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Area forecast discussion...updated 
National Weather Service Billings Montana
911 am MDT Thursday Aug 21 2014

forecast remains on track with cool and wet pattern evolving.
Looking at a couple of periods for strong convective potential but
slow storm motions and lack of capping seem to be limitations.
Warmer temperatures in southeast Montana could yield a near severe
storm or two...but not expecting any cells to stay discrete for
too long. No updates. Borsum


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

Current water vapor imagery indicates a weak shortwave pushing
through south central Montana this morning...with radar showing
ongoing showers near Hysham...with some more activity lingering
back around Billings. The main wave...that will become our active
weather producer today...can be seen pushing into western Idaho
this morning. Showers with some embedded lightning are ongoing
across western Montana and will continue to develop eastward with
the track of the wave.

Expect to see showers and thunderstorm become more widespread
later this morning through this afternoon across central and
western zones. Activity will remain convective in nature as some
minor instability remains in place in these zones. Forecast model
soundings indicate greater instability across southeast Montana
this the wave is better timed to arrive with peak
diurnal heating. Given the increasing shear profile with the
approach of the wave...would certainly not rule out some stronger
thunderstorms across southeast Montana later this afternoon and
early this evening. 00z high resolution model suite does hint at
the possibility for some organized convection in this area. In
fact...the NSSL WRF arw wants to evolve a line segment across
Powder River and Carter counties this afternoon. Sref also is
showing a slightly elevated risk of severe weather in this corner
of the state. Chose to mention thunderstorms with strong winds in
the forecast...including Broadus...Baker and Ekalaka. Didn\t
mention severe as probability of an isolated report seems fairly
low. Perhaps the more widespread threat with these stronger storms
in the east will be the ability to produce very heavy
rainfall...which could produce localized standing water and rising

The initial shortwave will push into Canada by Friday morning. The
larger scale trough will finally dig in over the Pacific northwest
by Friday morning. Given the break between the two waves...expect
a quieter period of weather late Thursday night into Friday
morning. Precipitation chances become much more widespread...and
less convective in Friday evening. Well defined
diffluent flow ahead of the approaching upper-level low pushes
strong qg forcing into central and western zones by Friday
evening...and continues to push east across the forecast area
through Saturday morning. Expect this period to produce the most
widespread and steady rainfall across the forecast area. Track of
the 700 mb will be in good position to develop deepened upslope addition to the low-level upslope that will already be
in place.

Also Worth mentioning that 700 mb temperatures fall to near 0c by
early Saturday morning...thus would not rule out a couple inches
of slushy snow in the high country...mainly at and above 10,000
feet. For the plains...these cooler temperatures and on going
precipitation across the area will result in high temperatures
running 10 to 20 degrees below normal by Friday. Also lowered high
temperatures slightly for guidance has continued to
trend cooler...which makes sense with the increasing low-level cold air advection
and increased chance of thick cloud cover and more widespread


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

Models still pointing to a very wet start to the extended period
with potential drying to end the forecast period. Friday night and
Saturday have all indications of the best chance of rainfall with
the upper trough to the west swinging across southern Montana.
Models were consistent on swinging the trough through Friday night
through Saturday and this period has the strongest forcing.
Saturday will be interesting as models track the upper low within
the trough farther north and this brings a dry slot into southern
zones Saturday afternoon. There was plenty of energy swinging up
from Wyoming on the south side of the trough which is prognosticated to
enter southeast Montana Saturday probability of precipitation will remain
high over the east. Precipitable waters around an inch will produce pockets of
heavy rainfall. The ec was producing over an inch of quantitative precipitation forecast over the
east Saturday afternoon and evening with much less amounts over
central and western zones. Would expect around an inch of quantitative precipitation forecast over
western and central zones Friday night through Saturday morning.

Models takes the upper low north Saturday night and Sunday and
this should dry the area out from south to north as forcing pulls
into northern Montana. Wrap around moisture will swing across the
northern and northeast parts of the forecast area Sunday but
should pull away Sunday night. The GFS brings in the next
shortwave trough Monday and Monday night. The ec buries the low
into California by Tuesday afternoon leaving a Flat Ridge in
place. The GFS would obviously be the wetter solution and have
leaned on it. Raised probability of precipitation Monday and Monday night...especially
west and south. Drying trend looks on track for Tuesday Onward.

Cooled temperatures down quite a bit for every period. Guidance
was keeping readings in the lower 60s Saturday and that seems very
reasonable with clouds and widespread showers. The warm up Monday
and Tuesday will be slow as heights remain low. Temperatures will
be cold enough for snow over the highest peaks Friday night and
again Saturday night. Models were not as cold this run...but
should see snow levels fall to around 10 thousand feet Saturday
night...which will put a couple inches of snow down over the
highest elevations. Twh


Scattered showers will work across area this morning. Activity
will increase in coverage and intensity this afternoon as
thunderstorms form along with the showers. The strongest showers
and storms will produce heavy rain with local MVFR conditions
developing as visibility drops. The showers and thunderstorms will
continue into the early evening with a bit of a break in activity
expected overnight. Mountains will be frequently obscured. Twh

Preliminary point temp/pops...

Today Friday Sat sun Monday Tuesday Wednesday
bil 070 053/068 053/064 048/068 048/070 050/074 055/081
6/T 56/T 98/T 42/T 23/T 33/T 22/T
lvm 069 050/066 049/062 044/066 045/068 046/072 047/080
7/T 78/T 96/T 53/T 35/T 53/T 22/T
hdn 078 054/074 055/066 051/069 050/073 052/075 053/083
6/T 45/T 98/T 43/T 23/T 33/T 22/T
mls 079 057/074 057/070 052/066 050/071 052/074 054/080
6/T 64/T 98/T 44/T 12/T 33/T 22/T
4bq 082 056/078 059/074 053/067 051/072 053/074 053/080
4/T 64/T 98/T 53/T 12/T 44/T 32/T
bhk 080 057/072 055/070 052/064 048/069 050/070 052/075
4/T 64/T 98/T 74/T 21/b 33/T 22/T
shr 079 051/073 053/068 048/067 047/072 049/071 050/078
4/T 44/T 86/T 43/T 23/T 33/T 22/T


Byz watches/warnings/advisories...



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