Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 160020

Area Forecast Discussion
National Weather Service Glasgow MT
520 PM MST Fri Dec 15 2017


Changes to the forecast focused first on getting the latest hourly
data into PoPs for the overnight period. A blend of RAP, NAMnest,
GFS1hr, CMCreg, and CMCnh NPoP were used to determine output. GAH

Overall forecast continues along the same track as before. Subtle
embedded disturbance this afternoon through tonight is expected to
spread light rain showers north to mix with snow showers southward
through tonight. Amounts will mainly be trace with light
accumulations possible south of Highway 200.

After today, colder temperatures will overtake NE Montana as the
previously strong western states ridge gives way to a series of
low pressure systems from the west. The next system to impact our
region would be Sunday night through Monday morning with maybe
half an inch of snow.

The main challenge and main story of the forecast remains the more
potent storm system and more impactful pattern change coming by
mid-week. Although there still remain some model differences, the
general picture is beginning to take shape. The main trough
energy digs through the Great Basin and the 4-corners regions, but
some connected energy remains northward through the trough axis.
For us, models are indicating that precipitation will swing around
and through NE Montana Tuesday afternoon through Wednesday night.
Snow accumulations for that 36-hour period look to be half an
inch over our SW zones and up to 3 inches for our NE zones. This
stronger weather system will bring a return to colder
temperatures, with below zero readings possible near our border
with Saskatchewan Wednesday night into Thursday morning. BMickelson

Sent an update this morning simply to include the latest near
short term model guidance. Still expecting a subtle short- wave
disturbance to bring trace to light precip amounts to the region
tonight and overnight. Starting as a rain/snow mix then changing
over to all snow. Maybe up to 0.5 inch snow accumulation for
points near Hwy 200 and south. Winds will be breezy at times,
gusting up to 25 mph. BMickelson

An upper ridge over the area will flatten as it translates
downstream of the forecast region and a new upper level trough
makes way for the Pacific shoreline. This will mean dry weather
for most of the day with increasing clouds.

Late this afternoon and especially tonight into Saturday as the
trough quickly translates eastward, cloudiness will increase and
rain and snow showers will move across the area. Temperatures will
cool enough tonight and Saturday that any lingering precipitation
should end in the form of snow. At this time, little or now snow
accumulation is expected for most places, though isolated amounts
of up to a half inch cannot be ruled out.

Colder and drier weather is expected in the wake of that system to
finish out the weekend, though it will be short-lived as a new
upper ridge builds across the western U.S. and extends into
northeast Montana into early next week. This will result in a
modest recovery in temperatures by Monday.

Latest 00z models continue to show fairly good consensus regarding
a pattern chance by the middle of next week. Tuesday into
Wednesday will feature a deepening trough into the western U.S
with a surface cold front expected to push into the region
sometime on Wednesday. Precipitation chances look to increase
ahead of and with this system but precise handling of placement
and amounts is still quite varied by the model solutions. While
probability is increasing that there will be a period of snow for
portions of northeast Montana sometime in the middle of next week,
higher confidence remains with the colder temperatures following
this next system. Maliawco




SYNOPSIS: Lowering ceilings and scattered rain and snow showers
will be possible across area terminals beginning tonight with some
MVFR conditions through 09Z. Afterwards ceilings will rise to VFR
through Saturday with dry conditions.

WIND: West to northwest at 10 to 15 kts.





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