FXUS65 KBYZ 221039
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
339 AM MST TUE DEC 22 2009
.SHORT TERM...VALID FOR TDY AND WED...
WEATHER PATTERN WILL GENERATE CHALLENGES TO HOLIDAY TRAVELERS OVER
THE NEXT 36 HOURS AS A VERY MOIST LOW LEVEL AIRMASS PERSISTS OVER
THE AREA. FOR THIS MORNING A LIGHT UPSLOPE FLOW IS CAUSING FOG
ACROSS NORTH OF THE I94 CORRIDOR WITH FOG PARTICULARLY DENSE OVER
YELLOWSTONE...MUSSELSHELL...TREASURE AND NORTHERN ROSEBUD
COUNTIES. CONCERNED THAT FOG IS NOT GOING TO MAKE MUCH IMPROVEMENT
TODAY AS SURFACE FLOW REMAINS UPSLOPISH AND BUFKIT SHOWS CONTINUED
BOUNDARY LAYER SATURATION. WOULD EXPECT A BIT OF IMPROVEMENT WITH
SOME DIURNAL IN THE TEMPERATURES...BUT SUN ANGLE IS LOW SO
VISIBILITIES MAY NOT EXCEED A MILE. WILL CONTINUE THE CURRENT
DENSE FOG ADVISORY UNTIL 10 A.M. AND WILL ASSUME SOME IMPROVEMENT
AROUND MID DAY.
BIGGER PICTURE SHOWS AN UPPER LOW OVER THE PACIFIC NORTHWEST
DIGGING INTO SOUTHERN NEVADA TODAY WITH SOUTHWEST FLOW ALOFT OVER
MOT NANA THIS MORNING BECOMING LIGHT THIS AFTERNOON. WESTERN WAVE
DOES GENERATE PRESSURE FALLS OVER WYOMING TODAY AND 850 MB WINDS
INDICATE THAT UPSLOPE LOW LEVEL FLOW WILL INCREASE TODAY. GIVEN
THE LOW LEVEL AIRMASS IS ALSO UNSTABLE EXPECT LIGHT SNOW TO
DEVELOP BUT FORCING IS LIMITED SO DO NOT EXPECT ACCUMULATIONS TO
BE SIGNIFICANT. MEANWHILE ANOTHER UPPER LOW TRACKING SOUTHWARD
THROUGH ALBERTA BEGINS TO DIG INTO MONTANA BY LATE TONIGHT AND IT
IS PUSHES AN ARCTIC THROUGH NORTHERN MONTANA LATE TONIGHT. IMPACT
OF AN ARCTIC MOVING THROUGH THE MOIST AIRMASS SHOULD BE TO PRODUCE
AN INCREASE IN SNOW AND COULD SEE A QUICK COUPLE OF INCHES OF SNOW
LATE TONIGHT OR EARLY WEDNESDAY ACROSS THE WESTERN ZONES...
SPREADING EASTWARD ON WEDNESDAY. HAVE DECIDED TO ISSUE AN ADVISORY
FOR SNOW EARLY FOR THIS EVENT BECAUSE IT IS GOING TO BE A BUSY DAY
FOR TRAVEL. ARCTIC LOOKS TO HAVE A CHANCE TO PRODUCE SOME BREEZY
WINDS MAINLY EAST OF BILLINGS AS IT DEEPENS OVER EASTERN SECTIONS
LATER ON WEDNESDAY AND WEDNESDAY NIGHT SO COULD SEE SOME BLOWING
SNOW BECOME A FACTOR. TEMPERATURES WILL BE FALLING BY WEDNESDAY
AFTERNOON AND MANY AREAS WILL SEE LOW TEMPERATURES NEAR ZERO BY
THURSDAY MORNING. ARCTIC AIRMASS DEEPENS QUICKLY WEDNESDAY NIGHT
AND HAVE DECREASING SNOW FROM WEST TO EAST.
SNOWFALL POTENTIAL IS GENERALLY 3 TO 5 INCHES ACROSS THE AREA
WITH A BIT MORE FALLING OVER SOUTHEAST MONTANA AS SNOW LASTS
LONGER. MAIN MESSAGE WILL BE THERE WILL BE A PERIOD OF HEAVIER
SNOWFALL...AND BUFKIT SHOWS SOME PRETTY DEEP DENDRITIC GROWTH
REGIONS DURING THE DAY ON WEDNESDAY. TRAVELERS WILL WANT TO PLAN
ON LONGER DRIVING TIMES ON WEDNESDAY AND WEDNESDAY NIGHT. BORSUM
.LONG TERM...VALID FOR THU...FRI...SAT...SUN...MON...
SEVERAL MINOR CHANGES TO THE EXTENDED PERIOD AS APPEARS IN PRETTY
GOOD SHAPE. MODELS APPEAR IN PRETTY GOOD AGREEMENT OVERALL...WITH
UPPER SYSTEM EXITING EAST TO START THE PERIOD AS AN UPPER RIDGE
BUILDS INTO THE REGION FOR THE WEEKEND. SOME TIMING DIFFERENCES DO
ARISE FOLLOWING THE RIDGE...BUT OVERALL PATTERN APPEARS PRETTY
SOLID AT THIS TIME.
THE EXTENDED BEGINS WITH WRAP AROUND PRECIPITATION FROM THE LATEST
LOW PRESSURE SYSTEM IMPACTING THE EASTERN ZONES. HAVE RAISED POPS
EAST...WITH LIKELY POPS IN EXTREME SOUTHEAST ON THURSDAY...DIMINISHING
THROUGH FRIDAY AFTERNOON. THE UPPER LEVEL RIDGE BUILDS IN LATE
FRIDAY AND REMAINS IN CONTROL THROUGH THE WEEKEND. THE RIDGE
BEGINS BREAKING DOWN AS A BACKDOOR FRONT SLIDES IN FROM THE
NORTHEAST LATE SUNDAY/EARLY MONDAY. MEANWHILE ANOTHER UPPER LEVEL
TROF IS TAKING SHAPE OVER THE PACIFIC COAST AND IS PROGGED TO PUSH
INTO THE REGION MONDAY. HAVE SLIGHT POPS SPREADING INTO THE PLAINS
MONDAY AND MONDAY NIGHT. SOME WEAK RIDGING APPEARS TO BEGINNING
TAKING HOLD AGAIN BY TUESDAY THROUGH WEDNESDAY. MODELS DO BEGIN TO
HAVE TIMING AND INTENSITY ISSUES WITH THE PACIFIC TROF...BUT
OVERALL PATTERN REMAINS PRETTY CONSISTENT...WITH TROF FOLLOWED BY
WEAK RIDGING.
AS FOR TEMPERATURES...MADE ONLY MINOR ADJUSTMENT...MAINLY TO LINE
UP WITH NEIGHBORS. MODELS DID APPEAR TO COME IN A BIT WARM...SO
DID END UP TRENDING UP SLIGHTLY. CONCERN WITH CHANGES ARE THAT
THIS APPEARS TO BE A BIT OF A DEPARTURE FROM PREVIOUS READ OF
ARCTIC POTENTIAL...SO WILL BARE WATCHING WITH FUTURE RUNS. DID INITIATE
SLIGHT WARMUP FOR NEW PERIODS...AS APPEARS SOME WEAK RIDGING
SHOULD MODERATE TEMPS. GILSTAD
&&
.AVIATION...
DENSE FOG IS IMPACTING MUCH OF THE NORTHERN TIER OF THE CWA THIS
MORNING...INCLUDING HARLOWTON...KBIL...KMLS...KBHK AND EKALAKA.
CONDITIONS WILL RANGE FROM MVFR TO IFR...AND PERIODIC LOCALIZED
LIFR AND VLIFR CONDITIONS IN FOG. FOG IS EXPECTED TO LIFT LATE THIS
MORNING...FROM NORTHWEST TO SOUTHEAST...AS DRIER NORTHWEST WINDS
PUSH INTO THE AREA. CHANCES FOR SNOW WILL INCREASE ACROSS THE
AREA THROUGH THE DAY TODAY...AS A WINTER STORM SYSTEM BEGINS
PUSHING THROUGH THE REGION....SO EXPECT PREVAILING MVFR/IFR
CONDITIONS UNDER LOW CEILINGS AND INCREASING SNOW INTENSITY.
LOCALIZED LIFR TO VLIFR CONDITIONS WILL OCCUR IN THE AREAS OF
HEAVIER SNOW. THERE WILL ALSO BE AREAS OF OBSCURATION OVER THE
MOUNTAINS THROUGH THE DAY TODAY. GILSTAD
&&
.PRELIMINARY POINT TEMP/POPS...
TDY WED THU FRI SAT SUN MON
-------------------------------------------------------
BIL 033 016/018 003/013 002/021 007/027 009/026 009/014
3/S 69/S 31/E 11/U 11/B 11/B 11/B
LVM 039 017/018 902/016 002/022 007/027 015/029 013/024
5/O 79/S 21/E 01/B 11/B 11/B 11/B
HDN 033 016/019 002/013 904/019 001/027 004/027 004/018
3/S 69/S 51/E 11/B 11/B 11/B 11/B
MLS 026 015/020 001/008 905/011 905/022 001/021 902/010
3/S 68/S 72/S 22/S 11/B 11/B 11/B
4BQ 032 016/024 004/013 904/017 002/027 003/024 003/020
4/S 69/S 83/S 22/S 11/B 11/B 11/B
BHK 025 011/018 002/009 906/014 907/022 905/019 903/011
3/S 69/S 84/S 32/S 11/B 11/B 11/B
SHR 032 017/022 006/015 000/021 004/027 008/029 008/022
4/O 79/S 72/S 12/S 11/B 12/S 12/S
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT FROM 11 PM THIS EVENING TO
5 PM MST WEDNESDAY FOR ZONES 28>30-34-35-39>42-56-63>66.
DENSE FOG ADVISORY IN EFFECT UNTIL 10 AM MST THIS MORNING FOR
ZONES 29>31-35.
WINTER WEATHER ADVISORY IN EFFECT FROM 5 AM TO 11 PM MST
WEDNESDAY FOR ZONES 31-32-38-57-58.
WINTER WEATHER ADVISORY IN EFFECT FROM 5 AM WEDNESDAY TO 5 AM
MST THURSDAY FOR ZONES 33-36-37.
WY...WINTER WEATHER ADVISORY IN EFFECT FROM 5 AM TO 11 PM MST
WEDNESDAY FOR ZONE 99.
&&
$$
WEATHER.GOV/BILLINGS
