Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 270946

Area Forecast Discussion
National Weather Service Billings MT
346 AM MDT Thu Apr 27 2017

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

Another strong storm to impact the area, with the biggest impacts
being over southern locations, and in particular southern zones
and Sheridan county Wyoming. Heavy snowfall is expected in the
Bighorn mountains with another round of heavy, wet snow for
southern Big Horn county and Sheridan county Wyoming.

Deep upper trough being pushed along by strong jet energy will
cut a low off over northern Wyoming today. This low will linger
over northern and central Wyoming through early Wyoming. At the
surface, a low will deepen and a trough will extend up into south
central Montana for convergence. Cyclonic and divergent flow along
with surface convergence and powerful frontogenesis forcing, will
produce an impressive precipitation event over south central
Montana into north central Wyoming today into Friday morning.
Total QPF varies with the ECMWF being heaviest, but expecting
upwards of 1.00-1.25 inches of water over Sheridan county through
Friday. The rainfall totals taper off northward with around a half
inch expected in Billings.

The precipitation will be all snow over the Bighorn mountains
with a foot to a foot and a half of new snow expected. Will
therefore upgrade the Watch to a Warning there. For the lower
elevations, this system looks a little warmer than the last one
and the start time looks during the daytime hours. This may allow
for more rain to be mixed in, especially early. 850mb temperatures
hover around 0c today and temperatures were starting out pretty
chilly at Sheridan this morning, so will not take much to change
to snow despite warmer 850mb model temperatures. Expect a rain and
snow mixture or at least a very wet snow today. This will change
to all snow tonight and continue into Friday. The foothills will
be easier to accumulate as opposed to lower elevations of central
and eastern Sheridan county. Expecting 6-10 inches along the
foothills west of Sheridan, with 4-8 inches over central Sheridan
county, including Sheridan itself. The worst conditions by far,
will be tonight as the snow rates crank up. Will upgrade the Watch
to a Warning for Sheridan county and southern Big Horn county.
The emphasis of highest QPF was over Sheridan county and the far
southern parts of southern Big Horn county, like around Aberdeen.
Will word the WSW product to reflect this.

Farther west, will be on the west side of the surface trough and
therefore the QPF totals will be lower. That being said, enough
dynamics will be there for likely PoPs, just not as much total
precipitation compared to central zones. Wet accumulating snow
expected along the foothills and will need to watch this tonight,
but for the moment, models were not hitting the west and foothills
that hard for this event, so will keep accumulations down.
Systems looks cold enough for some wet snow in Billings Friday
morning. Precipitation will continue Friday morning and taper back
during the afternoon. The east will be pretty much unimpacted by
this event other than cooler temperatures.

The added precipitation will cause hydro concerns for smaller
streams and significant standing water issues for Sheridan county,
especially along the foothills. Existing ESF product for this
area looks really good. Overall a wet, chilly and active period of
weather the next couple of days. TWH

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

Little in the way of changes for the extended forecast period,
with continuing unsettled weather across the region and more
seasonable temperatures.

Upper level low shifts southeast Saturday morning...and heights
build over the area. This should allow the airmass to dry out some
and surface high pressure will be in place to produce more
clearing and warming. That said, zonal to northwesterly flow
aloft will prevail...and a weak shortwave shifts across the region
Saturday evening, timing nicely with peak heating at this time.
Although airmass will have dried some, would not be surprised to
so some convection, especially with available sfc moisture and
some warming. Flow regime persists for Sunday through Tuesday, with
disturbances bringing showers and temperatures closer to seasonal
normals. The Tuesday weather system appears more
substantial, with a bit more upslope ,and therefore more
respectable precip potential. Precip with this system lingers
into Wednesday, with timing a little uncertain, as an upper level
ridge takes shape over the Pacific Northwest. Deeper northwest
flow Wednesday should keep temps cooler over the region, and
points to drier conditions. That said, some showers are possible
due to combination of available surface moisture and diurnal
heating. Warmer and drier conditions are expected for Thursday as
the ridge shifts eastward, with temps climbing back into the 60s.



Scattered showers continue to develop across western routes this
morning, with localized mvfr conditions in showers. Dense fog has
developed in KSHR in advance of approaching showers, with VLIFR
conditions, but expect conditions to improve as precip moves into
the area. Precip will overspread the region this afternoon and
evening, turning to snow or rain/snow mix overnight tonight.
Otherwise, VFR conditions will prevail prior precip development.
However, the mountains will be obscured throughout the day, with
persistent snow through the day and overnight. AAG



    Tdy Fri     Sat     Sun     Mon     Tue     Wed
BIL 043 032/045 033/053 036/060 040/057 039/055 038/061
    8/O 86/O    42/W    21/B    33/R    33/R    32/R
LVM 044 029/045 026/052 033/057 035/055 034/055 033/060
    6/O 77/O    32/W    24/R    33/R    43/R    32/R
HDN 046 034/049 033/056 035/062 039/059 039/057 038/061
    7/O 86/O    42/W    11/B    33/R    44/R    32/R
MLS 056 033/054 034/058 036/062 041/059 039/058 039/060
    2/R 33/O    21/B    11/U    33/R    23/R    22/R
4BQ 055 032/052 030/056 032/060 039/058 038/055 037/058
    3/R 43/O    21/E    21/U    33/R    24/R    22/R
BHK 052 028/053 029/056 031/059 037/056 035/055 034/056
    1/B 11/B    11/B    21/U    33/R    13/R    21/B
SHR 040 029/040 027/047 028/054 036/052 036/051 035/056
    8/O 98/O    42/W    21/B    33/R    44/R    32/R


MT...Winter Storm Warning in effect until midnight MDT Friday
      night FOR ZONE 38.
WY...Winter Storm Warning in effect until midnight MDT Friday
      night FOR ZONES 98-99.


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