Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 131746
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
1046 AM MST SAT DEC 13 2014

.UPDATE...
OVERALL FORECAST FOR TODAY IS IN GOOD SHAPE. STRONG SOUTHERLY JET
EXISTS OVER OUR CWA TODAY AS DEEP TROF MOVES SLOWLY THRU THE
INTERMOUNTAIN WEST. WEAK ECHOES OVER OUR WEST INDICATIVE OF SOME
LIGHT SHOWERS OVER THE MTNS. ENERGY LIFTING OUT OF UT AND WESTERN
WY IS PRODUCING SNOW AT BIG PINEY AND JACKSON...AND THIS SHOULD
TRANSLATE TO INCREASING SNOW SHOWERS OVER OUR WESTERN MTNS THIS
AFTERNOON...ESPECIALLY AS MID LEVEL BAROCLINIC ZONE SHIFTS FROM
WESTERN TO CENTRAL MT. LOW LEVEL DOWNSLOPE WINDS WILL LIMIT PCPN
CHANCES OVER OUR LOWER ELEVATIONS UNTIL LATE TODAY OR THIS
EVENING. HAVE RAISED SHOWER COVERAGE TO NUMEROUS OVER THE
BEARTOOTH ABSAROKAS. REGARDING TEMPS...LOCATIONS IN OUR EAST WILL
BE WELL INTO THE 50S WITH SOME LOWER 60S. PLACES SUCH AS SHERIDAN
WHICH HAVE STRUGGLED TO MIX AT ALL THE LAST COUPLE DAYS SHOULD SEE
A BETTER CHANCE OF WARMER TEMPS TODAY AS COLD ADVECTION/SHIFTING
WINDS PROMOTE GREATER MIXING. HAVE TWEAKED SOME TEMPS UP A BIT AS
LIVINGSTON HAS ALREADY HIT 53 AT 10AM...THOUGH COLD ADVECTION
SHOULD DROP TEMPS THERE SOON. JKL

&&

.SHORT TERM...VALID FOR TDY AND SUN...

SPLIT FLOW TROUGH MOVING ACROSS THE WESTERN UNITED STATES WILL BE
THE MAIN WEATHER FEATURE FOR THE SHORT TERM AS ITS INFLUENCE
SPREADS INTO THE REGION LATE TODAY. THE PRIMARY ENERGY WITH THIS
SYSTEM IS IN THE SOUTHERN BRANCH MOVING THROUGH ARIZONA AND UTAH.
HOWEVER THE SECONDARY BRANCH OF ENERGY WILL DROP OUT OF THE NORTH
AND MOVE ACROSS OUR REGION FOR THE LATTER PART OF THE WEEKEND AND
PERHAPS BE MUCH MORE OF AN IMPACT THAN THE STRONGER SOUTHERN
BRANCH. OUR MAIN MESSAGE WITH THIS SYSTEM IS A RETURN TO SEASONAL
WEATHER...BUT NO LARGE SNOWFALL ACCUMULATIONS OR ARCTIC AIR IS
EXPECTED. THUS...NO SIGNIFICANT IMPACTS.

FOR TODAY WE EXPECT SOUTHERLY FLOW TO PREVAIL AHEAD OF THE MAIN
TROUGH AXIS WHICH WILL KEEP MOST LOCATIONS ON THE MILD SIDE
YET...BUT WITH SOME ISOLATED TO SCATTERED RAIN AND SNOW SHOWERS
MOVING INTO THE BEARTOOTH/ABSAROKAS AND NEARBY FOOTHILLS. THE
CHANCE OF RAIN AND SNOW SHOWERS INCREASES THIS EVENING AND
OVERNIGHT AS THE TROUGH AXIS MOVES ACROSS. THE PATTERN DOES NOT
FAVOR MUCH PRECIPITATION IN BILLINGS OR NEARBY AREAS BEYOND THE
MOUNTAINS DUE TO WEAK FORCING AND NORTHWESTERLY LOW LEVEL FLOW.
BUT WE DO EXPECT AFTER AN INITIAL PERIOD OF FORCING OVER THE
BEARTOOTHS THAT THE FOCUS WILL TURN TO THE BIG HORNS REGION AND
NEARBY FOOTHILLS. SOME OF THE BETTER CIPS ANALOGS ALSO SUPPORT
THIS PATTERN FOCUSING ON THE BIG HORNS REGION. THE WRF AND ECMWF
HAVE ALSO TRENDED TOWARD A SLOWER PROGRESSION THAN THE GFS SO I
HAVE LINGERED SOME OF THE HIGHER POPS SUNDAY AFTERNOON AND EVENING
IN THE EAST AS THE OVERALL MODEST YET STEADY FORCING SHOULD
PRODUCE SOME LIGHT PRECIPITATION OVER OUR EASTERN ZONES AS WELL.
I HAVE OPTED TO HAVE FAIRLY HIGH POPS BUT KEPT OVERALL SNOWFALL
ACCUMULATIONS ON THE LOW SIDE DUE TO THE UNORGANIZED AND WEAK
NATURE OF THE FORCING. AT THIS TIME THE ZONES WITH THE HIGHEST
PROBABILITY OF SEEING A POTENTIAL HIGHLIGHT ARE THE BIG HORNS AND
PERHAPS SOUTHERN BIG HORN COUNTY. SNOWFALL AMOUNTS ARE ON THE
FENCE THOUGH AND CONFIDENCE BELOW AVERAGE AS TO THE EXTENT OF
SNOWFALL. SO WILL LET THE DAYSHIFT ADDRESS POTENTIAL HIGHLIGHTS
AFTER SEEING ANOTHER MODEL CYCLE OR TWO. BT

.LONG TERM...VALID FOR MON...TUE...WED...THU...FRI...

STILL A GOOD DEAL OF UNCERTAINTY AS TO HOW THE PATTERN IN THE
EXTENDED FORECAST WILL UNFOLD. GFS SPAGHETTI PLOTS SHOWED
CONSIDERABLE SPREAD LATE IN THE EXTENDED PERIOD WITH THE 500 MB
HEIGHTS. THE ECMWF SHOWED AN INCREASING STANDARD DEVIATION IN THIS
FIELD BEGINNING MIDWEEK.

ON MON...THE FORECAST AREA IS SANDWICHED BETWEEN A HIGH PRESSURE
RIDGE MOVING IN FROM THE W...AND CYCLONIC FLOW AND SHORTWAVE
ENERGY FROM AN UPPER LOW ROTATING S THROUGH CENTRAL CANADA.
Q-VECTOR CONVERGENCE WAS WEAK WITH THE SHORTWAVE. GFS CONTINUES TO
MOVE PRECIPITATION QUICKLY OUT OF THE AREA...WHILE THE ECMWF HAS
TRENDED SLOWER IN MOVING THE MOISTURE S...SO HAVE BLENDED POPS
WITH THE ECMWF TO REFLECT A COMPROMISE. SIMILAR TO LAST NIGHT/S
RUNS...THE GFS HOLDS THE CANADIAN LOW OVER THE DAKOTAS THROUGH WED WHILE
THE ECMWF SHIFTS IT OFF TO THE E. PACIFIC MOISTURE DOES RESURGE
INTO THE SW MOUNTAINS ON TUE. KEPT MON NIGHT DRY THEN HAD A SLIGHT
CHANCE IN THE SW MOUNTAINS FOR TUE.

THE NEXT PACIFIC TROUGH WAS WORKING INTO THE AREA ON WED WITH SW
FLOW ALOFT ON THE ECMWF AND WEAK FLOW ON THE GFS. MOISTURE REMAINS
LIMITED TO THE MOUNTAINS ON BOTH MODELS. THE UPPER LOW OVER THE
DAKOTAS ON THE GFS WOBBLES NW INTO CANADA ON THU AND BOTH MODELS
SHOW WEAK TROUGHING OVER THE AREA. UPPER RIDGING MOVES IN FOR FRI
THEN ANOTHER TROUGH FOR SAT. BASED ON THE ENSEMBLE SOLUTIONS MENTIONED
ABOVE...THERE WAS MUCH PATTERN UNCERTAINTY FROM WED ONWARD...SO
WENT WITH SUPERBLEND FOR POPS.

BECAUSE THE GFS HOLDS ONTO THE LOW PRESSURE OVER THE REGION FOR
MUCH OF THE PERIOD...IT/S SOLUTION WAS COLDER THAN THE ECMWF
SOLUTION. DID USE A BLEND OF TEMPERATURES FOR THE FORECAST WHICH
RESULTED IN HIGH TEMPERATURES AROUND SEASONAL VALUES. ARTHUR


&&

.AVIATION...

A PACIFIC COLD FRONT WILL MOVE ACROSS THE FORECAST AREA TODAY
BRINGING GUSTY WEST TO NORTHWEST WINDS DURING THE AFTERNOON. RAIN
AND SNOW SHOWER CHANCES AND POSSIBLE MVFR CONDITIONS WILL INCREASE
THIS AFTERNOON WEST OF KBIL WITH SNOW SHOWERS AND MOUNTAIN
OBSCURATIONS BECOMING LIKELY FOR THE CRAZY AND BEARTOOTH/ABSAROKA
MOUNTAINS. OTHERWISE FOR THE LOWER ELEVATIONS...VFR CONDITIONS
WILL PREVAIL TODAY. HOOLEY

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY SUN     MON     TUE     WED     THU     FRI
-------------------------------------------------------
BIL 054 032/038 022/034 019/033 018/035 020/039 021/039
    1/E 34/S    41/B    11/U    11/B    11/B    11/U
LVM 054 030/036 019/036 016/036 021/039 023/039 021/039
    3/W 43/S    21/B    11/U    11/B    11/B    11/N
HDN 055 028/038 020/034 013/033 011/034 013/036 015/038
    0/E 36/S    42/J    10/U    11/B    11/B    11/U
MLS 053 031/035 022/030 015/029 012/030 014/032 016/034
    0/B 26/S    41/B    10/U    10/B    11/B    11/U
4BQ 060 030/036 022/032 014/033 013/034 014/036 016/037
    0/B 26/S    52/J    10/U    11/B    11/B    11/U
BHK 057 028/033 020/029 014/027 012/029 014/032 016/032
    0/B 24/S    52/J    11/B    00/B    11/B    11/B
SHR 057 028/036 019/032 012/033 012/035 015/036 014/036
    0/B 46/S    62/J    10/U    11/B    11/B    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS



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