Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 290407

Area Forecast Discussion
National Weather Service Great Falls MT
1007 PM MDT Tue Mar 28 2017



No significant updates to the forecast this evening. Bulk of
forecast continues to be on track, but raised winds somewhat along
the east slopes of the Rockies and south into the Helena area to
better reflect the continued breezy winds. Am expecting them to
decrease after midnight, though.


Updated 0407Z.

VFR at the terminals and westerly flow aloft will persist. However,
the flow aloft will become increasingly moist. This will cause
periods of mountain obscuration and snow showers along the
Continental Divide and the higher terrain farther east in Central
and Southwest MT, especially after 12Z/Wed. Downslope flow, breezy
at times, should keep most of the terminals dry, but a few rain
showers are possible at KHLN after 18Z/Wed.


/ISSUED 503 PM MDT Tue Mar 28 2017/

Rest of today through Thursday Night...The main focus during this
period is the storm system that will impact the Rockies/northern
High Plains Wednesday night through Thursday night. Prior to then,
an upper level ridge combined with high pressure at the surface
should keep most of the area dry. Windy conditions will be found
along the Rocky Mtn Front through tonight and possibly again
Wednesday evening for a short time. Wind gusts of 40-55 mph are
likely there. Below are some main takeaways regarding the incoming
system that will drop SE through the Pac NW and close off/deepen
over the Four Corners region.

* RAINFALL: The setup with this system favors some decent liquid
  precip amounts, potentially on the order of 0.15-0.30", especially
  along/south of a Great Falls to Lewistown line. However, with this
  system, there will likely be one or more bands of heavier precip
  and it is simply too early to know where those bands will be. It
  must be stressed here that confidence in precip amounts is
  moderate at best. The heavier bands of precip could put down a
  half inch, liquid, or more, while areas outside of the bands may
  see much lower amounts.

* SNOWFALL: For most of the event, snow levels will likely hover
  around 6000-7000 feet. However, any area that sees heavier precip
  rates, especially by Thursday night, could see snow levels drop
  all the way down to the valleys/plains for a time. Light to
  moderate snowfall accumulations look likely above 6000 ft. Below
  this level, snowfall accumulations will be highly dependent on
  snowfall rates/temperatures and confidence in accumulating snow is
  much lower there.

* IMPACTS: At this time, significant impacts from rain and/or snow
  are not anticipated. However, there could be some travel impacts
  over mtn passes, especially SW MT passes. The impacts might be the
  greatest Thursday night as temps fall and road surfaces cool.
  Regarding rainfall amounts, we are not expecting widespread
  flooding concerns, but will monitor this closely during the event.

* CONFIDENCE: Overall confidence in the event is moderate. And,
  again, it must be stressed that QPF/snowfall amounts are very much
  subject to change as details become clearer over the next couple
  of days, and some details may not be ironed out until closer to
  the event, itself.


Friday through Tuesday...Fairly quiet weather will reside over the
region to begin the weekend. Showers will generally be ending on
Friday morning as the main storm system from the middle portion of
the week exits the region. By late in the weekend and into Monday,
significant difference develop between the EC and GFS. The National
Blend is significantly higher for pops for this period with the main
area of low pressure developing over far southeast MT. The EC has
very little precipitation as the main storm system develops over the
Central Plains. Thus blended the pops for now. Additionally,
temperatures look to be cooler during this period, with the GFS much
cooler. If the GFS does pan out, the airmass will be cold enough for
mostly snow, and a significant snow event would occur over the
region. Otherwise, seasonable temperatures are currently forecasted
through the period until some trend for early next week can be
determined from the models. Brusda


GTF  38  61  43  52 /  10  20  20  60
CTB  34  54  37  50 /  10  20  10  30
HLN  35  61  41  46 /  10  20  40  70
BZN  29  58  39  48 /  10  30  40  70
WEY  16  41  30  38 /   0  30  70  80
DLN  27  56  37  45 /  10  20  50  80
HVR  33  62  39  56 /  10  10  10  30
LWT  33  59  40  50 /  10  10  20  70



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