Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 222350

Area Forecast Discussion
National Weather Service Great Falls MT
550 PM MDT FRI JUL 22 2016

Updated Aviation Section


Tonight through Saturday...Vigorous shortwave trough currently
moving into the ID Panhandle will shift into NW MT tonight and lift
out to the NE across southern AB/SK Saturday. W to E moving cold
front ahead of the trough has entered NW MT and will sweep east
across the forecast area late this afternoon through early this
evening. Convection has initiated along a SW to NE axis from
Southern Beaverhead county through the Little Belts and this
activity is expected to increase some in coverage and strength
through the rest of this afternoon as it tracks NE across eastern
portions of central MT. Also seeing come convective initiation along
the Rocky Mtn front where a few storms are also expected to develop
and lift NE across Far NW portions of the forecast area through
early this evening. Primary threat from storms today will be strong
winds due to a dry low-level airmass, particularly over SW MT with
increasing winds aloft also contributing to the high wind threat.
Deep mixing has developed in the hot/dry airmass over SW MT where
winds will gust from the SW ahead of the front with a shift to W/NW
expected late this afternoon and evening. Convection diminished
rather quickly this evening with a few showers lingering in the
Glacier park vicinity, closest to the passing shortwave trough.
Surface low pressure trough shifts east into the Dakotas Saturday
while high pressure builds in from the west, maintaining enough
pressure gradient for breezy west winds across much of the area,
though temperatures will cool by about 10-15 degrees from todays
values and closer to seasonal averages. While most of the area will
be dry, some weak shortwave energy in NW flow aloft could set off a
few isolated showers and thunderstorms late Saturday afternoon,
primarily along the Canadian border and possibly over the Mtns of
central/SW MT. Hoenisch

Sunday Night through Friday...High pressure ridging centered
near/slightly west of the Four Corners area will remain in place
through this period. That will keep our region under west-southwest
flow aloft, leading to very warm temperatures and mostly dry
conditions.  Weak disturbances moving through the flow will combine
with a mix of Pacific and monsoonal moisture to produce isolated
thunderstorms each afternoon, mainly over the central and Hi-Line
counties.  Given the spotty coverage pattern of the moisture and dry
near-surface conditions (aftn humidities in the teens and low 20s),
convective activity on Mon-Wed will likely be a mix of wet and dry
(<0.1 inch rainfall) storms.  Gusty outflow winds and possible fire
starts from lightning are the primary threats from these storms in
the first half of next week. Storm type will trend wetter for
Thurs/Fri as slightly higher moisture is expected after a cool front
passes across the region Wed night. High temperatures will run 5-8
degrees (upper 80s to low 90s) above normal before the cool front
arrives and then drop back close to seasonal values (mid 80s) on
Thurs/Fri. Waranauskas


Updated 2350z.
Surface cold front will move across the area overnight. Gusty
southwest winds ahead of the front will shift to the west-northwest
behind the front and remain gusty through the night. Isolated to
scattered thunderstorms will gradually end by 06z. VFR conditions
prevail with MVFR conditions possible in the vicinity of
thunderstorms along with gusty erratic winds.


Deep layer mixing and increasing southwest winds this afternoon
will cause minimum relative humidity to fall below 15 percent over
the southern districts. A Red Flag Warning is in effect for MTZ118
this afternoon where fire danger ratings have reached high to very
high due to drying of fine fuels, especially grasses. A cold front
expected to move through the region late this afternoon will bring
cooler temperatures and higher humidity, but gusty west winds will
continue through early Saturday. Isolated dry lightning may be
possible over the higher terrain of southwest Montana where
moisture is increasing aloft while remaining dry at the surface.


GTF  56  80  51  86 /  10  10  10   0
CTB  55  76  51  81 /  50  20  10  10
HLN  60  82  55  88 /  10  10   0   0
BZN  52  81  47  86 /  30  10  10   0
WEY  43  72  39  76 /  20   0   0   0
DLN  49  79  47  84 /  10   0   0   0
HVR  59  80  53  85 /  20  20  10   0
LWT  56  78  51  83 /  40  10  10   0


Red Flag Warning until 9 PM MDT this evening for MTZ118.


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