Scientific Forecaster Discussion

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Area forecast discussion...updated 
National Weather Service Billings Montana
930 am MDT Thursday Apr 24 2014


Weak ridging builds across the forecast area today before the
next system approaching the Pacific northwest coast begins to move
into the area Friday. Satellite showing clouds moving in from the
west bringing a partly sunny day for most areas but the far east
should see a mostly sunny day. The ridge is not too strong as a
few weak disturbances will undercut the ridge this afternoon into
this evening bringing a very slight shower chance. Believe any
isolated shower will be from Billings and areas westward so have
removed probability of precipitation just a bit for areas east of Billings and south down
into Sheridan County. Winds will mix out once again today and be
gusty from the west but not nearly as windy as was the case
yesterday. Hooley


Short term...valid for today and Friday...

A dirty ridge builds over the area today for slightly warmer
temperatures. However Pacific moisture and energy sliding under
the ridge will bring snow showers to the mountains and isolated to
scattered showers to the lower elevations today. Downslope wind
gradient will keep much of the precipitation from reaching the
ground but could see a shower wet the ground here and there.
Breezy conditions will develop today but wind speeds will be
significantly less than yesterday. Temperatures tonight will be in
the 30s to lower 40s with with a good deal of cloud cover over the
region. Another weak disturbance crosses the area tonight keeping
low precipitation chances in the forecast.

For Friday...trough along the Pacific coast rapidly amplifies as
strong energy dives out of the Gulf of Alaska into the California
coast. This quickly backs the flow aloft to the southwest and then
south by Friday evening...with diffluence increasing across the
area through the day. Several pieces of energy and a copious
Pacific moisture fetch over ride the area during the afternoon and
evening hours. At the surface the increasingly diffluent southerly
flow induces surface cyclogenesis to the west of the area which
pulls the low level winds around to the east during the day. This
combination of moisture advection...upper level lift...middle level
energy and upslope winds is favorable for precipitation Friday and
Friday night. Expect precipitation to develop over southwestern
mountains Friday morning and expand northeastward through the
evening hours. A dry slot will begin working into the area late
evening from the south so trended probability of precipitation down overnight into
Saturday morning. For areas west of Rosebud County this looks like
an opportunity to pick up maybe a quarter of an inch of rain in
the lower elevations and 3 to 6 inches of snow for mountain
locations above 7500 feet. Chambers

Long term...valid for Sat...sun...Mon...Tue...Wed...

Developing trough along the Pacific coast will push into the
intermountain west over the next couple days...then intensify in
the High Plains this weekend into early next week...resulting in a
potentially significant and long duration precipitation event especially
for our eastern parts. Models are actually in decent agreement in
showing a middle level low closing off in eastern Colorado by 12z sun...
then lifting to NE/South Dakota by 12z Monday. Impressive magnitudes of
ascent/moisture transport will exist ahead of this low...with precipitation
becoming focused in our east along a low to middle level convergent
zone. There are a few factors that certainly give credence to a
slower evolving and more northwestward tracking low. These
include a strong blocking ridge to our north...a northwesterly jet with
additional shortwave energy from the Pacific northwest to central
rockies...and an anomalous SW-moving low which will cross the
Great Lakes and phase with the plains low toward the middle of
next week. So with confidence have raised probability of precipitation across our east
sun-Tue. Uncertainty exists regarding surface temperatures and potential
snowfall. 00z GFS remains the coldest of all models showing 850mb
temperatures to -2c Sun night and colder Monday night. Other models show
values closer to 0c. So some wet snowfall is a possibility
especially for the central/eastern ridges and the Big Horn
Mountains...which will be favored once northwest flow deepens on Sunday. Even
west/out the snow the period of cold and wet weather will be
hazardous to Young livestock.

Backing up to Saturday...the initial stage of this event...unstable
and increasingly diffluent south flow aloft will result in
plenty of showers and some thunderstorm activity Sat into Sat
night. This includes Billings. Shear profiles actually favor some
stronger storms in our southeast near inverted surface trough.

A period of below normal temperatures can be expected from Sunday perhaps
all the way to Wednesday as we remain under the influence of
strong cyclonic flow aloft...deep east winds and an eventual
Canadian surface high. Have dropped expected high temperatures through each of
these days...but left alone or raised low temperatures a bit given precipitation
and cloud cover anticipated through the period.

Should see drying and moderating temperatures by Wednesday or Thursday
of next week as the low finally departs.



VFR conditions will prevail today with scattered to broken middle
and high cloud. A Pacific disturbance will allow for isolated to
scattered showers along and west of a Roundup to kbil to Bridger
line this afternoon. Isolated showers will be possible over much
of the area this evening. There will be isolated showers west of kbil
overnight. Mountain obscurations will be widespread over the
beartooths and absarokas this afternoon and evening...with areas
of obscuration over the crazys and NE big horns. Expect areas of
obscuration over the beartooths...absarokas and crazys overnight.
Westerly winds will gust to 25-35 kts...especially near the
foothills and over southeast Montana this afternoon and evening. Arthur


Preliminary point temp/pops...

Today Friday Sat sun Monday Tuesday Wednesday
bil 061 040/061 041/058 040/050 035/053 036/051 038/059
2/west 15/west 56/T 87/west 33/west 33/west 21/b
lvm 054 036/054 036/054 038/056 034/055 034/058 035/059
3/west 36/west 68/T 85/west 32/west 23/west 11/b
hdn 062 036/064 039/064 037/049 033/052 032/051 032/059
2/west 25/west 54/T 78/west 54/west 33/west 21/b
mls 061 039/065 044/065 040/045 033/048 032/047 033/055
0/north 22/west 53/T 78/west 86/west 43/west 21/b
4bq 061 037/065 042/070 040/047 033/047 032/046 032/054
0/b 23/west 43/T 78/west 86/west 53/west 21/b
bhk 058 037/063 041/063 038/045 033/045 030/044 030/052
0/north 22/west 43/T 78/west 86/west 53/west 21/b
shr 059 035/062 038/067 038/048 034/049 033/050 032/056
1/b 24/west 53/T 68/west 64/west 33/west 22/west


Byz watches/warnings/advisories...