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Area forecast discussion...updated 
National Weather Service Boise Idaho
1046 PM MST Friday Nov 27 2015

..updated most temperatures colder through Sunday...

Discussion...updated most temperatures colder through Sunday generally
guided by persistence. Burns/or has already set new record lows
for both today and Saturday...and probably will again Sunday.
See pnsboi for more details. /End update/

Have updated most sites colder as many sites have already reached
their originally forecast mins. Fog has been slow to form this
evening and radiational cooling has dominated. Main area
of fog/stratus this evening has been southeast of Boise through Mountain
Home to near Gooding. A smaller area was near Weiser. Without the
fog Burns/or dipped to -8f at 6 PM PST. By sunrise we expect most
of the snake basin to be in fog or stratus...and continue through
the morning then partially clear in the afternoon. Inversion
conditions will intensify this weekend due to ridging and warming
aloft. No realistic breakdown of the inversion foreseen until about
next Thursday. No other forecast changes at this time.


Aviation...generally VFR. Patchy LIFR fog/low stratus in valleys...
especially near kmuo kboi kbno. Surface winds variable 10kt or less.
Winds aloft near 10k feet mean sea level...NE 20-30kt.


Previous discussion...
short term...tonight through Sunday...forecast area stuck in
northeast flow aloft as low over Nevada/Utah spins around and inches
eastward ever so slowly. Low is far enough away to have no threat
of precipitation in the short term. The forecast problem is the extent of
fog and stratus trapped in valley inversions through the
period...which is always very tricky and not handled well by
models. Fog/stratus formed in Magic Valley overnight...and then
moved westward into lower Treasure valley this morning. Thinned
quite a bit northwest of Boise...but stayed thick and foggy from
Boise to Glenns Ferry. We think the down-valley spread of this
moisture will help to re-develop a layer of fog/stratus again
tonight... both in the Treasure valley and the Magic
Valley...along with the areas in Harney County Oregon that have
persisted all day as well. We put patchy fog in all these
areas...although there could certainly be areas where it is
thicker than others...and areas where it is mostly stratus rather
than fog. After that...not much change through broke
out the fog/stratus each afternoon...but then redeveloped it in
the same areas each night. Moderated the valley temperatures a
bit...warmer at night and cooler during the day...due to the
increase in fog/stratus. Otherwise...temperatures in mountains
remain well above normal while valleys remain well below due to
strong inversion.

Long term...Sunday night through Friday. Cutoff upper low will
continue to move east of the area Sunday night into Monday. A
transitional upper ridge will set in for the early part of next week
which will keep conditions dry with below normal temperatures. For
Wednesday and beyond...models have come into a better agreement of
indicating another large upper low moving in from the pacnw coast.
SW flow ahead of this system and potential mixing of the atmosphere
will likely mix out the inversion conditions and warm temperatures
to closer to normal. Precipitation chances look minimal until what looks
like a cold front passage sometime Friday.


Air stagnation...strong valley inversions will persist through
early next week. Mixing heights generally below 1500 feet above ground level...with
light winds within that layer. Improvement probably starts Wednesday and
beyond as flow from the west increases and next trough approaches.

Boi watches/warnings/advisories...



previous short term...tb
previous long term....ep/dd
air stagnation....tb

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