Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/19/21

Area Forecast Discussion

National Weather Service Glasgow MT

 253 PM MDT Sun Apr 18 2021

.DISCUSSION...

...Accumulating snow expected today for the Little Rockies and
Petroleum County...

AFTERNOON UPDATE:
With the latest update, snow was trimmed back even further.
Southwest Phillips county over the Little Rockies now appears to
be the only place where significant snow is likely. Will however
leave the petroleum county Advisory up on the off chance that rain
could transition back to snow in a significant form later this
evening as the possibility while reduced still does exist. In fact
there was an hour this early afternoon at KGGW where the rain
attempted to transition to snow briefly before moving back to
rain. So a minor change in wet-bulb aloft could easily reverse
this fortune.

The rest of the forecast looks to remain mostly unchanged through
Thursday just before another cold front arrives. Ensemble data
sets appear to phase out of agreement with each other from Friday
onward with these time periods trending colder slightly.
Confidence from here onward is low. GAH

815AM UPDATE:
Snow coverage is highly sensitive to minor temperatures and
dewpoint fluctuations through the day today. Started from
observations and used the ConsShort diurnal curve to get the rises
and falls correct over the day. This raised hourly temperatures
and dewpoints over lower elevations which eliminated a lot of
snow today in the valleys and coulees. Meanwhile, mountains, ridge
tops and plateaus maintained most of their snow coverage which
kept the far west of petroleum county under significant enough
snow to maintain the Advisory. GAH

MORNING DISCUSSION:
A cold frontal passage today will lead to steady or falling
temperatures across the region. Meanwhile, a mix of rain and snow
will transition to snow as things shift south this evening. The
steadiest precipitation will occur over the Little Rockies and
Petroleum County where 2 to 4 inches of snow may accumulate. This
will lead to reduced visibility and slippery road conditions. In
addition, the cold and wet weather will likely stress out newborn
livestock. Consideration was given to adding blowing snow over the
Little Rockies, though wind speeds are a bit marginal. Especially
if it falls as a wetter snow or the ground starts off wet, it may
be a bit harder to get true blowing snow conditions. Drifting
snow across area roadways is certainly possible, and will need to
continue monitoring for the potential for blowing snow.
Regardless, a Winter Weather Advisory is now in effect for SW
Phillips and Petroleum Counties from 9 AM this morning until
Midnight tonight. A Lake Wind Advisory has also been hoisted due
to gusty conditions expected for the Fort Peck Lake area.

Snow will taper off tonight, though lingering instability driven
rain and snow showers are certainly a possibility into Monday as
the upper level low remains over the forecast area. Ensembles show
the height pattern reflecting a ridge toward the middle of the
week building across SW Canada and the Pacific Northwest extending
into the Northern High Plain, oriented in a west to east fashion.
This will lead to gradually moderating temperatures and dry
weather conditions due to larger scale subsidence.


&&

.AVIATION...
LAST UPDATE: 2015Z

FLIGHT CAT: VFR - IFR

ICING: With low clouds generating precipitation and surface
temperatures so close to freezing, there is a chance for icing on
aircraft surfaces with these clouds/ceilings. This threat should
begin to diminish around 06Z.

DISCUSSION: MVFR ceilings are expected through mid-afternoon. rain
could transition to snow over some higher elevations. This would
bring brief IFR visibilities to the areas southwest of the
terminals though it is not out of the realm of possibility that it
could briefly impact a single terminal like KGGW or KGDV before
the day is over. VFR ceilings are anticipated again after about
22Z this afternoon.

WIND: North to northeast at 10 to 20 kts gusting to 25 kts
through the early evening. Then becoming north and calming to 5
to 15 kts around midnight and lasting through Monday afternoon.

GAH


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight MDT tonight for
Petroleum...Southwest Phillips.

Lake Wind Advisory until 9 PM MDT this evening For Fort Peck
Lake for Central and Southeast Phillips...Central and Southern
Valley...Garfield...McCone...Petroleum.

&&

$$

weather.gov/glasgow