Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Boise Idaho
308 PM MDT Thursday Sep 18 2014
..included air stagnation segment...
Short term...at 2 PM MDT isolated thunderstorms continue in southeastern
Owyhee County and the western Magic Valley...moving northeastward. Air mass is
still unstable enough for thunderstorms to form in eastern Oregon...
Owyhee Mountains...Camas Prairie...and eastern Boise County through
this evening. Isolated coverage in these areas. Scattered
coverage in the southern Sawtooths where air mass is more unstable.
Air mass will dry and stabilize from the west later tonight. Friday
through Saturday will be dry. Extensive smoke from fires in calif
should decrease in our County Warning Area tonight and Saturday as upper winds
veer from southwesterly to more westerly. But there are also fires in
Oregon and some smoke will continue in our County Warning Area. Decreasing clouds
late tonight will allow temperatures to cool further than last night. Maximums
Friday should be slightly cooler than today. Mins Friday night
similar to tonight. Maximum temperatures Saturday 3 to 6 degrees warmer with
upper winds becoming southerly or even southeasterly...as upper low
in California comes toward US. Southeasterly winds would be best
for ridding our County Warning Area of remaining smoke.
Long term...Saturday night through Thursday...a pattern change next
week is expected to bring precipitation and cooler temperatures by
Thursday. Temperatures will continue above normal through Wednesday.
An upper level low over the California coast Saturday night will
lift northeast across the Great Basin Sunday reaching southwest
Idaho and southeast Oregon Sunday night...with a chance of showers
Sunday afternoon through Monday. Precipitation is expected to be
mainly over southwest Idaho and the central Idaho mountains. This
system will be followed by drier southwest flow aloft starting
Monday night and continuing across most the area through Wednesday.
Meanwhile a strong upper level jet from the North Pacific will reach
northern California Tuesday night and the northern rockies Wednesday
night. This feature plus a surface cold front crossing southeast
Oregon and southwest Idaho Wednesday night and Thursday will bring
cooler temperatures and a chance of showers.
Aviation...VFR. Widespread smoke layers aloft...plus local MVFR
visibilities in the valleys...will continue through this evening.
Some improvement is foreseen after midnight with the smoke shifting
south of a kreo-kmuo-Fairfield line. Also expect isolated
thunderstorms over the higher terrain and east of kmuo until about
06z. Surface winds...variable 10 kts or less except westerly 10-15
kts through the Snake River Valley east of kboi. Winds aloft...
northwest 15-20 kts up through 10k feet mean sea level.
Air stagnation...smoke from California fires should decrease
tonight and Friday as upper winds change from southwesterly to
west-southwesterly. But fires in Oregon will also contribute
some smoke. On Saturday an upper level low pressure system will
move in from Nevada. Circulation around the low will bring
southerly and then southeasterly winds into our area and greatly
improve air quality.