Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 211536
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
936 AM MDT Sat Jul 21 2018

.UPDATE...

Mid-level clouds were beginning to stream into the area out of the
southwest this morning ahead of an approaching upper trough and
associated cold front. Isolated to scattered showers and
thunderstorms are expected to develop over the higher terrain and
adjacent foothills late this afternoon and move east into this
evening. An area of strong to severe storms looks to develop near
and east of a Miles City to Broadus line late this afternoon and
move east into the evening as a surface trough interacts with
southeast winds at the surface. With modest instability and decent
deep layer shear in place, large hail and damaging winds look to
be the main threats. Have increased pops over western areas late
this afternoon and evening to account for the latest model
trends. Have also adjusted temperatures and sky cover to current
trends. The rest of the forecast remains on track and the previous
forecast discussion and an updated aviation discussion are below. STP

&&

.SHORT TERM...valid for Tdy and Sun...

The ridge of high pressure that has been over the forecast area
the past couple of days will shift east today as an upper level
disturbance and cold front approach the area. Skies will be partly
to mostly sunny this morning with increasing clouds this
afternoon. Isolated showers and thunderstorms will develop late
this afternoon over the mountains and adjacent foothills and move
east into this evening. Another area of showers and thunderstorms
will develop across northeast Wyoming and southeast Montana late
in the afternoon. Low-level surface convergence combined with an
upper level disturbance approaching from the west along with some
decent shear will result in the chance for a few thunderstorms to
become severe late this afternoon into the mid evening hours
across southeast Montana. Temperatures will be hot today with
lower to middle 90s common.

Sunday will experience much cooler readings under mostly sunny
skies. Afternoon temperatures will be a good 10 to 15 degrees
cooler with lower 80s across the forecast area. Expect gusty winds
throughout the day, mainly from Treasure and Big Horn Counties
eastward. Hooley

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

Overall patterns looks consistent from previous runs. Both the
GFS and ECMWF were in agreement through the end of next week.
Pattern looks seasonal, if not a touch below average, and mainly
dry early, with increasing shower chances by mid week.

Zonal flow progged for Monday with an upper ridge suppressed over
the southern Rockies and an upper trough crossing southern
Canada. Strongest forcing with the trough will reside well north
of the area, with Montana in a dry zonal flow.

The upper ridge builds northwest into the Great Basin, toward
northern Idaho, and this develops northwest flow over Montana for
Wednesday onward. This pattern will lock monsoon moisture to the
south, but tap into Pacific moisture off of southwest Canada.
Periods of shortwaves and increasing Pacific moisture will allow
for an increasing chance of showers and thunderstorms from mid
week on. At this time, convection does not look terribly strong
with low capes and precipitable water values generally below three
quarters of an inch. Low level flow will be primarily east to
northeasterly, and this will keep temperatures slightly below
seasonal averages. TWH

&&

.AVIATION...

LLWS is expected at KMLS early this morning. Isolated
thunderstorms will move in from the west this afternoon, affecting
areas around KLVM and KSHR. KBIL could even get an isolated
thunderstorm by early evening. Localized MVFR conditions are
possible with thunderstorms, along with gusty winds. Stronger
thunderstorms are possible east of a line from KMLS to 4BQ late
this afternoon and evening. Strong winds and hail will be the
primary threats, otherwise, VFR conditions are forecast today.
TWH/AAG

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Sun     Mon     Tue     Wed     Thu     Fri
-------------------------------------------------------
BIL 093 060/083 056/087 059/083 058/083 058/082 058/082
    2/T 21/U    00/U    11/U    01/B    22/T    33/T
LVM 091 047/082 045/085 051/083 051/082 051/081 050/079
    2/T 20/U    00/U    11/U    12/T    22/T    33/T
HDN 094 060/083 055/088 059/084 058/084 057/083 057/084
    1/B 21/U    00/U    11/U    01/B    22/T    33/T
MLS 095 065/082 055/085 059/084 056/081 057/082 058/082
    2/T 21/N    00/U    10/U    01/B    22/T    33/T
4BQ 096 065/084 055/087 060/086 057/083 058/082 057/081
    2/T 21/N    00/U    21/U    01/B    22/T    33/T
BHK 088 062/082 052/082 057/083 053/079 053/078 054/079
    2/T 32/W    00/U    20/U    00/U    22/T    22/T
SHR 095 060/082 053/087 056/084 054/081 053/081 052/080
    2/T 21/U    11/B    21/B    22/T    23/T    34/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Red Flag Warning in effect until midnight MDT tonight FOR
      ZONE 117.
WY...None.

&&

$$
weather.gov/billings



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