Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 161803
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
1103 AM MST TUE DEC 16 2014

.UPDATE...
A QUICK UPDATE TO EXTEND THE DENSE FOG ADVISORY FOR STILLWATER
SWEET GRASS AND WHEATLAND COUNTY THROUGH 2 PM THIS AFTERNOON.
DENSE FOG WITH VISIBILITY LESS THAN A 1/4 MILES IS CONTINUING
OVER THESE AREAS AS A RESULT OF A MOIST UPSLOPE SURFACE FLOW. WILL
KEEP AREAS OF FOG GOING FOR SHERIDAN NORTHWARD THROUGH BILLINGS
AND ROUNDUP INTO THE EARLY AFTERNOON HOURS ALSO. NO OTHER CHANGES
MADE TO THE FORECAST. RICHMOND

&&

.SHORT TERM...VALID FOR TDY AND WED...

MAIN FORECAST PROBLEM FOR THE SHORT TERM CONCERNS CONSIDERABLE
AREAS OF FOG ACROSS THE FORECAST AREA...PARTICULARLY IN THE LOWER
ELEVATIONS OF THE WESTERN ZONES. THE PATTERN FAVORS THIS TO
CONTINUE WITH A RIDGE ALOFT AND SURFACE LOW PRESSURE TO OUR
WEST/SOUTHWEST THIS IS KEEPING A SOUTHEAST LOW LEVEL FLOW
UPSLOPING INTO SOUTH CENTRAL MONTANA. LOCAL OBSERVATIONS SHOW A
QUARTER MILE VISIBILITY OR LESS IN AREAS JUST WEST OF BILLINGS TO
LIVINGSTON AND UP TO JUDITH GAP. MESOSCALE CROSS SECTIONS SHOW
THIS PERSISTING THROUGH MUCH OF THE MORNING FOR THIS AREA...AND
PERHAPS EVEN INTO THE AFTERNOON FOR PARK COUNTY AROUND LIVINGSTON.
THIS WILL ALSO TEND TO PREVENT MUCH IF ANY SOLAR RADIATION FOR
MUCH OF THE DAY AND SINCE MOS GUIDANCE IS NOT TAKING IT INTO
ACCOUNT I WILL BE SURE TO UNDERCUT GUIDANCE IN THESE AREAS. MAIN
MESSAGE...FOGGY AND CONTINUED CHILLY MOST LOCATIONS TODAY.

DENSE FOG ADVISORY...ISSUED ACROSS AREAS GENERALLY FROM LIVINGSTON
TO BIG TIMBER AND UP TO JUDITH GAP WHERE OBSERVATIONS INDICATE
PERSISTENT DENSE FOG. LOCALLY ICY ROADS WILL MAKE THIS EVEN MORE
DANGEROUS. AS MENTIONED BEFORE PROGGS SUGGEST THE WIDESPREAD FOG
WILL LINGER IN THESE AREAS UNTIL ABOUT 18Z.

IN THE MEANTIME...THE 500MB RIDGE BUILDING OVER US NOW WILL
QUICKLY BREAK DOWN LATE TODAY AND TONIGHT AS ANOTHER BROAD SPLIT
FLOW TROUGH MOVES INTO THE WESTERN UNITED STATES. A WEAKER SHORT
WAVE IN THE MEAN FLOW WILL SPLIT FROM THE SOUTHERN BRANCH AND
TRACK OVER OUR REGION TONIGHT AND INTO WEDNESDAY. QPF PROGGS ARE
NOT IMPRESSIVE BUT SEEMS PRUDENT TO BUMP UP SOME OF THE POPS NOW
FOR THE HIGH COUNTRY. WE MAY SEE SOME FLURRIES OR LIGHT SNOW IN
THE EAST AS IT MOVES THROUGH WEDNESDAY MORNING AS WELL. LOOK FOR A
MODEST WARM UP TO AROUND SEASONAL AVERAGES FOR WEDNESDAY. BT

.LONG TERM...VALID FOR THU...FRI...SAT...SUN...MON...

ENSEMBLE FORECASTS FROM THE GFS AND ECMWF WERE SHOWING MORE
CONFIDENCE IN THEIR SOLUTIONS FOR THE EXTENDED PERIOD THAN THEY
HAVE IN PREVIOUS RUNS.

FLOW GENERALLY BECOMES MORE PROGRESSIVE WITH TIME. WEAK NORTHERN
STREAM OF A PACIFIC TROUGH WILL BE OVER THE REGION ON THU. THIS
WILL BE FOLLOWED BY A SHORTWAVE RIDGE ON FRI AND ANOTHER WEAK
TROUGH FOR SAT. WENT WITH SUPER BLEND POPS FOR THIS PERIOD WHERE
MOISTURE AFFECTS MAINLY THE MOUNTAINS. A STRONG PACIFIC JET WMP/POPS...

    TDY WED     THU     FRI     SAT     SUN     MON
-------------------------------------------------------
BIL 027 020/036 022/039 023/039 026/042 025/043 035/045
    0/B 11/B    01/B    10/U    11/B    12/W    23/W
LVM 029 024/042 023/042 022/041 026/043 026/043 033/045
    1/E 22/J    11/E    11/U    11/B    13/W    33/W
HDN 029 014/033 015/037 017/038 019/040 019/041 028/043
    0/E 01/B    01/B    10/U    01/B    11/B    23/W
MLS 027 015/030 017/036 019/037 018/038 022/039 028/042
    0/E 01/B    01/B    10/U    01/U    11/U    23/W
4BQ 030 015/033 016/040 018/040 016/041 020/042 027/043
    0/E 02/J    01/B    10/U    01/U    11/B    23/W
BHK 024 012/028 015/035 019/037 016/038 020/039 025/041
    0/E 02/J    11/B    11/U    01/U    11/B    23/W
SHR 028 015/036 016/038 016/038 019/040 019/041 026/042
    0/B 01/B    01/B    10/U    01/B    12/J    33/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...DENSE FOG ADVISORY IN EFFECT UNTIL 2 PM MST THILL
MOVE INTO THE REGION LATE IN THE PERIOD WHICH RESULTS IN A FAST
WNW FLOW OVERTAKING THE AREA BEGINNING ON SUN. ENERGY WILL MOVE
THROUGH THIS FLOW ALONG WITH PERIODS OF PACIFIC MOISTURE. GEFS
SHOWED AN ATMOSPHERIC RIVER WILL AFFECT THE REGION SUN INTO MON
WHICH WILL CONTRIBUTE TO PRECIPITATION CHANCES. HAVE INCREASED
POPS OVER THE AREA BEGINNING ON SUN. MAY HAVE GAP WIND ISSUES SAT
NIGHT INTO MON AS MODELS AGREED ON STRONG LEE TROUGHING OVER THE
AREA. WILL CONTINUE TO HAVE STRONG WINDS IN THE FORECAST FOR THE
GAP AREAS. THE MODELS WERE IN GOOD AGREEMENT WITH TEMPERATURES
THROUGH THE EXTENDED AND SHOWED ABOVE NORMAL READINGS. ARTHUR
&&

.AVIATION...

LIFR TO VLIFR CONDITIONS IN STRATUS AND FOG WILL PERSIST FROM
ROSEBUD COUNTY W THROUGH MOST OF THE DAY. LATEST SHORT RANGE
GUIDANCE SHOWS LITTLE IMPROVEMENT. TONIGHT CONDITIONS WILL LIKELY
DEGRADE FROM ANY IMPROVEMENTS TODAY. MOUNTAIN OBSCURATIONS WILL
BE WIDESPREAD THROUGH TONIGHT. REIMER

&&

.PRELIMINARY POINT TEIS AFTERNOON
      FOR ZONES 28-34-41-63.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS


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