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Area forecast discussion 
National Weather Service Billings Montana
929 PM MDT Wednesday Sep 2 2015

Update...
winds have decreased this evening and rhs are beginning to recover
slowly...so have cancelled the red flag warning which was in
effect for western fire weather zones this evening.

Weak cold front is pushing through our west with modest pressure
rises...northwest winds at Judith Gap and a west wind now at Billings. We
will not see a lot of wind with the frontal passage but instead a gradual
veering of winds as cooler air oozes into our County Warning Area from the W-NW.
There are a few weak echoes showing up on blx radar near Miles
City but these are likely to be accus/virga...and perhaps a
sprinkle...rather than showers based on temperature-dewpt spreads that
are still on the order of 40-50 degrees. Have given Forsyth and
Miles City a mention of sprinkles through 06z. Otherwise our weather
will be quiet through the remainder of the evening. Latest models
are hinting at some weak energy from the SW making its way to our
SW mountains by late tonight. As low level winds turn from downslope to
upslope...we may see a few showers over our west late tonight and
Thursday morning...and cannot rule out isolated ts based on steep middle
level lapse rates. Have adjusted probability of precipitation from 09-18z to account for
this.

High of 102f at Miles City was a record for the day...and the 9th
triple digit high of 2015.

Jkl

&&

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

Cold front was through khvr and kgtf at 20z...per temperatures in
the 70s/80s...wind shift and pressure rises. It was hot and dry
ahead of the front over the forecast area with temperatures
climbing through the 90s from kbil east...and through the 80s west of
kbil. Winds were increasing over central and western parts of the
area...and klvm has been hitting red flag criteria with gusts over
40 miles per hour. Will keep the rfw going through midnight MDT. A few dry
thunderstorms have developed east of kbil this afternoon. Will watch
trends with these storms and add them to the evening pop grids if
needed.

The front will push south-southeast through most of the area tonight. WRF/GFS
developed some quantitative precipitation forecast over the western mountains overnight...but
relative humidity profiles looked too dry for precipitation so
will keep forecast dry. The front will stall out over southeast Montana/NE Wyoming
on Thursday as a surface low moves SW along the boundary into this
area. Weak shortwaves will move through the area in SW flow
aloft...but airmass continued to look mainly dry. Given the
increasing quantitative precipitation forecast trends in the models however...did expand the
western probability of precipitation a bit further east. Temperatures will range from the 70s
west to the 90s southeast near the front. Relative humidities near the front
will be in the teens...but winds are not expected to be strong so
fire weather is not a concern.

Models showed moisture increasing across the area Thursday night and
then shifting north on Friday. A strong wave is expected to skirt the east
Montana border on Friday...otherwise weak waves will continue moving
through the flow. NE low-level winds Thursday night will become east on
Friday...and models indicated some cape and shear on Friday afternoon
and evening...especially over the east. Kept southeast Montana dry Thursday night
based on drier air over this area...otherwise continued low probability of precipitation
across the area. Had southern areas dry on Friday morning then
brought low probability of precipitation back into this area Friday afternoon as the instability
should fuel thunderstorms. Friday will be cooler with highs in the
70s and 80s. Upper low/trough will be over or/north California Friday night. Jet
divergence...isentropic lift and low-level east flow will bring a
chance of precipitation to the entire area. Arthur

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

Latest models showing better agreement but the European model (ecmwf) is trending
quicker than with previous runs...bringing the movement of a
trough with a cutoff circulation passing from southwest Montana to
northeast Montana on Sunday now earlier than the GFS... supported
by GFS ensemble guidance which still has strong spread Saturday
and Sunday.

Moisture deepens in low level easterly flow and by late Saturday
and into Sunday afternoon supports scattered shower and
thunderstorm activity. The upper low moving across the area
maximizes lapse rates aloft but is more optimally timed for
diurnal heating cycle in the GFS. There are still good chances
for rainfall but the northward track of the upper low compared to
some previous model solutions does limit confidence. This is
emphasized in model trends which are not forcing wrap around
precipitation into southern Montana and northern Wyoming as
strongly. This suggests that by Sunday afternoon precipitation chances
should be ending.

By Monday models generally agree on dry SW flow transitioning to
zonal on Tuesday with a warming trend in temperatures continuing
to Wednesday. Mrowell

&&

Aviation...

VFR conditions will prevail tonight and Thursday. South to
southwest winds over western areas will gust to 30kts ahead of a
cold front that will slowly work across the forecast area tonight.
Isolated showers and thunderstorms are possible behind the
front...mainly after 06z. The chance for thunderstorms will
increase through the day tomorrow. Chambers/reimer

&&

Preliminary point temp/pops...

Thursday Friday Sat sun Monday Tuesday Wednesday
-----------------------------------------------------------
bil 060/080 053/072 054/074 049/065 043/071 045/072 046/074
01/b 22/T 35/T 66/T 31/u 11/b 11/b
lvm 052/080 046/072 046/073 040/063 036/072 038/073 038/076
22/T 34/T 45/T 55/T 31/b 11/b 11/b
hdn 057/085 053/077 053/079 049/069 043/073 044/075 044/076
01/b 22/T 34/T 55/T 31/u 11/u 11/b
mls 061/089 059/077 059/082 053/069 044/069 045/071 045/074
01/b 22/T 44/T 55/T 42/west 11/b 11/b
4bq 059/094 059/081 058/085 054/072 046/071 048/072 048/074
00/b 12/T 34/T 44/T 21/u 11/b 11/b
bhk 060/093 059/081 057/075 053/071 045/068 043/070 045/072
01/b 22/T 44/T 55/T 22/west 11/b 11/b
shr 055/091 052/080 051/083 047/071 039/072 040/074 042/074
01/b 22/T 34/T 44/T 21/u 11/u 11/u

&&

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

&&

$$
Weather.Gov/Billings

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