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000
FXUS63 KBIS 181824
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
124 PM CDT SAT MAY 18 2013

.UPDATE...
ISSUED AT 105 PM CDT SAT MAY 18 2013

THE DISCUSSION FROM THE PREVIOUS UPDATE REMAINS VALID AS THE MAIN
FOCUS IS STILL LOCATION AND TIMING OF CONVECTIVE INITIATION THIS
AFTERNOON.

THE ONLY NEW INFORMATION TO ADD IS THE PRESENCE OF LOW LEVEL
CONVERGENCE STRETCHING FROM DICKINSON TO BUFFALO SD. VISIBLE
SATELLITE INDICATES SOME AGITATED CUMULUS THERE...AND 18 UTC SPC
MESOANALYSIS INDICATES A MARKED INCREASE IN MIXED LAYER CAPE OVER
THE PAST HOUR. SHOULD THIS TREND CONTINUE...STRONGER STORMS MAY BE
REALIZED BY 4 PM CDT.

UPDATE ISSUED AT 1024 AM CDT SAT MAY 18 2013

THE TIMING AND LOCATION OF CONVECTIVE INITIATION IN THIS COMPLEX
SCENARIO IS THE MAIN FOCUS TODAY. PRECIPITATION CHANCES ALONG THE
MISSOURI RIVER HAVE GENERALLY BEEN LOWERED FOR THIS MORNING AND
EARLY AFTERNOON AS LOW LEVEL STRATUS WILL HELP TO STABILIZE THE
ATMOSPHERE UNTIL THE NEXT MID LEVEL SHORTWAVE ARRIVES THIS
AFTERNOON.

THE 12 AND 13 UTC HRRR HAVE PICKED UP ON THE CLEARING OVER
NORTHWESTERN SOUTH DAKOTA THIS MORNING...AND NOW INITIATES
CONVECTION THERE AND IN SOUTHWESTERN NORTH DAKOTA BY 21 UTC. 12
UTC GFS THERMODYNAMIC PROFILES SUPPORT THIS IDEA ALONG WITH THE 00
UTC ECMWF AS CAPE IS FORECAST TO EXCEED 1000 J/KG THERE.

THE CURRENT THINKING IS THAT CONVECTION WILL SPREAD GENERALLY
EAST-NORTHEASTWARD UNTIL MID/LATE AFTERNOON DESTABILIZATION AND
MIDDLE LEVEL HEIGHT FALLS FINALLY INITIATE ADDITIONAL CONVECTION
BETWEEN THE MISSOURI AND JAMES RIVERS ALONG THE DAKOTA BORDER.

UPDATE ISSUED AT 644 AM CDT SAT MAY 18 2013

UPDATE MAINLY FOR POP TRENDS TODAY. SHOWERS AND ISOLATED STORMS
HAVE PUSHED INTO THE FAR NORTHEAST EARLY THIS MORNING. RECENT RUNS
OF THE RAP HAVE A GOOD HANDLE ON NEAR TERM TRENDS...AND HAVE
REDUCED POPS THROUGH THE MORNING INTO EARLY AFTERNOON. STILL
EXPECTING THE FOCUS OF AFTERNOON CONVECTION ALONG A BOUNDARY TO
THE SOUTHEAST...WITH POTENTIAL FOR SOME SEVERE STORMS TO DEVELOP
BY MID AFTERNOON.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 430 AM CDT SAT MAY 18 2013

THE MAIN FOCUS IN THE SHORT TERM IS CONVECTIVE TRENDS AND
POTENTIAL FOR SEVERE WEATHER THIS AFTERNOON AND TONIGHT. IN THE
NEAR TERM...THE 18/07Z RAP MODEL HAS A GOOD HANDLE ON THE LOCATION
OF THE CURRENT STORMS ACROSS THE NORTHEAST HALF OF THE FORECAST
AREA. STORMS SHOULD CONTINUE TO LIFT NORTH THROUGH THE MORNING
HOURS. AFTERNOON REDEVELOPMENT IS EXPECTED TO FOCUS ON THE TROUGH
EXTENDING ACROSS THE SOUTHEAST COUNTIES. ML CAPES AROUND 1500 TO
2000 J/KG ARE EXPECTED ALONG WITH DEEP LAYER SHEAR AT OR ABOVE 40
KTS...SUFFICIENT FOR SUPERCELL DEVELOPMENT WITH LARGE
HAIL/DAMAGING WIND THREAT. IN THE EXTREME SOUTHEAST...LOW
LCL`S...DECENT LOW LEVEL CAPE...AND A NARROW AREA OF FAVORABLE
0-1KM SHEAR SUGGEST THERE MAY ALSO BE A SEVERAL HOUR WINDOW OF
TORNADO THREAT THROUGH EARLY EVENING.

THE SOUTHEAST HALF OF THE FORECAST AREA LOOKS FAVORED FOR THE
HEAVIER RAINFALL AMOUNTS THROUGH TONIGHT. SIGNIFICANT RISES ON
MAINSTEM RIVERS ARE NOT EXPECTED...BUT WILL BE MONITORING FOR
LOCALIZED HEAVY RUNOFF AND ISOLATED SHORT TERM FLOODING DUE TO
EXTREME RAINFALL RATES OR MULTIPLE ROUNDS OF STORMS.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 430 AM CDT SAT MAY 18 2013

A LARGE CLOSED H5 LOW IS FORECAST TO DRIFT THROUGH THE REGION
SUNDAY THROUGH TUESDAY. THE THREAT FOR SEVERE WEATHER WILL
DIMINISH DURING THIS PERIOD...BUT MODERATE TO LOCALLY HEAVY RAINFALL
WILL PERSIST. ADDITIONAL RAINFALL AMOUNTS OF 1 TO 3 INCHES ARE
POSSIBLE OVER THE WEEKEND THROUGH TUESDAY...WITH THE HIGHER TOTALS
TOWARD THE JAMES RIVER VALLEY. AGAIN...SIGNIFICANT RESPONSES ARE
NOT EXPECTED ON AREA RIVERS...BUT WILL BE WATCHING SMALLER CREEKS
AND STREAMS...AS WELL AS THE POTENTIAL FOR URBAN FLOODING. CLOUDS
AND RAIN WILL KEEP TEMPS DOWN IN THE 50S/LOWER 60S MONDAY AND
TUESDAY...BEFORE A WARMING TREND FROM MID TO LATE WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 105 PM CDT SAT MAY 18 2013

LOW STRATUS HAS BEEN VERY DIFFICULT TO FORECAST TODAY...BUT
SHOULD LIFT AT ALL SITES BY 20 UTC. SHOWERS AND THUNDERSTORMS WILL
CAUSE MVFR CONDITIONS AT MOST TAF SITES TODAY...WITH BRIEF PERIODS
OF IFR POSSIBLE IN STRONGER STORMS. IFR/LIFR FOG AND LOW STRATUS
WILL LIKELY RETURN AFTER MIDNIGHT TONIGHT IN THE WAKE OF
PRECIPITATION.

&&

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

$$

UPDATE/AVIATION...SCHECK
SHORT TERM/LONG TERM...RP KINNEY