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fxus66 kotx 072340 
afdotx 


Area forecast discussion 
National Weather Service Spokane Washington 
440 PM PDT Tuesday Oct 7 2008 


Synopsis... 
a exiting system will continue to leave cooler...and windy... 
weather Tuesday evening. Conditions improve overnight into 
Wednesday...as weak high pressure builds in. A deeper trough digs 
in for the end of work week...and systems pivoting around it will 
keep at least a slight risk for precipitation in the forecast 
through early next week. Below normal temperatures will continue 
through the weekend. 


&& 


Discussion... 


Updated aviation discussion 


Tonight...satellite loops are showing the upper level low moving 
through southern British Columbia at the time. The 12z models are 
very consistent showing the trough exiting the region this evening 
followed quickly by weak ridging. Instability associated with the 
cold core across the northern zones this afternoon will combine 
with up-sloping flow into the eastern mountains for a low end 
chance of showers through sunset. Cross Cascade flow is also 
resulting in a little slop over precipitation near the Cascades. 
Snow levels are on the decline and are expected to bottom out 
near 5000 feet tonight. As such some of these showers may drop 
some light snow on the higher elevations this evening. The showers 
will linger well into the evening hours. 


The main focus are the winds for this evening. Building surface 
pressure behind the exiting front has resulted in an 8mb pressure 
gradient from sea-geg. In addition there is a 30-40kt middle level 
jet and strong cold air advection. The pressure gradient begins to 
subside around 03z and the jet pushes east shortly after. As such 
the windy conditions will linger to 03z if not an hour or so 
later...and the Wind Advisory has been extended to cover this. 
Temperatures will be 15-20 degrees cooler than last night. Expect 
these cool overnight temperatures to continue through the 
week. /Tobin 


Wednesday to Friday...the region remains cool and unsettled with 
the long-wave pattern amplifying. Energy coming off the Asian 
continent digs a deep trough just east of the dateline. A ridge 
amplifies downstream across the Gulf of Alaska....and the low 
currently in the Gulf of Alaska migrates southeast and digs a trough 
across the inland northwest Thursday...and into the Great Basin and 
California Friday. 


Wednesday...a weak disturbance skirting by the North County warning area ejects 
east and weak short-wave ridging develops...as that Gulf of Alaska low 
starts to migrate down the coast. The westerly flow and lingering 
moisture near the Cascades and Idaho Panhandle mountains will bring mostly 
cloudy conditions and just a slight chance for showers in these 
areas. Snow levels are expected to range from near 3500 feet in the 
Cascades to near 5000 in the southeast County Warning Area. Otherwise look for 
partly cloudy to mostly sunny skies across the rest of the 
County Warning Area...with some marginal breezy conditions in the afternoon as the 
atmosphere gets mixed up in the daytime heating. Highs are 
expected to remain below average...by some 6-11 degrees. This is 
supported by 850 temperatures in the lower single digits and 1000/850 
thicknesses near 1330-1335 M. 


Wednesday night through Friday...the Gulf of Alaska trough digs south 
across the inland northwest and drops into the Great Basin. Moisture 
starts to increase from the west Wednesday night...leading to an 
increase in clouds and an increasing risk for precipitation in the 
Cascades. Thursday/Thursday night...the digging trough spreads 
synoptic lift around the west and southern periphery of the County Warning Area. 
Friday...the trough digs south and east and the best lift pivots 
around to the eastern side of County Warning Area and shifts out...and the flow 
turns northeasterly. The deepest moisture through this period 
rotates across the west and southern County Warning Area...while largely middle/upper 
level moisture spreads over the northeast part of the County Warning Area. Look for 
mostly cloudy/cloudy skies Thursday...with a precipitation risk increasing 
across County Warning Area from the west through the day. The main chances will be 
over the west and southern County Warning Area...but at this time the overall best risk for 
precipitation with the system looks just west and south of the County Warning Area. By 
Friday the main precipitation chances will retreat to the east/southeast County Warning Area with 
skies clearing elsewhere. Morning snow levels will range from near 
2000-4000 feet during the morning hours...rising to near 3000-5000 feet 
in the afternoon. Breezy northerly winds are also expected Friday 
with the increasing northerly flow. Below normal temperatures are 
expected to continue...with 850 temperatures in the lower single digits and 
1000/850 thicknesses around 1330-1335 M. /Jcote 


Friday night through Tuesday...extended forecast models are in 
good agreement from Friday night through the weekend...then begin to 
diverge for Monday and Tuesday. 


The pattern over the weekend will feature an upper ridge along 
130w and a cutoff low over Utah...Colorado...eastern Idaho...and 
western Montana. Will have to watch for potential wrap around 
bands of precipitation clipping north Idaho but models in good 
agreement that the best precipitation chances will remain south and east 
of our area...with just a slight chance of showers over the 
central Panhandle mountains and the Camas Prairie. The placement 
of the cutoff low to our east and the ridge axis along 130w will 
place eastern Washington and north Idaho in a deep north to 
northeast flow. This will result in a dry and cool air mass 
filtering down from the northeast. In fact...model dew points off 
the GFS and European model (ecmwf) drop down into the teens to low 20s. This dry 
air mass along with winds gradually dieing off will promote good 
radiational cooling conditions for the coldest low temperatures of the 
season so far. However the light winds will be more common Saturday 
night when pressure gradients go light. With the growing season 
still continuing in the lowest elevations will issue a hazardous 
weather outlook to address freezing temperatures. 


For Monday and Tuesday...the ridge begins to flatten out with the 
European model (ecmwf) model the most aggressive in breaking down the ridge and 
dropping a cold front into the area from the northwest. This idea 
looks aggressive given amplitude of ridge over the weekend so 
trended forecast more towards the GFS/UKMET/Canadian which hold 
onto the ridge at least through Monday afternoon. After this 
however went with more of a climatology forecast given uncertainty of 
timing of possible front passage Monday night or Tuesday. Jw 


&& 


Aviation... 
breezy to windy conditions will persist through 03z then dieing off 
quickly with the loss of daytime heating and consequent mixing 
potential. Meanwhile...the air mass has dried out today resulting in 
cloud bases remaining VFR except for some MVFR near the Cascade 
crest. After sunset the atmosphere will begin to stabilize leading 
to decreasing cumulus overnight as well as decreasing showers that 
as of 2330z were located near the Cascade crest and the mountains of NE 
Washington/north Idaho. Jw 


&& 


Preliminary point temps/pops... 
Spokane 34 54 33 50 31 53 / 0 0 10 20 20 10 
Coeur D'Alene 34 54 33 52 30 53 / 0 0 10 30 20 10 
Pullman 36 55 34 50 31 52 / 0 0 10 30 30 20 
Lewiston 40 60 37 53 36 56 / 0 0 10 30 20 20 
Colville 34 55 30 52 27 56 / 0 10 10 20 10 10 
Sandpoint 35 52 28 48 28 50 / 10 10 10 20 10 10 
Kellogg 39 51 33 49 30 49 / 10 10 10 40 30 20 
Moses Lake 35 59 33 56 32 60 / 0 0 0 20 10 10 
Wenatchee 37 57 36 55 35 57 / 0 0 10 20 10 10 
Omak 31 58 30 55 30 57 / 0 10 10 20 10 10 


&& 


Otx watches/warnings/advisories... 
Idaho...Wind Advisory until 11 PM PDT this evening for Coeur D'Alene 
area...Idaho Palouse...Lewiston area. 


Washington...Wind Advisory until 11 PM PDT this evening for lower Garfield 
and Asotin counties...Moses Lake area...Spokane area... 
upper Columbia Basin...Washington Palouse...Waterville 
Plateau...Wenatchee area. 


&& 


$$ 

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