Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 291715

Area Forecast Discussion
National Weather Service Great Falls MT
1115 AM MDT Sat Apr 29 2017

Updated Aviation Discussion


Satellite imagery this morning reveals an elongated shortwave
disturbance over Western MT moving east ahead of and upper level
ridge with axis along the Pacific NW coast. Mostly clear skies
across the forecast area this morning will give way to increasing
cumulus development as the disturbance moves east of the divide
this afternoon and the airmass destabilizes with plenty of low
level moisture in place. Showers and a few isolated thunderstorms
are likely to develop east of I-15 though coverage looks rather
limited with greatest concentration of showers likely to occur
over Judith Basin, Fergus and Blaine counties. Shear/instability
parameters are rather weak with small hail/graupel being the main
impact from the more intense cells that develop this afternoon.


Updated 1715z.

Scattered cumulus early this afternoon will evolve into scattered
showers and possibly an isolated weak thunderstorm or two, primarily
across eastern portions of central and north-central MT. VFR
conditions generally prevail with some brief periods of Mtn
obscuration and MVFR cigs/VIS in the vicinity of showers this
afternoon. Surface winds will become somewhat breezy from the SW
this afternoon then diminish tonight. Drier conditions this evening
will give way to increasing cloudiness late tonight into Sunday
morning as the next upper level disturbance approaches from the
west, spreading showers into western and SW MT by late Sunday
morning. Hoenisch


/ISSUED 306 AM MDT Sat Apr 29 2017/

Today through Sunday night...Upper disturbance roughly located
over western Montana this morning moves east while sharpening
slightly through this afternoon. Sufficient instability and low-
level moisture exists (despite increasing cross-barrier flow) for
isolated to widely scattered showers and a slight chance of
thunderstorms to develop mainly east of Interstate 15. The main
impacts from any of these showers/storms will be the potential to
produce graupel restricting visibility on roads. However, with the
showers/storms being quick movers significant accumulations on
roads like, which have occurred at times this past week with
slow-moving showers/storms, seem less likely. Very weak ridging
builds across the region this evening as this system tracks
quickly east away from our region, only to be followed by yet
another system moving toward the region from the Pacific NW.
Showers may develop as early as the early morning Sunday over the
Rocky Mountain Front, with shower/thunderstorm activity expanding
east through the remainder of the region through the day and
evening Sunday. Unsettled weather then continues Sunday night as a
front drops southeast from Canada across northern and eastern
areas of our region, with a chance of rain and high-elevation snow
showers continuing into early Monday morning. Cassell

Monday through Saturday...Overall active weather to start the
upcoming work week...becoming warm and dry mid week...then some
uncertainty towards next weekend. Unsettled northwest flow will be
found Monday through Tuesday as a large upper low is found across
the Midwest...and a ridge of high pressure builds in the Pacific
Northwest. Monday`s activity looks to be scattered with snow levels
above 5000 feet. A weak disturbance in the northwest flow may bring
more widespread showers on Tuesday...with snow levels possibly
lowering to 4000 feet on Tuesday morning. More instability and
increased shear from a strong jet streak will also be found
Tuesday...creating perhaps some scattered thunderstorms during the
afternoon hours. We then see the long awaited return of ridging on
Wednesday...which now looks to continue through the day Thursday.
Warm temperatures and mainly dry conditions are expected...with
perhaps some breezy winds at times. Most models indicate a cold
front will move through at some point on Friday...returning chances
for showers to much of the area. The weekend then becomes the most
uncertain part of the forecast. Most models develop some sort of
large disturbance across the western US coast. How it influences our
weather pattern by the weekend is still up for interpretation. For
now it is a monitor type weather may
continue through next weekend. Temperatures look to remain below
normal through Tuesday. Ridging and downsloping flow could then
return high temperatures in the 60s and perhaps 70s Wednesday and
Thursday. Friday into Saturday could even be near to above normal
temperatures. There is some concern warm temperatures combined with
melting of fresh mountain snow could bring some flooding concerns by
mid to late next week. Another item to keep a close eye on in the
long term. Anglin


GTF  56  41  58  35 /  10  10  20  20
CTB  54  40  55  35 /  10  10  20  20
HLN  59  42  59  37 /  10  10  30  10
BZN  53  35  57  33 /  10  10  30  30
WEY  44  26  46  25 /  10  10  30  30
DLN  53  37  55  32 /  10  10  20  20
HVR  60  41  63  38 /  20  10  20  20
LWT  52  37  57  34 /  40  20  30  20



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