FXUS65 KTFX 230529
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1029 PM MST TUE DEC 22 2009
...UPDATE TO AVIATION...
.EVENING UPDATE...
BIG SKY COUNTRY SITS BETWEEN TWO UPPER LEVEL LOWS...ONE WELL TO
THE SOUTH NEAR LAS VEGAS AND ANOTHER DROPPING SOUTHEAST OUT OF
CENTRAL ALBERTA. FORECAST LOOKS TO BE ON TRACK AT THIS TIME...ONLY
CONCERN IS THE TIMING OR ONSET OF SNOW ACROSS THE NORTHWESTERN
PORTIONS OF THE FORECAST AREA NEAR THE ROCKY MOUNTAIN FRONT...BUT
SOME LIGHT SNOW IS STARTING TO DEVELOP NEAR AND AROUND CUT BANK.
COSMETIC TWEAKS TO TEMPS...WINDS..AND CLOUD COVER TO ADD CURRENT
INFO...BUT OVERALL FORECAST IN GOOD SHAPE. UPPER LEVEL JET MAX
PUSHING SOUTH INTO WESTERN MONTANA WITH AREA IN PREFERRED LEFT
EXIT REGION WITH DECENT UPPER LEVEL DIVERGENCE SEEN IN THE H5 TO
H3 LAYER...ALLOWING FOR ENOUGH FORCING TO PRODUCE LIGHT SNOWFALL
THROUGH THE NIGHT AS THE UPPER LEVEL TROUGH DRIVES ACROSS THE
TREASURE STATE. ADVISORY REMAINS IN EFFECT THROUGH WEDNESDAY
MORNING. --SCHOTT
&&
.PREV DISCUSSION...
/ISSUED 447 PM MST TUE DEC 22 2009/
TONIGHT THROUGH WEDNESDAY NIGHT...A PROGRESSIVE WEATHER SYSTEM WILL
MOVE INTO THE NORTHWEST ZONES LATE TONIGHT THEN MOVE EAST THROUGH
THE REMAINDER OF THE AREA WEDNESDAY MORNING AND EARLY AFTERNOON.
MODELS ARE FASTER WITH THIS SYSTEM THAN THEY WERE ON MONDAY. IN LINE
WITH THIS HAVE LOWERED SNOW ACCUMULATIONS OVER THE PLAINS FROM 2 TO
5 INCHES TO 2 TO 3 INCHES. THE ARCTIC SURGE ASSOCIATED WITH THE
WEATHER SYSTEM WILL MOVE INTO THE NORTHERN ZONES THIS EVENING THEN
SPREAD SOUTH OVER ALL BUT FAR SOUTHWEST MONTANA BY WEDNESDAY
MORNING. WINDS ASSOCIATED WITH THIS SURGE IN COMBINATION WITH VERY
COLD TEMPERATURES WILL CAUSE WIND CHILLS OF 10 BELOW ZERO TO 20
BELOW ZERO ON WEDNESDAY. EVEN THOUGH EXPECTED SNOW ACCUMULATIONS ARE
LESS THAN WAS EARLIER THOUGHT...THE COMBINATION OF THE SNOW AND VERY
COLD WIND CHILL TEMPERATURES WILL STILL NECESSITATE THE CONTINUATION
OF THE WINTER WEATHER ADVISORY. SINCE THE SYSTEM IS EXPECTED TO BE
FASTER WILL DROP THE WINTER WEATHER ADVISORY EXCEPT IN THE FAR EAST
FOR WEDNESDAY AFTERNOON. BLANK
CHRISTMAS EVE THROUGH TUESDAY...AN UPPER-LEVEL RIDGE OF HIGH
PRESSURE BEGINS TO BUILD OVER THE PACIFIC NORTHWEST ON CHRISTMAS DAY
WITH DRY NORTHERLY FLOW AND MODERATING TEMPERATURES. OVERALL...A
QUIETER PATTERN IS ANTICIPATED FOR THE FORECAST PERIOD WITH THE
STRONG UPPER RIDGE PERSISTING OVER THE WESTERN U.S. THROUGH THE
HOLIDAY WEEKEND. THOUGH TEMPERATURES WILL TREND TOWARDS AVERAGE...A
FRESH SNOWPACK MAY STILL KEEP READINGS AROUND TO SLIGHTLY BELOW
SEASONAL AVERAGES. RIDGE AXIS WILL MOVE EAST BY SUNDAY WITH WESTERLY
FLOW DEVELOPING. DRY CONDITIONS ARE EXPECTED TO CONTINUE THROUGH
MONDAY...WITH INCREASING PACIFIC MOISTURE BY MONDAY NIGHT INTO
TUESDAY AS OUR NEXT SHORTWAVE APPROACHES. MLS
&&
.AVIATION...
UPDATED 0629Z.
LOW CLOUDS AND PATCHY AREAS OF DENSE FREEZING FOG WILL CONTINUE TO
IMPACT TAF SITES ACROSS NORTH CENTRAL AND CENTRAL MONTANA. SNOW
SHOWERS SHOULD CONTINUE TO DEVELOP LATE THIS EVENING ACROSS THE
AREA. LIGHT SNOW SHOWERS WILL PERSIST INTO THE OVERNIGHT PERIOD.
THIS SHOULD KEEP VIS AND CIGS DOWN IN THE IFR CATEGORY FOR MUCH OF
THE TIME. THERE IS THE POTENTIAL FOR SOME BLOWING AND DRIFTING
SNOW...AND VISIBILITY COULD DROP TO LESS THAN ONE MILE AT
TIMES...HOWEVER THIS IS NOT ANTICIPATED TO BE A PREVAILING WEATHER
CONDITION AT ANY SITE FOR AN EXTENDED PERIOD OF TIME. SUK
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 6 8 -6 17 / 80 80 10 0
CTB 0 4 -9 16 / 90 30 0 0
HLN 15 16 -5 16 / 60 50 10 0
BZN 17 18 -7 15 / 50 50 10 10
WEY 10 19 -13 12 / 60 80 20 10
DLN 13 23 -5 14 / 40 40 10 0
HVR 4 5 -16 3 / 90 80 10 0
LWT 8 9 -7 9 / 80 80 10 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 11 AM MST WEDNESDAY FOR CASCADE...
CHOUTEAU...EASTERN TETON...HILL...JUDITH BASIN...LIBERTY...
MEAGHER...SOUTHERN ROCKY MOUNTAIN FRONT.
WINTER WEATHER ADVISORY UNTIL 5 PM MST WEDNESDAY FOR BLAINE...
FERGUS.
WINTER WEATHER ADVISORY UNTIL 11 AM MST WEDNESDAY FOR EASTERN
GLACIER...EASTERN PONDERA...NORTHERN ROCKY MOUNTAIN FRONT...
TOOLE.
&&
$$
SHORT TERM...BLANK
LONG TERM...GUSTAFSON
AVIATION...SUK
UPDATE...SCHOTT
WEATHER.GOV/GREATFALLS
