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Area forecast discussion 
National Weather Service Billings Montana
908 PM MDT Wednesday Aug 20 2014

showers and some embedded thunderstorms moved across our western County Warning Area
during the late afternoon and early evening...with main impact
being 30-50 miles per hour gust front winds which are becoming much weaker
east of Billings. As of 9pm some lingering showers existed in an
area from Roundup to near Billings and toward Red Lodge...with
decreased lightning activity. Water vapor imagery shows a
shortwave dropping into Washington. This feature will offer a
period of ascent late tonight and tomorrow which along with some
middle level frontogenesis and instability...and developing low level
upslope winds...will bring our west and central parts a greater
chance of showers with again some embedded thunderstorms. For the update
have reduced probability of precipitation for the evening as much of the convection has
ended...and have raised probability of precipitation tomorrow morning from Billings
westward as ascent really expected to increase by 12-18z. Greater
chances of convection will reach our eastern areas tomorrow
afternoon and night. Jkl


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

Extended period of troughing expected across the region with the
pattern evolving into a cutoff low over Idaho by early weekend.
Initial impact is for unstable conditions to prevail and periodic
shower and thunderstorm activity will continue tonight and
Thursday. Thursday night upslope flow and better upper level
dynamics begin to cause a broader precipitation regime especially
for upslope regions. Conditions will be drier in southeast Montana
without the upslope influences.

Friday the development of the upper low over Oregon and Washington
sets up a diffluent southwest flow aloft over Montana and western
Wyoming while falling surface pressures over Wyoming maintain the
upslope flow. This will amplify the potential for widespread rain
across the central and western zones while scattered showers and
thunderstorms impact southeast Montana.

Energy ejecting from the base of the upper low Friday night begins
to spin up a surface low over southeast Montana with greatest
weather impacts expected during this period. The exact evolution
of the weather pattern at this point is at low confidence because
model trends are distinctly shifting this low furthering south
and west with time. This trend will impact where this surface low
develops...which will influence where a dry slot shows up and
where possible severe weather develops. Confidence is higher that
it will be east of Billings...which will put the foothills into a
strong upslope flow with an unstable moist airmass and favorable
dynamics aloft. Heavy rain showers and thunderstorms are expected
Friday night continuing into Saturday morning...and rainfall
amounts of 1 to 2 inches in some areas are possible. Billings
looks to be close to the heavy moisture so a half inch of
precipitation would be possible. Further east...shear profiles
could support severe weather...just not sure how far west this
threat could extend.

Saturday the upper low begins to shift northward and this shifts
the better precipitation zone northward but still wil be plenty of
shower activity around. Cloud cover and still upslope flow will
keep temperatures on the cool side. Friday and Saturday could see
temperatures anchored in the 60s west of Billings. Southeast
Montana looks to be warmer than first anticipated as the slower
progression of the upper low is warming up temperatures.

Bottom line is active weather is coming with below normal
temperatures. Those engaging in outdoor activities will need to
protect themselves from the elements. Borsum

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

Unsettled weather pattern will continue Sunday through Tuesday as
an upper level trough remains firmly in place over the western US.
Model guidance is in agreement with strong signal of precipitation over
most of Montana and placement 500mb low. As of the latest
runs...upped probability of precipitation for the Monday afternoon evening
period...mainly for the western zones. Temperatures will remain
somewhat mild Sunday and the 60s and 70s...and then a
gradual uptick with more the middle of next week.



Scattered showers and isolated thunderstorms will occur over much
of the area tonight with possible MVFR conditions. There will be
isolated showers and thunderstorms over kshr and from kmls east and
S. A cold front will cross the area on Thursday bringing a shift to northwest
surface winds. Showers and a slight chance of thunderstorms will
increase from west to east across the area with MVFR to IFR conditions.
Areas of mountain obscuration tonight will become more widespread
on Thursday. Arthur


Preliminary point temp/pops...

Thursday Friday Sat sun Monday Tuesday Wednesday
bil 059/072 055/072 052/067 048/069 049/077 053/074 055/081
46/T 56/T 76/T 33/T 23/T 33/T 32/T
lvm 051/074 050/069 046/065 044/068 045/075 048/072 047/081
57/T 77/T 97/T 43/T 34/T 43/T 32/T
hdn 058/078 055/077 053/071 051/071 050/079 052/076 053/083
35/T 45/T 76/T 33/T 22/T 33/T 32/T
mls 060/084 057/079 055/075 052/068 050/077 054/073 054/080
25/T 44/T 76/T 43/T 22/T 33/T 22/T
4bq 059/085 057/080 058/076 053/068 051/077 054/074 053/081
24/T 44/T 66/T 53/T 33/T 33/T 22/T
bhk 056/082 055/077 057/074 052/065 047/073 050/069 052/074
14/T 74/T 67/T 73/T 32/T 33/T 22/T
shr 054/082 052/078 050/073 048/068 047/076 050/072 050/079
24/T 44/T 66/T 43/T 32/T 33/T 32/T


Byz watches/warnings/advisories...



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