006 
FXUS65 KTFX 201747
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1145 AM MDT SAT OCT 20 2012

UPDATED AVIATION

.UPDATE...GOING FORECAST IS GENERALLY IN GOOD SHAPE WITH STRONG
WINDS EXPECTED ACROSS NORTH CENTRAL MONTANA AS A PACIFIC COLD
FRONT SWEEPS THROUGH THE REGION TODAY. HAVE MADE MINOR TWEAKS TO
THE GOING FORECAST PACKAGE TO INCREASE WIND GUSTS OVER THE PLAINS
THIS AFTERNOON AND TO RAISE SNOW LEVELS A BIT BASED ON LATEST
MODEL RUNS. THE CHANGES TO SNOW LEVELS RESULTED IN MORE OF A RAIN
SNOW MIX AROUND SOME OF THE MOUNTAIN AREAS. HAVE ALSO MADE TWEAKS
TO TEMPERATURES, POPS AND SKY CONDITION BUT MOST OF THESE CHANGES
ARE MINOR AND SHOULD NOT SIGNIFICANTLY AFFECT THE FORECAST
PACKAGE. WINDS ARE STILL EXPECTED TO DECREASE THIS EVENING WITH
COLDER TEMPERATURES EXPECTED BEHIND THE FRONT FOR SUNDAY. MPJ

&&

.AVIATION...
UPDATED 1800Z.
DOWNSLOPE WINDS IN THE WAKE OF A COLD FRONT HAVE PROMOTED DRIER 
CONDITIONS ACROSS THE PLAINS THIS AFTERNOON. ALONG THE ROCKY 
MOUNTAIN FRONT AND AREAS FARTHER SOUTH ALONG THE CONTINENTAL 
DIVIDE...RAIN AND SNOW CAN BE EXPECTED WITH WIDESPREAD MOUNTAIN 
OBSCURATION. CLOUDS MAY INCREASE OVER THE PLAINS THIS AFTERNOON AS A 
WEAK SHORTWAVE MOVES OVER THE CONTINENTAL DIVIDE...HOWEVER DRY 
CONDITIONS ARE EXPECTED. WINDS WILL CONTINUE TO INCREASE OVER THE 
PLAINS WITH WIND GUSTS OF 40 TO 50 KTS POSSIBLE. AT KBZN AND 
KHLN...WIND GUSTS OF 25 TO 35 KTS ARE POSSIBLE. WINDS WILL DECREASE 
THIS EVENING. OVERALL...VFR CONDITIONS ARE EXPECTED IN THE NEXT 24 
HOURS. MLV

&&

.PREV DISCUSSION...
/ISSUED 530 AM MDT SAT OCT 20 2012/
A PACIFIC FRONTAL SYSTEM AND ASSOCIATED STRONG UPPER LEVEL JET MOVING
ACROSS THE NORTHERN ROCKIES EARLY THIS MORNING WILL MOVE QUICKLY
EAST ACROSS CENTRAL AND SW MT TODAY AHEAD OF A DEEPENING LARGE
SCALE TROUGH ALONG THE WEST COAST. EXPECT WIDESPREAD PRECIPITATION
TO REMAIN MOSTLY CONFINED TO AREAS NEAR THE CONTINENTAL DIVIDE
WITH SOME SHOWERS SPREADING EAST OVER CENTRAL AND SW MT ALONG AND
BEHIND THE FRONT LATER THIS MORNING AND AFTERNOON. SNOW LEVELS
HAVE REMAINED WELL ABOVE PASS LEVELS OVERNIGHT...BUT SHOULD LOWER
THIS MORNING AS COOLER AIR MOVES IN BEHIND THE FRONT. MAIN IMPACT
TO THE FORECAST AREA WILL BE STRONG WINDS TODAY AS THE SURFACE LOW
PRESSURE CENTER TRACKS EAST ACROSS SOUTHERN ALBERTA AND
SASKATCHEWAN AND MIXING ALONG AND BEHIND THE COLD FRONT FRONT
BRING STRONG WINDS ALOFT DOWN TO THE SURFACE OVER NORTH CENTRAL MT.
CONFIDENCE IN HOW FAR EAST THE STRONG WINDS SPREAD IS NOT HIGH AS
MODELS HAVE BACKED OFF SOME ON WIND SPEEDS AT AND BELOW THE 700MB
LEVEL...HOWEVER COMBINATION OF STRONG PRESSURE GRADIENT AND AFTERNOON
MIXING BEHIND THE FRONT AS WELL AS A 120 KT JET OVERHEAD IS HARD
TO IGNORE...SO HAVE UPGRADED THE HIGH WIND WATCH TO A WARNING FOR
THE EASTERN PORTION OF NORTH CENTRAL MT AS WELL TODAY. WINDS
DIMINISH THIS EVENING AS WEAK HIGH PRESSURE BUILDS INTO THE
NORTHERN ROCKIES AND MT TONIGHT. TEMPERATURES WILL LIKELY REMAIN
STEADY OR GRADUALLY COOL TODAY AS COOLER AIR AIR MOVES IN BEHIND THE 
FRONT WITH MOST AREAS FALLING BELOW FREEZING TONIGHT. TEMPERATURES 
WILL REMAIN AROUND 10 DEGREES BELOW SEASONAL AVERAGES SUNDAY AND 
MONDAY AS THE UPPER LEVEL TROUGH CONTINUES TO DEEPEN. BY MONDAY...A 
SHORTWAVE EMBEDDED WITHIN THE TROUGH AND UPPER LEVEL JET WILL ROTATE 
NE INTO THE REGION FROM THE GREAT BASIN...SPREADING PRECIPITATION 
INTO THE AREA. THERE IS STILL A GREAT DEAL OF UNCERTAINTY WITH THE 
TIMING OF THIS DISTURBANCE AND THE DEGREE OF WARMING THAT WILL MOVE 
IN FROM THE SOUTH...HOWEVER THE AIRMASS WILL BE COOL TO SUPPORT SNOW 
LEVELS NEAR VALLEYS FLOORS AND PLAINS. HOENISCH

MONDAY NIGHT THROUGH SATURDAY...AS NOTED IN LATEST NATIONAL-LEVEL 
FORECAST MODEL DISCUSSION...THERE REMAINS A LOT OF UNCERTAINTY IN 
THE DETAILS FOR THE WEATHER IN THE WEEK AHEAD.  AT THE START OF 
FORECAST PERIOD A CLOSED LOW/DEEP UPPER LEVEL TROF WILL BE OFF THE 
BC/WASH COAST WITH WELL-DEFINED AND VERY MOIST SOUTHWEST FLOW ALOFT 
OVER MONTANA. THIS WILL BRING WIDESPREAD MIX OF MTN SNOW AND VALLEY 
RAIN LATE MON THROUGH MIDDAY TUES.  A SHORTWAVE TROF EJECTING FROM 
THE CLOSED LOW IS EXPECTED TO TRACK FROM ERN WASH TO FAR SOUTHEAST 
ALBERTA ON TUES AND PUSH A COLD FRONT THRU CENTRAL AND SOUTHWEST MT 
TUES AFTN.  COOLING BEHIND THE FRONT SHOULD CHANGE ALMOST ALL OF THE 
PRECIPITATION TO LIGHT SNOW BUT MOST OF THE INITIAL MOISTURE WILL BE 
DOWNSTREAM AT THAT POINT SO AREAS OF ACCUMULATION WILL GENERALLY BE 
LIMITED TO THE CENTRAL MT MTN RANGES (LITTLE BELTS/SNOWIES/BEARS 
PAW).  MODEL DIFFERENCES ARE MOST PROMINENT IN THE WED-FRI TIME 
FRAME WITH THE CANADIAN AND EUROPEAN MODELS BRINGING A WEAK 
RIDGE...MOSTLY DRY CONDITIONS AND HIGH TEMPERATURES IN THE LOW-MID 
30S WHILE THE GFS HAS SCATTERED SNOW SHOWERS AND TEMPS ABOUT 10 DEG 
COLDER THAN THE OTHER MODELS. CURRENT FORECAST IS ROUGHLY BETWEEN 
THESE TWO SOLUTIONS WITH REDUCED CHANCES OF PRECIP AND TEMPS 
AT/SLIGHTLY ABOVE FREEZING.  THE CLOSED LOW BEGINS TO WEAKEN ON 
THURS AND THEN TRACKS ALONG THE US/CAN BORDER THROUGH EARLY 
FRI...BRINGING ANOTHER ROUND OF LIGHT SNOW ACROSS MUCH OF THE 
FORECAST AREA.  BY SAT...EACH OF THE THREE MODELS HAS ITS OWN UNIQUE 
SOLUTION WITH TEMPERATURES RANGING FROM THE TEENS (GFS) TO THE UPPER 
40S (CANADIAN).  GIVEN THE LOW CONFIDENCE IN ANY PARTICULAR 
SOLUTION...CURRENT OUTLOOK GOES WITH MOSTLY A PERSISTENCE FORECAST 
OF UPPER 30S WITH A SLIGHT CHANCE OF LIGHT SNOW.
WARANAUSKAS

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  56  27  48  27 /  20  10   0  10 
CTB  50  23  43  21 /  20  10  10  20 
HLN  55  28  49  27 /  30  10   0  10 
BZN  61  28  50  29 /  40  10  10  20 
WEY  49  26  45  26 /  40  20  20  30 
DLN  56  26  49  26 /  30  10  10  20 
HVR  61  27  49  27 /  20   0   0  10 
LWT  57  27  46  28 /  20  10  10  20 

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 9 PM MDT THIS EVENING BLAINE...CASCADE...
CHOUTEAU...EASTERN GLACIER...EASTERN PONDERA...EASTERN TETON...
FERGUS...HILL...JUDITH BASIN...LIBERTY...NORTHERN ROCKY MOUNTAIN 
FRONT...SOUTHERN ROCKY MOUNTAIN FRONT...TOOLE.

&&

$$

WEATHER.GOV/GREATFALLS