Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 010429

Area Forecast Discussion
National Weather Service Great Falls MT
1030 PM MDT Sun Apr 30 2017



The initial shortwave that brought scattered showers to the area
earlier today is pushing east of the area at this time, with showers
diminishing for most areas. At the same time, a developing cold
front over southern Alberta is just about to push into our far
northern counties (the wind has already shifted around to the NW/N
just north of the International Border). This front is moving a bit
quicker than earlier model and forecast guidance indicated and I
adjusted the wind forecast to reflect this. Ahead of that front,
showers have developed from Cut Bank to Havre. There is very
little in the way of instability in this area. However, LAPS
soundings show an inverted-v profile in this area, indicative of
dry air at the SFC. Because of this, showers along the Hi-line
should be able to mix down some of the stronger winds aloft over
the next hour or so. The Inverness DOT site recently gusted to 50
mph as a shower moved through. That said, the loss of daytime
heating should limit the strongest wind gusts seen earlier, but
gusts of around 30 mph will remain possible. Also of note, the
thinking is showers will gradually diminish along the Hi-line by
Midnight, but trends will be monitored as some short-term guidance
suggests showers may continue a bit longer than currently

The rest of the forecast looks pretty good. The only change I
made was to up QPF/snowfall amounts a bit over Kings Hill Pass as
decent low/mid level moisture enhanced by upslope flow should be
efficient at snow shower development there. Still only looking at
1-3", with little to no accumulation on the pass, itself, due to
warm ground/road temps. Martin


Updated 0430Z.

VFR conditions are mostly expected to continue over the next 24
hours, but brief periods of MVFR conditions and mountain obscuration
may occur with showers. A northwesterly flow aloft will continue low
VFR ceilings and scattered showers across the forecast area. Snow
levels will lower to around 4000 feet by 12Z, so some showers may be
mixed with snow. Partly to mostly cloudy skies with decreasing
showers will are expected after 16Z in the wake of the disturbance.
However, another disturbance will bring another chance for showers
after 00Z. Breezy westerly winds will also persist through the
period over the plains.  Coulston


/ISSUED 535 PM MDT Sun Apr 30 2017/

Tonight through Monday Night...Broad upper level trough exists from
the Northern Rockies into Western Canada today with multiple
embedded shortwave disturbances extending from N-central MT NW into
BC. At the surface, low pressure over SE AB will move east into SK
tonight with low and mid level winds shifting from W to NW tonight
as the troughs shift east. Widely scattered showers forming in the
less stable airmass behind the initial shortwave should be very
light through early this evening before dissipating. Another round
of showers looks to push south from AB into N-central MT later
tonight as additional shortwave energy moves in from the NW and
moves SE across central MT Monday morning. Another weak disturbance
moves from NW to SE across the region Monday evening, triggering yet
another period of shower activity with its passage. Overall
precipitation amounts with all of these disturbances are rather
light with precipitation coverage also somewhat limited. Gradual
cooling aloft will allow snow levels currently at 6000-7000ft to
fall to 4000-5000 feet by Monday morning with afternoon temperatures
on Monday also a few degrees cooler than that of today. Hoenisch

Tuesday through Sunday night...a weak clipper system will dive
southeast through the morning hours on Tuesday, with moist northwest
flow in its wake throughout the remainder of the day and into the
evening hours. This will bring the chance for widely scattered light
rain/snow showers for the day on Tuesday, and even the chance for a
few afternoon thunderstorms generally east of a Havre to White
Sulfur Springs line. It should be noted that the threat for
thunderstorms has decreased significantly from 24 hours ago, and am
thinking that any thunderstorms that do form on Tuesday will be
short-lived (much like the past week). Northwest flow aloft (H700 to
H500) will continue into the day on Wednesday, with lower low level
flow (surface to H850) becoming more westerly. This low level
downsloping flow should bring drier air across the region, with only
some mid to high level cloudiness for the day on Wednesday. Upper
level ridging then quickly builds into the Intermountain West and
Northern Plains Wednesday evening and into the day on Thursday.
Unseasonably warm temperatures for the first week of May should
occur on Thursday, with most locations reaching into the 60s and
70s, which is 10 to nearly 20 degrees above normal. Even warmer
temperatures are then expected to occur on Friday, as the upper
level ridge shifts ever so slightly to the east. Southerly low to
mid level flow will continue, with H850 temperatures reaching 20C to
nearly 25C. These warm H850 temperatures should translate to daytime
highs in the 70s to even low 80s, which is well above normal values.
Was concerned about cloud cover potentially holding down highs on
Friday given the eastward propagation of the upper level ridge and
southwest flow at H500, however, moisture is very limited. Long term
guidance wants to hold onto the warm temperatures even into the day
on Saturday as the ridge transitions to the east and height falls
occur across the region, however, am not confident enough to go as
high as guidance is suggesting. Models then begin to diverge with
the upper level pattern for the second half of the weekend and into
the following work week with the evolution of a significant
trough/closed low. What can be said with some degree of certainty is
that a period of active and cooler weather is in store from Sunday
and into the first half of the work week. - Moldan


GTF  35  54  34  55 /  20  20  30  30
CTB  33  53  33  54 /  20  20  20  30
HLN  38  57  35  58 /  20  10  30  20
BZN  33  54  34  54 /  20  10  60  40
WEY  25  44  25  46 /  30  10  50  30
DLN  32  54  33  56 /  10  10  20  20
HVR  39  59  34  59 /  30  20  20  30
LWT  36  51  33  51 /  30  30  30  50



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