FXUS65 KBYZ 241128
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
428 AM MST THU DEC 24 2009
.SHORT TERM...VALID FOR TDY AND FRI...
SURFACE HIGH PRESSURE IS OVER THE REGION THIS MORNING BRINGING
COLD TEMPERATURES. THE APPROACH OF A STRONG VORT CENTER IS CAUSING
SOME RAPID PRESSURE FALLS OVER CENTRAL AREAS AT THIS TIME. THIS IS
HELPING TO KEEP WEST TO SOUTHWEST WINDS GUSTY FROM BILLINGS WEST.
THESE GUSTY WINDS HAVE HELPED TO HOLD TEMPERATURES UP IN THE
SINGLE DIGITS ABOVE ZERO WHERE WINDS ARE BLOWING. WHERE WINDS ARE
CALM...AND OVER EASTERN AREAS TEMPERATURES HAVE DROPPED BELOW ZERO
WITH MILES CITY AND BAKER IN THE TEENS BELOW ZERO. WINDS IN BAKER
ARE STILL IN THE 10 TO 15 MPH RANGE RESULTING IN WIND CHILL VALUES
AROUND 30 BELOW ZERO. WILL KEEP THE WIND CHILL ADVISORY THERE IN
PLACE INTO THE MORNING HOURS. IN ADDITION TO KEEPING THE WINDS UP
OVER WESTERN AREAS TODAY...THE APPROACHING VORTICITY CENTER ALONG
WITH PERIODIC IMPULSES RIDING THE UPPER JET SOUTHWARD INTO THE
AREA WILL GENERATE ISOLATED TO SCATTERED AREAS OF LIGHT SNOW
TODAY...ESSENTIALLY EAST OF A ROUNDUP TO BILLINGS TO SHERIDAN
LINE. DO NOT EXPECT MUCH ACCUMULATION WITH THIS ACTIVITY...BUT
SOME AREAS COULD SEE HALF AN INCH OR SO.
STORM SYSTEM OVER THE NORTHERN PLAINS LOOKS LIKE IT WILL SPIN
ENOUGH MOISTURE TO THE WEST TO BRING ACCUMULATING SNOW TO THE
EASTERN PORTION OF THE FORECAST AREA BEGINNING EARLY FRIDAY AND
CONTINUING INTO SATURDAY. LATEST PROGS SHOW TOTAL ACCUMULATIONS
DURING THIS TIME OF 3 TO 6 INCHES FOR FALLON AND CARTER
COUNTIES...WITH LOCALLY HEAVIER ACCUMULATIONS POSSIBLE. THERE IS
STILL UNCERTAINTY AS TO HOW FAR WEST THE SNOW LINE WILL GO...AND
IT DOES LOOK LIKE A PRETTY HARD LINE BETWEEN ADVISORY TYPE AMOUNTS
AND NOTHING. INCREASED POPS AND SNOW ACCUMULATIONS TOWARD HPC
GUIDANCE FOR THIS PERIOD. WILL LET THE DAY SHIFT SEE IF THE SYSTEM
SHIFTS EASTWARD AT ALL BEFORE GOING WITH ANY HIGHLITES. GUSTY
NORTHERLY WINDS SEEM A CERTAINTY...THUS WILL PROBABLY SEE AREAS OF
BLOWING SNOW OVER FAR EASTERN AREAS WHETHER SNOW DEVELOPS THERE OR
NOT. HAVE MENTION OF BLOWING SNOW IN THE GRIDS FOR THESE AREAS
BEGINNING FRIDAY.
TEMPERATURES WILL BE TRICKY. COLD HIGH PRESSURE WILL REMAIN OVER
THE AREA FOR THE NEXT FEW DAYS WHICH SHOULD KEEP TEMPERATURES
DOWN...ESPECIALLY AT NIGHT. HOWEVER DISTURBANCES SLIDING THROUGH
WILL BRING OCCASIONAL BUT SIGNIFICANT PRESSURE CHANGES TO THE AREA
WHICH WILL INCREASE WIND SPEEDS FOR A TIME. WHEN THE WIND SPEEDS
INCREASE TEMPERATURES SHOULD GO UP AS WELL...WHILE CALM WINDS
ESPECIALLY OVERNIGHT WILL LEAD TO RAPID TEMPERATURE DROPS WHEN
COMBINED WITH FRESH SNOW COVER AND BREAKS IN CLOUD COVER. DIDN'T
STRAY TOO FAR FROM PREVIOUS HIGH TEMPERATURES...WENT A BIT COLDER
FOR LOWS BASED ON HOW TONIGHTS MODEL RUNS HAVE TRENDED. CHAMBERS
.LONG TERM...VALID FOR SAT...SUN...MON...TUE...WED...
LATEST MODELS INDICATED THE POSSIBILITY OF A TROWAL LINGERING BEHIND
THE DEPARTING STRONG LOW PRESSURE SYSTEM MOVING THROUGH THE UPPER
MIDWEST SAT THROUGH SAT NIGHT. THE LAST FEW RUNS OF THE GFS HAVE
BEEN TRENDING TOWARD THIS SOLUTION AND THE LATEST WRF/ECMWF
SUPPORTED IT AS WELL. DID NOT SEE STRONG LIFT WITH THIS FEATURE AT
THIS TIME...BUT BASED ON LATEST TRENDS...HAVE INTRODUCED LOW POPS
INTO THE FAR EASTERN ZONES SAT THROUGH SAT NIGHT. WILL NEED TO KEEP
AN EYE ON FUTURE MODEL SOLUTIONS TO SEE IF FURTHER ADJUSTMENTS TO
THESE PERIODS WILL BE NEEDED. AN UPPER RIDGE WAS FORECAST TO MOVE
INTO THE AREA FOR SUN AND SUN NIGHT. MOISTURE WAS RATHER SPARSE
UNDER THE RIDGE SO HAVE KEPT POPS LOW AND CONFINED TO THE SOUTHERN
MOUNTAINS.
UPPER RIDGE WILL THEN SHIFT E THROUGH TUE NIGHT AS THE NEXT
PACIFIC SYSTEM WORKS IT/S WAY INLAND. MODELS WERE ADVERTISING AN
ELONGATED SPLITTING TROUGH WITH THE NORTHERN BRANCH MOVING THROUGH
THE FORECAST AREA. MODELS DIFFERED IN DETAILS OF THE FLOW AND
ASSOCIATED MOISTURE SO KEPT POP ADJUSTMENTS MINIMAL.
WED LOOKED UNSETTLED WITH CYCLONIC NW FLOW ALOFT SO WENT NEAR
CLIMATOLOGY POPS OVER MUCH OF THE AREA. WED NIGHT POPS WERE ALSO
NEAR CLIMO AND LOOKED FINE AT THIS POINT AS MODELS WERE NOT IN GOOD
AGREEMENT WITH THE PATTERN.
ONLY TEMPERATURE CHANGES WERE FOR SAT...AS MODELS WERE NOT IN GOOD
AGREEMENT WITH TEMPERATURE PROFILES FOR MUCH OF THE EXTENDED
PERIOD. HAVE LOWERED TEMPS ON SAT BASED ON PROJECTED SOUNDINGS AND
POSSIBLE CLOUDS AND PRECIPITATION WITH THE TROWAL. ARTHUR
&&
.AVIATION...
A FEW AREAS OF LIGHT SNOW WILL BE POSSIBLE FROM KBIL E AND S TODAY
AS A DISTURBANCE PUSHES S THROUGH E MT. MVFR CONDITIONS WILL BE
POSSIBLE IN THE SNOW...AS WELL AS AREAS OF MOUNTAIN OBSCURATION OVER
THE NE BIG HORNS. OTHERWISE...VFR WILL PREVAIL ACROSS THE REGION
TODAY. AREAS OF SNOW WILL OCCUR FROM KBIL E AND S TONIGHT WITH
MVFR/IFR CONDITIONS. AREAS OF MOUNTAIN OBSCURATION WILL CONTINUE OVER
THE NE BIG HORNS. ARTHUR
&&
.PRELIMINARY POINT TEMP/POPS...
TDY FRI SAT SUN MON TUE WED
-------------------------------------------------------
BIL 012 000/020 003/028 009/033 013/028 014/030 015/028
2/S 20/B 01/B 01/U 11/B 11/B 22/S
LVM 015 002/023 006/030 014/035 015/030 016/030 019/031
0/B 00/B 01/U 01/B 11/B 12/S 22/S
HDN 012 902/017 001/024 005/032 008/029 006/029 010/030
2/S 32/S 20/B 01/U 11/B 11/B 22/S
MLS 007 905/010 903/017 901/026 004/024 005/024 008/023
3/S 33/S 32/S 11/U 11/B 11/B 11/B
4BQ 008 901/013 001/023 002/030 004/028 005/028 008/030
3/S 34/S 42/S 11/B 11/B 11/B 12/S
BHK 005 905/007 903/016 000/025 005/023 005/021 007/025
3/S 46/S 62/S 11/B 11/B 11/B 11/B
SHR 011 905/017 005/026 006/032 003/030 004/032 007/029
2/S 32/S 21/B 12/S 12/S 22/S 22/S
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WIND CHILL ADVISORY IN EFFECT UNTIL 10 AM MST THIS MORNING
FOR ZONES 33-37.
WY...NONE.
&&
$$
WEATHER.GOV/BILLINGS
