FXUS65 KGGW 270316
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
816 PM MST THU NOV 26 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SATURDAY...
UPDATES FOR TONIGHT INCLUDES A WARMING OF TONIGHTS LOW
TEMPERATURES ACROSS MOST OF THE REGION. THE SOUTHERN AREAS OF THE
CWA APPEARED TO NEED THE MOST ATTENTION DUE TO CLOUD COVER
GENERATED BY A CHINOOK ARCH TO THE WEST. THIS HAS ALSO BEEN
CREATING OCCASIONAL GUSTS THAT BREAK UP A MODERATE TO WEAK
INVERSION AT THE LOWER LEVELS AND RE-ELEVATE TEMPERATURES AT
HIGHER LEVELS BRIEFLY EVERY FEW HOURS. IN ADDITION... DEWPOINTS
ARE STAYING HIGHER THAN ANTICIPATED KEEPING TEMPS FROM BOTTOMING
OUT. CLOUDS MAY BE ABLE TO EXIT NORTHERN PORTIONS OF THE CWA
ALLOWING SURFACE INVERSION TO STRENGTHEN AFTER MIDNIGHT AND
CLOSER TO SUNUP. GAH
PREVIOUS SHORT TERM DISCUSSION...
AN UPPER LEVEL RIDGE AXIS WILL BE PUSHED EASTWARD BY AN
APPROACHING UPPER TROF FROM THE WEST TONIGHT. BLACK FRIDAY SHOULD
BE ANOTHER MILD DAY WITH ABOVE AVERAGE TEMPERATURES FOR THIS TIME
OF THE YEAR. EXPECT THICKER CLOUD COVER FRIDAY AFTERNOON AS AN
UPPER SHORTWAVE TROF APPROACHES THE REGION. THE COLD FRONT AHEAD
OF THE UPPER LEVEL TROF WILL MOVE THROUGH EASTERN MONTANA FRIDAY
EVENING/NIGHT AND DEPENDING ON WHICH MODEL YOU SUBSCRIBE TO COULD
BRING A LITTLE PRECIPITATION IN THE FORM OF A RAIN SNOW MIX ALONG
WITH ITS PASSAGE. SINCE THE ATMOSPHERE IS STILL RELATIVELY
DRY...THE PRECIPITATION WILL REMAIN VERY LIGHT.
THE SHORTWAVE TROF WILL ARRIVE IN NORTHEAST MONTANA BY SATURDAY
MORNING AND 1000-500 MB THICKNESS LEVELS WILL DROP TO AROUND 528
DM...WITH 850 MB TEMPERATURES WILL DROPPING TO BETWEEN -5 TO -7
DEGREES CELSIUS. LIFT WILL BE STRONGEST RIGHT AHEAD OF THE SHORTWAVE
TROF AND THE MODELS OVER THE PAST FEW DAY HAVE ALL INDICATED QPF
RIGHT AHEAD OF THE SHORTWAVE BUT PLACEMENT AND TIMING HAS BEEN THE
ISSUE. THE SURFACE COLD FRONT WILL BE EAST OF THE REGION AND IT
LOOKS LIKE MOST OF THE MOISTURE WITH THIS SYSTEM WILL BE RIGHT
AHEAD OF THE SHORTWAVE. WITH ONLY LIGHT PRECIPITATION ANTICIPATED
WITH THE INITIAL PASSAGE OF THE COLD FRONT FRIDAY NIGHT THE
SURFACE SHOULD REMAIN RELATIVELY DRY...OR AT LEAST FAR FROM SATURATED.
WE ARE GOING TO NEED THE UPPER LEVEL MOISTURE TO FALL INTO THE
LOWER ATMOSPHERE...KNOWN AS WET BULBING...WHICH WILL SLOWLY MOISTEN THE
LOWER ATMOSPHERE. THIS WILL HELP THE TEMPERATURE DROP FASTER AND
GET CLOSER TO THE DEW POINT. AT THIS POINT IF THE PRECIPITATION
WERE TO START IT WOULD FALL MOSTLY AS SNOW SATURDAY MORNING AND
EARLY AFTERNOON.
ANOTHER PROBLEM IS THE RATHER MILD WEATHER OVER THE LAST SEVERAL
DAYS. MOST OF THE SNOWFALL WILL MELT ON CONTACT TO START OFF WITH
WITH...SINCE GROUND TEMPERATURES ARE STILL MOSTLY IN THE MID TO
LOWER 40S. ANY SNOW ACCUMULATION SHOULD BE CONFINED IN THE HIGHER
ELEVATION AND NOT EXPECTED TO BE MORE THEN A HALF AN INCH OR SO.
WITH THIS IN MIND IMPACTS ACROSS THE REGION SHOULD BE MINIMAL. THE
12Z NAM AND ECMWF ARE KEEPING MOST OF THE PRECIPITATION ASSOCIATED
WITH THE SHORTWAVE IN SOUTHERN SASKATCHEWAN. THE 12Z GFS DOES
BRING IT ACROSS NORTHEAST MONTANA BRIEFLY...AFTER THIS THE MODELS
ARE INDICATING A DRY SLOT WHICH SHOULD BRING ANY PRECIPITATION TO
AN END. HIGHS PROBABLY WILL REMAIN IN THE LOWER TO MID 30S ACROSS
THE REGION SATURDAY AFTERNOON. RSMITH
.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
COLDER WEATHER TO ARRIVE. LARGE-SCALE PATTERN BECOMES MORE
AMPLIFIED. UPPER RIDGE EARLY IN THE PERIOD FOR A CONTINUATION OF
THE DRIER AND MILDER THAN NORMAL WEATHER. A SHORTWAVE UPPER TROUGH
FROM S AK MOVES SE TOWARD MT AND INTENSIFIES...AS THERE IS STRONG
UPPER RIDGING BEHIND IT INTO AK. THE SHORTWAVE CLOSES OFF BOTH
SURFACE AND ALOFT TO OUR NE-E AND BECOMES A LONGWAVE CLOSED LOW
OVER THE MIDWEST. NE MT IN STRONG NNW FLOW BETWEEN THEM. THIS WILL
MEAN A TURN TO COLDER WEATHER. THICKNESSES DROP TO THE 510S
DM...AND LATEST GFS HAS 850 MB TEMPS DOWN TO -15 BY THU. 12Z ECMWF
LOOKS MORE IN LINE WITH REST OF THE MODELS AS WELL AS THE ONGOING
FORECAST.
STRONG COLD FRONT ARRIVAL IS TUE...TIMING WILL MAKE HIGH TEMPS FORECAST
A LITTLE TOUGH. LIMITED MOISTURE WITH THE TROUGH FOR OUR AREA...BUT
WILL BE WINDY...WITH STRONG COLD ADVECTION TUE. 12Z GFS HAS 850 MB
WINDS OF 50KT AT 12Z TUE...BEFORE COLD FRONT PASSAGE THOUGH.
PROBABLY NO MORE THAN ISOLATED RAIN AND SNOW SHOWERS WITH THE
FRONT. MODEL QPF WOULD SUGGEST THAT AS WELL. COULD BE A SECONDARY
SHORTWAVE FROM THE NNW ABOUT WED/THU...BUT MODELS VAGUE ON THIS AS
WELL AS TIMING. CURRENT 10 PCT OR SO POPS LATE IN THE PERIOD LOOKS
REASONABLE FOR NOW. SIMONSEN
PREVIOUS LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...EXTENDED
PERIOD OPENS WITH UPPER TROF EXITING THE REGION AND UPPER RIDGE
FOLDING OVER THE PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES. ANY
PRECIP THAT OCCURS WITH THE UPPER TROF SHOULD EXITED THE REGION
SATURDAY NIGHT WITH THEN DRY CONDITIONS EXPECTED INTO MONDAY.
TEMPERATURES WILL ALSO BE WARMING AGAIN WITH HIGH PUSHING INTO THE
40S FOR MONDAY.
NEXT SHORTWAVE TROF DIVES THROUGH SOUTHERN BC MONDAY NIGHT AND
MODELS IN RELATIVELY GOOD AGREEMENT WITH ARRIVAL OF WAVE INTO
MONTANA. STRONG COLD FRONT DROPS THROUGH MONTANA ON TUESDAY WITH
SOME CHANCE OF SNOW. POTENTIAL FOR STRONG WINDS HIGHER THAN FOR
PRECIP WITH TIGHT PRESSURE GRADIENT AND COLD AIR ADVECTION WITH
STACKED LOW PRESSURE CENTER TRACKING THROUGH SOUTHERN
SASKATCHEWAN.
FAIRLY MAJOR MODEL DIFFERENCES DEVELOP FOLLOWING THIS WAVE
ALTHOUGH GOOD AGREEMENT WITH SETTLING ARCTIC AIRMASS OVER THE
NORTHERN PLAINS. MAIN QUESTION IS HOW FAR WEST WILL THIS AIRMASS
PUSH...GFS PULLS THE TROF INTO THE UPPER MIDWEST WITH RIDGE ALONG
THE WEST COAST...WHILE THE ECMWF IS MUCH FURTHER WEST. FOR NOW
STICKING WITH TEMPERATURES NEAR CLIMATOLOGICAL NORMS WITH THE IDEA
OF A MORE EASTWARD LONGWAVE POSITION. EBERT
&&
.AVIATION...
VFR. LIGHT AND VARIABLE WINDS TONIGHT BECOMING NORTHERLY LATE
MORNING FRIDAY AFTER A WEAK COLD FRONTAL PASSAGE. SOME SCATTERED
TO BROKEN CLOUDS AROUND 20 000 FEET TONIGHT BECOMING OVERCAST WITH
CEILINGS LOWERING TO 10 000 FEET LATER ON FRIDAY. MARTIN
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
WEATHER.GOV/GLASGOW
