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228
FXUS65 KBYZ 210230
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
830 PM MDT SAT SEP 20 2014

.UPDATE...
NO UPDATE NECESSARY THIS EVENING. CLEAR SKIES AND DECREASING WINDS
WILL RESULT IN A SEASONABLY COOL NIGHT. MORE SUNSHINE AND MILD
TEMPS FOR TOMORROW. BT

&&

.SHORT TERM...VALID FOR SUN AND MON...

BEAUTIFUL WILL AGAIN BE THE OPERATIVE WORD ON SUN AND LIKELY AGAIN
ON MON IN MANY AREAS...BUT BY THEN THE PRECIPITATION CHANCE SHOULD
BE ON THE INCREASE...ESPECIALLY FOR THE MOUNTAINS AND NORTHERN WY.

TONIGHT...SURFACE HIGH PRESSURE WILL BE IN CONTROL FOR A CLEAR SKY
AND LIGHT WINDS...PROMOTING EFFICIENT RADIATIONAL COOLING AND THUS
ALLOWING FOR LOWS MAINLY IN THE 40S F. THE SURFACE RIDGE AXIS WILL
BE IN SOUTHEASTERN MT BY LATE NIGHT AND THAT IS OFTEN A CASE WHERE
GUIDANCE UNDERESTIMATES COOLING...SO WE ARE ADVERTISING SOME 30S F
THERE IN LINE WITH A BIAS-CORRECTED...MULTI-MODEL CONSENSUS OF THE
12 UTC MOS OUTPUT WHICH WE USED TO CREATE TONIGHT/S LOW FORECAST.

SUN...RIDGING WILL BE IN CONTROL ALOFT WITH MID-LEVEL WARMING ATOP
EAST-SOUTHEAST NEAR-SURFACE WINDS. THIS SCENARIO WILL LIKELY LIMIT
THE DEPTH OF THE MIXED LAYER TO BETWEEN 3000 AND 4000 FT AGL BASED
ON 12 UTC GFS FORECAST SOUNDINGS...BUT THAT IS ENOUGH FOR HIGHS IN
THE 70S F AND DRY WEATHER. BY LATE SUN NIGHT...A LOW SHOWER CHANCE
SHOWS UP IN THE MOUNTAINS WITH INCREASING MOISTURE CONTENT ALOFT.

BY MON...THE WEAK...INITIALLY-CUT-OFF 500-MB LOW SEEN OVER CA THIS
AFTERNOON IS PROJECTED TO MOVE INTO WY UNDER THE MEAN RIDGE. THERE
IS ABOVE-AVERAGE CONFIDENCE IN THIS SCENARIO WITH A WELL-CLUSTERED
MODEL CONSENSUS...WHICH ALSO SUPPORTS A SEASONABLY ANOMALOUS PLUME
OF MOISTURE OVER NORTHERN WY AND FAR SOUTHERN MT /THE PRECIPITABLE
WATER VALUES FROM NAEFS ENSEMBLE DATA ARE A ONE IN TEN-YEAR TO ONE
IN THIRTY-YEAR MAGNITUDE FOR THIS TIME OF YEAR/. THE MOUNTAINS MAY
RECEIVE LOCALLY HEAVY RAIN DESPITE WEAK SYNOPTIC-SCALE FORCING. IT
IS NOT CLEAR HOW FAR NORTH PRECIPITATION WILL EXTEND...BUT SOME OF
OUR STATISTICAL TOOLS SUPPORT POPS AROUND 30 PERCENT NORTHWARD ALL
THE WAY TO AROUND BILLINGS. CLOUD COVER OR THE LACK THEREOF SHOULD
DICTATE THE DEGREE OF HEATING IN A GENERALLY WARM AIR MASS...SO WE
LEANED ON CONTINUITY WITH A DASH OF THE 12 UTC MODEL CONSENSUS FOR
THE TEMPERATURE FORECAST. WE ARE THUS CALLING FOR ANOTHER DAY WITH
MAINLY 70S F AND EVEN AROUND 80 F WHERE SUNSHINE MAY PREVAIL ALONG
AND NORTH-NORTHEAST OF I-90 AND I-94. SCHULTZ

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

MODELS ARE IN GOOD AGREEMENT TO START THE EXTENDED PERIOD WITH A
LARGE RIDGE OF HIGH PRESSURE OVER THE NORTHERN ROCKIES RESULTING
IN DRY CONDITIONS AND WELL ABOVE NORMAL TEMPERATURES TUESDAY
THROUGH THURSDAY. MODELS THEN BEGIN TO DIVERGE LATE THURSDAY AND
ARE COMPLETELY OUT OF PHASE FRIDAY INTO NEXT WEEKEND. AS A
RESULT...FORECASTER CONFIDENCE THURSDAY THROUGH NEXT WEEKEND IS
VERY LOW.

BOTH MODELS BRING A LARGE UPPER LOW AND TROUGH ONTO THE PACIFIC
NORTHWEST COAST FRIDAY WITH THE ECMWF BEING THE SLOWER SOLUTION.
THE GFS BRINGS THE TROUGH INTO THE AREA LATE FRIDAY THEN KEEPING
AN UPPER LOW STATIONARY OVER THE GREAT BASIN AREA THROUGH THE
WEEKEND. THIS SCENARIO WOULD BRING A WET AND COOL PERIOD TO OUR
FORECAST AREA. HOWEVER...THE ECMWF KEEPS THE TROUGH AND LOW OVER
THE PACIFIC NORTHWEST THROUGH SUNDAY WHICH WOULD RESULT IN
CONTINUED WARM TEMPERATURES INTO NEXT WEEKEND WITH THE POSSIBILITY
OF SHOWERS AND THUNDERSTORMS. AS A RESULT OF SUCH DIVERSE MODEL
SOLUTIONS...DID NOT MAKE AND CHANGES TO THE LATTER HALF OF THE
EXTENDED. HOOLEY
&&

.AVIATION...

CLEAR SKIES AND VFR CONDITIONS WILL PREVAIL THROUGH THE NIGHT. NO
AVIATION HAZARDS ARE EXPECTED. HOOLEY

&&

.PRELIMINARY POINT TEMP/POPS...

    SUN     MON     TUE     WED     THU     FRI     SAT
-----------------------------------------------------------
BIL 049/076 051/079 055/083 055/085 057/087 057/080 053/069
    00/U    13/T    21/B    11/U    11/B    11/U    22/T
LVM 042/077 048/077 050/079 048/084 049/084 049/077 046/066
    00/U    13/T    21/B    10/U    01/B    22/T    23/T
HDN 045/078 048/080 052/084 052/087 056/087 056/082 051/072
    00/U    03/T    21/B    11/U    11/U    11/U    12/T
MLS 042/075 048/081 054/084 054/088 058/088 058/083 054/073
    00/U    01/U    11/B    11/U    11/U    11/U    11/B
4BQ 041/075 049/081 054/083 052/087 057/088 057/083 052/073
    00/U    03/T    32/T    11/U    11/U    11/U    11/U
BHK 038/072 044/079 050/080 050/084 054/084 054/082 051/073
    00/U    01/U    21/B    11/U    11/U    11/U    11/U
SHR 041/077 049/075 050/079 049/084 052/085 052/081 051/070
    00/U    14/T    42/T    10/U    01/U    11/U    22/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS




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