Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 240248

Area Forecast Discussion...Updated
National Weather Service Billings MT
848 PM MDT Sun Apr 23 2017

Convection moving generally east through the area tonight ahead of
an attendant cold front was the focus for the evening.
Thunderstorms moving through KBIL produced wind gusts of 52 mph,
and very small hail was reported with some of the storms. The
front was just E of KBIL at 02Z, and an inverted trough was
located from Sheridan County into Musselshell County.
Thunderstorms continued moving E into Rosebud County. Mesoanalysis
showed that CAPE had decreased across the area, especially over
the SE zones where 500 j/kg of surface CAPE was over the area
earlier in the evening.

The front/inverted trough will push E of the area by Mon. morning.
Adjusted overnight PoPs based on radar trends and ConSShort
guidance. Also adjusted winds to fit latest trends. Extended
mention of thunder through 06z, with convection going strong and
decent mid-level lapse rates.

An upper trough will deepen over the region Monday into Tuesday.
Chances for precipitation will spread E through the area and a
backdoor front will push into the area late Monday. The flow will
become upslope and 850 mb temperatures over the E will fall below
zero degrees C Mon. night and remain low on Tuesday. Mountain snow
is likely and the lower elevations will see a mix of rain and
snow. The Winter Storm Watch for the Beartooths/Absarokas looked
good. Will need to watch the NE Bighorns, Red Lodge/Beartooth
Foothills and other upslope areas for possible winter highlights.


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

One last afternoon of mild weather conditions before a wet and
chilly week kicks in. A very dynamic and unsettled weather pattern
will take over tonight through Tuesday. Concerns are heavy
mountain snow, and some mixed precipitation or snow at lower
elevations by Tuesday morning. This all leads to some increasing
hydro related concerns.

For this afternoon and is currently pretty quiet
across our CWA as initial piece of energy ahead of upper trough to
the west tracks over central Montana. Much broader energy will
sweep across our CWA from SW to NE tonight spreading showers and
thunderstorms over the area. Deep convection will be somewhat
muted by cloud cover, but a few thundershowers/storms still a
good bet based on soundings. This activity will be exiting to the
east by morning. A few inches of snow is possible overnight in
the mountains from convective snow showers.

Monday into Tuesday...much stronger short wave energy moves
across the central Rockies and carves out a broad trough across
the entire region. This energy has a good deal of Pacific moisture
associated with it as it pours into the SW mountains. Cross
sections show strong ageostrophic flow aiding height falls. This
really kicks in by Monday afternoon and continues through
Tuesday in the high country. Therefore, we have issued a Winter
Storm Watch for the Absaroka/Beartooth Mountains during this time.
West facing slopes will be hit hard Monday, transitioning to the
north facing slopes Monday night into Tuesday.

In the meantime, the lower elevations will see scattered showers
and possibly some thunder spread across the west and central zones
Monday. Monday night a back door cold front is progged to slip in
from the east. This will create upslope over the southwestern
foothills and an overrunning pattern. The 850 mb progs have temps
dropping below zero even at Billings, so we may see showers turn
to snow for the Tuesday morning commute. However, mainly just
grassy or natural areas would likely see some accumulations. But
there may be a tight band of intense wet snow that develops over
Yellowstone, Big Horn and Stillwater counties, and this will need
to be monitored going forward for possible advisories early
Tuesday. The bulk of forcing ends by Tuesday evening with
precipitation winding down.

As for temps, we expect Monday to be relatively seasonal, but
Tuesday will be rather chilly and brisk with highs only in the

The entire week continues to look unsettled, so we will continue
to update the Hazardous Weather Outlook. Some model scenarios
produce 1 to 2 inches of precipitation for some locations in the
foothills and nearby areas. We will need to watch closely to see
how the land handles all the additional precipitation. For now, we
will stick with mentioning some ponding of water in low lying
areas and some rising water in area streams. Muddy rural roads
will probably become more problematic as well. BT

.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, with great spread still exhibited by the models.
Latest 12z runs suggest heaviest precipitation along strong
baroclinicity to our south in WY. This seems most plausible at
this time given the strongly amplified upper jet, but could still
give us a somewhat significant period of precipitation especially
in our southern upslope areas, in the form of rain and snow. Low
level temps shown by operational models and most ensembles are
suggestive of some wet snow for our foothills, possibly including
Red Lodge and Sheridan if not places further north, and this will
need to be watched. For now, have adjusted pops to show highest
chances in our south. Have also lowered temps for Friday. After a
couple days with highs in the upper 40s and 50s Wednesday and
Thursday, it looks as if much of our cwa will struggle to rise
above the 40s Friday.

Fate of upper low as it cuts off to our south is still very much
uncertain, as the EC actually lifts it north to the Dakotas and
allows for wrap-around precipitation in our east thru Sunday. A
drier GFS solution keeps ascent to our south by Saturday. For the
forecast, will stick with a blend and show lower pops with the
onset of a warming trend by Saturday. We may see the effects of
next Pacific shortwave by Sunday.



Chances for showers and thunderstorms will continue through 06Z
from Rosebud County E. Otherwise, low chances for rain and snow
showers will be over the area for the rest of the night. MVFR
conditions will occur with the precipitation. A cold front E of
KBIL at 02Z will push E through the rest of the area overnight,
shifting surface winds to the WNW. There will be areas of mountain
obscurations. Showers and isolated afternoon thunderstorms will
increase from W to E across the area on Monday with MVFR/IFR
conditions. Mountain obscurations will become widespread. Arthur


    Mon     Tue     Wed     Thu     Fri     Sat     Sun
BIL 042/058 038/046 036/054 037/051 035/048 034/055 037/059
    35/T    88/O    34/W    54/W    45/R    32/W    11/B
LVM 036/055 034/050 033/053 032/050 030/048 029/053 032/056
    46/T    76/T    46/T    45/W    66/O    42/W    22/W
HDN 042/060 039/048 034/057 038/053 036/049 034/057 035/061
    34/T    87/O    23/W    54/W    44/R    32/W    11/B
MLS 041/058 035/048 032/055 036/051 035/052 035/056 037/061
    41/E    23/O    12/W    32/W    22/R    21/B    10/B
4BQ 042/059 036/048 028/052 032/049 034/047 033/052 035/058
    42/W    65/O    12/W    23/W    24/R    32/W    11/B
BHK 035/054 028/046 025/050 028/050 031/050 031/054 032/057
    51/E    22/S    11/B    12/W    12/O    21/B    10/B
SHR 039/056 037/045 032/053 035/049 034/043 032/049 033/054
    26/T    87/O    23/W    45/W    66/O    52/W    11/B


MT...Winter Storm Watch in effect from Monday afternoon through
      Tuesday afternoon FOR ZONE 67.


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