Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 281750
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1149 AM MDT THU JUL 28 2016

...Aviation Section Updated...

.UPDATE...

In the wake of last night`s s/w, skies are clearing out across the
area, with generally quiet conditions at this time. For this
afternoon, still expecting a lower coverage of showers and storms
(ie. isolated to widely scattered) as there isn`t any significant
lifting mechanism expected (outside of the higher terrain). With
the NW flow in place, storms should mainly be confined along and
SE of the higher terrain and mainly across central Montana. That
said, short term models suggest a few storms may be able to move
off the terrain and into the plains by late this afternoon or
evening, especially SE of the Little Belts/Snowies. Increased
pops a bit in this area to account for this. Elsewhere, no
significant changes were needed. Of note, though, added slight
chance pops along the Hi- Line after midnight as a weak s/w may
provide just enough lift for a few showers or storms to develop
there overnight.

Like with yesterday, the main threats from any storm today will be
frequent lightning, gusty winds, and heavy rainfall. PWats are
still running above normal for late July (ie. 0.94" on the 12z TFX
sounding this morning) and storms have been efficient precip
producers lately. For those areas that do see a stronger storm
through tonight, amounts of over 0.50" cannot be ruled out.
Martin

&&

.AVIATION...
Updated 1749Z.

A moist and unstable NW flow should allow isolated to scattered TSRA
to develop this afternoon and evening, especially across central
Montana. TSRA should generally be confined along and to the SE of
the higher terrain. However, a few TSRA may make it out into the
plains of north-central Montana. In general, confidence is lower
regarding TSRA at any TAF site, so kept with VCTS for now, and only
at KCTB/KGTF/KHLN/KLWT. Amendments may be needed later if confidence
increases. Gusty winds and MVFR VIS will be possible with any TSRA
that develops. Otherwise, expect VFR conditions to prevail through
18z/FRI. Martin

&&

.PREV DISCUSSION...
/ISSUED 555 AM MDT THU JUL 28 2016/

Today through Saturday...Northwest flow aloft continues over the
region with weak embedded disturbances. Mid-level temperatures are
gradually warming, but still expect just enough instability to
generate isolated to scattered afternoon showers and
thunderstorms. Most of this activity will be confined to the
higher terrain, but any storms that can develop could produce
brief downpours as precipitable water remains above about 0.8 inches.
Temperatures remain near to just below seasonal averages today,
but then trend warmer through the weekend. The warmest
temperatures are expected Saturday as highs reach the mid-90s for
many locations. PN

Saturday night through Thursday...Not a lot of change regarding the
medium range forecast. Very warm westerly flow aloft develops Sunday
as a closed upper low moves across central Canada. Precipitation
from this feature continues to look as though it will stay north of
the border. Winds will increase a bit Sunday as the pressure
gradient tightens and the combination of the very warm temperatures,
low relative humidity, and increasing winds could raise fire weather
concerns. Also Sunday, monsoonal moisture is drawn up into southwest
Montana where isolated afternoon thunderstorms will be possible.
Monday will be dry and not as warm as cooler air will make its way
across the area in the wake of the upper low pushing east. By
Tuesday, another closed upper low approaches western Montana as it
moves along the international boundary. The models differ in their
structure and movement of this feature. The GFS depicts this feature
as a closed upper low while the ECMWF depicts it as a broad upper
trof. Regardless, scattered afternoon and evening thunderstorms will
be possible across the north and over the eastern portion of the
county warning area. By Wednesday, isolated thunderstorms will be
confined to the Hi-Line as the upper disturbance continues to slowly
move east. 500 mb heights rise on Thursday bringing dry conditions
but, as was the case with the earlier scenario, cooler air will
filter across the area as the second upper disturbance moves east.
Temperatures will be above seasonal averages Sunday but afternoon
readings will slowly decline to below seasonal averages by the end
of the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  83  60  88  58 /  20  20  10  10
CTB  81  56  84  56 /  20  20  10  10
HLN  86  61  91  61 /  20  10  10  10
BZN  83  55  89  53 /  20  10   0   0
WEY  79  47  79  44 /  20  10  10  10
DLN  83  55  87  54 /  10   0   0   0
HVR  82  60  86  60 /  10  10  10  10
LWT  77  58  83  58 /  20  20  10  10

&&

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

$$

weather.gov/greatfalls



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