Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Billings Montana
837 PM MDT Wednesday Apr 23 2014

Update...
winds are diminishing across the entire area this evening. Night
time temperature inversion is setting up and winds aloft are
already decoupling from the surface. Main forcing with the upper
level trough of low pressure has shifted into the datkoa's this
evening. There remains weak jet dynamics over the area with left
exit region of the jet. Expect a few isolated showers to continue
across our far northern zones for several more hours. Isolated
snow should continue over the Southwest Mountains with the weak
lift aloft and orographic lifting. Air mass drying out late
tonight as a ridge of high pressure begins to builds in over the
forecast area. Other change to the going forecast was some minor
tweaks to temperatures. Richmond

&&

Short term...valid for Thursday and Friday...

Gusty winds will continue for the remainder of the afternoon and
into the early evening hours behind the strong Pacific front that
moved through our forecast area last night. Plenty of subsidence
behind the front with strong winds aloft have been mixing down to
the surface this afternoon. Many areas have been gusting in the 30
to 40 miles per hour range with a few higher gusts. Satellite currently
showing this subsidence as well as skies have become partly to
mostly sunny across our central and western areas. An isolated
shower will be possible into this evening but mainly across the
east toward the Dakota borders. Have removed probability of precipitation for tonight as
loss of daytime heating will eliminate shower chances except for
the possibility over and the near the mountains.

High pressure ridging builds back across the forecast area for
Thursday into Friday resulting in mostly dry conditions and warmer
temperatures. Some weak instability will undercut the ridge
however bringing a slight chance for a shower Thursday night and
Friday along and west of a Sheridan-Billings-Roundup line. A
surface low develops on the Montana/Wyoming border Friday night
placing a warm front acros the center of our forecast area. Models
put a large area of precipitation along the front late Friday night into
Saturday morning. Have put likely probability of precipitation for this time period for
all but the far south and southeast areas of our forecast area.
Temperatures look warm enough for precipitation to be rain or a rain/snow
mix except for the beartooth/Absaroka Mountains and foothills
where some minor snow accumulations may occur. Temperatures will
be at to slightly above normal Thursday and Friday with readings
in the lower to middle 60s. Hooley

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

The GFS had been showing a warmer and drier solution for the
weekend when compared to the wetter and colder European model (ecmwf). In
addition...model details have varied from run-to-run with quantitative precipitation forecast
placement and 850 mb temperature values. However...the new European model (ecmwf)
has come in fairly similar to the GFS in terms of showing a warmer
and drier weekend solution. Thus have trended the forecast toward
a blend of the two models.

A split upper trough will cross the western U.S. Through Monday. The
models continued to cutoff a low well to the S of the region and
rotate it into the central/Southern Plains on Monday. The forecast
area will be affected by the northern stream of the trough which
brings a surface low into S Montana on Sat. Much of the precipitation
was forecast to move north of the area with the system/S warm front on
Sat morning...while other precipitation moves into western areas.
Southeast Montana will be in the warm sector Sat afternoon. Have scaled back
probability of precipitation over the east based on these solutions and added a chance of
thunder to the forecast for Sat afternoon and evening supported by
convective available potential energy on the GFS. Also raised temperatures on Sat...especially
from kbil east. Inverted surface trough will be over the area Sat
night supporting the inherited likely probability of precipitation. The warm 850 mb
airmass will support rain or a rain/snow mix. A quarter to a half
inch of precipitation will be possible Sat night from kbil west based
on the latest model runs.

The inverted trough shifts east during sun which will allow
precipitation chances to decrease over the west. Precipitation
amounts could exceed a half inch over southeast Montana. Nudged temperatures
higher on sun as well. Precipitation will gradually taper off from
west to east Sun night through Monday as the northern branch weakens over
the area. Deformation over the area will bring a slight chance of
showers to the region Monday night into Tuesday. Kept the forecast mainly
dry for Wednesday for now even though there was some model disagreement
with the pattern. Monday will be a cooler day but there will be a
warming trend for Tuesday and Wednesday. Arthur
&&

Aviation...

Overall...surface winds are expected to remain fairly light the
rest of tonight...though west to SW gusts over 25 kts are still
possible in the klvm area. Low level wind shear may be a problem
across the east tonight...including kmls and kbhk. Mostly VFR
conditions will prevail through Thursday morning. Thursday
afternoon...the airmass will become more unstable as a disturbance
generates scattered showers from kbil west. A few thunderstorms
are also possible over western mountains Thursday afternoon. Stc

&&

Preliminary point temp/pops...

Thursday Friday Sat sun Monday Tuesday Wednesday
-----------------------------------------------------------
bil 037/062 040/063 039/061 042/051 035/054 036/060 039/063
12/west 22/west 64/T 66/west 32/west 22/west 11/u
lvm 037/055 034/063 035/059 039/055 034/055 034/064 036/067
12/west 23/west 66/T 65/west 32/west 22/west 11/u
hdn 034/061 038/063 037/067 037/051 032/055 032/060 031/064
11/b 22/west 44/T 66/west 42/west 22/west 11/u
mls 036/062 039/061 038/065 040/048 032/054 032/055 034/063
11/north 21/b 65/T 77/west 74/west 32/west 11/u
4bq 034/060 037/058 038/071 041/051 032/054 032/054 031/062
11/north 11/b 34/T 77/west 64/west 32/west 11/u
bhk 033/058 038/060 036/058 036/046 029/049 028/051 030/056
11/north 11/b 65/T 67/west 75/west 32/west 11/u
shr 032/060 035/065 039/068 039/050 034/052 033/057 032/063
11/b 22/west 43/T 66/west 43/west 22/west 21/u

&&

Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.

&&

$$
Weather.Gov/Billings