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000
FXUS65 KTFX 150441
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1041 PM MDT Tue May 14 2013

UPDATED AVIATION DISCUSSION

.DISCUSSION...
Update forthcoming. No significant changes made to the current
forecast. Have adjusted sky grids to better reflect the chinook arch
and cloud shield further downstream as depicted on current satellite
imagery. Westerly flow aloft will continue overnight maintaining dry
and stable conditions. At the surface, radar returns indicated a
weak boundary moving through the Great Falls area earlier this
evening with winds shifting to the north-northwest. Winds will shift
back to the west by midnight and remain generally light. Emanuel

&&

.AVIATION...
UPDATED 0500Z.
VFR conditions will persist through the next 24 hrs as the area
remains under a relatively dry and stable westerly flow aloft
through early Wednesday. High level moisture within the flow will
keep a fair amount of high clouds over the region, especially over
northern and central MT. Breezy winds early this evening over SW MT
will continue to diminish overnight with light winds continuing
through Wednesday. Flow aloft shifts to more southwesterly late
Wednesday afternoon and a weak weather disturbance and slight
increase in moisture and instability late Wednesday may produce a
few isolated showers, mainly over SW MT.  Hoenisch

&&

.PREV DISCUSSION...Issued 254 PM MDT Tue May 14 2013

Tonight through Thursday...Expect a westerly flow aloft tonight. A
weak weather disturbance aloft will move through the northern
zones. It should produce some cloudiness but no rain. Southwest
flow aloft will develop Wednesday and expect to see weak
instability over far southwest Montana during the afternoon and
so will continue with the mention of a slight chance of
showers/thunderstorms. Southwest flow aloft will continue into
Thursday and embedded in this flow will be several weather
disturbances. Models are not in good agreement with the details of
these disturbances and associated precipitation patterns. What
models agree on is that there will be an increase in moisture
Wednesday night and Thursday. Despite the differences with the
details of the disturbances and precipitation due to the expected
increase in moisture have increased the chances of precipitation.
It does not look like it will be unstable enough for thunderstorms
Thursday so have removed their mention expect for the area near
and east of a line from Bozeman to Havre where there is an outside
threat of thunderstorms. Gusty winds will diminish by dark tonight
and expect relatively light winds Wednesday through Thursday.
Blank

Thursday Night through Tuesday...An unsettled weather pattern is
expected through the period with temperatures generally around to
slightly below seasonal averages. Models begin the period in fair
agreement as a broad upper-level trough and several embedded
shortwaves push through the Treasure State. One of these shortwaves
will move over southwest Montana on Friday with ample Pacific
moisture and instability associated with it so have increased pops
with the possibility for thunderstorms over this area through
Saturday. Though precip chances will be less over north-central
Montana...have kept at least a slight chance as models suggest
marginal instability over the area. This broad upper-level trough
will remain the dominant weather feature through the weekend with
additional precipitation chances across the forecast area, however
long-range models indicate some differences in the timing of each
shortwave. For now have kept highest pops in the mountains with at
least a slight chance in the plains/valleys. Models suggest a
stronger Pacific storm system may affect the Northern Rockies early
next week, however the GFS and ECMWF diverge on the timing and
amplitude of this system so have continued the trend of chance
pops in the mountains and slight chance in the plains/valleys. MLV

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  71  42  66 /   0   0  30  50
CTB  36  69  40  66 /   0   0  20  30
HLN  43  73  44  67 /   0   0  30  50
BZN  39  75  41  68 /   0  10  20  40
WEY  36  70  41  61 /  10  20  30  30
DLN  40  72  43  65 /   0  10  40  40
HVR  40  74  44  71 /   0   0  10  30
LWT  39  70  43  64 /   0   0  20  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING until 9 PM MDT this evening Fergus.

&&

$$

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