Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 301526
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
926 AM MDT Sun Apr 30 2017

.UPDATE...

Chinook arch cloud formation covers much of north central and
central MT this morning as westerly flow, moist in the mid-upper
levels, moves over the Rockies. Embedded shortwave energy now
moving across NW MT/SW AB should help to kick the chinook arch
cloud feature off to the east this afternoon as cooler/less stable
air aloft follows. Showers so far this morning have been
primarily confined to areas along the continental divide with a
few light showers also occurring in some areas beneath the chinook
arch. Expect showers to become a bit more scattered and
convective in nature this afternoon as the airmass becomes less
stable and some breaks of sunshine allow for some surface heating.
Still, westerly flow will likely limit precipitation potential
for areas immediately east of the Rocky Mtn Front. Moderate
westerly flow aloft and surface low pressure moving across
southern AB will provide breezy to windy conditions to much of the
region with afternoon gusts of 20-30kts common across north-
central MT. Hoenisch

&&

.AVIATION...
Updated 1200Z.

Mainly VFR conditions will start the period...then a weak
disturbance will begin to introduce scattered showers this
morning...possibly bringing some brief MVFR conditions. A weak
cold front could then bring another round of scattered showers
this afternoon...with brief MVFR conditions also possible with any
shower activity. Thunderstorm potential looks fairly low today...although
a few isolated storms are possible from KHVR to KLWT and east.
Gusty winds may also follow this front this afternoon across
northern and central sites with gusts to 35 knots. Mainly VFR
conditions are then expected this evening into tonight with
diminishing winds. Showers may then return early Monday
morning...mainly from KCTB to KGTF to KLWT. Anglin

&&

.PREV DISCUSSION...
/ISSUED 546 AM MDT Sun Apr 30 2017/

Today through Monday night...Weak clipper systems looks to return
our recent scattered shower pattern today through Monday. Today`s
clipper will push through this morning with a weak cold front
moving across the region this afternoon and evening. As a result
scattered showers are expected for much of the area...with snow
levels above 5000 feet. Behind this system winds shift to an
increased westerly flow...bringing some gusty winds by this
afternoon to many areas...with gusts of 30 to 40 MPH possible.
These gusty downsloping may also help diminish scattered shower
activity today across some northern and central portions...as the
dry downsloping air will hinder shower chances. Instability looks
to be weak today...however...can`t rule out a few isolated
thunderstorms across eastern and some southern portions this
afternoon and early evening. This initial round of precip then
diminishes tonight...with winds also expected to go on a
diminishing trend. Unsettled nw flow will then be found for
Monday...brining most areas at least a slight chance to chance for
shower activity...with snow levels again remaining around 5000
feet or higher. Instability on Monday again looks weak...although
there is better shear from an exiting jet streak. Isolated
thunderstorms will again be possible on Monday...mainly across
eastern portions. With the mentioned nw flow pattern expected to
continue through Monday night...scattered shower activity could
linger through the night. Temperatures will be fairly close to
normal today...with cooler temperatures expected for Monday behind
today`s cold front. Anglin

Tuesday through Sunday...Much of Montana will be on the cool side of
a northwesterly jet streak Tuesday, with a residual 700-mb front
across the plains slowly washing out through the day. This will keep
showers and possibly a few thunderstorms across the region, and will
allow for maximum temperatures to remain below normal. A pattern
change then begins to take shape for Wednesday through the remainder
of the week as a pronounced ridge moves over the region. This will
result in a dramatic warming trend, with daytime maximum
temperatures rising above normal Wednesday and then continuing
warmer Thursday through Saturday with temperatures as much as 10 to
20 degrees above normal. In fact, the first 80-degree reading of the
season for Great Falls is definitely possible by the end of the
week. By Saturday into Sunday, a large and strong upper level low
will look to close off somewhere over the Southwest US or adjacent
Pacific waters. Such a scenario would cause a highly amplified jet
stream pattern, and may lead to an unsettled weather returning by
the weekend in the form of showers and thunderstorms. Uncertainty is
high at this time but it certainly bears watching. Another more
likely impact from this sudden warming pattern is rising stream
levels from snowmelt at higher elevations. We will continue to
monitor for this potential as we approach the late-week warming
period. Cassell

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  58  34  54  33 /  20  30  40  20
CTB  56  34  53  33 /  10  30  30  30
HLN  59  36  56  35 /  20  10  10  20
BZN  56  32  54  34 / 100  20  10  30
WEY  45  25  44  25 /  30  20  10  30
DLN  55  30  53  32 /  20  20  10  20
HVR  63  37  58  35 /  20  30  20  20
LWT  56  34  51  33 /  40  30  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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