Tuesday, December7, 2021
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Marine Weather and Tides
Big Sky, MT

Version 3.4
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3/30/2021 -- ANZ330 has been split into ANZ331 and ANZ332. Click EDIT in Marine Forecast and select your new zone.
1/26/2021 -- The West Coast Satellite images havd been updated. They now use GEOS-17.
1/1/2021 -- The 7 day forecast are now working well. Thank you NOAA for your support.

Sunrise 7:48AMSunset 4:42PM Monday December 6, 2021 11:18 PM MST (06:18 UTC) Moonrise 10:45AMMoonset 7:13PM Illumination 9% Phase: Waxing Crescent; Moon at 3 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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7 Day Forecast for Marine Location Near Big Sky, MT
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location: 45.26, -111.31     debug


Area Discussion for - Great Falls, MT
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FXUS65 KTFX 070553 AFDTFX

Area Forecast Discussion National Weather Service Great Falls MT 1050 PM MST Mon Dec 6 2021

. UPDATED AVIATION SECTION .

SYNOPSIS.

A disturbance in the northwest flow aloft will bring periods of light snow to the region the remainder of this afternoon into tonight, with the greatest amounts focusing in the central Montana mountain areas. Temperatures in the southwest will remain near seasonal averages, but frigid conditions remain on the plains. Westerly winds will likely increase Tuesday into Wednesday, causing temperatures to warm up to 10 degrees above normal by Wednesday, but also potentially bringing another round of strong winds.

UPDATE.

The evening update has been published. Snow continues to wind down tonight, but some light snow continues over the southwest passes and will likely persist into the overnight hours. The Winter Weather Advisory for the Little Belt Mountains and surrounding area was canceled early since things were clearing up ahead of schedule. Some partial clearing has taken place over north-central areas, but low stratus is filling in some of the gaps. Pops, wind, sky, and low temperature grids were freshened to keep up with current trends. -RCG

AVIATION. 1050 PM MST Mon Dec 6 2021 (07/06Z TAF period)

North Central (KCTB KHVR) and Central (KGTF KLWT KHLN) Montana: Areas of low VFR/MVFR ceilings and patchy fog will linger over the plains through around 10Z, causing mountain obscuration. Between 10Z and 16Z, the low clouds and fog will dissipate, leaving mainly mid- and high-level cloudiness to pass overhead for the remainder of the 24-hour period. However, westerly downslope winds will increase during the day, potentially causing gusts in excess of 35 kt, mainly after 00Z and mainly close to the Rocky Mountain Front, as well as causing mountain wave turbulence and periods of low level wind shear.

Southwest Montana (KBZN KEKS): Low VFR/MVFR ceilings with areas of light snow and patchy fog will cause some mountain obscuration through around 14Z. After 14Z, fog and snow will diminish and ceilings will mostly lift to lower-level VFR, continuing as such through the remainder of the day. -Coulston

Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information.

PREV DISCUSSION. /ISSUED 140 PM MST Mon Dec 6 2021/

Today through Tonight .

Current snow event is now underway with snow primarily developing along the north and east side of a stationary front over the area. Current thinking with the Winter Weather Advisory area still looks good and no changes were made with the early afternoon forecast package. Max temperatures this afternoon were lowered to only the 5th percentile of the NBM range of probabilities, but this in line with statistical guidance across much of the state, resulting in much colder forecast high temperatures especially for areas north and east of Great Falls on the cold side of the front. Once the disturbance passes through the area this evening, any lingering light snow will be mostly limited to the mountains of central and southwest Montana overnight into Tuesday morning. I again lowered overnight temperatures to the NBM 10th percentile to match up with MOS guidance, especially on the cold side of the front over north-central Montana. Lows fall back into the single digits below zero to lower teens above zero over the plains, but 20s are likely in the southwest.

Tuesday through Wednesday .

The flow aloft will shift more westerly during this period, as a high pressure ridge off the Pacific coast starts to move back onshore. With initially weak warm advection initially for Tuesday helping to strengthen the low-level inversion and keep the near- surface cold in place, I trended max temperatures for Tuesday lower to near the NBM 25th percentile across the region, again in line with MOS (statistical) guidance. Weak disturbances riding over the ridge will steadily flatten it and cause winds to become quite strong, as 700-mb winds increase to around 80 kt on the Rocky Mountain Front Tuesday night with 60 to 70 kt wind spreading out onto the plains. Winds in the layer from 700 mb to near the surface will similarly increase to around 65 kt on the Front and between 45 and 55 kt over the plains. The surface pressure gradient will only be strong close to the Rocky Mountain Front Tuesday night, allowing the strong winds to initially remain there overnight. The gradient will then spread out onto the plains on Wednesday ahead of a shortwave trough and associated Canadian cold front approaching from the northwest. As of right now, this does not appear to be a widespread damaging wind event, but gusts up to 60 mph are possible in the Cut Bank area and gusts up to 75 mph are possible close to the Front. Though admittedly marginal, we may also need to issue a High Wind Watch for Judith Basin County in the lee of the Highwood and Little Belt Mountains for Wednesday morning for gusts approaching 60 mph. I have kept the High Wind Watch for the Rocky Mountain Front for Tuesday evening through Wednesday evening with no other changes for the afternoon package. The passage of the disturbance and cold front will help decrease the winds Wednesday evening. Overall, the downsloping effect from the winds will limit any precipitation to the mountains and temperatures warming up to 10 degrees above normal will likely help keep mountain pass snow minimally impactful. Cassell/Coulston

Thursday through next Monday . The progressive weather pattern continues through the late-week and weekend periods into early next week, as breezy westerly downslope winds generally keep any precipitation in the mountains. A large-scale broad low pressure trough will move into Montana for Thursday and Friday, which will keep temperatures close to seasonal averages for that period. Another low pressure trough moving out of the Gulf of Alaska will likely shift a high pressure ridge from of the Pacific coast onshore. This familiar pattern will likely bring warmer than normal temperatures once again, but this could also be another period of potentially strong winds over the plains, especially on Saturday. -Coulston

PRELIMINARY POINT TEMPS/POPS. GTF 9 37 34 47 / 60 10 10 0 CTB 0 33 27 41 / 30 0 10 20 HLN 16 40 34 48 / 60 10 0 20 BZN 23 40 29 47 / 70 20 0 20 WYS 17 29 24 33 / 70 30 30 70 DLN 26 40 27 44 / 40 10 0 30 HVR -8 19 14 44 / 40 0 10 0 LWT 7 33 27 45 / 80 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES. High Wind Watch from Tuesday evening through Wednesday evening Eastern Glacier . Northern Rocky Mountain Front . Southern Rocky Mountain Front.



http://www.weather.gov/greatfalls


Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Bozeman, Gallatin Field, MT38 mi22 minW 46.00 miLight Snow Fog/Mist29°F27°F92%1015.7 hPa

Link to 5 minute data for KBZN

Wind History from BZN (wind in knots)
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This dayS6SE60SE40SE3SE4N3000N60300SE3W9W5SW6W60SW5W4
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