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KEY MESSAGES

- Blizzard Warning & High Wind Watch this afternoon through Wednesday exist for possible whiteout conditions.

- A significant change in the weather pattern begins tonight with below normal arctic temps starting Wednesday and lasting through Friday before a slow rise to near normal early next work week.

DISCUSSION

WEATHER PATTERN OVERVIEW: A surface low pressure system will form a quasi-lee side trough/frontal boundary oriented from northwest to southeast and drive that east across eastern Montana. This boundary will become the focus of a strong pressure gradient force on both sides pulling the wind in from the east northeast of it and west to northwest on the southwest side. Winds will reach high enough for high wind on both sides this afternoon with a brief drop off as the boundary passes any given point this afternoon into this evening. A line of rain showers is expected to form up along the boundary this afternoon and move east with... then thicken up as it transitions to all snow into the evening. This currently looks like a one and done precip event until it reaches about Valley county where it should swing north and then stall along the international border overnight. And snow that snow that fills in with the high wind areas could easily start whiteout conditions into the night and perhaps somewhat into the morning hours. Currently the big sheeps do not look like they will be impacted long enough and by nearly enough snow to generate the white out conditions, so those counties were determined to be more Winter Weather Advisory level.

Much colder Arctic air moves into NE Mont filling in the trough tonight with lows Wednesday night becoming near or below zero again. The Arctic air will remain over the area into Friday and then a very slow warm up to near normal is expected early next work week.

FORECAST CONFIDENCE & DEVIATIONS: HIGH confidence in a period of blowing snow with potential whiteout conditions in most of the northern/eastern zones tonight.

MODERATE confidence in snow totals for this event. There has been some slow reductions in snow totals 6" to 4" along the international border from run to run which has lowered this confidence in the last 2 updates.

HIGH confidence in strong winds (40-50 mph) through Wednesday morning.

MODERATE confidence in high winds (55-60 mph) looking at NBM and HREF probabilities.

GAH

AVIATION

LAST UPDATE: 0800Z

FLIGHT CAT RANGE: VFR - Airport shutdown.

DISCUSSION: VFR ceilings & Vis through roughly 20Z.

A strong system moving in will gradually lower ceilings in the late morning and early afternoon with MVFR ceilings settling in across the north around mid-afternoon along with light rain. Incoming cold air will transition rain to snow through the later afternoon and early evening. IFR and then possible LIFR conditions will be possible with any snow once it turns over. Strong to high winds winds could lead to blizzard conditions and possible airport shutdown if only briefly at the KOLF and KGGW terminals. Snow should end at all the TAF terminals with only MVFR ceilings by about 12Z Wednesday.

LLWS: There is a chance for low level wind shear at the terminals through 14Z this morning.

GAH

GGW WATCHES/WARNINGS/ADVISORIES

High Wind Warning from 11 AM this morning to 5 AM MST Wednesday for Central and Southeast Phillips-Dawson-Garfield-McCone- Petroleum-Prairie-Southwest Phillips.

Blizzard Warning from 2 PM this afternoon to 5 PM MST Wednesday for Central and Southern Valley-Daniels-Eastern Roosevelt-McCone- Northern Phillips-Northern Valley-Sheridan-Western Roosevelt.

Winter Weather Advisory from 4 PM this afternoon to 6 AM MST Wednesday for Dawson-Prairie-Richland.