601 
FXUS65 KTFX 041550
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
945 AM MDT Sat May 4 2013

.UPDATE...
Latest radar/satellite imagery showing broad area of mostly cloudy 
to overcast skies thru central and southwest MT with some scattered 
areas of light rain from southern/eastern Cascade County eastward to 
central Fergus County.  Forecast still on track for easterly flow 
aloft to bring in additional moisture this aftn/eve and generate 
scattered rain showers over all parts of the forecast area except 
the Hiline counties which should remain mostly dry. Only slight 
forecast grid adjustments this morning, mainly to reduce precip 
chances and cloud cover along the Hiline and increase them over the 
Little/Big Belt Mtns.
Waranauskas

&&

.DISCUSSION...

Today through Monday...Deep moisture combined with a deep and
persistent northerly upslope flow will keep at least scattered
showers around north central and southwest Montana today. The
shortwave trough that brought widespread precipitation to the area
yesterday and overnight has begun cutting off into an area of low
pressure as it moves west across the northern Great Basin. As a
result, the aforementioned moisture is wrapping around the upper
low from the Great Plains and into Montana. With the upper low
still in the vicinity, the greatest potential for measurable
precipitation will be this morning. Showers this afternoon will be
more scattered due to weak instability, along with possible
isolated thunderstorms in far southwest Montana in the vicinity of
the cold front that moved through the area yesterday. Clouds and
showers will diminish overnight, which may allow patchy fog to
form along the east slopes of the Rockies and in the southwest
Montana valleys. Lingering easterly winds across the eastern half
of the area will likely hinder fog development there. As the
upper low gradually moves west toward the California coast through
the remainder of the period, weak high pressure aloft will build
into the area, for mostly dry and warming conditions. Temperatures
will warm from near seasonal averages today to 70s at most lower
elevations by Monday. With this warming, afternoon/evening
instability will develop for Sunday and Monday. However, moisture
be fairly limited to southwest Montana, so have kept the mention
of afternoon and evening showers and thunderstorms only in that
area.  Coulston

Monday night through Saturday...Monday night through Tuesday will
see an east-west oriented upper ridge across southern Canada with
an upper low over the southwest U.S. The upper ridge should keep
the north dry while weak instability over southwest Montana could
help in producing scattered showers and isolated thunderstorms.
Tuesday night and Wednesday the upper ridge will shift south as a
weather disturbance aloft moves to central Canada. Associated with
this disturbance a slightly cooler Canadian airmass will spread
into the forecast area. The main precipitation associated with
disturbance should stay north of the border however by Wednesday
instability could spread farther north so will continue with the
idea of having at least isolated showers over central Montana.
Again there will be a threat of thunderstorms over southwest
Montana. With the surge of Canadian air highs Wednesday should be
5 to 10 degrees cooler than those of Tuesday. Thursday models
agree on a northwest flow aloft but do not agree on precipitation
details so will go with the idea of scattered showers for the
mountains and isolated showers for the lower elevations. There
will also be a small threat for thunderstorms over all but north
central Montana. Friday into Saturday northwest flow aloft is
expected to increase. A Canadian cold front and associated
precipitation will spread south over Montana. The GEM and ECMWF
model runs are faster than the GFS with the precipitation bringing
it into Montana Friday while the GFS brings in the precipitation
later Friday night. The GFS has lingering precipitation into
Saturday while the other models tend to diminish precipitation.
Due to model differences will not go above the chance category for
the threat of precipitation at this point. Blank

&&

.AVIATION...
UPDATED 1120Z.
For this morning confidence is on the low side with regard to 
whether conditions will be MVFR or VFR over southwest Montana. 
Although not mentioned in the tafs there could be a period of MVFR 
ceilings and possibly MVFR visibilities in rain showers at KBZN and 
KHLN. Had higher confidence for a period of MVFR conditions at KGTF 
so have a tempo group. KCTB and KHVR should not see MVFR conditions. 
Confidence in conditions at KLWT is low as could see anywhere from 
LIFR to VFR conditions. By this afternoon expect VFR conditions at 
all TAF sites. There will be scattered showers into this afternoon 
with snow showers over the mountains and areas of mountain 
obscurement. Conditions will improve late this afternoon into this 
evening as showers end and clouds decrease. Expect widespread clear 
skies by midnight. Blank
&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  36  68  40 /  40  10   0   0 
CTB  62  36  67  39 /  20   0   0   0 
HLN  60  35  67  39 /  50  20  10   0 
BZN  60  31  67  34 /  50  10  10  10 
WEY  53  26  59  27 /  40  10  20  20 
DLN  58  32  65  38 /  40  20  20  20 
HVR  66  36  71  39 /  30  10   0   0 
LWT  57  33  63  37 /  50  10  10   0 

&&

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

$$

SHORT TERM...COULSTON
LONG TERM...BLANK
AVIATION...mpj

weather.gov/greatfalls