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Area forecast discussion 
National Weather Service Billings Montana
330 am MST Friday Mar 6 2015

Short term...valid for today and Sat...

Northwest flow was over the forecast area this morning per water vapor
imagery. Middle and high level moisture was in the flow based on
satellite imagery and surface observations. Laps data indicated a
south-southwest to north-northeast surface pressure gradient over the SW portion of the
area. This gradient was combining with cold temperatures in
Yellowstone Park and warmer air over klvm to create gap flow. The
gradient was supporting windy conditions at Big Timber as well. So
far...winds in both areas were remaining below advisory
criteria...and local guidance suggested that advisory
probabilities were low. Also...models had the pressure gradient
slackening after 18z today. Thus will continue with no advisories
for these areas.

850 mb winds will be around 30 knots today...especially central and
east. Decent mixing will allow the winds to mix down...creating
breezy conditions. Have reflected the increased wind speeds in the
forecast. Otherwise...today will be dry with middle and high
cloudiness. 850 mb temperatures of +4 to +8 degrees c will support
high temperatures in the 50s.

Dry northwest flow will continue over the area tonight...before a
shortwave drops down into the area from Canada late on Sat. This
wave will be accompanied by q-vector convergence as it moves S
through Sat night. Weak frontogenesis will also accompany the
wave. Model lapse rates indicated a fairly unstable airmass
through Sat night and there will be enough low-level moisture to
support low precipitation chances. Expanded probability of precipitation further S Sat
afternoon and increased them to chance over kbhk and kmls. Had
slight chance probability of precipitation across most of the area Sat evening...then
confined them to the southern mountains late Sat night.
Precipitation type will be mainly rain through Sat evening as Sat
high temperatures will reach the 50s again. Winds will be lighter
on Sat than they will be today due to lighter winds aloft. Arthur

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

Made a few changes to the extended forecast period. Models remain
in pretty good agreement for most of the extended
period...continuing with a drier signature than previously
advertised. Overall...the forecast indicated well above average
temperatures and mainly dry conditions.

An upper ridge over the Great Basin dominates the
pattern...keeping dry northwest flow over the region through
Tuesday. Lack of moisture and general weakness of shortwave
activity point to persistent dry conditions over the region. Cleared
slight probability of precipitation from the forecast additionally...downslope flow should
further inhibit any precipitation development...as well as bolster
warming trend. Upper level ridging...although somewhat
shallow...shifts across the region Tuesday night through
Wednesday...continuing the warmup and dry conditions. Cleared
inherited slight probability of precipitation from the extended period through
Wednesday...and continued to trend temperatures up slightly.

A stronger Pacific disturbance follows the ridging...bringing
precipitation potential to western mountains Wednesday night. Models are
in pretty good agreement on initial timing of this system coming
into the region...but diverge by Thursday night...disagreeing on
how quickly the system crosses the region. The European model (ecmwf) is much
slower...and indicated some precipitation potential through the end of
the extended period. The GFS brings the County Warning Area under the influence of
another upper level ridge amplifying over the Great Basin once
again. Chose to include slight probability of precipitation and continued with warm temperatures
through the end of the extended period. Aag



&&

Aviation...

Gusty west to southwest wind...with gusts around
40knots...continue at klvm and k6s0 this morning...but will begin
to taper off this evening. Breezy conditions can also be expected
across the rest of the region...but with lesser gusts.
Otherwise...VFR conditions are expected. Aag

&&

Preliminary point temp/pops...

Today Sat sun Monday Tuesday Wednesday Thursday
-------------------------------------------------------
bil 056 030/056 031/056 035/062 035/062 036/062 034/059
0/north 01/east 20/u 00/u 00/u 01/b 12/west
lvm 054 033/055 028/055 035/059 037/059 039/063 035/058
0/north 00/north 10/u 00/u 01/north 11/north 12/west
hdn 059 027/057 028/057 031/063 032/064 033/063 032/062
0/b 01/east 20/u 00/u 00/u 01/b 12/west
mls 055 027/051 028/053 032/061 033/061 032/060 032/057
0/north 03/west 20/u 00/u 00/u 01/b 11/b
4bq 052 024/052 025/052 028/061 030/062 030/063 031/059
0/north 02/west 20/u 00/u 00/u 01/b 11/b
bhk 053 024/049 023/051 029/059 031/059 029/057 027/053
0/north 03/west 20/u 00/u 00/u 01/b 11/b
shr 051 026/051 026/051 027/060 029/061 031/063 030/059
0/b 00/b 20/u 00/u 00/u 01/b 12/west

&&

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

&&

$$
Weather.Gov/Billings

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