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000
FXUS63 KBIS 171833
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
133 PM CDT FRI MAY 17 2013

.UPDATE...
ISSUED AT 114 PM CDT FRI MAY 17 2013

THE MAIN FOCUS THIS UPDATE WAS PRECIPITATION CHANCES TODAY AND
TONIGHT.

BASED ON MODEL CONSENSUS AND COORDINATION WITH SURROUNDING
OFFICES...PROBABILITIES WERE SCALED BACK TO BETTER REFLECT THE
BEST CHANCES FOR SHOWERS AND THUNDERSTORMS. UNFORTUNATELY...THE
AVAILABLE 12 UTC THROUGH 16 UTC GUIDANCE DISAGREES WITH
TIMING...BUT THERE IS GENERAL AGREEMENT THAT AN AREA OF CONVECTION
WILL DEVELOP OVER SOUTHEASTERN MONTANA THIS AFTERNOON AND MOVE
NORTHEASTWARD. TIMING THE NEXT MID-LEVEL SHORTWAVE USING WATER
VAPOR SATELLITE IMAGERY INDICATES THE LEADING EDGE OF DYNAMIC
FORCING WILL SPREAD INTO SOUTHWESTERN NORTH DAKOTA AROUND 23 UTC.
WHILE THAT WILL LIKELY BE THE BEST CHANCE FOR STRONGER
THUNDERSTORMS...CURRENT RADAR AND VISIBLE SATELLITE SHOW THAT SOME
DESTABILIZATION HAS ALREADY OCCURRED...THOUGH NO LIGHTENING HAS
BEEN OBSERVED.

LOOK FOR THIS TREND TO CONTINUE AND FILL IN THROUGH THE AFTERNOON
AS MORE FAVORABLE DYNAMIC FORCING MOVES INTO THE REGION.

UPDATE ISSUED AT 1001 AM  CDT FRI MAY 17 2013

THE MAIN FOCUS TODAY WILL BE SEEMINGLY UNENDING PRECIPITATION
CHANCES. THIS UPDATE MADE SIMPLE ADJUSTMENTS TO PRECIPITATION
PROBABILITIES TODAY. WHILE THERE LOOKS TO BE A BREAK THAT WILL
LAST SEVERAL HOURS OVER MUCH OF THE MISSOURI SLOPE AND JAMES RIVER
VALLEYS THROUGH EARLY AFTERNOON...ECHOES ON SOUTH DAKOTA RADARS
INDICATE AT LEAST LIGHT SHOWER ACTIVITY MOVING NORTHEASTWARD FAST.
THE NEXT FEW HOURS SHOULD GIVE A BETTER FEEL FOR FORCING
MECHANISMS AND LIKELIHOOD OF INTENSIFICATION.

PREVIOUS FORECASTS OF SUB-SEVERE CONVECTION OVER SOUTHWESTERN NORTH
DAKOTA LOOK TO BE ON TRACK FOR LATER TODAY/TONIGHT.

UPDATE ISSUED AT 637 AM CDT FRI MAY 17 2013

UPDATE FOR MINOR CHANGES TO POPS ACROSS THE NORTH THIS MORNING AS
BATCH OF SHOWERS AND ISOLATED THUNDERSTORMS CONTINUES TO HEAD
NORTHEAST. OTHERWISE...MAINTAINED GENERALLY INCREASING POPS
THROUGH LATE AFTERNOON AND EVENING.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 349 AM CDT FRI MAY 17 2013

THE MAIN CONCERN FOR TODAY INTO TONIGHT WILL BE THE CHANCE OF
THUNDERSTORMS AND POTENTIAL SEVERE WEATHER. EARLY MORNING RADAR
MOSAIC SHOWED ISOLATED SHOWERS FROM SOUTHWEST NORTH DAKOTA INTO
NORTHWEST MINNESOTA. MUCH OF THIS ACTIVITY DEVELOPED IN AN AREA OF
H85 WARM AIR ADVECTION THAT HAS BEEN MOVING FROM SOUTH TO NORTH
ACROSS THE REGION. THE STRONGEST WARM AIR ADVECTION SHIFTS NORTH BY
AFTERNOON AS SOUTHWESTERLY FLOW ALOFT BRINGS A SERIES OF WAVES ACROSS
THE STATE. WILL MAINTAIN FAIRLY HIGH POPS TODAY...ESPECIALLY IN
THE NORTH AND WEST WHERE THE MAJORITY OF MODEL SOLUTIONS FAVOR THE
HIGHER PRECIPITATION CHANCES.

THE FOCUS THEN TURNS FARTHER SOUTH AS SURFACE LOW PRESSURE GATHERS
IN EAST CENTRAL WYOMING. A WARM FRONT STRETCHING OUT OF THE LOW
INTO SOUTHERN SOUTH DAKOTA IS EXPECTED TO LIFT NORTH TONIGHT...BRINGING
INCREASING CHANCES OF SHOWERS AND THUNDERSTORMS TO CENTRAL AND
WESTERN NORTH DAKOTA. CAN NOT RULE OUT AN ISOLATED SEVERE STORM
LATE THIS AFTERNOON / EVENING ACROSS THE SOUTHERN PART OF THE
FORECAST AREA WHERE INSTABILITY WILL BE GREATEST. THE SPC DAY 1
SEVERE WEATHER OUTLOOK KEEPS THE SLIGHT RISK SOUTH OF THE FORECAST
AREA...HOWEVER THE 5 PERCENT PROBABILITIES FOR SEVERE HAIL / WIND
ARE DRAWN SOUTH OF I-94 INTO SOUTHERN NORTH DAKOTA WHICH APPEARS
REASONABLE.

TEMPERATURES TODAY WILL BE TRICKY DUE TO THE CLOUDS AND RAIN. WILL
GENERALLY STAY ON THE COOL SIDE OF GUIDANCE WHICH SUGGESTS MID
60S NORTH TO LOWER 70S SOUTH.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 349 AM CDT FRI MAY 17 2013

THE MAIN FORECAST ISSUES THROUGH THE LONG TERM PERIOD ARE CONVECTIVE
TRENDS...AND POTENTIAL FOR PROLONGED MODERATE TO HEAVY RAIN AND
SOME SEVERE WEATHER ON SATURDAY. THE LATEST 17/00Z MODEL RUNS HAVE
SOME SIGNIFICANT DIFFERENCE IN THE PROGRESSION OF A CLOSED UPPER
LOW THROUGH THE REGION THROUGH EARLY NEXT WEEK. THE NAM IS AMONG
THE FARTHEST WEST...WHILE THE GFS FAVORS A FASTER...MORE EASTERLY
PATH. THE ECMWF REPRESENTS A REASONABLE COMPROMISE...AND WOULD
KEEP SHOWERS AROUND INTO TUESDAY BEFORE PUSHING EAST. THE FAVORED
PERIOD FOR SEVERE WEATHER WILL BE SATURDAY...WITH SOUTHWEST FLOW
ALOFT AND A WARM FRONT NOSING INTO THE SOUTHEAST PORTION OF THE
FORECAST AREA. SPC CONTINUES TO HAVE THE SOUTHEAST OUTLOOKED IN
SLIGHT RISK FOR DAY 2. BUFR SOUNDINGS SUGGEST STORMS WILL DEVELOP
RELATIVELY EARLY IN THE DAY. AM EXPECTING SOME STRONG TO SEVERE
STORMS WITH LARGE HAIL/STRONG WIND GUSTS THE PRIMARY THREATS.
STRONG MOISTURE TRANSPORT INTO THE BOUNDARY WILL CONTINUE THROUGH
SATURDAY NIGHT AS A DECENT SHORT WAVE TROUGH MOVES THROUGH EASTERN
NORTH DAKOTA. THE SEVERE WEATHER THREAT DIMINISHES SUNDAY...BUT
MODERATE TO LOCALLY HEAVY RAIN IS EXPECTED TO CONTINUE OVER MUCH
OF WESTERN AND CENTRAL NORTH DAKOTA. THIS SCENARIO WILL LIKELY
CONTINUE MONDAY...BEFORE SHOWERS TAPER OFF IN COVERAGE AND
INTENSITY ON TUESDAY. TOTAL RAINFALL AMOUNTS OF 1 TO 3 ARE
EXPECTED THROUGH THE PERIOD...WITH AMOUNTS AROUND 4 INCHES
POSSIBLE...ESPECIALLY IN THE JAMES RIVER VALLEY. CONDITIONS ARE
SUCH THAT SOILS CAN ABSORB SIGNIFICANT RAINFALL. THUS...SIGNIFICANT
RISES ON MAIN STEM RIVERS SUCH AS THE SOURIS AND JAMES ARE NOT
EXPECTED. HOWEVER...ENHANCED RAINFALL RATES OR SEVERAL ROUNDS OF
STORMS COULD PRODUCE LOCALIZED RUNOFF...LEADING TO RISES ON SMALL
CREEKS AND STREAMS...AND POSSIBLY FLASH FLOODING.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 114 PM CDT FRI MAY 17 2013

VFR CONDITIONS AT ALL TAF SITES WILL EVENTUALLY BECOME MVFR
TONIGHT AS WIDESPREAD SHOWERS AND THUNDERSTORMS ACCOMPANY LOWER
CEILINGS. THE OFFENDING LARGE LOW PRESSURE SYSTEM WILL REMAIN OVER
THE NORTHERN PLAINS THROUGH AT LEAST MONDAY. THUNDERSTORMS WILL BE
MORE WIDESPREAD SATURDAY AFTERNOON AND EVENING.

&&

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

$$

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