Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
924 am MDT Thursday Aug 27 2015
Discussion...not nearly as active today as yesterday when
thunderstorms brought heavy rain and a huge number of lightning
strikes to eastern Elmore and northern Camas counties.
Little change in temperatures today then a few degrees warmer Friday as
upper flow backs ahead of approaching Pacific trough. Windy
and significantly cooler Saturday as Pacific cold front moves
through...frontal passage in Oregon Saturday morning...in Idaho midday and
afternoon hours. No updates at this time.
Aviation...VFR with few-scattered high clouds clearing through the day.
Wildfire smoke producing occasional MVFR north of a line from kbno-
ksnt. Surface winds...generally 12 kts or less...with a few gusts to
20 kts in the valleys after 27/21z through sunset. Winds aloft near
10 feet mean sea level...southwest 10-15 kts.
short term...today through Friday...water vapor shows moisture
plume across eastern Oregon which will spread east across Idaho
this afternoon. Southwest flow aloft will gradually increase
through Friday while upper level forcing remains weak. So probability of precipitation/quantitative precipitation forecast
from the nmm and GFS were favored as they were highest over south
central Idaho/S Boise Mountains. Secondary moisture plume off the
Oregon coast was fastest in the 00z GFS /moving to Steens Mountain this
afternoon/ but chance for thunder there is very low. Temperatures
remain 5-10 degrees above normal through Friday but records are
another 10 degrees above that.
Long term...Friday night through Thursday...upper level trough off
the coast of western Canada will be the main influence on the
forecast area through the period. This will bring mainly cooler
temperatures and periods of cloudy skies. A shortwave moving through
central Oregon on Saturday should bring enough of the inch plus
precipitable water inland for showers Saturday afternoon mainly in
the higher terrain...and windy conditions across southeast Oregon. Moderate
30-50 kts southwesterly middle level jet should cause shadowing in the
lower elevations which the models have picked up on rather well.
Minimal instability should limit thunderstorm develop to the higher
terrain as well. A dry cold frontal passage late Saturday and early
Sunday morning could provide enough to produce showers mainly over
south central Idaho. Models continue to indicate a series of
shortwaves within the flow that could produce some mountain
convection through Thursday...but confidence is low in timing and
moisture availability. Expected temperatures to remain below normal.
Air stagnation...northeast Oregon smoke impacts continued due to
closer proximity to fires than SW Idaho and other factors.
Southwest flow aloft and mainly nocturnal winds are expected to
continue through Friday morning resulting in areas of smoke across
Baker County and patchy smoke elsewhere northwest of a line from Rome
Oregon to Fairfield Idaho. Stronger winds and a cold frontal
passage are expected Saturday which will bring increased mixing
and cooler temperatures. Expect below normal temperatures to last through
next week. Southwest Idaho continued to see improved conditions as
faster southwest flow aloft was less smoke-filled. Please see
aqaboi issued 255 PM Wednesday for Baker County air quality alert
for smoke. Also please see state deq websites at www.Deq.Idaho.Gov
and www.Oregon.Gov/deq for more information.
previous short term...vm
previous long term....jds