Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 160314

Area Forecast Discussion...Updated
National Weather Service Billings MT
914 PM MDT Fri Sep 15 2017


Minor adjustments to the going forecast this evening. Broad storm
system continues over the northern Rockies/Plains this evening
with two distinct circulations, one over North Dakota that brought
the heaviest rain as it moved through the area this morning and
the core of the upper low still over SE Idaho. Models drag this
core slowly northeast across the area tonight through early
tomorrow afternoon, with an uptick in QG forcing aloft and
continued low level isentropic and upslope lift to keep at least
light precipitation going. Bumped pops up to 100 percent for
western half of the forecast area overnight into tomorrow morning
while eastern areas see a break through late tonight before
additional forcing arrives around sunrise increasing pops again.
Precipitation should really start diminishing over western zones
by noon and quickly translate northeast as the core of the system
exits to the northeast. Overall QPF for the next 18 to 24 hours
will be in the 0.01-.02 per hour range with this light

The next challenge is snowfall. KBLX Dual-Pol data showing a
freezing level over Billings at about 5100 feet at 9 pm. Have seen
some SNOTEL data and pics/cams of accumulating snow below 5700
feet this evening. Expect that a mix of rain/snow will drop to
around 4200-4500 feet overnight, but will keep any accumulations
mainly above 5000-5500 feet. So far mountain snow accumulations
per SNOTELS looks pretty meager with 3 to 6 inches in the
Beartooth and only an inch or two for the Bighorns so far. Some
pics/cams in the higher elevations suggest more up there than
SNOTELS are showing and this could be due to warm ground/snow
pillows in the open areas the SNOTELS are located in melting snow
as it falls, while its sticking better in other locations. At any
rate will keep the winter highlites going at this point for this
early season event and with colder temperatures overnight in the
mountains should see an additional 3 to 6 inches across the board.
Metro model indicating road temperatures on I-90 over Bozeman
Pass will hit the freezing mark shortly and remain that way
through 10 am tomorrow morning. Drivers should be alert for slick
conditions there, as well as any foothills/mountain roadways above
5000 feet. The Beartooth Highway remains closed tonight as well.


.SHORT TERM...valid for Sat and Sun...

Upper low is situated over the Idaho and western Montana border
area. An associated spoke of short wave energy was moving north
across southeastern Montana with some drying behind it showing up
in the southeast corner of our CWA at mid-afternoon. As upper low
shifts east tonight we expect height falls and isentropic wrap
around to hit our western and central zones good and eventually
push north and east tomorrow hitting the eastern sections again.
System should wind down by tomorrow evening as upper low lifts
quickly into North Dakota as jet max rounds its southern flank.

Thus, overall, the forecast is going well with categorical PoP`s
for most areas. The southeast corner will see the chance of
precipitation drop a little now while areas to the west and
around Billings continue to be categorical overnight. The Winter
Storm Warnings for the mountains has not panned out quite as well
(yet anyway) as temps have not dropped quite enough for efficient
accumulations. However, Beartooth Pass was closed due to drifting
snow and ice, and Red Lodge Mountain had picked up several inches
of snow as of this morning. We will keep the warnings due to
potential impacts, but may reduce total snowfall estimates in our
products. BT

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

Weak upper ridging early Monday will give way to cyclonic flow by
Monday evening. Expect temps to be a little above normal Monday
in a pre-frontal regime. Some locations in our east should reach
80F on Monday, before temps crash again.

A fairly deep Pacific low will move over the northern/Canadian
Rockies Monday night. This along with a cold front will bring a
good chance of showers to the area into Tuesday. Expect a period
of windy conditions Monday night behind the cold front. Models
begin to diverge here as the low splits, with a northern
circulation forming in Alberta and (a) a strong jet driving
toward the Great Basin and central Rockies on the ECMWF, or (b) a
second closed low forming over the Great Basin on the GFS. The
splitting nature of such a high-amplitude trough results in low
confidence in any specifics in the latter portion of the extended
period. There is some consensus for a bit of drying and gusty west
winds Tuesday night into Wednesday, then perhaps a better chance
of precipitation as a shortwave rotates around the trough and
lifts thru WY by Thursday. Expect below normal temps Tuesday
through Friday as we remain under the influence of the cold upper
trough. Also, mountain precipitation will be in the form of
rain/snow showers as 700mb temps remain below zero. Anyone with
outdoor plans in the high country next week should be prepared for
the cold.




Light rain and high elevation snow will persist across the region
overnight. Expect MVFR-LIFR conditions for lower elevations,
along with persistent mountain obscurations overnight and
through Saturday morning. AAG



    Sat     Sun     Mon     Tue     Wed     Thu     Fri
BIL 038/050 038/067 045/075 045/056 039/060 042/061 039/062
    ++/R    10/B    01/B    45/T    22/W    34/W    33/W
LVM 034/047 032/062 040/067 037/050 030/052 032/056 031/057
    ++/O    10/B    01/N    55/T    33/T    34/W    33/W
HDN 040/052 037/068 043/079 042/060 035/064 036/064 038/065
    98/R    10/B    01/B    44/W    32/W    24/W    33/W
MLS 040/051 038/067 045/080 047/062 036/065 037/066 040/068
    88/R    20/B    00/U    24/W    22/W    24/W    33/W
4BQ 040/050 037/067 044/079 047/062 035/064 036/066 039/067
    55/R    10/U    00/U    13/W    32/W    44/W    43/W
BHK 038/049 036/065 043/079 047/066 037/064 037/067 040/067
    46/R    20/B    00/U    13/W    32/W    24/W    42/W
SHR 037/049 033/065 041/076 043/056 030/058 033/060 033/061
    98/R    10/U    00/U    25/W    43/W    34/W    33/W


MT...Winter Storm Warning in effect until 6 PM MDT Saturday FOR
      ZONES 67-68.
WY...Winter Storm Warning in effect until 6 PM MDT Saturday FOR
      ZONE 98.


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