FXUS65 KBYZ 220516
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT 
1016 PM MST MON DEC 21 2009

.SHORT TERM...VALID FOR TUE AND WED...

UPDATED FORECAST TO EXPAND THE DENSE FOG ADVISORY TO YELLOWSTONE
AND TREASURE COUNTY. VISIBILITY AT THE BILLINGS AIRPORT QUICKLY
DROPPED TO 1/4 OF A MILE AROUND 930 PM...AND LAW ENFORCEMENT
REPORTED VERY LOW VISIBILITY IN HYSHAM AROUND 10 PM. EXPECT THE
DENSE FOG TO PERSIST WELL INTO TUESDAY MORNING. CHAMBERS

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

THE EXTENDED STARTS OFF WITH WRAP AROUND PRECIPITATION FROM THE
LATEST LOW PRESSURE SYSTEM IMPACTING THE EASTERN ZONES. THE GFS
AND ECMWF AGREE VERY WELL ON THE PLACEMENT OF THE MOISTURE AND
BOTH HAVE LOW QPF. RAISED POPS IN THE THURSDAY AND EARLY FRIDAY
PERIODS TO MATCH THE INCREASING CONFIDENCE IN THIS SOLUTION.
HIGH TEMPERATURES IN THE TEENS FOR THIS PERIOD WILL KEEP ANY SNOW
FROM THE PREVIOUS SYSTEM AROUND FOR A WHITE CHRISTMAS ON FRIDAY.

AN UPPER LEVEL RIDGE BUILDS IN FOR THE WEEKEND AND TEMPERATURES
RISE OVER THE WEEKEND. AS THE COLDEST AIR EXITS THE REGION TO THE
SOUTHEAST...LOW LEVEL FLOW REMAINS NORTHERLY AND KEEPS OUT
TEMPERATURES BELOW FREEZING FOR THE WEEKEND.

EARLY NEXT WEEK THE GFS AND ECMWF SOLUTIONS BEGIN TO DIVERGE. THE
GFS PULLS THE LOW OVER THE UPPER MISSISSIPPI VALLEY BACK INTO THE
HUDSON BAY LOW AND BEGINS TO RETROGRADE THE WHOLE SYSTEM CAUSING
COLD NORTHERLY FLOW INTO MONTANA AND SETS US UP FOR ANOTHER ARCTIC
FRONT EARLY IN THE WEEK. THE ECMWF KEEPS A MORE ELONGATED TROUGH
OVER THE EASTERN US AND BUILDS A STRONGER RIDGE OVER THE WEST
COAST WITH MUCH WARMER AND SETTLED CONDITIONS FOR THE AREA. THE
GEFS ENSEMBLE MEAN CURRENTLY SUPPORTS A SIMILAR SOLUTION AS THE
GFS...SO WE CONTINUED THE COOLING TREND FOR EARLY NEXT WEEK. ALSO
RAISED POPS DURING THIS PERIOD SOME TO INDICATE THE THREAT OF THE
ARCTIC FRONT. LEACH/SOLUM.

&&

.AVIATION...

AREAS OF FOG...LOCALLY DENSE...AND STRATUS WILL OCCUR ACROSS 
NORTHERN PORTIONS OF THE AREA TONIGHT. EXPECT FOG OVER AND NEAR 
HARLOWTON...KBIL...KMLS...KBHK AND EKALAKA. CONDITIONS WILL RANGE 
FROM MVFR TO IFR IN THE FOG AND STRATUS...WITH LOCAL VLIFR 
CONDITIONS. THERE WILL ALSO BE A SLIGHT CHANCE OF SNOW WITH THE FOG. 
EXPECT AREAS OF MOUNTAIN OBSCURATION TONIGHT AS WELL. SW WINDS AT 20 
TO 30 KT OVER KLVM WILL GRADUALLY DIMINISH OVERNIGHT. 

CHANCES FOR SNOW WILL INCREASE ACROSS THE AREA THROUGH THE DAY ON 
TUE. MVFR/IFR CONDITIONS WILL OCCUR IN THE SNOW. THERE WILL ALSO BE 
AREAS OF OBSCURATION OVER THE MOUNTAINS. ARTHUR
 

&&

.PRELIMINARY POINT TEMP/POPS...

    TUE     WED     THU     FRI     SAT     SUN     MON     
-----------------------------------------------------------
BIL 029/033 014/018 004/013 002/018 007/027 009/026 009/014
    03/S    68/S    31/E    11/U    11/B    22/S    22/S
LVM 037/039 015/019 000/016 002/019 007/027 015/029 013/024
    25/O    68/S    21/E    11/B    11/B    12/S    12/S
HDN 027/033 014/019 001/013 904/019 001/027 004/027 004/018
    03/S    68/S    31/E    11/B    11/B    12/S    22/S
MLS 018/026 013/018 001/008 905/012 905/022 001/021 902/010
    23/S    68/S    62/S    11/B    11/B    22/S    21/B
4BQ 022/032 014/022 004/013 904/017 002/027 003/024 003/020
    24/S    68/S    62/S    11/E    11/B    22/S    21/B
BHK 017/025 009/016 002/009 906/011 907/022 905/019 903/011
    53/S    68/S    63/S    21/E    11/B    22/S    11/B
SHR 026/032 015/021 006/015 000/021 004/027 008/029 008/022
    04/O    68/S    62/S    12/S    11/B    12/S    23/S

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...DENSE FOG ADVISORY IN EFFECT UNTIL 10 AM MST TUESDAY FOR
      ZONES 29>31-35.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS