Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Billings Montana
1032 am MDT Thursday Jul 28 2016


Vorticity maximum is currently moving through southern Carter and Powder
River counties heading southeastward and dragging cloud cover and
precipitation with it. In clearing to the west of this feature
already seeing cumulus development in its wake. Quick look at
06/12z model runs show good instability and shear axis over
western zones where middle level frontogenesis and low level upslope
will reside this afternoon. This area...along and west of a
Roundup to Sheridan line...looks like the best location for a
stronger thunderstorm with perhapse isolated small hail this
afternoon. Further to the east middle level lapse rates drop to
barely conditionally unstable this afternoon and shear is under 20
kts which would inhibit strong storm development except for areas
right along the Wyoming/Montana state line. Though instability aloft is
diminished there is plenty of moisture and low level instability
for showers and general thunderstorms over southeast Montana and
high scattered probability of precipitation seem reasonable there. Temperature forecast
seems reasonable...though cloud cover may keep a few locations a
bit cooler than forecast.

For the immediate Billings area hi-res models pointing to a
stronger thunderstorm or two moving through between 3pm and 6pm
this evening. Hail up to penny size would be the main threat.


Short term...valid for tdy and Fri...

Area of pv tracking across south central Montana is currently producing
a large area of showers and thunderstorms from Big Timber to
Billings down to Sheridan. This energy will move into northeast Wyoming
over the next several hours and would expect pcpn to do the same.
Have adjusted pops up thru the remainder of the night til 15z this
morning to account for this activity.

Moist and unstable northwest flow with more shortwave energy will bring
showers and thunderstorms across the cwa this afternoon and
evening. Convective available potential energy on the order of 500-1200 j/kg is enough for severe
storms but shear will take a notable drop from Wednesday. Current
ncar ensemble is consistent with latest rap runs in showing
greatest shear of 30-40 kts across our west and south, but only
20-25 kts across our north and northeast. Cannot discount a few
severe strong or severe storms today but our central to south
central parts may be most favored as this is also where pv will
exist late this afternoon, and northwest flow may result in a boundary in
the Lee of the snowies. Will continue messaging for storm
potential today. By this evening, shortwave will pass and we will
introduce subsidence from the west. This will allow for convection
to diminish quickly after sunset, I.E. It will not be a repeat of
the current night.

Another weak shortwave will emerge from North Pacific trof and
drop thru eastern Montana on Friday. Low levels will remain fairly
moist with easterly sfc winds, and although mid level temps will
begin to warm, convective temps in the upper 80s should be
achievable. Have expanded isolated pops to cover the mountains and
our central and eastern lower elevations. Any convection on Friday
will be non-severe.

Today will be the coolest day of the week with highs in the lower
to mid 80s, and perhaps only upper 70s in the east near Baker.
Warming trend begins Friday with highs back to the upper 80s or
near 90f.


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

The latest models are in good agreement through the extended
period. High pressure ridging will build over the forecast area in
response to an upper low and trough that will be situated over
southwest Canada Saturday into Sunday. This will result in rising
heights with dry conditions and temperatures well into the 90s.

As the upper low and trough move across southern Canada it will
bring a cold front across the forecast area Sunday
afternoon/evening resulting in a slight chance for a shower or
thunderstorm. Otherwise, the front will not have much impact
except to lower temperatures just a few degrees for Monday. Weak
ridging builds Monday into Tuesday before a stronger system moves
across the northern portions of the state bringing another front
across the area late in the day Tuesday or Tuesday night along
with a returned chance for showers and thunderstorms. Temperatures
will cool down to normal or just slightly below normal Wednesday
and Thursday with middle to upper 80s for most areas. Hooley


Some localized low ceilings from kbil to kmls will continue
through late morning. Scattered showers and thunderstorms and
associated MVFR to IFR conditions will be possible across the
entire forecast area later this afternoon and evening. Otherwise,
skies will be partly to mostly sunny with VFR conditions
prevailing. The mountains will be obscured at times throughout the
day. Hooley/reimer


Preliminary point temp/pops...

Tdy Fri Sat sun Mon Tue Wed
bil 083 059/089 062/096 066/095 062/090 060/092 060/087
4/T 22/T 11/u 12/T 21/b 12/T 21/u
lvm 084 050/090 053/093 057/094 051/091 052/092 051/086
3/T 21/u 12/T 22/T 21/b 12/T 21/u
hdn 084 056/090 059/097 064/097 060/092 059/095 057/089
3/T 22/T 11/u 12/T 21/b 12/T 21/u
mls 082 059/088 062/096 067/096 064/092 062/095 062/089
3/T 22/T 11/u 12/T 21/u 12/T 21/b
4bq 082 057/089 061/094 067/098 064/094 062/096 062/090
4/T 32/T 11/u 12/T 21/u 12/T 22/T
bhk 077 054/083 057/091 063/095 061/090 057/091 059/086
4/T 32/T 11/u 12/T 22/T 12/T 22/T
shr 084 052/090 056/093 060/096 058/092 056/095 056/089
4/T 32/T 11/u 12/T 21/b 12/T 21/u


Byz watches/warnings/advisories...



National Weather Service Glossary of Abbreviations