Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 171422
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
822 AM MDT SUN AUG 17 2014

.UPDATE...
EARLY MORNING CONVECTION IS LEAVING OUR CWA FOR THE DAKOTAS AS
SHORTWAVE RESPONSIBLE FOR THIS ACTIVITY CONTINUES TO SLIDE EAST.
850-700MB FLOW IS SHIFTING TO THE W-NW BEHIND THIS ENERGY...AND
FOCUS OF ANY STRONG TO SEVERE CONVECTION LATER TODAY WILL ALSO BE
TO OUR EAST. CYCLONIC/COOLER AIR ALOFT ASSOCIATED WITH SLOW-
MOVING UPPER LOW TO OUR NORTHEAST WILL SUPPORT SOME SHOWERS AND
GENERALLY WEAK TSTM ACTIVITY FOR US LATER TODAY...WITH GREATEST
COVERAGE IN OUR EAST AS OUR WEST WILL SEE INFLUENCE FROM DOWNSLOPE
WINDS. WEAK Q-VECTOR CONVERGENCE FROM 18-00Z IN OUR EAST WILL
ALSO HELP SHOWERS TO DEVELOP. W-NW WINDS OF 15-25 MPH WILL BE
COMMON BY THIS AFTERNOON.

FOR THE UPDATED HAVE SCALED BACK MORNING POPS IN OUR EAST AND
MADE MINOR TWEAKS TO SKY COVER AND WINDS. HAVE ALSO ADJUSTED TEMPS
DOWN SLIGHTLY IN OUR NORTHEAST PER WEAK COLD ADVECTION TODAY.

JKL

&&

.SHORT TERM...VALID FOR TDY AND MON...

SLOW MOVING UPPER LOW WAS SITTING OVER SOUTHWEST SASKATCHEWAN AT
THE MOMENT. A 70KT JET WAS ENTERING SOUTH CENTRAL MONTANA ON THE
SOUTH SIDE OF THE LOW. THIS JET WAS DEVELOPING CONVECTION FROM
AROUND BILLINGS EASTWARD INTO CARTER COUNTY. THE JET WILL DART
INTO WESTERN NORTH DAKOTA BY LATE MORNING. THIS WILL DRAG THE
SURFACE TROUGH CURRENTLY SITTING OVER WESTERN CUSTER COUNTY INTO
THE DAKOTAS BY NOON. THIS WILL SERVE TO SWEEP THE HIGHER DEWPOINT
AIR...CURRENTLY IN THE UPPER 50S TO AROUND 60 OVER THE EAST...OUT
OF THE AREA. THE UPPER LOW TO THE NORTH WILL DRIFT EAST...VEER THE
FLOW TO THE NORTHWEST...AND SEND ENERGY INTO THE EASTERN HALF OF
THE FORECAST AREA. SHORT RANGE HIGH RESOLUTION MODELS PUSH THE
HIGHEST CAPE AND FORCING EAST QUICKLY THIS MORNING...SO FEEL
SEVERE THREAT WILL BE EAST OF THE AREA TODAY. CENTRAL AND WESTERN
ZONES WILL BE UNDER THE INFLUENCE OF DOWNSLOPE WINDS AND THUS
DRIER AIR. WILL MAINTAIN LOW POPS WITH CYCLONIC FLOW.

NORTHWEST FLOW TONIGHT WILL TAKE FORCING EAST THROUGH THE NIGHT.
WILL DRY THINGS OUT FROM WEST TO EAST. UPPER RIDGE OVER THE
SOUTHERN ROCKIES BUILDS NORTHWARD A BIT FOR MONDAY AND CYCLONIC
FLOW IS REPLACED WITH ANTICYCLONIC FLOW. MODELS TRY TO PULL IN
SOME MONSOON MOISTURE INTO THE MOUNTAINS MONDAY AFTERNOON AND
EVENING. FLOW AROUND THE UPPER RIDGE SHOULD KEEP THE CHANCE OF
SHOWERS AND THUNDERSTORMS OVER WESTERN AND SOUTHERN ZONES. SOME
HINT THAT THE SHOWERS MAY HOLD TOGETHER LONG ENOUGH TO GET INTO
SOUTH CENTRAL ZONES...BUT WANING INSTABILITY DURING THE EVENING
HOURS WILL WORK AGAIN THAT. WILL CONFINE POPS TO THE MOUNTAINS FOR
THE TIME BEING AND WATCH HOW THIS EVOLVES. TWH

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

THE OVERARCHING THEME IN THE EXTENDED REMAINS A TRANSITION TO
COOLER AND WETTER CONDITIONS BY THE END OF THE WEEK. MODELS
CONTINUE TO ADVERTISE A PATTERN CHANGE TO TROUGHING IN THE WESTERN
CONUS. WHILE THE DETAILS REMAIN SOMEWHAT MURKY IN THE EXACT
EVOLUTION OF THE TROUGH AND INTERACTION WITH A CUTOFF LOW IN
CALIFORNIA...CONFIDENCE REMAINS HIGH FOR THE COOLER AND WETTER
CONDITIONS DEVELOPING BY THURSDAY INTO FRIDAY.

ON TUESDAY...SOUTHWESTERLY FLOW ALOFT DEVELOPS OVER THE FORECAST
AREA AS TROUGHING STARTS TO DEVELOP ALONG THE WEST COAST. A
SHORTWAVE WILL MOVE ACROSS THE AREA BY TUESDAY AFTERNOON...AS
MOISTURE INCREASES. EXPECT TO SEE SCATTERED SHOWERS AND
THUNDERSTORMS DEVELOP OVER THE MOUNTAINS IN THE EARLY AFTERNOON
AND SPREAD ACROSS THE PLAINS BY LATER IN THE DAY AS THE WAVE. THE
SOUTHWESTERLY FLOW ALOFT WILL ALSO ALLOW WARM AIR ADVECTION AT
700 MB MAKING TUESDAY THE WARMEST DAY IN THE EXTENDED...WITH LOW
90S EXPECTED.

WEDNESDAY WILL BE SLIGHTLY COOLER BEHIND THE INITIAL SHORTWAVE AND
AS THE MEAN TROUGH CONTINUES TO BUILD OVER THE PACIFIC NORTHWEST.
SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE ON
THURSDAY...AND SHOULD CONTINUES TO INCREASE IN COVERAGE. THE MAIN
SOURCE OF MODEL DISAGREEMENT REMAINS HOW TO HANDLE THE CUTOFF LOW
OFF THE CALIFORNIA COAST. EACH MODEL RUN IN THE GFS AND EC
CONTINUE TO FLIP-FLOP ON WHETHER TO PICK THAT LOW UP IN THE
NORTHERN TROUGH OR TO RETROGRADE IT OFF THE PACIFIC COAST.
THE 00Z GFS SOLUTION PICKS UP THE LOW...WHILE THE 00Z EC DOES NOT.

WHILE THIS IS AN INTERESTING PIECE OF THE PUZZLE...IT SEEMS ITS
IMPLICATIONS ARE MORE IMPORTANT FOR FAR EASTERN MONTANA AND INTO
THE DAKOTAS. FORTUNATELY FOR US...THE MODELS DO HAVE A GOOD
HANDLE ON A SHORTWAVE IN THE NORTHERN STREAM THAT DIGS INTO THE
MEAN TROUGH INTO THURSDAY EVENING. THIS HELPS TO SLOW UP THE
PROGRESSION OF THE TROUGH AND DEEPEN IT ALONG THE WEST COAST. THE
SHORTWAVE ROTATES AROUND THE BASE OF THE TROUGH AND ACROSS OUR
FORECAST AREA BY FRIDAY EVENING. GIVEN THE ALL AROUND AGREEMENT ON
THIS FEATURE BETWEEN THE MODELS...FEEL FAIRLY CONFIDENT IN A WET
DAY ON FRIDAY/FRIDAY NIGHT AND HAVE TRENDED POPS UP SLIGHTLY WITH
THIS FORECAST PACKAGE. TEMPERATURES WILL BE COOLER FRIDAY INTO
SATURDAY WITH THE TROUGH IN PLACE AND AND WHATEVER PRECIPITATION
FALLS. MODEL GUIDANCE SUGGESTS HIGH TEMPERATURES IN THE MID
70S...OR ABOUT 10 DEGREES BELOW NORMAL. THE 00Z EC GUIDANCE EVEN
SUGGESTS A HIGH OF ONLY 68 DEGREES ON FRIDAY. WHILE THAT MAY BE
POSSIBLE IF THE PRECIPITATION STARTS EARLY IN THE DAY AND IS
PERSISTENT...HAVE CONTINUED WITH A BLEND OF THE GUIDANCES TO SHOW
MID 70S.

CHURCH

&&

.AVIATION...

ISOLATED SHOWERS AND THUNDERSTORMS HAVE PUSHED INTO THE DAKOTAS
THIS MORNING. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
DEVELOP THIS AFTERNOON...WITH BEST POTENTIAL MAINLY EAST OF KBIL.
MVFR/IFR CONDITIONS ARE POSSIBLE ALONG WITH GUSTY WINDS IN ANY OF
THE STRONGER CELLS. OTHERWISE...VFR CONDITIONS WILL PREVAIL FOR
ALL ROUTES TODAY. AAG

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY MON     TUE     WED     THU     FRI     SAT
-------------------------------------------------------
BIL 088 059/088 062/091 062/089 060/082 059/079 058/078
    2/T 21/B    12/T    33/T    33/T    35/T    54/T
LVM 088 050/089 053/090 053/086 051/079 050/076 050/076
    1/N 12/T    22/T    33/T    44/T    45/T    54/T
HDN 090 056/089 058/093 059/091 056/086 055/083 054/082
    2/T 21/B    12/T    23/T    33/T    35/T    54/T
MLS 087 060/087 062/091 063/091 060/085 059/083 058/079
    3/T 31/B    12/T    22/T    33/T    45/T    54/T
4BQ 088 058/086 059/091 061/092 060/087 059/085 057/080
    3/T 21/B    12/T    23/T    32/T    35/T    54/T
BHK 085 056/084 055/088 057/089 056/084 056/081 054/076
    3/T 31/B    12/T    23/T    33/T    45/T    53/T
SHR 088 052/086 055/090 055/089 054/085 053/082 051/078
    1/B 11/B    12/T    32/T    22/T    34/T    44/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS



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