262 
fxus65 kpih 300932 
afdpih 


Area forecast discussion 
National Weather Service Pocatello Idaho 
332 am MDT Sat Aug 30 2008 


Discussion...southwest low aloft in place across eastern Idaho 
this morning...with some middle and high level moisture already 
working across the state. Enough moisture will be present to 
interact with terrain and a cold front which stalls out across the 
central mountains this afternoon to create isolated thunderstorms. The most likely 
area to see any thunder today will be across the central mountains 
gusty winds and little rainfall will be the threat. Winds will 
pick up in general across the entire area especially along and 
behind the front. A lake Wind Advisory has been issued for 
American Falls Reservoir from middle afternoon into this evening. A 
deepening storm system will continue to work onshore and slide 
across the pacnw/rockies through Monday. The forecast becomes very 
tricky by Sun afternoon. All models indicate the base of the trough 
digging into northern California and Nevada and then swinging northeast into 
Wyoming by Monday night/Tuesday am. There are some differences between the 
models. Have gone with a blend of the NAM/GFS/ECMWF for this 
forecast. For Sunday...showers and thunderstorms will be on the increase 
especially across the eastern and central mountains the potential for 
any storms that can tap into maximum instability to become strong 
to possibly severe as shear profiles are somewhat favorable. 
Lapse rates are decent but not terribly high. The main threats 
would be hail as wet bulb temperatures will be lowering...and gusty 
winds. I would expect this to be mainly for storms that develop 
outside of the central mountains precipitable water values will increase so storms 
could produce locally heavy downpours. For the entire 
event...some decent precipitation amounts are in the forecast for the 
higher elevations especially in the eastern mountains the bigger story 
is the colder weather expected after frontal passage and lowering 
snow levels. The colder weather really doesnt arrive until Sunday 
night as the front gets held up across the eastern third of the 
County Warning Area as the front becomes parallel to upper flow. The front should 
push east Sun night/Monday am as upper trough begins to swing more 
toward the east. Snow levels will drop to around 8000 to 8500 feet 
heading into Monday...and to around 7500 to 8000 feet Monday night. 
Snow is possible especially above 9000 feet. Preliminary snow totals 
for Sun night through Monday night are 2 to 5 inches in the 
central mountains with up to 4 inches elsewhere. More snow would be 
possible across the eastern mountains but snow levels will remain high 
enough for mostly rain until later in the event. As far as 
temperatures...mondays highs should be around 30 degrees cooler in many 
areas compared to this afternoon. 


By Monday night...the system would be pushing farther with rain 
and snow showers lingering across northern and eastern portions of 
the area. Will need to monitor temperatures on Monday night. Current 
NAM/met guidance would indicated a very cold night across all of 
eastern Idaho...with a hard freeze for the lower elevations. For 
now...went with warmer temperatures from previous forecast. For the rest of 
the extended...models keep a general northwest flow with the 
occasional system clipping across the forecast area. Have kept the 
idea of moderating temperatures with low probability of precipitation across the northern and 
eastern mountains Keyes 






&& 


Aviation...VFR conditions will continue through Saturday. Winds 
will increase at the taf sites Saturday afternoon to the 10 to 20 
miles per hour in the Snake River Plain sites as a cold front approaches. Gk/receiver station 




&& 


Fire weather...the first fall like low pressure system will move 
into Idaho Saturday through Monday. A Pacific cold front will cross 
the Salmon-Challis Forest area by noon today and continue slowly 
eastward through the upper Snake River Valley and Caribou Highlands 
by Sunday morning. Wind gusts to 30 miles per hour and relative humidity below 
15 percent are expected in zones 476...477...and 412 where a red 
flag warning is in effect today. The cold front will bring isolated 
thunderstorms to areas north of MacKay this afternoon and progress 
to the Caribou Highlands overnight. Showers will become scattered 
Sunday and Monday and temperatures will be 25 to 30 degrees colder 
by Monday. For Lemhi County mixed rain and snow are possible above 
7500 feet Sunday night. Snow levels should slope upwards to 8000 
feet near Bear Lake by Monday night as the system crosses Idaho. 
Receiver station 




&& 


Pih watches/warnings/advisories... 
lake Wind Advisory from 2 PM this afternoon to 9 PM MDT this 
evening for idz021. 


Red flag warning from 2 PM this afternoon to 9 PM MDT this 
evening for idz412-476-477. 


&& 


$$