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Area forecast discussion...updated 
National Weather Service Billings Montana
917 PM MDT Sat may 23 2015

Update...
none of the models are handling the quantitative precipitation forecast timing and placement very
well this evening...which is no surprise due to the subtle
dynamics over our particular region. Best diffluence aloft is over
eastern Wyoming where some lightning can be found. Most of this
activity is headed west and a little northwest...and may breach
the northern big horns later tonight. Overall though I have
reduced probability of precipitation tonight and removed thunder from all but the very
south/southeast border areas. There is an axis of instability
linked to the short wave that pushed north through the area
earlier this afternoon...from SW of Billings up to Miles City.
Some showers could still develop at times here overnight...though
the areas further north may just be sprinkles. Upslope into the
northeas facing beartooths still producing shower activity
there...and it may persist in spotty fashion overnight. Batch of
energy and moisture come into our southeast sections tomorrow. The
diffluence aloft seems to include our southeast tomorrow as well...so
our categorical probability of precipitation look good in the southeast tomorrow. Bt

&&

Short term...valid for sun and Monday...

A weak upper low over western Montana with a second low over the
Utah/Colorado border will continue to bring a chance for showers
and isolated thunderstorms for the remainder of this afternoon
into this evening. Believe any thunder will be quite isolated as
early cloud cover has stabilized the atmosphere better than what
the case was yesterday. Coverage in the activity will diminish by
late evening.

However...this will be short-lived as the above upper low moves
northeast late tonight and will be located across eastern Wyoming
Sunday. At the same time...a surface will develop across the
vicinity of northeast Colorado Sunday afternoon and reamin fairly
stationary into early Monday morning. This surface low will wrap a
good deal of precipitation northwest across northern Wyoming into
southeast Montana late tonight through Sunday. Will maintain
likely to categorical probability of precipitation for Sheridan County northeast to Baker
during this time period. Models paint anywhere from around 0.50"
to just over an 1.00" of rain for these areas during this time.
Elsewhere across the forecast area...scattered showers with
isolated thunderstorms will continue Sunday but with chances
lessening by Monday.

A split flow aloft with weak steering winds will be over the
forecast area Monday. An isolated shower/thunderstorm chance will
continue with the best chances east near the Dakota borders.
Temperatures will continue to be on the cool side Sunday but with
a bit more sunshine readings will moderate to seasonal or just
below seasonal values with readings closer to 70 degrees on
Monday. Hooley

Long term...valid for Tuesday...Wed...Thu...Fri...Sat...

An upper low within a broad trough will be situated over the
Pacific northwest extending into the northern rockies through most
of the extended period. The flow aloft will remain fairly week as
well as the main jet energy will be north and south of the state.
This will lend itself to a relatively stagnant weather pattern for
most of next week. However...the flow aloft will be southwest with
various pieces of energy ejecting out of the low. As a
result...expect unsettled weather to continue with chances for
showers and isolated thunderstorms each day. Precipitable waters
will be around 0.50"-1.0" and this combined with weak steering
winds will result in the possibility of any shower/thunderstorm to
contain heavy rain.

Models still bring a cold front south across the forecast area
Thursday night into Friday resulting in a stronger and cooler
easterly surface flow across the forecast area Friday into next
Saturday. Temperatures continue to look to be around normal
through the period with a cool down by Friday and Saturday behind
the cold front. Hooley
&&

Aviation...

Isolated to scattered showers are expected overnight with
ceilings lowering from VFR/MVFR to IFR toward 12z sun. LIFR
ceilings are expected at kshr late tonight. Ceilings will lift to
MVFR during Sun morning and will continuing rising in the
afternoon. MVFR visibilities will occur with showers and
associated fog. There will be a break in the showers Sun
morning...except over southeast Montana and the kshr area. Scattered showers
will then redevelop across the entire area by Sun afternoon with
more numerous showers over southeast Montana and the kshr area. There will
also be a slight chance of thunder across the entire area Sun
afternoon. Expect areas of mountain obscuration...with widespread
obscuration over the NE big horns on sun. Arthur
&&

Preliminary point temp/pops...

Sun Monday Tuesday Wednesday Thursday Friday Sat
-----------------------------------------------------------
bil 045/062 045/069 049/071 048/070 049/069 047/065 046/069
36/T 32/T 23/T 33/T 33/T 33/T 32/T
lvm 043/060 039/070 045/068 043/065 044/068 042/065 042/067
34/T 33/T 36/T 64/T 43/T 33/T 33/T
hdn 046/063 045/069 046/074 048/072 049/072 047/067 045/070
36/T 43/T 23/T 33/T 33/T 33/T 32/T
mls 047/064 047/068 048/073 049/072 050/070 048/066 044/069
27/T 54/T 22/T 33/T 33/T 33/T 32/T
4bq 046/059 046/066 044/072 048/071 050/069 047/065 043/067
29/T 65/T 22/T 44/T 43/T 33/T 33/T
bhk 046/061 045/066 046/070 047/069 048/067 045/063 042/065
26/T 76/T 32/T 34/T 43/T 33/T 32/T
shr 045/056 043/064 044/069 045/068 046/068 044/065 042/066
59/T 64/T 24/T 43/T 33/T 33/T 33/T

&&

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

&&

$$
Weather.Gov/Billings

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