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000
FXUS65 KTFX 231156
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
555 AM MDT Thu May 23 2013

UPDATED AVIATION SECTION

.DISCUSSION...
A shortwave and upper level jet maximum lifting north through
western MT around a vigorous upper low centered over the Pacific NW
continues to produce widespread precipitation over areas near the
Continental divide this morning. This feature will continue north
into Canada later this morning with precipitation diminishing from
south to north. Snow levels have lowered to around 5500 feet this
morning along the Continental divide and western portions of SW MT
with snow briefly being reported in Dillon overnight but occurring
for last several hrs in Butte as the cold airmass deepens
significantly west of the divide. Some wet snow is likely over
Homestake, Elk Park, MacDonald and Rogers Pass through early this
morning, but with temperatures at or above freezing, little
accumulation is expected on roadways. The next shortwave, an upper
level jet maximum, currently seen on satellite imagery moving into
SW Oregon, will rotate around the main upper low into the region
tonight with showers and thunderstorms redeveloping this afternoon
over SW MT ahead of this feature then spreading north this evening.
This wave tracks a bit further east than the previous one and should
bring a period of steady precipitation across much of forecast area
tonight through Friday morning before this wave lifts north into
Canada by midday Friday. Colder air associated with the upper low
will spread a bit further east late tonight with snow levels remain
around 6000 feet along the Continental divide and lowering to around
7000 feet by Friday morning as far east as the Little/Big Belt Mtns.
The main upper low center lifts north into BC late Friday through
Saturday and a somewhat drier SW flow aloft will result in drier
conditions overall, but weak disturbances within the flow and
afternoon instability will keep a small chance for showers/isolated
thunderstorms in the forecast Friday afternoon/evening with somewhat
better coverage of late day showers and thunderstorms expected
Saturday. Hoenisch

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.

&&

.AVIATION...
UPDATED 1155Z.
An upper disturbance moving across the area this morning will
continue to generate showers. Showers will begin to decrease in
areal coverage from south to north after 17z. Showers and
thunderstorms will become more widespread again after 00z as another
upper disturbance moves across the area. VFR conditions prevail with
MVFR conditions in the vicinity of showers. Conditions will become
predominately MVFR with areas of IFR after 00z due to lowered
ceilings and precipitation. Mountains will become obscured after 00z.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  59  42  63  40 /  40  80  20  10
CTB  53  40  59  37 / 100  90  30  10
HLN  58  39  61  38 /  50  70  20  20
BZN  60  38  63  38 /  50  40  10  10
WEY  56  34  55  34 /  30  30  10  10
DLN  57  35  59  35 /  70  60  10  10
HVR  69  49  66  46 /  40  90  60  20
LWT  64  44  63  43 /  60  90  30  10

&&

.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...HOENISCH
LONG TERM...EMANUEL
AVIATION...EMANUEL

weather.gov/greatfalls