Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 241539
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
939 AM MDT Mon Apr 24 2017

.UPDATE...
Showers were spreading E a little faster than expected this
morning per radar imagery and KLVM was reporting rain. Used the
SREF to increase PoPs a bit and spread them further E faster than
previous forecast. Backdoor front was over the SE zones this
morning with stratus and patchy fog behind the front. RAP
soundings had the stratus lifting this afternoon. Kept patchy fog
in through 18Z over the E and adjusted afternoon cloud cover. SREF
showed possible surface CAPES greater than 250 j/kg with weak
shear and decent lapse rates central and W this afternoon, so
thunder placement looked good. Temperatures in the 50s were
supported by RAP soundings. Adjusted winds based on ADJLAV. No
changes to rest of forecast until new model data is in. Arthur

&&

.SHORT TERM...valid for Tdy and Tue...

Broad and deep upper trough was moving on shore over the Pacific
northwest coast and this will impact our weather the next couple
of days. An initial shortwave that kicked out from the main
western trough moved through Sunday evening and night and
generated a round of showers and thunderstorms. That activity was
working out of the far southeast early this morning. The next
shortwave to kick out from the trough was working into Idaho and
will generate another round of showers and isolated thunderstorms
today. The bigger story will be mountain snowfall and the chance
of accumulating snow over areas of the southeast as the shortwave
this afternoon cuts off over northeast Wyoming tonight and
Tuesday.

Will upgrade the Winter Storm Watch to a Warning for this
afternoon through Tuesday for the Beartooth/Absarokas. The
heaviest snowfall will be tonight and early Tuesday. Models have
backed off some on the QPF but guidance stil indicates 8-14 inches
of snow over the Beartooth/Absarokas with pockets of heavier snow
possible. Outdoor activities will certainly be impacted by the
heavy, wet snowfall. The Bighorns will also see snowfall increase
this afternoon and continue tonight and Tuesday. QPF amounts were
not progged to be quite as high over the Bighorns and have gone
with an Advisory at this time.

The shortwave will cut off an upper low over northeast Wyoming
tonight and linger it through Tuesday. This will place an area of
strong ascent over far southeast Montana and northeast Wyoming.
The ECMWF has been very consistent with this scenario and
continues to place over 8 tenths of QPF over southeast Montana as
cold air gets pulled in with the surface low wrapping up. The GFS
had the strongest ascent, and thus higher QPF, farther south (in
northeast Wyoming) but was trended toward the EC solution. Has the
potential to be a significant wet snow event, (should the EC
verify), over locations south of a line from Lodge Grass to
Ashland to Broadus to south of Ekalaka. Will issue a Winter Storm
Watch for these locations, including Sheridan County. Snow amounts
may well end up in Advisory criteria, but wanted to get the word
out for the potential for heavy wet snow.

The last area that will need to be monitored will be the lower
elevations of south central Montana tonight. 850mb temperatures
were colder over the east, but higher hills could be cold enough
to allow for some snow accumulation. May need to sprinkle a few
Advisories in places as the event gets going, but very difficult
to pin point those at this time. Will need to keep an eye on Park
county along with the foothills. Will put a couple inches of snow
in at this time and brief the day crew to take a closer look.
Billings could get a brief period of wet snow late tonight and
early Tuesday, but does not look like much, if any, will
accumulate at this time. TWH

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

Active and generally cool weather anticipated through the latter
half of the week.

Next in a series of Pacific shortwaves will bring a good chance of
showers Wednesday afternoon and night. Flow over the western
CONUS will amplify by Thursday/Friday, resulting in a developing
cut off low over the Great Basin and central Rockies. This gives
us the opportunity for a combination of dynamic/upslope
precipitation. Looks like mostly rain for the lower elevations
with perhaps some wet snow over Fallon and Carter Counties Friday
morning. 850 mb temperatures are progged to be a few degrees C
warmer than those for the Monday night-Tuesday system, so think
that snow should be less of an issue with this system. However,
the mountains look to get another round of accumulating snowfall.

Both the EC and GFS bring upper low well south of the area Friday
night, which should help to decrease the number of showers
occurring over our region. A shower or two is still possible on
Saturday as EC shows some energy hanging around the area. Models
then bring in some shortwave ridging for Sunday, which might
produce our first area-wide dry day in nearly a week.

High temperatures should generally be in the 50s during the
extended. Friday should be a bit cooler with highs in the 40s due
to rain and low-level northeasterly flow advecting cooler air
into the region. RMS/TWH
&&

.AVIATION...

VFR should prevail today over south central MT and north central
WY. MVFR CIGs look to hang on longer into the early afternoon
over southeast MT. Showers and isolated afternoon thunderstorms
will increase from W to E across the area today with temporary
MVFR/IFR conditions. Mountain obscurations will become widespread
today. RMS/TWH

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Tue     Wed     Thu     Fri     Sat     Sun
-------------------------------------------------------
BIL 058 038/046 036/055 039/050 036/046 034/053 036/059
    6/T 88/W    33/W    45/W    55/W    32/W    11/B
LVM 055 035/050 033/053 034/049 031/046 028/052 030/056
    7/T 77/T    45/W    55/W    54/W    42/W    22/W
HDN 060 038/048 034/057 038/052 037/049 035/055 034/061
    5/T 87/W    22/W    35/W    55/W    32/W    11/B
MLS 058 034/047 032/054 036/051 036/050 035/055 036/060
    1/E 23/W    12/W    33/W    33/W    21/B    11/B
4BQ 059 034/041 028/052 031/048 033/045 031/050 033/057
    2/W 78/W    12/W    34/W    35/W    32/W    11/B
BHK 053 028/044 025/050 028/050 030/050 030/054 031/056
    0/E 02/J    11/B    12/W    12/W    11/B    11/B
SHR 057 035/040 031/051 034/047 034/043 030/047 032/054
    7/T 88/W    22/W    35/W    65/W    43/W    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch in effect from 6 PM MDT this evening
      through Tuesday afternoon FOR ZONES 36>38-58.
     Winter Storm Warning in effect until 6 PM MDT Tuesday FOR
      ZONE 67.
WY...Winter Storm Watch in effect from 6 PM MDT this evening
      through Tuesday afternoon FOR ZONE 99.
     Winter Weather Advisory in effect from 6 PM this evening to 6
      PM MDT Tuesday FOR ZONE 98.

&&

$$
weather.gov/billings


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