Dec 7, 2011 10:10 AM by Meteorologist Mike Heard
The long range forecast up to Dec. 23 utilizes the GFS weather model. Of course conditions could change during the next three weeks, but this is the latest forecast data we are analyzing.
Large high pressure system off the Pacific NW coast which has kept Montana under a NW flow and cold lately will begin to swing inland by Friday. Right now this off shore ridge and NW flow aloft over Montana will push a weak system in tonight and Thursday morning with a weak cold front and scattered light snow for the valleys and mountains, enough snow to cause icy roadways to develop.
Beginning Friday and into the weekend the off shore ridge moves inland and weakens just a bit, but overall it should produce a prolong period of dry stable atmospheric conditions with a minor short wave undercutting the ridge periodically with limited impacts.
Under such a large stable ridge will come air stagnation problems in the form of inversions with worsening air quality and patchy valley fog. This pattern could continue throughout most of next week. Not the best news for ski resorts hoping for new snow as many of our local resorts will open on a limited bases this weekend.
When do we expect the next round of active weather to hit? The latest GFS model run this morning has storm systems arriving on Dec. 16, it looks weak right now and it should be a quick shot of moisture through Montana.
Right on its heels is a larger storm that will impact the state Dec. 18 through the 20. This system digs along the Pacific NW coast and into Northern California before moving inland. These types of storms tend to favor the upslope mountain ranges along the Montana/Idaho border with heavier snow and with drying downsloping conditions east of the divide with plenty of wind. For SW Montana it appears the 19th and 20th will be our best shot for new snow over the ski resorts.
Another storm system builds off shore on Dec. 21 and digs into the Pacific NW and northern California. A SW surface flow could develop for Montana producing a slight warm up in temperatures. A developing low pressure system will move into Utah and Colorado by the 23rd. This type of weather pattern can bring a good fetch of moisture into eastern Idaho, Yellowstone National Park and across SW Montana or areas South of I-90.
Recapping the weather scenario for the next couple of weeks then, next week looks fairly calm and quite with High pressure overhead. December 16th through 23rd will be an active weather period across much of the western US and especially throughout the pacific NW and Rocky mountain states.
Good news for ski resorts looking for new snow right before the holiday vacation season!