000
FXUS63 KBIS 140621
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
121 AM CDT FRI JUN 14 2013

.UPDATE...
ISSUED AT 121 AM CDT FRI JUN 14 2013

MAIN FORECAST CONCERNS ARE CONVECTIVE POTENTIAL OVERNIGHT AND
PRECIP CHANCES THROUGH FRIDAY. FORECAST WAS GENERALLY ON
TRACK...BUT FURTHER TRIMMED POPS ACROSS THE WEST BASED ON CURRENT
RADAR TRENDS IN MONTANA. FIRST AREA OF THUNDERSTORMS THAT
APPROACHED WESTERN NORTH DAKOTA EARLIER THIS EVENING DIMINISHED.
ANOTHER AREA OF THUNDERSTORMS...SOME SEVERE...WAS MOVING THROUGH
SOUTHEAST MONTANA. 00Z NAM APPEARED TO INITIALIZE THIS FAIRLY
WELL...MOVING IT NORTHEAST AND POSSIBLY CLIPPING OUR NORTHWEST
CWA. NAM ALSO PICKED UP ANOTHER AREA OF ISOLATED/SCATTERED
THUNDERSTORMS NEAR RAPID CITY THAT IT BRINGS INTO SOUTHWEST AND
SOUTHCENTRAL ND. WITH REGARD TO CONVECTIVE POTENTIAL ON
FRIDAY...DESPITE SURFACE BASED CAPE APPROACHING 1000 J/KG AHEAD OF
THE COLD FRONT THAT WILL BE ACROSS CENTRAL ND BY 18Z...FORECAST
SOUNDINGS INDICATE A SUBSTANTIAL WARM LAYER/CAP ALOFT THAT SHOULD
SUPPRESS CONVECTIVE POTENTIAL. SPC HAS ALSO REMOVED SLIGHT RISK OF
SEVERE AREA FROM MOST OF EASTERN NORTH DAKOTA.

UPDATE ISSUED AT 955 PM CDT THU JUN 13 2013

THE AREA OF SHOWERS THAT MOVED INTO SOUTHWEST NORTH DAKOTA DIED AS
IT ENTERED LESS UNSTABLE AIR AND OUTRACED THE AREA OF LARGE SCALE
RISING MOTION AHEAD OF THE NEXT MID LEVEL TROUGH.

OF NEXT INTEREST IS A LINE OF SCATTERED THUNDERSTORMS FROM NEAR
GLASGOW TO SOUTHWEST OF MILES CITY MONTANA...AND MOVING NORTHEAST.
THIS LINE WAS MOVING INTO LESS UNSTABLE AIR AS THE BOUNDARY LAYER
COOLED. HOWEVER...EASTERN MONTANA WAS UNDER THE INFLUENCE OF THE
LARGE SCALE RISING MOTION WITH THE NEXT MID LEVEL TROUGH...AND
STEEP MID LEVEL LAPSE RATES WERE ALSO EVIDENT THERE.

FOR THE IMMEDIATE SHORT TERM WILL DROP ALL POPS IN THE WEST...
INCREASING THEM AGAIN AROUND MIDNIGHT. THE QUESTION IS...WILL THE
STORMS IN MONTANA MAKE IT INTO WESTERN NORTH DAKOTA IN TACT...OR
IN A MUCH MORE WEAKENED STATE.

UPDATE ISSUED AT 700 PM CDT THU JUN 13 2013

THUNDERSTORMS THAT WERE AT OR NEAR SEVERE LIMITS IN NORTHEAST
WYOMING INTO SOUTHEAST MONTANA WERE WEAKENING RAPIDLY AS THEY
MOVED NORTHEAST...TOWARD NORTH DAKOTA...INTO MUCH LESS UNSTABLE
AIR. THE NUMBER OF LIGHTNING STRIKES WAS ALSO DECREASING RAPIDLY. BY
THE TIME THIS CONVECTION GETS INTO SOUTHWEST NORTH DAKOTA IT COULD
BE DOWN TO JUST RAIN SHOWERS.

HAVE LOWERED THE POPS NORTHWEST FOR THE IMMEDIATE SHORT TERM...AND
ALSO IN THE SOUTHWEST. THE NEXT NEAREST UPSTREAM CONVECTION IS IN
THE BILLINGS MONTANA AREA. CONVECTION FIRING IN EASTERN WYOMING
WAS MOVING EAST...INTO SOUTH DAKOTA. IT TOO WAS WEAKENING AS OF
THE WRITING OF THIS DISCUSSION.

REST OF FORECAST WAS ON TARGET.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 307 PM CDT THU JUN 13 2013

THE MAIN FORECAST CONCERN FOR THE PERIOD WILL BE THE CHANCES FOR
SEVERE CONVECTION WEST OF HIGHWAY 85 THIS EVENING AND AGAIN ALONG
AND EAST OF HIGHWAY 83 FRIDAY AFTERNOON.

THIS AFTERNOON...SPC HAS PLACED MOST OF EASTERN MONTANA IN A SEVERE
THUNDERSTORM WATCH GIVEN THE INCREASING CAPE AND DEEP LAYER SHEAR.
ANY ACTIVITY THAT DEVELOPS OVER MONTANA WILL LIKELY MOVE NORTHEAST
ALONG THE 850MB-300MB MEAN WIND VECTOR. THIS COULD ALLOW FOR SOME
SEVERE STORMS THAT HAVE ALREADY DEVELOPED TO CROSS THE BORDER INTO
THE EXTREME WESTERN COUNTIES OF NORTH DAKOTA...PRIMARILY BETWEEN
00Z-06Z TONIGHT.

OTHERWISE...AN UPPER LOW IS PROGGED TO CONTINUE TO PUSH EAST ACROSS
THE NORTHERN PLAINS TONIGHT. ITS ATTENDANT SURFACE BOUNDARY IS
PROGGED TO ENTER WESTERN NORTH DAKOTA AROUND 12Z FRIDAY. ALONG WITH
IT WILL BE INCREASING CHANCES FOR THUNDERSTORMS ALONG AND WEST OF
HIGHWAY 85. HOWEVER...CAPE VALUES SHOULD BE DECREASING AFTER
MIDNIGHT SO THEREFORE THINK THE SEVERE THREAT WILL BE LOW.

FOR FRIDAY...THE UPPER LOW AND ITS SURFACE BOUNDARY ARE PROGGED TO
PUSH ACROSS WESTERN NORTH DAKOTA FRIDAY MORNING...AND EAST OF
HIGHWAY 83 FRIDAY AFTERNOON. GIVEN THE TIMING AND POSITION OF THE
UPPER LEVEL/SURFACE BOUNDARY...THINK SEVERE WEATHER HAS THE
POTENTIAL TO DEVELOP PRIMARILY ALONG AND EAST OF HIGHWAY
83...CONSISTENT WITH THE DAY 2 SLIGHT RISK BY SPC. THE ONLY FLY IN
THE OINTMENT IS IF WE REMAIN CAPPED THROUGH THE DAY. HOWEVER...THINK
THE UPPER LEVEL FORCING SHOULD SUFFICE TO ERODE THE MID-LEVEL
CAPPING. AS A RESULT...INTRODUCED THE CHANCES FOR SEVERE
THUNDERSTORMS ALONG AND EAST OF HIGHWAY 83 IN THE FORECAST. LARGE
HAIL AND DAMAGING WINDS WOULD BE THE BIGGEST THREATS.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 307 PM CDT THU JUN 13 2013

NO SIGNIFICANT WEATHER TO HIGHLIGHT THE EXTENDED WITH SLIGHTLY
BELOW NORMAL TEMPERATURES TO BEGIN THE PERIOD WITH NEAR
CLIMATOLOGICAL FORECAST TEMPERATURES AND PRECIPITATION CHANCES
EARLY TO MID NEXT WEEK.

OVERALL...THE 12 UTC GUIDANCE SUITE IS IN GOOD AGREEMENT AND
UTILIZED A BLEND FOR MOST FIELDS. A BREEZY...BUT DRY SATURDAY IS
FORECAST IN THE DRY SLOT OF THE UPPER LEVEL LOW ACROSS
SASKATCHEWAN. AS THIS LOW FILLS AND PROPAGATES SOUTHEAST THROUGH
SUNDAY...THERE IS A CHANCE FOR ISOLATED TO SCATTERED DIURNAL SHOWERS
AND THUNDERSTORMS ACROSS NORTHERN NORTH DAKOTA AND THE JAMES RIVER
VALLEY WITH THE COLD CORE ALOFT. THEREAFTER...UPPER LEVEL RIDGING
BUILDS MONDAY THROUGH WEDNESDAY...WITH THE NEXT BEST CHANCE FOR
THUNDERSTORMS BEING POTENTIALLY THURSDAY WITH THE NEXT SIGNIFICANT
UPPER LEVEL WAVE. THAT SAID...TIMING OF THIS WAVE HAS BEEN
INCONSISTENT OVER THE PAST FEW RUNS AMONGST THE GUIDANCE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 121 AM CDT FRI JUN 14 2013

MAINLY VFR CONDITIONS EXPECTED AT TAF SITES ALTHOUGH BRIEF MVFR
CONDITIONS COULD DEVELOP IN ANY SHOWERS...ISOLATED THUNDERSTORMS
AND ASSOCIATED LOWER CEILINGS. WINDS WILL TURN OUT OF THE WEST AS
A COLD FRONT MOVES ACROSS THE STATE TODAY.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...JNS
SHORT TERM...TM
LONG TERM...AYD
AVIATION...JNS