Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 311535
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
935 AM MDT Thu Jul 31 2014

.UPDATE...
Satellite imagery was showing some clouds over Blaine and Fergus
Counties this morning so changed sunny skies to partly cloudy. In
line with this radar was indicating isolated showers so have added
isolated precipitation to the same two counties for this morning.
Do not foresee any thunderstorm development over most of southwest
Montana for the remainder of this morning so removed their mention
except near the Idaho border. For this afternoon the airmass will
be unstable and expect isolated to scattered thunderstorms which
is in line with the inherited forecast. Forecast highs for today
look on track. Blank

&&

.AVIATION...
UPDATED 1128Z.
VFR conditions will prevail through this TAF period. Scattered CB
will overspread the area by the mid to late afternoon as SHRA and TS
develop. Chances across the lower elevations are fairly low...but
did mention VCTS at all terminals. Feel best probability will be
near an area of convergence close to KGTF, KHVR, and KLWT between
22z-03z. The Main threat will being gusty erratic outflow winds.
Uttech

&&

.PREV DISCUSSION...
/ISSUED 528 AM MDT Thu Jul 31 2014/

Today and Friday...The hot temperatures will continue. Highs are
still forecast to be in the lower/middle 90s. In general,
afternoon and evening MLCAPE will peak in the 500-1000 J/kg range
across the area. However, on Friday afternoon a weak boundary and
associated wind shift will move southward out of Alberta into
northern NC Montana. The air mass behind the boundary
will be fairly moist with surface dewpoints in the 50s which will
potentially increase MLCAPE to near 1500 J/kg. 0-6 km shear will
remain below 30 kts, so only a few isolated strong storms are
possible mainly NW of Cascade County.

NAM and GFS both depict area of high 500 mb RH developing near the
Sierra Mountains Thursday evening...which they then track
northeastward across the NW portion of my CWA Friday night. The NAM
seems to be overdoing the QPF attendant to this feature and paints
an area of greater than 0.30 inches. The GFS and EC have benign
sensible effects associated with the disturbance so opted to ignore
the NAM for now.

Saturday...As the aforementioned air mass sags southward through
north-central Montana PW will increase to near 1 inch as far south
as Great Falls. Isolated to scattered showers and storms are
expected with some likely producing brief heavy rain. Highest
instability will once again be found up along the Hi-line...MLCAPE
values approach ~1000-1500 J/kg. More widespread convective cloud
development should hold temps in the mid/upper 80s. Uttech

Saturday Night through Thursday...Very warm temperatures and
isolated to scattered thunderstorms are expected across the Treasure
State this weekend through early next week. There still remains some
uncertainty regarding precipitation amounts/coverage due to
differences in the various forecast model solutions, however the
best precipitation chances will be along the Continental Divide and
southwest Montana. As for timing of precipitation, latest forecast
models suggest that the best chances will be Saturday and Sunday
afternoon/evening with stronger shortwave troughs and Monsoonal
moisture. Drier conditions will return by the latter half of next
week as a ridge of high pressure builds over the Northern Rockies.
MLV

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  93  59  91  61 /  20  20  10  20
CTB  91  53  88  55 /  20  20  20  30
HLN  95  60  93  61 /  20  20  10  20
BZN  90  53  90  54 /  20  20  10  20
WEY  79  42  79  43 /  40  40  30  30
DLN  86  53  86  54 /  30  30  20  30
HVR  98  57  96  59 /  20  20  20  20
LWT  92  56  91  56 /  20  20  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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