Winter Storm in Montana, April 2, 2018

Area Forecast Discussion
National Weather Service Great Falls MT
942 AM MDT Mon Apr 2 2018

.UPDATE...

Upper low is starting to push across the CWA this morning bringing
widespread snow. Central areas are currently being hit the hardest
with visibility a half mile or less and snowfall rates around an
inch per hour. This heaviest snow will continue to push eastward
with the mentioned disturbance through the morning and into the
afternoon hours. Snow will then taper off to widespread light
snow behind this initial push. There could still be some times of
moderate snow from upslope enhancement through the afternoon. Snow
should then taper off throughout the evening hours. Given the
delay in snow start...total snow accumulations look be slightly
lower than previous forecast with generally 2 to 4 inches in the
plains and higher amounts in the mountains. Eastern portions of
the CWA could still get 4-6 inches in some heavier snow. Despite
the lower accumulations...reduced visibility in falling and
blowing snow...combined with snowfall rates of an inch per
hour...will support continuing the Warning across the area. Anglin

&&

.SYNOPSIS...

Active weather will continue through the day today with widespread
snow likely across the entire area. Snow will diminish by tonight
leaving behind clearing and drying conditions Tuesday and
Wednesday. We will see the next storm system deliver more rain and
snow chances by later this week with temperatures remaining below
normal through the upcoming weekend.

&&

.AVIATION...
Updated 1140Z.

Widespread mountain obscurations and IFR/MVFR conditions due to low
clouds and snow will prevail across the forecast area this morning
and into the afternoon. Conditions improve gradually from the
northwest during the afternoon and evening hours but areas of light
snow and low clouds producing temporary IFR/MVFR conditons could
persist through early Tuesday morning. mpj

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT Mon Apr 2 2018/

Today through Wednesday...The main focus early this week for any
impactful weather will continue to be today and into early
tonight, as a quick moving disturbance continues to push east
across the Northern Rockies. Latest radar trends continue to
illustrate increasing snow showers across a large portion of the
CWA, which will continue to increase in coverage and intensity
later this morning. A few caveats exist with this system based on
the latest mesoscale analysis early this morning, which has pushed
overall confidence down slightly with this system today. While
dynamic ascent is rather sufficient aloft, it seems that most
model guidance had a difficult time handling the drier boundary
layer conditions that existed all afternoon yesterday through
overnight last night. Because of this, projected snow totals have
come down some area wide, with the bulk of snow accumulations
continuing to reside in higher elevations today, especially along
the Divide and across higher terrain of central and southwestern
MT. Once the system departs to the east later this afternoon and
evening, there may likely be some lingering convective snow bands
across central and southwestern Montana, given very impressive
deep mixed layer aloft yielding impressive lapse rates. Any
additional snowfall will remain primarily located to higher
terrain in these areas, where intense snowfall rates may be
possible at times. The good news is this system and widespread
snow exits to the east tonight, leaving behind cold, yet dry
conditions. Where snow fell today, temperatures will likely
plummet tonight with single digits to even some sub-zero
temperatures across the Hi-Line. This drying trend will continue
into the day on Tuesday with increasing clouds Tuesday night.
Wednesday will be a lot like the day on Sunday, with mostly
cloudy skies and remaining rather cool. By Wednesday afternoon,
light snow showers will increase from the west along the Divide,
and eventually try to spread east across the Plains. But dry
boundary layer conditions will keep any snow chances primarily
confided to higher terrain, while any lower elevations remain
mostly dry. KLG

Wednesday night through Monday...Medium range models are beginning
to converge toward a common solution early in the forecast period.
ECMWF now agrees with the GFS in bringing a Canadian cold front
southward through Montana Wednesday night. The combination of a cold
and relatively deep airmass over the plains combined with several
waves of Pacific moisture and shortwave energy aloft will produce
periods of widespread precipitation from Wednesday night through
Friday. Accumulating snow is likely for much of the region,
especially across northern portions of the forecast area, but
increased atmospheric thickness values support areas of rain in
southwest and central Montana at times during this period. Shortwave
ridging aloft is expected to build over the northern Rocky Mountains
Friday night into Saturday before the next upper level trough sweeps
through the region over the weekend. Medium range model solutions
are somewhat different for the Saturday night through Monday time
period, but both are now showing a closed surface low sweeping
through Wyoming Saturday night before developing a blizzard over the
Dakotas for Sunday. It should be noted that this feature is now
about 100 to 200 miles further south than was indicated by the GFS
over the last few model runs so it will be interesting to see how
both models evolve this solution in the coming day. As a result,
confidence in the last few days of the forecast period is fairly
low. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  20   4  38  22 / 100  50  10  10
CTB  16  -4  30  15 / 100  40  10  10
HLN  28  13  40  28 / 100  50  10  20
BZN  31  13  40  26 / 100  60  10  20
WEY  32   3  32  18 /  80  50  10  30
DLN  33  15  40  25 /  70  40   0  10
HVR  19  -5  23   9 /  90  40  10  10
LWT  19   2  32  19 / 100  70  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until midnight MDT tonight Broadwater...
Cascade...Central and Southern Lewis and Clark...Eastern
Glacier...Eastern Pondera...Eastern Teton...Jefferson...Judith
Basin...Meagher.

Winter Storm Warning until midnight MDT tonight Blaine...
Chouteau...Fergus...Hill...Liberty...Toole.

Winter Weather Advisory until 6 PM MDT this evening Beaverhead...
Madison.

Winter Storm Warning until midnight MDT tonight Gallatin.

Winter Storm Warning until midnight MDT tonight Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
950 AM MDT MON APR 2 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0722 AM     SNOW             3 NW SUN RIVER          47.56N 111.77W
04/02/2018  M3.0 INCH        CASCADE            MT   TRAINED SPOTTER

            VISIBILITY LESS THAT A QUARTER OF A MILE.

&&

JAA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
953 AM MDT MON APR 2 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0953 AM     HEAVY SNOW       12 NE EAST HELENA       46.72N 111.75W
04/02/2018  E1.3 INCH        LEWIS AND CLARK    MT   TRAINED SPOTTER

            REPORTED AT YORK. VISIBILITY 200 YARDS.

&&

JAA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
955 AM MDT MON APR 2 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0955 AM     HEAVY SNOW       2 NW HELENA             46.62N 112.05W
04/02/2018  E2.0 INCH        LEWIS AND CLARK    MT   TRAINED SPOTTER

&&

JAA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
958 AM MDT MON APR 2 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0958 AM     SNOW             BELGRADE                45.78N 111.18W
04/02/2018  E3.0 INCH        GALLATIN           MT   TRAINED SPOTTER

&&

JAA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1002 AM MDT MON APR 2 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1002 AM     SNOW             HELENA                  46.60N 112.02W
04/02/2018  E1.0 INCH        LEWIS AND CLARK    MT   TRAINED SPOTTER

            REPORTS POOR VISIBILITY.

&&

JAA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1003 AM MDT MON APR 2 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0738 AM     SNOW             FAIRFIELD               47.62N 111.98W
04/02/2018  E3.0 INCH        TETON              MT   TRAINED SPOTTER

&&

JAA