Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 200512

Area Forecast Discussion
National Weather Service Great Falls MT
1112 PM MDT Tue Sep 19 2017

...Updated Aviation Discussion...


Moist westerly flow aloft will continue to bring clouds and
showers to the western and southwest Montana mountains. Breezy
conditions and continued cool temperatures with isolated showers
are expected over the plains. This pattern is expected to
continue tonight through Friday.



Widely scattered rain and mountain snow showers continue to move
from west to east across the Northern Rockies and Central and
Southwest Montana. There have also been a few lightning flashes
over the southwest. The overall forecast remains in good shape
this evening, needing only a minor update to freshen relative to
observed trends. PN


Updated 0512z.

Upper level trough/low centered over AB/BC will maintain fast and
unsettled westerly flow aloft across the northern Rockies and MT
with several embedded disturbances passing east across SW MT through
Wednesday. Showers will primarily affect western and SW MT with
drier conditions prevailing across the plains. Occasional MVFR
conditions can be expected at SW MT terminals along with mountain
obscurement. The most widespread precipitation and lowest ceilings
are anticipated on Wednesday across far SW MT.


/ISSUED 537 PM MDT Tue Sep 19 2017/

Tonight through Thursday...An upper level trough of low pressure
will remain over southwestern Canada through Thursday. This
pattern will allow cool temperatures to continue across the
region, while west to southwest flow aloft will bring abundant
Pacific moisture to the region. Periods of rain and snow are
expected over the mountains of Southwest Montana and along the
Continental Divide through the short term. Meanwhile, mostly dry
conditions are anticipated over the Plains with only an isolated
shower or two moving off the mountains. Surface low pressure
system currently in southern Alberta will remain in place tonight
and Wednesday before ejecting eastward Wednesday night and
Thursday. As a result, tight pressure gradients will fuel gusty
west to southwest winds along the east slopes of the Rocky
Mountains and through the higher terrain of Southwest Montana.
Breezy to windy conditions are also anticipated over the plains,
although they are not expected to be as strong as in the higher
terrain. At this time, it does not appear than any highlights will
be necessary but this will continue to be monitored. mpj

Friday through Tuesday...Though there are still discrepancies to
resolve between the various global models and their ensembles, there
is moderate confidence that an area of deformation combined with a
strong surface front over south-central and northeastern Montana
will result in a potentially widespread area of rain and high-
elevation snow. The less-confident aspect of forecasting this event
at this point is just how widespread the precipitation is, with
lowering confidence as one moves north and west through our CWA.
Within the region of widespread precipitation, there will be the
potential for significant snow accumulations above 5500-ft
elevation. This system will finally begin to slowly exit the region
to the east late Friday into Saturday, with just residual rain and
mountain snow showers remaining behind. A quieter weather pattern
with periods of sun and clouds and perhaps a stray shower or two can
be expected early next week as northwesterly flow increases across
the region ahead of a potentially robust upper level ridge moving
onto the PacNW coast. CC


GTF  42  54  35  53 /  10  30  20  20
CTB  39  52  33  47 /  10  10  10  30
HLN  37  52  35  53 /  30  40  30  30
BZN  34  51  34  49 /  50  50  40  30
WEY  25  41  25  39 /  60  60  70  60
DLN  34  51  30  44 /  30  50  30  40
HVR  41  59  36  56 /  10   0  10  10
LWT  38  51  36  52 /  40  40  20  10



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