877 
fxus65 kpih 211655 
afdpih 


Area forecast discussion 
National Weather Service Pocatello Idaho 
1000 am MST Sat Nov 21 2009 


Short term...today through Monday. Current forecast in reasonably 
good shape as far as today is concerned. After reviewing the latest 
guidance however...we are looking at near warning snowfall amounts 
in The Sawtooth mountain region Sunday with brisk winds which tips 
the scale toward a Winter Storm Warning. The remainder of the central 
and eastern mountains will likely see advisory level snowfall with wind 
as well Sunday afternoon through Sunday night. These highlights will 
follow shortly after noon today with the updated forecast following 
as soon as we complete the grids for the afternoon package. See 
previous discussion below. Huston 


Cold front has pushed through much of the area this morning. As a 
result...winds have dropped below advisory level however they remain 
generally elevated. Gap flow has diminished with winds turning more 
southwesterly but gusts to 35 miles per hour remain common in snake plain. 
Precipitation has spread throughout the region but temperatures 
remain above freezing everywhere except the central mountains and 
the higher elevations of the eastern Highlands. Cold air will filter 
into the region today...so expect little diurnal temperature rise 
today before falling off through this afternoon. Precipitation will 
continue through the morning then diminish as the trough quickly 
lifts into Wyoming this afternoon. Precipitation amounts are 
generally expected to be light with only a few inches expected in 
the highest elevations. Winds will remain breezy 
today...especially in the Snake River Plain. Expect winds to be 
just below advisory level today. 


Ridging ahead of the next system will bring a brief break in the 
weather this afternoon and tonight. The next fast moving trough 
arrives Sunday morning. With cold air in place...this system will 
bring snow across the area with the highest quantitative precipitation forecast amounts again 
expected in the central mountains and southeastern Highlands. 
Models indicate at least advisory level snow amounts associated 
with this system...however with its fast moving nature and recent 
model tendency to over-estimate the precipitation will hold off 
issuing any headlines for now. The Snake River Plain will escape 
much of the snowfall however an inch or so is possible. Also of 
concern will be another round of gusty winds ahead of the cold 
front on Saturday night. Hanko 




Long term...Monday night through Saturday...isolated showers will 
linger mainly in the northern mountains Monday night as a high 
pressure ridge begins to build. Model consensus favors a higher 
amplitude high pressure ridge and drying conditions Tuesday through 
Thursday. Current forecast reflects much lower probability of precipitation and less clouds 
during that time period. Diurnal temperature range was also 
increased. The ecm is faster than the GFS with the next disturbance 
around Friday morning and depicts more of a stretched...weak trough. 
Therefore stayed close to climatology with probability of precipitation for Friday and 
Saturday time frame. Receiver station 
&& 


Aviation...Post frontal precipitation just now moving through kida 
and kpih and should be limited to the next couple hours. Cold 
advection at or just above cloud level increasing and snow levels 
estimated only 500 to 1000 feet above the valley floor. Cloud cover 
continues to move up the Magic Valley and could keep MVFR ceilings 
pinned against the east benches as the nam12 suggest until about 
18z. Westerly surface pressure gradient will support breezy 15 to 25 
miles per hour winds through 24z. Ceilings improve to VFR tonight. The second 
of two disturbances moves into southeast Idaho after 22/1500z...cold 
frontal passage at kida and kpih near 22/2100z...and snow levels 
about 4400 feet mean sea level. Receiver station 
&& 


Pih watches/warnings/advisories... 
Winter Storm Warning for The Sawtooth mountains and Wood River 
region for Sunday. 


Winter Weather Advisory for the Lost River/pahsimeroi region for 
Sunday. 


Winter Weather Advisory for the eastern mountains Sunday afternoon 
through Sunday night. 
&& 


$$