Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/02/21

Area Forecast Discussion

National Weather Service Glasgow MT

 231 PM MST Fri Jan 1 2021

.DISCUSSION...

AFTERNOON DISCUSSION:
Synoptic Setup: Forecast begins with a ridge of warm air being
kicked out and a weak disturbance moving across northeast Montana
overnight. Behind this a large ridge and trough exist over the
Pacific Northwest with another ridge setting off the Pacific
Coast. With flow being zonal this parade of pacific systems will
be the main story through the forecast keeping things unseasonably
warm or nearly 15 to 30 degrees above normal.

This afternoon through Saturday: The ridge will exit the area
around midnight with a weak cold front on its heels. This passage
will have just enough moisture to put down a trace to maybe two
hundredths of an inch of precip. With the very strong warm nose
aloft much of the snow will melt into rain, which may in turn
freeze on pavement. Timing of the passage is from around 09Z to
18Z. Models are in broad disagreement about QPF/PoPs with the
passage of this system and about half the ensembles hint at no
precip happening with the passage. So, confidence this close to
the event is low with impacts being marginal. Therefore, have
decided not to issues winter weather advisory for freezing rain
yet and allow the the evening shift one last stab at it.

Saturday night through Sunday night: While Saturday night will be
uneventful with a ridge, the second the ridge exits a relatively
strong cold front will come barrelling through. Its expected to
hit around the middle of the day Sunday with CAA lasting well
through the evening. Looking at lapse rates hitting nearly 8 *C/km
and 850 mb windspeeds bumping to 50 kts in multiple models have
high confidence and decided to go ahead and issue a High Wind
Warning for southwest Phillips county. This could expand to
surrounding areas down the line but for now other areas look
marginal and not likely to hit that 40-50 kt range needed.

Monday throuh Wednesday: These periods look similar to the
previous forecast periods with unseasonably warm conditions
continuing, if maybe trending down a degree or two each day.
There is even another frontal passage with weak QPF expected and
rain/snow/freezing rain possible Tuesday.

Wednesday night onward: Models ensembles are too far apart to
predict more than unseasonably warm conditions continuing.
Confidence from here onward is low. GAH


815AM UPDATE:
Changes to the forecast this morning were mainly to bring sky
conditions back into alignment. The bulk of NBM`s ensembles
appeared to previously had fog hanging in quite awhile today which
increased sky coverage. With the GOES NightFog Product showing the
bulk of it dissipating from southwest to northeast it should be
gone by about 18Z. The latest model ensembles seem to have finally
caught on are rapidly clearing the afternoon and evening hours to
partly cloudy for the northern half of the CWA.    GAH


MORNING DISCUSSION:
High pressure has brought some patchy areas of low clouds and
freezing fog along the International border and near the Montana
North Dakota state line that should last through the morning of
the New Year. The weak ridge will keep conditions dry today with
periods of sunshine for northeastern Montana.

A trough currently off the US west coast will pass through the
region, increasing the potential for light precipitation and
stronger winds this weekend. Temperatures will continue to warm
through this timeframe. Overnight temperatures will be cold
enough for snow, but warm westerly winds will promote a variety of
wintery options Saturday morning. Prepare for the potential for
any precipitation type if you plan to travel, especially in the
morning. Precipitation that falls in the afternoon should be rain.
Once the sun sets, temperatures will cool to below freezing, and
any POP and thus ptype will change over, but by then could be on
its way into the Dakotas. On Sunday, some folks could have
temperatures hitting 50 degrees. With 850mb winds in the 40 to 55
kt range across the area, confidence is growing for a breezy
weekend with westerly wind gusts in excess of 40 mph. Higher lapse
rates in the west and southwest in addition to potential
downsloping from higher terrain may increase daytime high
temperatures above model guidance and bring locally higher wind
gusts to the surface on Sunday.

A progressive pattern will continue through the forecast period,
with warmer and drier than normal weather into next week. Episodic
shortwaves will bring a couple more opportunities for moisture,
however light.

Roxy


&&

.AVIATION...
LAST UPDATED: 2130Z

FLIGHT CAT: VFR

DISCUSSION: A cold front will move through the area from
09-18Z. Very light precipitation will be possible but not likely
with its passage. With ground frozen, any potential rain could
easily freeze on contact with runsways increasing breaking
distance.

LLWS: Around 14Z Saturday to just beyond the end of the TAF
cycle, low level wind shear will become a problem as a cold front
works its way past northeast Montana. Strong winds above may not
be able to reach the surface initially. This will create a strong
speed shear difference for aircraft approaches.

WIND: West and southwest at 5 to 10 kts this afternoon through
tonight. Veering to the west and increasing to 10 to 20 kts
Saturday afternoon.

GAH


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 11 AM to 11 PM MST Sunday for Southwest
Phillips.


&&

$$

weather.gov/glasgow