Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 311536

936 AM MDT Sun Aug 31 2014


Today...A broad upper level trof is slowly moving east. The air mass
remains unsettled under the influence of this trof although
instability will remain weak. Strongest instability will be over
Southwest Montana where isolated to scattered thunderstorms are
expected. Farther to the north, the air mass is nearly stable and
isolated to scattered showers are expected. Updated to freshen
winds, pops, and wx. Zelzer


Weak upper-level trof will continue to track eastward across MT
today, generating widespread BKN-OVC conditions with ceilings
generally at/above 6000-8000 ft. Isolated -SHRA beginning to develop
east of the Continental Divide may reach KHLN/KBZN this morning, but
showers should hold off at remaining TAF sites until this aftn.
Expect only scattered precipitation coverage with predominantly VFR
conditions through this evening, then showers will dissipate with
gradually decreasing cloud cover.


/ISSUED 525 AM MDT Sun Aug 31 2014/
Today through Tuesday...A low pressure trough covers much of western
U.S. today keeping a northwest flow aloft over north-central and
southwest Montana. An embedded weather system that pushed through
Saturday afternoon and evening is exiting to the east this morning.
There are several other smaller weather systems embedded in the flow
that will be pushing through today and tonight, however at this time
it appears that these are generally weak, and available moisture
is relatively limited. As a result, they are expected to trigger
only isolated showers and thunderstorms, mainly from southwest to
central Montana this afternoon and evening. Once these systems
get past, only isolated showers and thunderstorms are expected
through Tuesday. As the flow aloft remains from the northwest,
temperatures will continue to run near to a few degrees below
seasonal normals.

Tuesday Night through Sunday...Current forecast models solutions
showing some slight improvement over continuity/agreement issues
discussed here yesterday, but significant differences still exist
that affect latest outlooks for latter half of next week.  Period
begins with dry conditions for most of the forecast area on Wed,
except for scattered light rain showers over parts of the Hiline
counties on Wed aftn/eve as the northern portion of an upper-level
trof and surface cold front moves through central MT.  Meanwhile the
southern part of the upper trof splits off and extends through OR/WA
to the California coast.  Southwest flow aloft ahead of the trof
axis begins to bring in a plume of monsoonal moisture on Thurs, with
scattered showers and a few thunderstorms expected over southwest
MT. The GFS model solution, which yesterday indicated widespread
precipitation with some rainfall values in the 0.5 to 1.0 inch range
for Thurs through Sat, now shows much less precip coverage and <0.10
inch of rainfall, which is more in line with the drier ECMWF
solutions from both yesterday and today. However, the models vary
widely on the predominant weather pattern for next weekend, with
pronounced high pressure ridging on the ECMWF, while the GFS deepens
the trof along the Pacific coast and develops a cut-off low pressure
center over northern California.  Some moisture moving through the
trof may generate scattered showers over the southwest counties. So,
like yesterday, confidence is low in any particular model solution
and used a blend of climatological PoPs to cover any slight chances
of rainfall.


GTF  69  47  69  48 /  30  20  10  10
CTB  66  46  68  47 /  30  20  10  10
HLN  70  46  71  47 /  20  20  20  10
BZN  65  42  67  41 /  30  30  20  10
WEY  55  32  58  31 /  40  30  20  10
DLN  63  44  66  42 /  20  20  20  10
HVR  74  48  73  49 /  10  20  20  10
LWT  68  47  67  47 /  30  20  20  10



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