Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 190300

Area Forecast Discussion
National Weather Service Boise ID
900 PM MDT Wed Oct 18 2017

.DISCUSSION...Warm temperatures will continue on Thursday ahead of
a Pacific cold front. Highs will be in the 70s once again in the
Snake River Plain. Skies will remain mostly clear, although
clouds will be increasing in southeast Oregon Thursday afternoon
ahead of the front. Breezy conditions will also develop in
southeast Oregon and the higher terrain of southwest Idaho. No


.AVIATION...VFR. Increase in mid-upper level cloud cover Thursday
afternoon. Surface winds, mostly southerly 10-15 kts with
afternoon gusts 20-28 kts. Winds aloft to 10k feet MSL, southwest
20-45 kts.


SHORT TERM...Tonight through Saturday...Tonight and Thursday will
be 5-10 degrees warmer than normal under southwest flow aloft
ahead of an approaching north Pacific cold front. Skies will
remain mostly clear over southwest Idaho through Thursday, but
southeast Oregon will see clouds increasing from the west Thursday
afternoon. Model soundings predict an inversion again in the
lower valleys tonight. But with increasing southeast to southwest
surface winds and mostly clear skies Thursday morning, the
inversion should be shallow and mix out before noon, allowing high
temperatures to reach their full potential. Southeast Oregon
could be an exception due to more afternoon cloud cover. The cold
front is still timed to reach southeast Oregon Thursday evening,
the Boise area around midnight, and the Magic Valley early Friday
morning. The heaviest precipitation will be over the mountains
Thursday night and Friday morning. Snow levels will be above 7000
feet Thursday night, then lower to about 5000 feet by Friday
afternoon. Snow totals of 1 to 4 inches are expected above 5000
feet before precipitation tapers off Friday night. Rainfall
amounts in the Snake River Valley are expected to be relatively
light due to shadowing by higher terrain. A cold upper level
trough will move over our CWA on Friday, lowering daytime
temperature by 15 to 20 degrees. On Saturday an approaching warm
front will bring another round of mountain snow and valley rain,
with high temperatures around 10 degrees below normal.

LONG TERM...Saturday night through Wednesday...Pacific warm front
will bring rain Saturday night, heaviest in the north. Drier
zonal flow aloft Sunday and Monday will evolve into a high-
amplitude upper ridge over western North America Tuesday and
Wednesday. The ridge will bring strong warming aloft but less
warming at the surface due to only light mixing winds, lower sun
angle, and decreased hours of daylight. With stronger surface
winds the valleys could warm to the 70s, but for now there is no
clear signal of this in the models. In any case, Tuesday and
Wednesday will be dry and generally clear.





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