Weather Service Report


319 
FXUS65 KTFX 201753
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1050 AM MST Mon Feb 20 2017

Aviation Section Updated

.UPDATE...

Little changes needed to this morning's update. Upper level wave
in WA will stream moisture into the region...and lift a warm front
from south to north today. As a result...isolated to widely
scattered showers are possible. Best chances of snow will come in
the western and southern Mountains...mainly above 6500 to 7000
feet. Meanwhile...most of the rest of the CWA will have at least a
slight chance for rain or snow. Some very isolated thunderstorms
are possible this afternoon across central portions under weak
instability...and may bring some brief graupel at times. 
Advisories continue across far southwest MT for impacts from wet 
possibly heavy snow. Anglin

&&

.AVIATION...
Updated 1750z.
Mostly VFR conditions are expected at lower elevations for areas 
north of I-90 through the period. A passing shower could affect the 
Cut Bank/Havre around 00z Tue...but nothing significant. Lower 
ceilings and more widespread rain/snow is expected to move into 
Southwest MT tonight/Tue morning. Some short impacts could develop 
as far north as Bozeman on Tue morning due to rain/snow/low 
ceilings. The Rocky Mountain Front/SW MT could have mountains 
obscured at times through the period. Brusda

&&

.PREV DISCUSSION...
/ISSUED 420 AM MST Mon Feb 20 2017/

Today through Tuesday night...
A very active weather pattern is in store for the next several 
days. Transitory upper ridging and associated large-scale 
subsidence quickly exits north and east this morning as the next 
upper disturbance pushes a front across the SW MT by late 
afternoon. To the south of this front in the warm sector, 
instability will increase enough for rain and some mountain snow 
showers to develop during the afternoon heating. A stray bolt of 
lightning and clap of thunder can not be ruled out late in the
afternoon, especially toward the Continental Divide. Meanwhile, 
over the far southern areas toward the high-elevation passes over
the MT/ID border, a more sustained upslope push of moisture will 
allow for steady snow to develop by early afternoon and continue 
into tonight and early Tuesday morning. A Winter Weather Advisory 
for Snow has been issued for these areas for minor impacts to 
travel. Snow levels will be quite marginal, so am expecting rain to 
mix in at times especially by evening into the overnight tonight and 
greatly limit potential snow accumulations at pass levels. 

Things become a bit more interesting Tuesday as a stronger weather
system approaches and pushes another stronger warm front across SW
MT to somewhere over the north-central Plains. The warm front will
have more moisture to work with and will thus allow for some rain
and snow to develop ahead of it as it moves into the Plains and
becomes stationary. Meanwhile, to the south of the warm front in
the warm sector, instability will become relatively impressive for
this time of year, and combined with a good amount of available
moisture and upper level dynamics will allow for at least a 
slight chance of thunderstorms along with scattered to numerous
rain and snow showers to develop over SW MT. The other concern for
Tuesday behind the departing surface low is the potential for
windy conditions over SW MT during the day Tuesday. However, the
greatest threat has appeared to drop a little more to the south
where there will be greater subsidence, and thus any wind hazards
at this time do not appear likely. By Tuesday night, a nearly 
stationary 700-mb front will reside roughly west-east somewhere
over central MT. This feature will become the focus of a 
potentially more widespread band of snow that may develop 
especially on the north side of this front as northerly low-level 
upslope flow develops over much of the Plains combines with 
isentropic lift aloft. Stay tuned.  Cassell

Wednesday through Friday...A broad mid- to upper-level trough is 
expected to overspread the CWA during this time period, contributing 
to a cooling trend in temperatures. Simultaneously, a surface cold 
front trailing the aforementioned surface low may stall along the 
Rocky Mountain Front and Central MT mountains. Deep lift along this 
front and ahead of the aforementioned mid- to upper-level trough may 
combine with sufficient moisture to generate widespread 
precipitation, especially in North-Central MT and during the 
Wednesday into Thursday time frame. While most of this precipitation 
should fall as accumulating snow, some rain may mix-in at lower 
elevations during the daylight and early evening hours of Wednesday. 
By Friday, snow looks to taper off in most North-Central MT 
locations. Farther south, snow should become more probable in 
Southwest MT as surface high pressure builds south-southeastward 
from the Canadian Prairies, causing the aforementioned front to 
advance southward and eastward. This potential widespread 
accumulating snow will have to be monitored closely. 

Saturday through Monday...Below-normal temperatures will prevail 
during this period courtesy of a predominantly northwesterly flow 
aloft. Mid- to upper-level troughing should persist Saturday into 
Sunday morning, while later on Sunday, shortwave ridging may briefly 
crest over our region. By late Sunday evening into Monday, another 
mid- to upper-level trough looks to overspread the CWA from the 
northwest. This pattern looks to allow weakening surface high 
pressure to reside over the CWA Saturday. Thereafter, a weak lee 
surface trough should materialize. Additional snow showers are 
expected during the period, especially on Saturday and Monday.
Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  37  51  29 /  20  20  60  40 
CTB  45  30  42  23 /  30  30  20  30 
HLN  45  29  43  26 /  30  30  30  30 
BZN  45  31  45  24 /  20  30  30  40 
WEY  35  32  36  20 /  90 100  90  50 
DLN  44  34  44  26 /  30  30  40  20 
HVR  51  35  48  29 /  20  20  20  40 
LWT  52  36  53  30 /  10  20  40  40 

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 8 AM MST Tuesday Beaverhead...
Gallatin...Madison.

&&

$$

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Western Regional Climate Center, wrcc@dri.edu