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000
FXUS65 KTFX 240451
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1100 PM MDT Thu May 23 2013

UPDATED AVIATION SECTION

.UPDATE...
The upper trough is still forecast to swing northeast through the
forecast area later tonight and Friday morning. As of 830 pm one
band of precipitation extended from the western portions of
southwest Montana north to the Rocky Mountain Front. This was
associated with the upper trough. Another band of precipitation
over southcentral Montana was moving into central Montana and will
continue north the rest of this evening. The inherited high
chances of precipitation for the rest of tonight look good so did
not change them. Did add a mention of thunder over portions of
southwest Montana and central Montana for the rest of this evening
based on current observations/instability data. Also based on
current observations have lowered snow levels over western
portions of southwest Montana where snow levels are approaching
5000 feet MSL. Adjusted late evening winds to better reflect
current observations and made some minor adjustments for after
midnight as well. Forecast lows for tonight look on track so did
not make any changes to them. The forecast chances of
precipitation for the east slopes might be too high for Friday
morning as downslope should have kicked in along with drier air so
do not expect any precipitation. However will let midnight shift
make the final determination on this as they will have the benefit
of later model data and being able to see how the situation
evolves. Blank

&&


&&

.AVIATION...
UPDATED 0500Z.
An upper disturbance will move northeast through the area late
tonight and Friday morning. Expect showers/rain ahead of the
disturbance. Most locations will see a period of MVFR or possibly
even IFR ceilings and visibilities in the precipitation. Along with
the lower conditions expect areas of mountain obscurement. Conditions
will improve to scattered clouds after the passage of the upper
disturbance and gusty downslope winds will develop over the plains.
Blank

&&

.HYDROLOGY...Widespread rain and high elevation snow will continue
at times through Friday morning. Snow levels should lower enough
to lessen the impact of moderate precipitation on the remaining
mtn snowpack in these areas, however local streams and rivers
could see delayed rises through the upcoming weekend. Persons
living near or planning activities near the mentioned areas during
the holiday weekend should be alert for rising river levels and
increased stream flows.

&&

.PREV DISCUSSION...
/ISSUED 600 PM MDT Thu May 23 2013/

Tonight through Saturday...A deep closed low pressure system will
remain over the Pacific tonight and another shortwave will rotate
around the low tonight. This will produce good lift across most of
the forecast area for widespread showers. At lower levels, a surface
low pressure trof will move into eastern Montana winds will become
westerly after midnight. This will help dry the airmass across the
plains Friday as the low pressure system weakens. Elsewhere, low
level moisture will be available and the airmass will become
slightly unstable during the afternoon, mainly across Southwest
Montana. However the airmass will be capped at higher levels and
thunderstorms should be shallow. Zelzer

Saturday night through Thursday...The period begins with a closed
upper low quasi-stationary as it fills over southwest Canada.
Circulation around this feature will continue to bring moisture and
instability to the area with scattered showers and/or thunderstorms
remaining a possibility through Sunday. The airmass will remain
unstable Monday as an upper trof remains over the west coast.
Diffluent flow aloft will aid in another round of scattered showers
and thunderstorms. The models begin to diverge with their solutions
on Tuesday. Though the airmass will remain unstable, drier air will
move into northern Montana while afternoon showers and thunderstorms
will continue to develop over southwest Montana. Unsettled and wet
conditions will continue Wednesday and Thursday as the west coast
upper trof rotates across the area. Showers and thunderstorms will
become widespread across the central and northern portions of the
county warning area. Temperatures will remain above seasonal
averages through the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  64  40  68 / 100  30  10  10
CTB  38  60  35  65 / 100  30  10  10
HLN  38  63  38  69 /  90  30  10  20
BZN  34  65  35  72 /  80  50  10  20
WEY  30  57  33  66 /  40  10   0  10
DLN  32  61  34  69 /  80  30  10  30
HVR  47  68  42  73 /  90  60  10  10
LWT  42  65  39  68 / 100  50  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until Noon MDT Friday FOR ELEVATIONS
ABOVE 5500 FEET FOR Northern Rocky Mountain Front...Southern
Rocky Mountain Front.

&&

$$

SHORT TERM...BLANK
LONG TERM...BLANK
AVIATION...BLANK

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