Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211720

1120 AM MDT Sun Sep 21 2014


.UPDATE...High clouds from a cutoff upper level low over Central
California/Nevada are already moving up into far Southwest
Montana. Have updated to increase cloud cover from clear to partly
cloudy in this region. Remainder of the forecast looks to be in
good shape with a warm and mostly sunny day on tap. mpj


An upper level ridge of high pressure will maintain dry conditions
with mainly clear skies through today with just some thin high
clouds spreading into extreme SW MT. The upper level ridge drifts
east tonight through Monday, allowing for clouds to further increase
over SW MT with dry and mainly clear conditions persisting farther
north. Surface winds will remain relatively light with a slight
uptick in SE winds over the plains this afternoon. VFR conditions
will prevail. Hoenisch


/ISSUED 508 AM MDT Sun Sep 21 2014/

Today through Tuesday...The upper level ridge of high pressure
over Montana will keep the area mostly sunny and dry today as
temperatures warm to around 10 degrees above normal. Forecast
models continue to indicate that the cutoff low currently over
California and Nevada will be lifted northeast toward Montana by
a deep trough over the eastern Pacific. The chance for scattered
showers and thunderstorms will increase over southwest Montana
tonight into Monday due to the moisture and instability along the
leading edge of this system. Models also indicate that some storms
could develop as far north as the mountain areas of central and
northwest Montana, so have continued the mention of storms there.
Instability with this system remains a bit on the weak side, so
the chance for strong to severe storms remains low, but brief
heavy rain is possible. Temperatures will warm another 5 degrees
or so over today across most of the area, but clouds/storms in
southwest Montana will keep high temperatures similar to those
today. The system will weaken and become more of an open wave
Monday afternoon then move east of the area Monday night, for a
decreasing chance of showers and storms. High pressure aloft will
rebuild from the southwestern United States as the deep trough
mentioned above will approaches the CONUS from the west. The
resulting increasing southwesterly flow aloft will bring breezy
westerly winds to the area, along with a slight chance of
thunderstorm development over the mountains. Temperatures will
also cool a few degrees as a weak disturbance moves through the
area.  Coulston

Tuesday Night through Sunday...An upper level ridge will amplify
over the region early Wednesday while temperatures warm to well
above seasonal averages. The ridge axis moves away to the east on
Thursday as a deep trof moves ashore over the Pacific Northwest.
Wednesday should be the warmest day of the week ahead, and only
slightly cooler on Thursday. Isolated showers and thunderstorms will
begin to develop Thursday night with decreasing stability over the
higher terrain of western and southwest Montana.

Confidence is growing in a solution of widespread showers and
thunderstorms on Friday evening. However, model differences begin to
develop Friday night. The GFS moves the trof through the northern
Rockies more rapidly than the ECMWF and GEM...both of which split
the trof and dig it further south along the west coast. Have raised
POPs on Friday night and Saturday, but keeping below the likely
category given uncertainties in timing and position. Temperatures
will drop back into the 60s as the trof swings through over the
weekend. At this time, it appears any snow would be limited to the
highest mountain peaks Saturday night.


GTF  78  50  83  55 /   0   0  10  10
CTB  77  44  83  49 /   0   0  10  10
HLN  81  51  83  52 /   0  10  20  10
BZN  77  47  76  47 /   0  20  40  20
WEY  73  39  63  37 /  10  50  60  30
DLN  78  52  75  49 /  10  30  40  20
HVR  79  45  83  51 /   0   0   0  10
LWT  76  49  82  51 /   0  10  20  10



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