Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 302103
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
303 PM MDT THU APR 30 2015

.SHORT TERM...VALID FOR FRI AND SAT...

THE LAST REMNANTS OF SHOWER ACTIVITY WAS EXITING MONTANA AND
THE NORTHERN WYOMING REGION THIS AFTERNOON AS THE TROUGH AXIS
ALOFT SHIFTS EAST OF OUR REGION. DRIER AIR AND ZONAL FLOW ALOFT
WILL PREVAIL OVERNIGHT AND INTO FRIDAY. LOOK FOR SEASONAL LOWS
TONIGHT AND A NICE REBOUND IN TEMPERATURES TOMORROW BACK INTO THE
70S TO NEAR 80 DEGREES.

ZONAL FLOW CONTINUES INTO SATURDAY. HOWEVER...WE DO HAVE A SERIES
OF WEAK WAVES WHICH TURN THE FLOW SOMEWHAT CYCLONIC OVER MONTANA
AND MAY PRODUCE A FEW SHOWERS. I DO NOT PLAN TO CHANGE MUCH WITH
THIS PACKAGE REGARDING POPS LATE SATURDAY INTO SATURDAY NIGHT WITH
MAINLY ISOLATED ACTIVITY POSSIBLE OVER THE MOUNTAINS SPREADING
ONTO THE PLAINS. I WILL CARRY SOME THUNDER LATE SATURDAY OVER
AREAS WEST AND SOUTHWEST OF BILLINGS WHERE DIFFERENTIAL HEATING
MAY PRODUCE ENOUGH INSTABILITY COMBINED WITH WEAK ENERGY ALOFT
TO PRODUCE SOME CONVECTION. BT

.LONG TERM...VALID FOR SUN...MON...TUE...WED...THU...

MODELS CONTINUED TO HAVE ISSUES IN RESOLVING THE EVOLUTION OF A
PACIFIC LOW PRESSURE SYSTEM THAT WILL AFFECT THE REGION BEGINNING
MIDWEEK. NOTED THE GFS SPAGHETTI PLOTS WERE DIVIDED IN THE
PLACEMENT OF THE UPPER LOW...WHILE THE ECMWF ENSEMBLES SHOWED
UNCERTAINTY WITH THE PATTERN. OTHERWISE...MODELS WERE IN DECENT
AGREEMENT SUN THROUGH TUE.

A RELATIVELY ZONAL FLOW WILL BE OVER THE REGION THROUGH SUN NIGHT
WITH JET ENERGY IN THE FLOW BRINGING UPPER DIVERGENCE TO THE
AREA. LOW-LEVEL SE FLOW WILL PROVID INCREASING MOISTURE OVER THE
AREA...AND SOME INSTABILITY WILL SUPPORT A SLIGHT CHANCE FOR
SHOWERS AND A FEW THUNDERSTORMS OVER AND NEAR THE MOUNTAINS.
CHANCES FOR SHOWERS WILL BE A BIT HIGHER SUN NIGHT AS MOISTURE
CONTINUES TO INCREASE OVER THE AREA. TEMPERATURES WILL CLIMB WELL
INTO THE 60S ON SUN OVER MOST OF THE AREA.

A RIDGE OF HIGH PRESSURE WILL SLIDE ACROSS THE REGION MON AND MON
NIGHT...GIVING WAY TO SW FLOW ALOFT. CONTINUE LOW-LEVEL MOISTURE
INFLUX...ALONG WITH SOME INSTABILITY...WILL BRING ISOLATED TO
SCATTERED SHOWERS THROUGH MON NIGHT WITH ISOLATED THUNDERSTORMS
MON AFTERNOON. TEMPERATURES WILL CLIMB THROUGH THE 60S ONCE AGAIN
ON MON.

PACIFIC LOW PRESSURE OVER THE PACIFIC NW WILL APPROACH THE REGION
ON TUE. THE ECMWF THEN HAD A LOW BREAKING AWAY FROM THE MAIN LOW
AND MOVING N OF THE MT/CANADA BORDER ON WED...WHILE THE GFS HAD AN
AREA OF LOWER PRESSURE OVER WY. THE ECMWF BROUGHT A COLD FRONT
INTO THE AREA TUE NIGHT AND MOVED IT E OF THE AREA ON WED...WHILE
THE GFS SET UP AN INVERTED TROUGH OVER THE REGION. RESULTS WERE A
CHANCE OF SHOWERS AND THUNDERSTORMS OVER THE AREA THROUGH TUE
NIGHT ON BOTH MODELS...WITH A MUCH WETTER SOLUTION ON WED OVER THE
AREA ON THE GFS THAN THE ECMWF. SURFACE CAPES ON THE GFS SUPPORTED
POSSIBLE STRONG THUNDERSTORMS OVER THE AREA TUE THROUGH WED. KEPT
THE POPS THE SAME AS THE PREVIOUS FORECAST FOR THIS PERIOD DUE TO
UNCERTAINTY WITH THE SYSTEM EVOLUTION. MODEL DIFFERENCES CONTINUED
THROUGH THU...BUT BOTH MODELS LOOKED UNSETTLED WITH THE LOW
PRESSURE SYSTEM IN THE AREA. TUE LOOKED WARM AHEAD OF THE SYSTEM
WITH HIGHS IN THE 70S. WENT WITH A MODEL BLEND FOR TEMPERATURES
FOR WED AND THU. ARTHUR
&&

.AVIATION...

A SLIGHT CHANCE OF SHOWERS WILL PERSIST THROUGH THE REST OF THE
AFTERNOON S AND E OF KBIL. LOCALIZED MVFR CONDITIONS ARE POSSIBLE
WITH THE SHOWERS BUT CONDITIONS SHOULD REMAIN MAINLY VFR. EXPECT
LOCALIZED MOUNTAIN OBSCURATION OVER THE NE BIG HORNS. VFR WILL
PREVAIL ACROSS THE AREA TONIGHT THROUGH FRI. ARTHUR
&&

.PRELIMINARY POINT TEMP/POPS...

    FRI     SAT     SUN     MON     TUE     WED     THU
-----------------------------------------------------------
BIL 043/080 047/079 044/067 043/069 044/075 046/069 043/060
    00/U    00/B    22/T    32/T    22/T    33/T    43/W
LVM 035/076 040/075 038/068 037/071 039/075 040/066 039/060
    00/U    01/B    13/T    32/T    23/T    34/T    44/W
HDN 038/082 043/083 041/069 041/070 043/076 044/073 044/061
    00/U    00/B    21/B    32/T    12/T    34/T    43/W
MLS 040/078 046/079 044/066 042/066 044/072 047/069 044/063
    00/U    00/B    11/B    32/T    11/B    33/T    43/W
4BQ 038/078 043/081 043/068 042/065 045/071 046/068 045/062
    00/U    00/U    11/B    33/T    12/T    34/T    43/W
BHK 037/079 043/081 040/064 039/061 040/068 045/066 042/062
    00/U    00/B    21/B    33/T    11/N    34/T    34/W
SHR 036/075 040/077 039/067 040/066 041/069 040/066 043/057
    00/U    00/U    12/T    33/T    23/T    33/T    44/W

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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