Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 272107

Area Forecast Discussion
National Weather Service Billings MT
307 PM MDT Thu Oct 27 2016

.SHORT TERM...valid for Fri and Sat...

Livingston has gusted over 50 mph fairly often today, with a peak
of 59 mph noted around noon at the western DOT station. This a
result of gap flow modified by mixing into increasing
southwesterly mid level flow. RAP shows mountain top winds
increasing to 50 kts early this evening, so would expect 50+ mph
gusts to continue for a while longer, with pressure rises from the
west arriving around 03z likely to signal the start of a
decreasing trend. Have issued a wx story to highlight gusty cross
winds on I-90 at Livingston into this evening.

Water vapor imagery shows moist southwest flow over the western
CONUS with a split upper trof off the coast. It should be noted
that moisture is being aided by the remnants of Hurricane Seymour,
and pwats are expected to rise to around 0.75 inches in our region
by tomorrow, an impressive number for late October. Energy off the
coast of the Pacific NW will flatten the ridge tonight and allow
for cooler Canadian air to advect into our cwa. Expect highs back
to the 50s to mid 60s tomorrow, warmest in our southeast. Southern
split shortwave currently off the CA coast will lift through the
great basin tomorrow and bring a period of ascent in our cwa into
early Saturday. This will coincide with deepened upslope winds as
Canadian high pressure settles over the northern high plains.
Model spread remains high regarding the exact track of this trof
and mid level frontogenesis, with latest GFS/NAM showing a more
southern track, while the ECMWF is further north and affects more
of our cwa. Will keep forecast as a consensus between these two
possible solutions, raising pops across our south and lowering
them a bit in our north, as even the EC shows strongest
frontogenesis along the MT/WY border. Though this system will not
be overly dynamic, moisture content will be enough to yield over a
half inch of precipitation over our southern high terrain/upslope
areas. Snow will accumulate to several inches above 8000 ft, but
model wet bulb zero heights down to 6500 ft suggest a mix with wet
snow could occur over the slopes just above Red Lodge and Story.
Otherwise this is a mild system and will bring only rain to the
lower elevations. Precipitation will taper off from west to east
Saturday morning. Mostly dry conditions will prevail Saturday
afternoon. Our western mountains may see more rain/snow showers by
Saturday night as next Pacific shortwave approaches. Temps on
Saturday will be the coolest we have seen in quite awhile, maybe
two weeks, with highs in the upper 40s to mid 50s across the lower
elevations as lee side surface high is slow to exit.

Will continue to highlight Friday night precipitation in our
weather story. Hunters should take note of this upcoming period of
wet and cooler weather.


.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...

GFS/GEFS showed increasing model disparities with the pattern
beginning on Monday. The ECMWF ensembles did not show much
disagreement, however, the deterministic GFS and ECMWF were in
poor agreement with the pattern beginning on Tuesday. Kept changes
minimal to the forecast beginning on Tuesday due to the above. The
uncertainty in the models could be a result of Hurricane Seymour
getting into the model initializations.

Upper ridging will be over the forecast area on Sunday, but energy
from the next Pacific system will ride through the ridge, as well
as moisture into the western zones. Continue the slight chance to
chance PoPs from KBIL W per the previous forecast with the highest
PoPs in the far W. Noted LI`s fell to -2 deg/c on the GFS, but
soundings did not look like they would support thunder. It will be
warm with temperatures in the 60s across the area. The Pacific
energy moves into N WY/S MT Sun. night along with good moisture.
Models develop a strong surface low over NE WY/W SD by 12Z Monday
with decent QPF wrapping around the low into the area. Thus have
raised PoPs all areas to high chance/likely, except over SE MT
where models forecasted a dry slot. A few inches of snow are
possible over the western mountains. Energy lingers over the area
on Monday, as moisture gradually lessens from W to E. Raised PoPs
for this period as well. Expect a cooler day with highs around
normal. Monday night looks drier with chances of precipitation
confined to the mountains.

The model disagreement begins when the GFS brings a shortwave
through the area on Tuesday, while the ECMWF has upper ridging.
Both models were generally dry. An upper ridge develops on the GFS
for Wednesday while the ECMWF has an elongated trough from MT to
the four-corners region. Differences continued through Thursday.
Despite the differences, models were dry Wed. and Thursday. Model
blends kept temperatures near normal through the period. Arthur



VFR will prevail over the area through tonight. Chances for rain will
increase over the area from W to E, through the day on Friday.
MVFR/IFR conditions are possible with the rain in KLVM with
possible MVFR in KBIL/KSHR. Expect areas of mountain obscuration
beginning late tonight and increasing on Friday. Gusty SW surface
winds with gusts to 40 kt will occur over KLVM through around 09Z
Friday, when a cold front will move through the area causing winds
to decrease somewhat. Arthur



    Fri     Sat     Sun     Mon     Tue     Wed     Thu
BIL 051/059 040/053 041/064 044/056 037/054 034/055 037/058
    04/R    62/R    12/W    54/W    11/B    11/B    11/B
LVM 049/057 038/055 042/061 041/054 035/052 034/055 037/057
    25/R    72/R    24/W    55/W    11/B    11/B    11/B
HDN 046/062 040/055 037/067 042/056 035/056 033/056 034/059
    03/R    63/R    11/B    54/W    11/B    11/B    11/U
MLS 047/062 039/052 038/063 043/052 035/055 032/053 033/056
    02/R    32/R    11/B    45/W    11/B    11/B    11/B
4BQ 048/065 039/052 038/069 043/055 034/057 031/056 033/059
    02/R    75/R    00/B    44/W    11/B    11/U    11/U
BHK 046/063 036/048 034/062 040/049 032/053 029/052 030/055
    01/B    22/R    01/B    35/W    11/B    11/B    11/U
SHR 046/064 037/054 036/067 039/055 031/055 029/057 031/059
    03/R    75/R    01/B    43/W    11/B    11/U    11/U




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