDT Thursday Aug 28 2008 


..updated aviation and synopsis... 


Synopsis... 
following transient middle and high level clouds tonight will be a 
warm up on Friday as a cold front approaches the Pacific northwest 
coast. This rather dry cold front will move through the inland 
northwest by Friday night...and will be the precursor to 
breezy...cooler and more showery conditions for the weekend. 


&& 


Previous discussion... /issued 430 PM PDT Thursday Aug 28 2008/ 
tonight through Sunday...broad ridge remains over the County 
Warning Area this afternoon. Moist westerly flow will continue 
through the evening hours keeping a fairly thick middle and high 
level cloud deck. Drier air will move in overnight and clouds will 
thin and decrease. The drier air will not make it to the Canadian 
border and some residual moisture will linger across the north. 
Kept partly cloudy in the forecast for Friday for this area. The low 
level flow on Friday will turn to the southwest and usher in some 
warmer temperatures to the forecast area. Temperatures Friday will 
be at or slightly above average for this time of the year. Our one 
day of slightly above average temperatures will end by Saturday. A 
cold front moves across the area Friday night and a trough will 
remain over the Pacific northwest for the remainder of the weekend. Best 
chance of precipitation will occur in the mountains through the 
weekend. Temperatures will return to 5 to 10 degrees below 
average for Sat and sun. /Nisbet 


Sunday night and Monday...an upper trough will continue to migrate 
across the northwest and Great Basin. Some synoptic lift is found over 
the southeast County Warning Area...though deepest lift remains east. One tentacle-like 
surface trough/trowal/deformation zone extends north into eastern Washington/northern 
Idaho. This provides an additional focusing mechanism for precipitation. 
Idaho is situated in a south-southeast flow while the west in a north-northeast flow. 
Some moisture wraps into the inland northwest this period for the 
features outlined above to work with...though there remains some 
disagreement as to how far west the moisture invades. All these 
factors are most prominent through Monday am...before short-wave 
ridging and a west-northwest flow develops. This translates to a risk for 
rain showers across the Idaho and southeast Washington Mountain zones...with partly to 
mostly cloudy skies over the rest of the County Warning Area. If guidance begins 
to suggest a further west invasion of moisture...some probability of precipitation will 
need to added to the Washington Palouse and/or Spokane area for Sunday 
night/early Monday. 


Monday night to Thursday...the trough fills a bit and migrates 
east a bit...while a ridge amplifies over the eastern Pacific. 
This puts the region in mean west-northwest flow and a least a couple upper 
disturbances break across the inland northwest. None of the disturbances 
carry deep moisture and there remains some differences regarding 
precise timing. Loose agreement brings one disturbance by 
Tuesday...with a general increase in clouds as well as some 
breeziness for the County Warning Area. Otherwise the forecast calls passing 
middle/high clouds and only a slight risk for mountain showers 
Tuesday to Thursday. 


Temperatures are projected to remain below normal through this 
period (on average by 5 degrees)...with 850 temperatures (near 10 degree c) 
and 1000/500 mb thicknesses (near 555 dam) not varying much from 
day to day. The 12z GFS suggested a moderation closer to normal by 
the end of the period...but consistency and support from other 
models is not yet tight. /Jcote 


&& 


Aviation... 
VFR conditions will remain in the forecast for all taf sites through 
at least 06z Saturday. Following scattered to occasional broken hi cloud ceilings 
tonight at taf sites...the main aviation issue will be winds late 
Friday following cold frontal passage. These gusty west winds...mainly confined 
to the western Columbia Basin including kmwh and keat...should peak 
between 23z and 04z Sat with sustained surface winds 16-20kt likely. 
The best chance of rain showers will be over the northern mountains Friday afternoon 
and evening...and should be no more than scattered areal coverage. Bz 


&& 


Preliminary point temps/pops... 
Spokane 54 82 55 73 47 68 / 0 0 0 10 10 10 
Coeur D'Alene 51 81 53 73 44 68 / 0 0 0 10 10 10 
Pullman 50 83 52 73 41 69 / 0 0 0 10 10 10 
Lewiston 60 91 61 81 52 73 / 0 0 0 10 10 10 
Colville 46 77 49 72 42 70 / 10 10 10 10 10 10 
Sandpoint 45 76 50 72 39 66 / 10 10 10 10 10 20 
Kellogg 48 79 55 69 44 65 / 0 0 10 10 10 30 
Moses Lake 56 86 55 78 48 76 / 0 0 0 0 10 10 
Wenatchee 60 85 58 75 51 74 / 0 0 0 10 0 10 
Omak 53 84 53 77 46 74 / 0 0 10 10 0 10 


&& 


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


$$