Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 282105

Area Forecast Discussion
National Weather Service Great Falls MT
305 PM MDT THU JUL 28 2016


Thursday through Saturday...The unsettled pattern of late will
gradually transition into a drier pattern heading into the
weekend. That said, the threat of at least a few thunderstorms
will exist each day through Saturday.

For the rest of today, storms have begun to develop in and just
to the SE of the higher terrain. Still thinking that will be the
favored area for storms through this evening. A weak s/w moving
through the area tonight may be enough to keep at least a low-end
chance of showers and storms going through the night, especially
across north-central Montana. With higher than normal PWats still
over the area, the strongest storms through tonight could put down
some heavier rainfall totals with isolated amounts up to 1 inch
not out of the question. Again, though, these higher amounts will
be the exception. Most storms will likely put down 0.25" or so.
Shear will increase some later today, but weaker instability
should limit the threat of stronger storms. Frequent lightning,
gusty winds, and heavy rainfall should be the main threats. Friday
looks similar to today with storms mainly being confined along and
just SE of the higher terrain within the NW flow pattern. And,
again, gusty winds, frequent lightning, and heavy rainfall look to
be the main threats. Shear/instability may be a bit better Friday
compared to today, so some hail cannot be ruled out with the
strongest cores.

On Saturday, an upper level trough will begin to build into the
Pacific NW with a SW flow pattern developing. With less moisture
and instability, though, thinking most areas will remain dry
Saturday. The only exceptions will be across SW MT and up along
the Hi-Line where isolated showers/storms will be possible. Along
the Hi-Line, modest shear/instability is expected which may lead
to the potential of a few stronger storms. However, for now, it
appears the best coverage of storms will be north of the
International Border, but something to keep an eye on. The wind
may increase some on Saturday as well, which combined with well
above normal temperatures and and low RH values could cause some
fire wx concerns. At this time, the wind doesn`t look strong
enough for any fire weather highlights, but something we will be
monitoring. Martin

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.


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


GTF  60  88  58  94 /  20  10  10   0
CTB  57  83  56  88 /  20  10  10  10
HLN  61  91  61  95 /  20  10  10  10
BZN  55  88  53  93 /  20  10  10  10
WEY  49  78  44  81 /  10  10  10  10
DLN  55  87  54  90 /   0   0   0  10
HVR  60  85  60  92 /  20  20  10  10
LWT  56  83  58  89 /  20  20  10  10



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