Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 221531

Area Forecast Discussion...Updated
National Weather Service Billings MT
931 AM MDT Sun Oct 22 2017

Forecast in pretty good shape. Adjusted PoP`s a bit based on
current radar and high-resolution progs. Wind has hit 69 mph at
Livingston so far and over 70 mph in the Nye vicinity. By midday,
we should see the higher winds spread to the Big Timber-Harlowton
corridor and eastward. BT


.SHORT TERM...valid for Tdy and Mon...

Are you ready for wind?

Latest water vapor imagery shows a strong westerly jet nosing into
the Pacific northwest, with large area of warm advection high
clouds spilling from western into central MT. Main area of
precipitation is well to our west, but we have seen occasional
orographic light snow in Cooke City since last evening. At the
surface, pressures have been falling at a good clip in central MT,
and the 09z IDA-LWT difference is up to 16.4mb. Increasing
westerly flow, mid level warm advection and favorable gradient
have all led to an increase in gap flow at Livingston and Nye,
with gusts into the upper 60s (mph) so far.

As surface trof deepens in central MT, gap winds will continue to
increase through 12-15z this morning, with 75 mph gusts expected
to occur, and will make no changes to the High Wind Warning in
effect for Livingston and Nye. High winds will spread to Big
Timber and Harlowton as the pressure fall axis shifts east, and as
mixing taps into the strong mid level flow (65-70 kts at 700mb)
expect warning gusts to be realized at these locations. Will thus
make no changes to these highlights either.

It now appears that the upstream trof w/ a 130-150 kt H3 jet will
drive a bit further south thru our cwa later today and tonight.
This will be associated with a period of strong surface pressure
rises from NW to SE this afternoon and evening, with synoptic
scale subsidence spreading into our northwestern cwa by late this
afternoon. Low level lapse rates will be quite steep and expect
some shower activity by this afternoon, and this convection could
add to the gust threat away from the foothills. Add it all up, and
it seems that we have high wind issues at locations other than
the usual locations discussed earlier. Have opted to issue a high
wind warning for Golden Valley/Stillwater eastward to northern
Rosebud Counties (this includes Billings) from late morning
through this evening, i.e. the region which will see subsidence
and a good chance of surfacing high wind gusts before sunset. Core
of strong 850mb winds will spread across our east tonight, but
feel that there is an opportunity for some surface decoupling, so
will keep nighttime winds at 40-50 mph. The other interesting
location to watch is our south central parts...particularly the
higher hills and slopes on the east side of the Bighorn Mountains,
where NW winds are enhanced by the terrain. Strongest pressure
rises expected to arrive after 00z in this area, but with some
geographic help we could see high winds. The latest LAMP guidance
impressively shows a peak of 49 kts at Sheridan by 08z. Have
issued a High Wind Watch for the Sheridan Foothills in addition to
southern Big Horn and southern Rosebud Counties from late this
afternoon through tonight. Will let day shift make final call if a
warning is needed here.

Lots of wind today and outdoor travel and recreation will
certainly be impacted. Also, don`t forget those outdoor Halloween
decorations which will be blown around.

Otherwise, expect snow showers with a little accumulation over the
mountains, and some brief rain showers along baroclinic zone for
the lower elevations mainly this afternoon and early evening. Dry
weather will then prevail late tonight through Monday night as
ridge builds back in from the west. NW winds will remain gusty in
our east on Monday, with 35-50 mph gusts expected. Temperatures
will be mild today with highs mostly in the 60s, then cooler
tomorrow with 50s for highs.


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

The 00Z GFS and ECMWF were much more in line with each other
tonight concerning the Wednesday night/Thursday system than they
were last night. That being said, the ECMWF ensembles did show
pattern uncertainty with the system, and the GEFS plumes had large
temperature spreads from Thursday onward. The above suggests that
there is still uncertainty with how this system will play out and
that models may tend to change their solutions with any given run.
This is something to be watched with time.

Did not make many changes to the going extended forecast which
starts out dry and warm under anticyclonic flow on Tuesday.
Models bring a shortwave SE into the region on Wednesday and move
it through the area through Thursday morning. A cold front will
accompany the wave Wed. night. The system will bring isolated rain
showers to the NW zones Wed. afternoon, then a good chance of
rain showers changing to rain and snow showers Wed. night. Chances
of rain and snow showers will decrease from NW to SE during
Thursday. At this point, given the progressive nature of the
system, and relatively warm lows Wed. night in the mid to upper
30s, snow accumulations will be light and limited mainly to the
mountains and foothills. There will be a large change in
temperatures from Wednesday (highs in the lower 70s) to Thursday
(highs in the 40s). Gusty winds will accompany the system as well. Will
continue to highlight the system in a Weather Story.

The system will be E of the area on Friday leaving the region
under a northerly slightly cyclonic flow which continues through
Saturday. Upper ridging builds E toward the area on Sunday. The
models had periods of moisture coming through the region in this
flow, and differed on the placement and amounts of moisture. Thus
used model blends for low PoP chances over various parts of the
area through Sunday. Cool weather will continue on Friday with a
slight warming trend for the weekend. Arthur



Strong winds at LVM with gusts around 60 kts currently ongoing
will continue through the day. Gusts at MLS, SHR, BIL will
increase to around 50 kts by late this afternoon as winds
transition from west to east across the region. As winds decrease
overnight at MLS, BIL, and SHR there is some potential for LLWS as
winds above the surface will remain quite strong. Vicinity
showers possible at all terminals this afternoon although no
reduced visibility or ceilings are expected at this time. Walsh



    Tdy Mon     Tue     Wed     Thu     Fri     Sat
BIL 067 043/059 037/069 044/072 038/045 025/046 032/055
    2/W 10/N    00/N    01/N    53/W    10/B    11/B
LVM 062 041/058 036/068 042/069 034/044 023/050 032/055
    4/W 30/N    00/N    01/N    63/W    10/U    21/B
HDN 070 041/060 032/069 039/073 036/047 021/047 027/057
    2/W 20/N    00/U    01/U    53/W    10/B    12/J
MLS 067 041/057 032/065 040/072 036/043 020/042 024/051
    3/W 10/N    00/U    01/U    43/W    10/B    01/B
4BQ 068 041/056 031/064 039/073 035/043 020/040 025/050
    2/W 30/N    00/U    00/U    44/W    10/B    01/B
BHK 065 040/054 030/060 037/066 034/038 019/037 022/047
    3/W 20/N    00/U    01/U    34/W    10/B    01/B
SHR 068 038/055 029/067 037/074 034/042 019/043 024/053
    0/N 40/N    00/U    00/U    63/W    10/U    02/W


MT...High Wind Warning in effect until 9 PM MDT this evening FOR
      ZONES 28-41-63.
     High Wind Warning in effect until midnight MDT tonight FOR
      ZONES 29>31-34-35-42-57.
     High Wind Watch in effect from 4 PM MDT this afternoon
      through late tonight FOR ZONES 38-58.
     High Wind Warning in effect until 6 PM MDT this evening FOR
      ZONES 65-66.
WY...High Wind Watch in effect from 4 PM MDT this afternoon
      through late tonight FOR ZONE 99.


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