Heavy Snow in Montana, December 7 to 8, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1055 PM MST Thu Dec 6 2012

UPDATED AVIATION SECTION

.DISCUSSION...
LIGHT SNOW CONTINUES TO AFFECT SOUTHWEST MONTANA...WITH THE
BOZEMAN AREA SEEING THE HIGHEST SNOW TOTALS SO FAR THIS EVENING.
ABOUT 5 INCHES OF NEW SNOW HAS FALLEN SINCE 3 PM TODAY A FEW
MILES SOUTH OF BOZEMAN PER A SPOTTER REPORT. THE LIGHT SNOW
EXTENDS BACK TOWARDS THE BUTTE AREA...BUT IS MUCH LIGHTER IN
INTENSITY. SINCE NEW ACCUMULATIONS FOR THE REMAINDER OF THE
OVERNIGHT HOURS SHOULD ONLY BE AROUND AN INCH OR SO IN THE BOZEMAN
AREA...WE WILL HOLD OFF ON UPGRADING TO A WARNING FOR THIS AREA
AT THIS TIME. OTHERWISE LIGHT SNOW WILL AFFECT MAINLY THE MOUNTAIN
AREAS OF CENTRAL AND NORTH CENTRAL MONTANA OVERNIGHT TONIGHT. THE
SNOW WILL LIKELY TAPPER OFF IN MANY AREAS DURING THE MORNING HOURS
ON FRIDAY BUT A STEADY SNOW WILL PICK BACK UP LATE FRIDAY
AFTERNOON AND DURING THE EVENING HOURS. THIS SECOND ROUND OF SNOW
ON FRIDAY EVENING SHOULD BE MORE WIDESPREAD...AND AFFECT ALL
ELEVATIONS ACROSS MUCH OF NORTH CENTRAL AND SOUTHWEST MONTANA.
AGAIN SNOW AMOUNTS TOMORROW NIGHT DO NOT LOOK EXCESSIVE...BUT A
FEW INCHES ARE POSSIBLE AT LOWER ELEVATIONS...WITH SEVERAL INCHES
EXPECTED IN THE MOUNTAINS. OVERNIGHT LOWS TONIGHT LOOK ON
TRACK...AND TEMPERATURES WILL LIKELY NOT RISE MUCH DURING THE DAY
ON FRIDAY. EXPECT ANOTHER PUSH OF COLDER TEMPERATURES TO MOVE INTO
THE REGION FRIDAY NIGHT...THUS MAKING SATURDAY A COLD DAY. BRUSDA

&&

.AVIATION...
UPDATED 0555Z.
WESTERLY FLOW ALOFT CONTINUES. AN UPPER DISTURBANCE ALOFT WILL
CONTINUE TO BRING SNOW TO THE WESTERN MOUNTAINS AND SOUTHWEST
MONTANA OVERNIGHT. SNOW WILL GRADUALLY END BY 10Z. SURFACE WINDS
WILL INCREASE AFTER 18Z AND BECOME GUSTY. SNOW WILL INCREASE OVER
THE AREA AFTER 00Z. VFR CONDITIONS PREVAIL WITH MVFR CONDITIONS DUE
TO LOWER CEILINGS IN THE VICINITY OF SNOW SHOWERS. MVFR/IFR
CONDITIONS WILL PREVAIL AFTER 00Z AND MOUNTAINS WILL BE OBSCURED.

&&

.PREV DISCUSSION...
/ISSUED 604 PM MST Thu Dec 6 2012/

TONIGHT THROUGH SATURDAY...FORECAST MODELS STILL ON TRACK FOR A
COUPLE OF SHORTWAVE TROUGHS FROM THE PACIFIC OCEAN TO USHER IN
COOLER TEMPERATURES AND WIDESPREAD LIGHT SNOW FOR THE WEEKEND. THE
FIRST DISTURBANCE WILL MOVE THROUGH THE AREA TONIGHT...CONTINUING
THE SNOW SHOWERS IN THE MOUNTAINS. ACCUMULATIONS WILL GENERALLY BE
LIGHT IN THE MOUNTAINS (3 TO 5 INCHES)...BUT BECAUSE THERE WILL BE
BREEZY WESTERLY WINDS AND MEASURABLE SNOW THERE IN ADDITION TO
SNOW FROM THE MAIN SHORTWAVE...HAVE DECIDED TO ISSUE A WINTER
WEATHER ADVISORY FOR SNOW AND BLOWING SNOW STARTING IMMEDIATELY
AND CONTINUING THROUGH THE DAY ON SATURDAY. SCATTERED SNOW SHOWERS
WITH LITTLE IF ANY ACCUMULATION ARE EXPECTED AT LOWER ELEVATIONS.
SNOW WILL DECREASE SOMEWHAT AT THESE LOWER ELEVATIONS FRIDAY
MORNING AS THE INITIAL SHORTWAVE EXITS THE AREA.
HOWEVER...WESTERLY WINDS WILL INCREASE ACROSS THE AREA FRIDAY
AFTERNOON AS THE NEXT (AND STRONGER) DISTURBANCE APPROACHES. THERE
SHOULD BE ENOUGH INSTABILITY FOR ANOTHER ROUND OF SHOWERS AT LOWER
ELEVATIONS BY FRIDAY AFTERNOON...WHILE SNOW PERSISTS IN THE
MOUNTAINS. THE MAIN BRUNT OF THIS STRONGER SYSTEM WILL BE FRIDAY
NIGHT INTO SATURDAY...AS A CANADIAN COLD FRONT MOVES SOUTH THROUGH
THE AREA. THE BREEZY WESTERLY WINDS WILL SHIFT MORE NORTHERLY AND
SNOW WILL BECOME MORE WIDESPREAD ACROSS THE AREA. AM NOT EXPECTING
SIGNIFICANT ACCUMULATIONS AT LOWER ELEVATIONS (MOSTLY 2 TO 4
INCHES)...BUT THE GUSTY SHIFTING WINDS WILL CAUSE AREAS OF BLOWING
SNOW. THEREFORE...HAVE EXPANDED THE WINTER WEATHER ADVISORY TO THE
LOWER ELEVATIONS OF THE TFX CWA BEGINNING LATE FRIDAY AFTERNOON.
OVERALL...IN THE MOUNTAINS FROM TODAY THROUGH SATURDAY...SNOW
ACCUMULATIONS WILL MOSTLY BE 6 TO 12 INCHES...WITH SOME HIGHER
PEAKS RECEIVING UP TO 16 INCHES. TEMPERATURES WILL REMAIN NEAR
NORMAL THROUGH FRIDAY NIGHT...BUT TEMPERATURES BEHIND THE COLD
FRONT WILL DROP BELOW SEASONAL AVERAGES...WITH HIGHS ONLY REACHING
INTO THE UPPER TEENS TO MID 20S. COULSTON

SATURDAY NIGHT THROUGH THURSDAY...LITTLE CHANGE SEEN IN LATEST
FORECAST MODEL SOLUTIONS THROUGH TUESDAY WITH PERSISTENT
NORTHWEST FLOW ALOFT BRINGING COOLER TEMPERATURES AND OCCASIONAL
PERIODS OF LIGHT SNOW BEFORE POSSIBLE STRONG COLD SNAP ARRIVES
WED. FORECAST PERIOD BEGINS WITH SATURDAY WEATHER SYSTEM
DESCRIBED ABOVE EXITING INTO ERN MT AND WY. SNOW SHOWERS MAY
LINGER OVER SOUTHWEST MT INTO SUN MORNING BUT MOST OF THE REGION
WILL SEE DECREASING CLOUD COVER ON SUNDAY WITH COOLER-THAN-AVERAGE
TEMPS AS HIGHS ONLY MAKE IT TO THE LOW-MID 20S. THE NEXT SHORTWAVE
TROF EMBEDDED IN THE FLOW SHOULD ARRIVE MON MORNING WITH ANOTHER
ROUND OF LIGHT SNOW SHOWERS MAINLY OVER CENTRAL AND SOUTHWEST
COUNTIES. THIS SYSTEM MOVES DOWNSTREAM BY TUES MORNING WITH JUST
SOME ISOLATED SNOW SHOWERS ALONG THE ROCKY MTN FRONT AND SOUTHWEST
MTNS ON TUES. A STRONG HIGH PRESSURE RIDGE OVER THE ERN PACIFIC IS
FORECAST TO EXPAND INTO THE NRN ROCKIES ON TUES/EARLY WED...WHICH
WILL BRIEFLY SHIFT THE FLOW ALOFT MORE WESTERLY AND ALLOW AFTN
HIGHS TO REACH THE UPPER 30S TO LOW 40S.

AT THIS POINT...IF CURRENT MODEL SOLUTIONS HOLD TRUE...A STRONG
UPPER LEVEL TROF WILL SWING ACROSS SRN CANADA AND SWEEP THRU
MONTANA ON WED AFTN/EVE. DEVELOPMENT OF DEEP LEE SIDE SURFACE
TROF AHEAD OF THIS SYSTEM LIKELY CAUSE WIDESPREAD STRONG/GUSTY
WINDS ALONG THE ROCKY MTN FRONT AND OVER THE CENTRAL
PLAINS...POSSIBLY REQUIRING HIGH WIND HEADLINES TUES EVE INTO WED
MORNING. BY WED MORNING A SHARP COLD FRONT PUSHES QUICKLY FROM
THE US/CAN BORDER TO AROUND HELENA/LEWISTOWN AND THEN THROUGH
SOUTHWEST MT IN THE AFTN. THE FRONT WILL COMBINE WITH A SWATH OF
PACIFIC MOISTURE TO PRODUCE WIDESPREAD SNOW ALONG/BEHIND THE
FRONT. RIGHT NOW MOST OF THE SNOW LOOKS TO BE LIGHT...GENERALLY AN
INCH OR TWO ACROSS THE CENTRAL PLAINS AND HI-LINE...THOUGH MARKED
NORTHERLY LOW-LEVEL FLOW BEHIND THE FRONT COULD LEAD TO HIGHER
ACCUMULATIONS IN FAVORED UPSLOPE PRECIPITATION AREAS. THE GUSTY
WINDS AHEAD OF THE FRONT WILL ALLOW TEMPS TO BRIEFLY REACH THE UPPER
30S TO LOW 40S...BUT ONCE THE FRONT PASSES TEMPS WILL FALL QUICKLY
THRU LATE MORNING/AFTN AND LEAD TO OVERNIGHT LOWS IN THE TEENS TO
SINGLE DIGITS ON THURS MORNING. SNOW ACTIVITY SHOULD TAPER OFF THURS
MORNING WITH SOME LINGERING SHOWERS POSSIBLE OVER THE CENTRAL AND
SOUTHWEST MTNS AND HIGH TEMPS REACHING THE LOW-MID 20S. WARANAUSKAS

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  25  37  16  21 /  30  30  60  70
CTB  21  32  11  17 /  40  30  80  50
HLN  22  35  17  25 /  70  50  80  50
BZN  22  35  15  25 / 100  50  80  40
WEY  19  27  12  19 / 100  60  70  60
DLN  23  34  16  23 /  70  50  80  40
HVR  21  31  12  15 /  30  40  80  60
LWT  20  35  14  19 /  30  40  60  70

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 5 PM MST Saturday Central and
Southern Lewis and Clark above 5000 feet.

WINTER WEATHER ADVISORY until 5 PM MST Friday until 5 PM MST
Saturday Central and Southern Lewis and Clark below 5000 feet.

WINTER WEATHER ADVISORY from 5 PM Friday to 5 PM MST Saturday
Blaine...Hill...Liberty.

WINTER WEATHER ADVISORY until 5 PM MST Saturday Beaverhead...
Broadwater...Gallatin...Jefferson...Madison...Meagher.

WINTER WEATHER ADVISORY until 5 PM MST Saturday Cascade...
Chouteau...Fergus...Judith Basin above 5000 feet.

WINTER WEATHER ADVISORY from 5 PM MST Friday until 5 PM MST
Saturday Cascade... Chouteau...Fergus...Judith Basin below
5000 feet.

WINTER WEATHER ADVISORY from 5 PM Friday to 5 PM MST Saturday
Eastern Glacier...Eastern Pondera...Eastern Teton...Toole.

WINTER WEATHER ADVISORY until 5 PM MST Saturday Northern Rocky
Mountain Front...Southern Rocky Mountain Front above 5000 feet.

WINTER WEATHER ADVISORY until 5 PM MST Friday until 5 PM MST
Saturday Northern Rocky Mountain Front...Southern Rocky Mountain
Front below 5000 feet.

&&

weather.gov/greatfalls

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
816 PM MST THU DEC 6 2012

MTZ008>015-044>055-071200-
BEAVERHEAD-NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-
CASCADE-CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-
TOOLE-LIBERTY-EASTERN PONDERA-BLAINE-
SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON-JUDITH BASIN-FERGUS-
JEFFERSON-BROADWATER-MEAGHER-GALLATIN-
816 PM MST THU DEC 6 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA.

.DAY ONE...TONIGHT

A WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW IS IN EFFECT
FOR PORTIONS OF NORTH CENTRAL AND SOUTHWEST MONTANA TONIGHT.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

A WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW IS IN EFFECT
FOR PORTIONS OF NORTH CENTRAL AND SOUTHWEST MONTANA THROUGH
SATURDAY AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

ANY SPOTTER REPORTS OF SNOWFALL OR REDUCED VISIBILITIES WOULD
GREATLY BE APPRECIATED.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
915 PM MST THU DEC 06 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0905 PM     SNOW             5 SW BOZEMAN            45.63N 111.12W
12/06/2012  M5.0 INCH        GALLATIN           MT   TRAINED SPOTTER

            5 INCHES ON THE GROUND - SNOWING LIGHTLY

&&

EMANUEL