Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 182022

Area Forecast Discussion
National Weather Service Great Falls MT
222 PM MDT Sun Mar 18 2018


Areas of snow, along with some fog and patchy freezing drizzle,
will continue to cause minor impacts across Central Montana
through this morning, mainly from Helena and Great Falls north.
Snow showers will develop areawide this afternoon and again Monday
afternoon. Temperatures moderate early this week, before a cooler
and more unsettled pattern potentially returns late in the week.



Today through Monday night...Areas of light snow and snow showers will
continue into this evening and overnight across the area in
association with a weakening shortwave that had been a closed
upper low across our area. A more focused area of snow will
develop this evening along the Northern Rocky Mountains this
evening in association with another disturbance rotating the upper
low in southern Canada. This will bring another round of
accumulations from Marias Pass north as well as extending eastward
along and east of the Hi-Line. A Winter Weather Advisory continues
for the Northern Rocky Mountain Front beginning at 9 pm this
evening and extending through Monday morning. Advisories may need
to be extended east once confidence increases in snow
accumulations to the east across far north-central Montana. In
the wake of the upper level disturbance passage, downsloping and
subsidence aloft should help to scour out the lower clouds that
have plagued Central MT of late. Precip will wind down as well,
but may linger a bit longer in the mountains. CC

Tuesday through Saturday...Main forecast concerns are warming
temperatures, followed by a return to wet and unsettled weather.

H500 ridge over the Desert Southwest/Great Basin will amplify over
the Rockies Tuesday and into the day on Wednesday, all the while a
shortwave over the Gulf of Alaska digs towards the Pacific Northwest
and deepens. A weak shortwave traversing the amplifying ridge Tuesday
afternoon will bring some slight chance POPs to Southwest Montana
where better low- to mid-level moisture resides, but otherwise will
generally just bring some high clouds to the remainder of North
Central Montana for the afternoon/evening hours on Tuesday. During
the day on Wednesday the H500 ridge axis slides east across
Southwest and North Central Montana, with the flow becoming
increasingly southwesterly by the evening/overnight hours. 1000-500
mb thickness values on Wednesday climb to around 435-445dam and warm
air advection increases ahead of the approaching H500 trough over
the Pacific Northwest, which should support high temperatures in the
40s/50s south and west of a Browning, to Great Falls, to Lewistown
line, and the 30s north of this line (with the coolest reading over
Blaine and Hill counties where a substantial snowpack still
resides). Precipitation chances over the mountains of Southwest
Montana and along the Continental Divide on Wednesday will be on the
increase as the H700-H500 southwest flow begins to usher in
additional Pacific moisture, but will likely be very showery in
nature. High temperatures on Thursday will be similar to that of
Wednesday as 1000-500mb thickness values remain in the 435-445dam
range, however, increasing mid-level clouds and precipitation
coverage could hold temperatures down slightly. As just stated,
precipitation coverage is expected to be on the increase across most
of Southwest and North Central Montana during the day and night on
Thursday, as synoptic scale ascent associated with a shortwave
rotating through the main H500 trough moving from the Pacific
Northwest and towards the Northern Rockies overspreads the region.
Model solutions begin to diverge with the evolution of the upper
level pattern from Friday onwards, which will have an affect on the
timing of additional rounds of precipitation for Southwest and North
Central Montana. However, continued wet and unsettled weather is
expected to end the work week and persist into the first half of the
weekend. - Moldan


Updated 1740Z.

Snow continues to be showery in nature and will spread south into
SW MT this afternoon. By tonight, SHSN activity will diminish
some, but low clouds/fog/mtn obscurations will remain a concern
areawide with LIFR/IFR/MVFR conditions likely. A band of heavier
snow will develop after 00z this evening over the Northern
Rockies, then will move/expand east-southeast across the northern
tier counties during the overnight into the morning Monday.


Updated 18/400 AM.

Daytime high temperatures will be on the rise at both low and high
elevations into the middle of the upcoming work week, with
temperatures peaking on Wednesday and Thursday in the 40s and 50s
across most of Southwest and North Central Montana. Precipitation
coverage will be on the increase from Wednesday and into the first
half of the weekend, with some of the precipitation falling in the
form of rain, especially at lower elevations (i.e. valleys and over
the plains of North Central Montana). Increased snowmelt is likely
by the middle of the work week, as the combination of warming
temperatures and rain falling on the antecedent snowpack occurs.


GTF  22  40  24  43 /  20  10  10   0
CTB  17  34  21  38 /  80  60  10  10
HLN  22  41  25  44 /  20  10  10  10
BZN  20  39  21  43 /  60  20  20  10
WEY  12  31  12  34 /  30  20  30  20
DLN  17  36  17  39 /  20  10  10  10
HVR  16  31  18  35 /  60  80  30  10
LWT  19  37  23  40 /  30  30  20   0


Winter Weather Advisory from 9 PM this evening to noon MDT
Monday Eastern Glacier...Northern Rocky Mountain Front.


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