Weather Service Report


371 
FXUS65 KBYZ 200943
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT 
343 AM MDT Fri Oct 20 2017

.SHORT TERM...valid for Tdy and Sat...

The story is WIND.

Latest satellite imagery and upper air analysis show height falls
over our region as ridge departs to the east and a Pacific trof 
moves inland. At the surface, downslope gradients exist in central
MT, and a Pacific cold front is moving into western ID.

First regarding fire weather: Warm and dry conditions will exist
pre-frontally today, with the front itself likely adding a little
compressional warming this afternoon. Frontal passage is expected
to occur around 21z at LVM, 23z at BIL, 01z at SHR/MLS and 02z at
BHK. Combination of the heat/low humidity and strong wind shift 
(w/ gusts possibly exceeding 50 mph) will create difficult 
conditions for those with fire wx interests from mid afternoon 
thru the evening. A Red Flag Warning is in effect for Ryegate-
Fishtail eastward. West of this area, greater cloud cover and 
cooler temps should keep humidities from falling below 20 pct, but
the winds will obviously be an issue.

Although we are not issuing any wind highlights at this time, 
shower activity and the frontal push (at an ideal time of day) 
could yield locally higher wind gusts than the anticipated 40-50 
mph widespread gusts. Something to watch today if you have outdoor
plans. Temps will be quite mild and have pushed expected highs a
bit above the usual guidance, due to the expectation of some
pre-frontal help. Look for highs ranging from the mid 60s in our
west to lower 80s to our east. Temps will fall quickly to the 40s
and 50s behind the front. Could also see a few showers behind the
cold front, and a few lightning strikes are even possible, but not
expecting much as downslope effects will be significant. Western
mountains should see some snow showers.

Gusty westerly winds will continue tonight and Saturday, with
cooler and mostly dry conditions. Expect temps in the 50s with
30-45 mph wind gusts tomorrow.

Bigger wind issues emerge Saturday night as strong Pacific jet
(130-150 kts) moves into the northern Rockies. Lee side pressures
will fall as 700mb winds increase to 65-70 kts. This set up
will easily produce advisory level wind gusts at Livingston and 
Nye. There is potential for 70+ mph gusts, and have opted to issue
a High Wind Watch from late Saturday night through Sunday. Strong
mixed westerly winds will spread eastward across the region on 
Sunday.

JKL

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

Expect windy conditions to continue through Monday as a strong
Pacific jet crosses the area on Sunday and gradually becomes N-S
oriented as it moves out of the region on Monday. 700 mb winds of
50-70 kt will cross the area Sun. morning and remain strong into
late Sun. night. Winds decrease during the day on Monday. Pressure
gradient will be favorable for strong winds in the gap flow areas
on Sunday which will necessitate a High Wind Watch. Cannot rule 
out possible highlights further E, but areas of Q-vector 
convergence will provide ascent which will limit the high wind 
threat. Windy conditions will continue in the foothills areas Sun.
evening, then Monday will be generally breezy to windy everywhere.
Atmospheric river was forecast to move into the area on Sunday
which will provide mountain precipitation through Sun. night with
just a slight chance of showers over the plains. Temperatures on
Sunday will be a bit above normal, while Mon. will be cooler under
NW flow. Monday will also be the start of a drier period as an
upper ridge moves into the area. Next chance of precipitation is
Wednesday night as a shortwave and cold front dive SE through the
area. A drier NNW flow will overtake the area for the rest of the
period. Temperatures will climb into the 70s on Wed. ahead of the
cold front, then drop back into the 50s for Thursday behind the
front. Arthur 

&&

.AVIATION...

SW surface winds will gust to near 30 kt early this morning in 
the KLVM area and along the western foothills. These winds will 
increase by mid-morning with gusts into the 40s. Expect gusts of 
25 to 35 kt from KBIL W this morning. A strong cold front will 
move through KLVM around 21Z, with a shift to gusty west winds 
and isolated thunderstorms. The gusty west winds will continue 
this evening. The front will pass through KBIL with a gusty 
westerly wind shift around 22Z, through KSHR around 01Z Saturday 
with a NW wind shift and through KMLS around 02Z with a shift to 
NW winds. VFR will prevail through this evening. Lower conditions
are possible in any showers or thunderstorms. Mountain 
obscurations will increase this afternoon. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Sat     Sun     Mon     Tue     Wed     Thu     
-------------------------------------------------------
BIL 073 040/057 042/068 047/061 039/065 045/071 037/051
    2/T 10/N    21/N    21/N    00/U    00/U    42/W
LVM 065 037/051 045/063 044/058 036/064 041/067 034/051
    5/T 31/N    33/W    41/N    00/N    00/N    62/W
HDN 078 038/058 036/070 044/062 035/066 039/073 035/052
    2/T 20/N    21/N    21/N    00/U    00/U    42/W
MLS 080 040/058 035/068 043/060 034/062 039/071 035/050
    0/U 30/N    12/W    21/N    00/U    00/U    21/N
4BQ 081 040/056 034/069 044/059 034/061 039/072 034/050
    0/U 20/N    01/N    21/N    00/U    00/U    31/N
BHK 080 040/056 033/067 041/056 032/058 038/066 033/047
    0/B 10/N    01/N    21/N    00/U    00/N    21/N
SHR 080 035/055 032/069 041/059 033/063 036/072 033/051
    1/B 10/U    11/B    32/W    00/U    00/U    62/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Watch in effect from late Saturday night through
      Sunday afternoon FOR ZONES 65-66.
     Red Flag Warning in effect from noon today to midnight MDT
      tonight FOR ZONES 125>133.
WY...Red Flag Warning in effect from noon today to midnight MDT
      tonight FOR ZONE 274.

&&

$$
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