Area Forecast Discussion
Issued by NWS Billings, MT

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171
FXUS65 KBYZ 200316
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
916 PM MDT Sun Mar 19 2017

.UPDATE...
Scattered to numerous showers over the northern half of the CWA
this evening. These will slowly propagate east. By morning
another surge of colder air will push into the CWA from the north
and reinforce the baroclinic zone up against the foothills west
and south of Billings, so expect this area to be focus of precip
tomorrow, with some of it spreading onto the plains late in the
day as well.

For this evening, adjusted PoP`s according to current radar and
short term progs. BT

&&

.SHORT TERM...valid for Mon and Tue...

The models were in good agreement through the short-term period
and have not changed the gist of the forecast which looks cooler
and unsettled. Water vapor imagery showed a subtropical fetch of
moisture moving toward the region this afternoon. This moisture
will provide above normal precipitable waters for the forecast
area through the period. Aloft, the pattern will feature west flow
tonight. This will be followed by upper ridging building in from
the SW on Monday. The ridge will continue to build into the area
through Tue., then a shortwave will approach the area from the SW
Tue. night. Periods of weak jet divergence will aid lift over the
region.

At the lower levels, a cold front backed into the central part of
the forecast area this afternoon, spreading low clouds and showers
further W into areas like KBIL and Roundup. Steep mid-level lapse
rates noted on the RAP, contributed to a report of graupel over
Shepherd. A few lightning strikes have also occurred this
afternoon. The front will become stationary W to E across the
forecast area tonight with weak upslope flow along the boundary.
Showers will be likely through 06Z N and W of KBIL, with lesser
chances in other areas. Good chances for showers continue along
the boundary late tonight, when rain will change to a rain/snow
mix with temperatures in the 30s. 850 mb temperatures will stay
above zero degrees c, so hardly any accumulations are expected.
Several inches of snow will occur in the western mountains. Monday
will be a colder day with 850 mb temperatures falling to around
zero degrees c by day`s end. Low-level ENE winds strengthen
through the day allowing precipitation chances to increase in the
upslope areas. A mix of rain/snow Mon. morning will change to
mainly rain in the afternoon. Highs will be in the 40s to lower
50s.

Precipitation focus starts shifting E Mon. night due to the
building upper ridge from the W. Continued E flow at the surface,
and ESE flow at 850 mb, will provide upslope and moisture along
the boundary. 850 mb temperatures will fall below zero degrees C,
and the rain/snow mix will change to all snow over most of the
area by 12Z Tuesday. Right now, looking at an inch or less across
the low elevations with 2 inches possible in the foothills.
Several inches are expected in the mountains. The dendritic growth
level remains very high through the period which will limit
accumulations even in the mountains. Will message the Mon. night
snow on Social Media. The frontal boundary weakens on Tuesday as
warm advection begins at 850 mb, and PoPs will decrease through
the day. Temperatures will average in the 40s for highs. Airmass
will dry out Tue. night, but the approaching wave from the W will
bring increasing chances for showers to the western mountains.
Arthur


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

After some morning showers, Wednesday looks dry/warmer with
subsidence and mixed west winds behind a shortwave passage early
in the day. Have tweaked up temps and wind gusts a bit. Expect
highs well into the 60s across west & central parts.

Stronger trof will move thru the central and southern Rockies
Thursday and Thursday night. Models remain in disagreement with
the battle between a drier northern branch of the jet, and a more
dynamic shortwave lifting out of the southern trof thru WY.
Today`s 12z runs stayed the course, with the GFS being wetter than
the EC in our cwa. Even with weaker forcing, some mention of
showers is warranted, so will keep solid chance pops across the
region beginning late Wednesday night. It should also be pointed
out that even under a wetter scenario, lower elevation temps
should stay warm enough to keep p-type as rain. We should see
drying by late Thursday night as the energy departs to the central
U.S.

After what appears to be a dry Friday, model consensus is for
another Pacific trof to move into our region next weekend,
bringing our next chance of showers.

Overall temps will remain above normal. Wednesday looks like the
warmest day of the extended period. Highs Thursday thru the
weekend should generally range from the upper 40s to lower 60s.
Saturday should be the warmest day of next weekend.

JKL


&&

.AVIATION...

Showers and areas of light rain will be common across the forecast
area overnight and into Monday. Expect mainly VFR through evening,
but local MVFR flight conditions. Mountains will be frequently
obscured. The risk for local IFR conditions increases later
tonight into Monday from KLVM to KBIL. BT

&&

.PRELIMINARY POINT TEMP/POPS...

    Mon     Tue     Wed     Thu     Fri     Sat     Sun
-----------------------------------------------------------
BIL 036/044 030/047 035/066 040/056 034/059 036/061 037/055
    75/W    63/W    22/W    35/W    31/B    11/E    23/W
LVM 035/045 029/050 037/062 035/055 030/057 036/059 034/054
    46/W    63/W    22/W    45/W    31/B    23/W    33/W
HDN 036/049 031/051 032/067 038/058 033/059 033/063 035/057
    55/W    63/W    21/B    35/W    31/B    11/E    23/W
MLS 037/051 031/044 034/064 040/059 034/056 034/061 036/056
    52/W    43/W    22/W    15/W    20/B    11/B    23/W
4BQ 036/052 030/045 032/065 038/057 033/057 032/062 035/057
    34/W    64/W    21/B    35/W    21/B    01/B    23/W
BHK 034/050 025/039 028/056 035/056 030/053 029/056 032/053
    53/W    43/W    22/W    14/W    20/B    00/B    23/W
SHR 036/050 030/053 035/065 037/056 033/058 033/063 035/054
    15/W    62/W    11/B    45/W    41/B    01/B    23/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
weather.gov/billings



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