Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 220916

Area Forecast Discussion
National Weather Service Billings MT
316 AM MDT Thu Jun 22 2017

.SHORT TERM...valid for Tdy and Fri...

Upper trof digs into the area today with jet stream dropping south
across the Beartooth then east along the MT/WY border. This will
bring cooler air (about 10 degrees off of yesterdays highs) and a
slight chance for showers/tstms (mainly for the
mountains/foothills). Stronger winds aloft will mix down to the
surface this afternoon with gusts 25 to 40 mph common. Relative
humidities will drop into the lower 20s combining with the gusty
winds to bring elevated grass fire concerns to the area through
this evening. Northwesterly jet stream remains over the area on
Friday keeping temperatures cool and at least a slight chance for
a shower or thunderstorm (mainly west of Billings). Breezy
conditions will continue Friday, but speeds will be lower than

Hydrology...may need a flood warning for the Clarks Fork of the
Yellowstone this morning at Belfry and possibly Edgar as well.
Latest readings are at 7.74 feet on an upward trajectory at
Belfry with a diurnal crest around 7am. This is water from
Tuesday, and with water from a warm Wednesday still to come seems
reasonable we will get up to bankfull either this morning or
tomorrow morning. Will keep an eye on this for an hour or so
before making final decision. Any flooding will be minor and
similar to what occurred a couple of weeks ago. Right now it looks
like the Boulder will crest this morning 0.2 feet below bankfull.
Will continue Hydrologic Outlook to highlite the continued dangers
of fast water flows coming out of the Beartooth and Absaroka
mountains. Chambers

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

There were some model differences throughout the extended period,
especially later in the period. The ECMWF ensembles pointed to
some uncertainty in the pattern for Saturday.

The forecast area will be under a NW/weakly cyclonic flow on
Saturday with a jet over the region. There was some moisture over
the area and model QPF was mainly confined to the mountains. Given
that models have been underdoing precipitation of late, and low-
level upslope flow plus weak dynamics support precipitation
chances, have forecast low PoPs through Sat. evening. Included a
slight chance of thunder due to steep lapse rates. Kept the
remainder of the weekend dry as upper ridging builds over the
area. Saturday will be a cooler day in the lower 70s and Sunday
will be warmer, with highs in the upper 70s.

The next chance of precipitation will be on Tuesday, as the flow
becomes more active. The GFS had a WSW flow over the area and the
ECMWF showed a shortwave trough moving into the region. Went with
chances for thunderstorms in the afternoon and evening with ML
CAPES between 500 and 1000 j/kg. It will be very warm Mon. and
Tue. with highs in the 80s to lower 90s. Models were not in good
agreement with timing and placement of upper trough/low in the
region late in the period, so went with climo PoPs. Wednesday and
Thursday blended guidance showed cooler conditions for the end of
the extended period. Arthur



VFR conditions will prevail today and tonight. Expect gusty NW
surface winds with gusts of 25 to 30 kt this afternoon,
diminishing early this evening. There will be a slight chance of
showers and thunderstorms late tonight E and S of KBIL. Arthur



    Tdy Fri     Sat     Sun     Mon     Tue     Wed
BIL 072 045/069 045/072 048/078 053/088 059/088 057/082
    0/N 11/B    22/T    20/U    00/U    12/T    22/T
LVM 068 038/068 039/071 040/078 045/086 051/083 049/078
    1/N 21/B    22/T    20/U    00/U    13/T    23/T
HDN 073 045/070 043/074 046/080 052/090 058/091 058/085
    0/N 21/B    22/T    20/U    00/U    11/B    22/T
MLS 072 046/068 043/073 047/080 052/089 061/092 061/086
    1/N 21/B    12/T    10/U    00/U    01/U    22/T
4BQ 073 046/067 043/071 046/078 050/087 059/091 058/085
    0/N 21/B    12/T    10/U    00/U    11/U    22/T
BHK 070 044/065 042/069 042/075 045/084 055/088 056/083
    1/N 21/N    11/B    10/U    00/U    01/B    22/T
SHR 071 043/066 041/070 043/076 047/085 054/087 053/082
    1/U 21/B    22/T    20/U    00/U    12/T    22/T




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