Severe Thunderstorm Warning 18, NWS Grand Forks, ND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND FORKS ND
926 PM CDT SUN MAY 23 2010

.DISCUSSION...
WEAK HIGH PRESSURE IS OVER THE REGION...WITH A DEEP TROUGH CARVED
OUT OVER THE SW CONUS. AN ACTIVE FRONTAL BOUNDARY IS CURRENTLY
STRETCHED FROM SOUTHERN NB NORTHEAST INTO THE ARROWHEAD OF MN.
STORMS CONTINUE TO FIRE ON THIS BOUNDARY WHERE THERE IS AMPLE
MOISTURE AND INSTABILITY.

FOR TONIGHT...A LOW LEVEL JET WILL DEVELOP FROM 03-06Z INTO
CENTRAL SD. THIS JET WILL IMPINGE ON THE WARM FRONT THAT WILL SURGE
NORTH LATER TONIGHT INTO MON MORNING. EXPECT THUNDERSTORMS TO MOVE
INTO THE FAR SOUTH AFTER 06Z...THEN PERHAPS INTO THE GFK AREA LATE
TONIGHT OR MON MORNING. SPC DOES HAVE A SLIGHT RISK IN THE FAR
SOUTH LATE TONIGHT FOR ELEVATED CONVECTION GIVEN THE RAPID
MOISTURE ADVECTION AND STRONG INSTABILITY WITH SHOWALTERS FALLING
TO AROUND -6C AFTER 09Z IN THE SOUTH. THERE WILL ALSO BE AMPLE
DEEP LAYERED SHEAR...SO A FEW SEVERE STORMS POSSIBLE IN THE SOUTH
LATE TONIGHT. THERE WILL ALSO BE A MARKED INCREASE IN
MOISTURE...WITH PWATS INCREASING TO NEARLY 1.75 INCHES IN THE
SOUTH LATE TONIGHT. THIS WILL ALSO MEAN HEAVY RAIN POSSIBLE NEAR
ANY STORMS. GIVEN ALL OF THIS...WILL ADD A SEVERE MENTION TO THE
FAR SOUTH LATE TONIGHT INCLUDING HEAVY RAIN.

&&

.AVIATION...
SHOULD BE A CALM AND FAIRLY CLOUD FREE EVENING BEFORE CLOUDS/WINDS
BEGIN TO INCREASE AGAIN. THUNDER CHANCES WILL INCREASE LATER
TONIGHT AND MONDAY MORNING...WITH CONDITIONS LOWERING INTO THE
MVFR RANGE WITH THUNDER BY MONDAY.

&&

.PREV DISCUSSION... /ISSUED 240 PM CDT SUN MAY 23 2010/

DISCUSSION...FORECAST CHALLENGE CONCERNS MAINLY THUNDERSTORM THREAT
LATE TONIGHT THROUGH MONDAY...POTENTIAL FOR MORE HEAVY
RAIN/HEADLINES WITH LOCATION MAIN CHALLENGE.

MODELS IN GOOD AGREEMENT WITH SURFACE THROUGH MID LEVEL FEATURES AS
WELL AS THERMAL AND WIND FIELDS. MAIN DIFFERENCES CONTINUE TO BE QPF
LOCATION AND AMOUNTS WITH DEVELOPING DEEP CONVECTION. GFS IMPLIES
LIFTING THUNDERSTORM COMPLEX NORTHWARD SIMILAR IN LOCATION TO LAST
NIGHTS EVENT WHILE NAM/GEM/ECMWF/SREF FOCUSING CONVECTION MORE E-W
ALONG NORTHWARD LIFTING WARM FRONTAL BOUNDARY. LATER SOLUTION SEEMS
MORE REASONABLE BUT WITH LAST NIGHTS BAND OF HEAVY RAIN LOCATION OF
DEVELOPING COMPLEX TONIGHT WILL HAVE TO BE MONITORED CLOSELY FOR
POTENTIAL FLASH FLOOD HEADLINES FOR TOMORROW.

NEXT STRONG MID LEVEL LOW MOVING ONSHORE ACROSS SW US TO REACH UTAH
BY MORNING. AS IT DOES ASSOCIATED SURFACE LOW WILL ORGANIZE ACROSS 4
CORNERS REGION THIS EVENING LIFTING INTO THE CENTRAL HIGH PLAINS BY
MORNING. E-W ORIENTED WARM FRONT THROUGH NE THIS EVENING WILL LIFT
INTO SD BY MORNING. AS ALL THIS TRANSPIRES INCREASING LOW LEVEL JET
TO 50KTS WILL TRANSPORT MOIST AND UNSTABLE AIRMASS NORTHWARD
OVERNIGHT. BASED ON BOUNDARY LOCATION AND CONVECTIVE PARAMETERS
STRONG STORMS COULD REACH BORDER AREA LATE FIRST OR EARLY SECOND
PERIOD. WILL BE INCREASING POPS ACROSS FAR SOUTH HOWEVER
NATIONAL/SPC GUIDANCE SUGGEST CONVECTION MAY NOT LIFT INTO S ND TILL
AFT FIRST PERIOD SO WILL LEAVE OUT SEVERE MENTION. CONFIDENCE LOWER
FARTHER NORTH SO WILL KEEP POPS LOW. MAIN SURFACE MOISTURE FLUX WILL
BE CONFINED TO FAR SOUTHERN FA WHERE 60 DEGREE DEWPOINTS WILL HOLD
TEMPERATURES UP. FAR NW WILL STAY IN DRIER AIRMASS FOR COOLEST
TEMPERATURES.

SURFACE LOW TO LIFT DUE NORTH INTO SW ND BY EVENING. ASSOCIATED WARM
FRONT IN AGREEMENT FROM MODELS EXTENDING ROUGHLY ALONG INTERSTATE 94
CORRIDOR THEN NORTHEAST TO LAKE OF THE WOODS IN NORTH CENTRAL MN. A
STRONG LOW LEVEL JET DRIVING WARM ADVECTION NORTHWARD WITH MOIST
UNSTABLE AIRMASS IN WARM SECTOR WILL LIKELY KEEP SEVERE THREAT GOING
DURING THE DAY. ANOTHER SEVERE THREAT MONDAY AFTERNOON COULD BE
ALONG PREFRONTAL TROUGH ACROSS CENTRAL DAKOTAS WHICH COULD SPREAD
ACROSS SOUTHERN FA. HEAVY RAINFALL ALSO A POSSIBILITY WITH
PRECIPITABLE H2O VALUES AROUND 1.5 INCHES. CONVECTION SHOULD BE
SOMEWHAT PROGRESSIVE HOWEVER WITH PAST HEAVY RAINFALL ACROSS WESTERN
FA AND HEAVY RAIN POTENTIAL ALONG WARM FRONT WILL ISSUE FLASH FLOOD
WATCH FOR WESTERN AREAS INTO DVL BASIN WHERE FLASH FLOOD GUIDANCE
LOW. WILL KEEP HIGHEST POPS FROM VALLEY WEST IN BETTER CONVERGENCE
WITH FRONTAL BOUNDARY. ANOTHER DAY OF SHARP THERMAL CONTRAST WITH
WARMEST TEMPERATURES IN WARM SECTOR WITH COOLER TEMPERATURE NORTH OF
WARM FRONT AND ASSOCIATED CLOUDS/RAIN.

BLOCKING WILL FORCE SURFACE LOW NORTHWARD INTO SE SASK BY TUESDAY
MORNING. WARM FRONT WILL CONTINUE TO LIFT NORTH DURING EVENING WITH
BEST POTENTIAL FOR PCPN ACROSS NORTHERN HALF OF FA. BASED ON TIMING
OF WARM FRONTAL BOUNDARY PASSAGE WILL KEEP HIGHEST POPS IN THIS AREA
WITH LESSER POPS SOUTHWARD TO COVER ANY T WHICH OCCURS ALONG
PREFRONTAL TROUGH. COLD ADVECTION PUSHES INTO WESTERN FA WITH AREAS
EAST OF VALLEY REMAINING VERY MILD.

IMPROVING CONDITIONS TUESDAY INTO MIDWEEK AS DRIER AIR WRAPS AROUND
SURFACE LOW AS IT LIFTS NE ACROSS S CANADA AND FILLS. COOLEST
TEMPERATURES INTO MID WEEK WILL ACROSS NORTHERN FA IN STRONGER COLD
ADVECTION. TEMPERATURES ELSEWHERE WILL BE AT OR A LITTLE ABOVE
SEASONAL AVERAGES DEPENDING ON LINGERING CLOUD COVER.

LONG TERM [THU-SUN]...
LONGER TERM MODELS IN PRETTY GOOD AGREEMENT OVERALL THROUGHOUT THE
THU THRU SUNDAY TIME PERIOD. 500MB RIDGE BEGINS TO PUMP BACK UP OVER
THE NATIONS MIDSECTION FOR AT LEAST THU INTO FRIDAY...POSSIBLY EVEN
INTO SATURDAY. THIS WILL KEEP THINGS MOSTLY SUNNY WITH NO CHANCES
FOR PCPN. PICTURE GETS A LITTLE CLOUDIER BY LATER SAT INTO SUNDAY AS
THE RIDGE SHIFTS EAST. MODELS BRING A SFC LOW UP INTO THE NORTHERN
PLAINS BY SUNDAY...BUT DISAGREEMENTS IN EXACTLY WHERE. EC IS THE
MODEL OF CHOICE BY HPC WHICH PUTS THE LOW OVER CENTRAL ND. CANADIAN
MODEL IS FURTHER EAST AND SHOWS IT IN WEST CENTRAL MN WHILE THE GFS
IS MORE DIFFUSE AT THIS POINT. IN ANY REGARD WILL INCLUDE PCPN
CHANCES BY SUNDAY.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...FLASH FLOOD WATCH FROM 7 AM CDT MONDAY THROUGH LATE MONDAY NIGHT
     FOR NDZ006-014-015-024-026>029-038-054.

MN...NONE.
&&

DK

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GRAND FORKS ND
330 PM CDT SUN MAY 23 2010

NDZ006-014-015-024-026>029-038-054-242030-
TOWNER-BENSON-RAMSEY-EDDY-NELSON-GRAND FORKS-GRIGGS-STEELE-BARNES-
WESTERN WALSH COUNTY-
330 PM CDT SUN MAY 23 2010

...FLASH FLOOD WATCH FOR MONDAY MORNING THROUGH LATE MONDAY
NIGHT...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN NORTH
DAKOTA...WEST CENTRAL AND NORTHWEST MINNESOTA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO REDEVELOP
ALONG AND SOUTH OF THE HIGHWAY 200 CORRIDOR AFTER MIDNIGHT.
HOWEVER SEVERE WEATHER IS NOT ANTICIPATED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

LOW PRESSURE IS EXPECTED TO LIFT NORTHWARD ACROSS THE WESTERN
DAKOTAS ON MONDAY. OUT AHEAD OF THIS SYSTEM...MOIST AND UNSTABLE
AIR WILL MOVE BACK INTO THE ENTIRE REGION. SHOWERS AND
THUNDERSTORMS WILL BE LIKELY THROUGHOUT THE DAY. SOME OF THESE
STORMS MAY BE STRONG TO SEVERE AND PRODUCE LOCALIZED HEAVY
RAINFALL. SOME HEAVY AMOUNTS OF RAIN FELL IN THIS AREA SATURDAY
NIGHT...SO ADDITIONAL HEAVY RAIN COULD RESULT IN MORE FLASH
FLOODING MONDAY MORNING THROUGH LATE AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED.

MNZ001>009-013>017-022>024-027>032-040-NDZ007-008-016-030-039-049-
052-053-242030-
WEST POLK-NORMAN-CLAY-KITTSON-ROSEAU-LAKE OF THE WOODS-
WEST MARSHALL-EAST MARSHALL-NORTH BELTRAMI-PENNINGTON-RED LAKE-
EAST POLK-NORTH CLEARWATER-SOUTH BELTRAMI-MAHNOMEN-
SOUTH CLEARWATER-HUBBARD-WEST BECKER-EAST BECKER-WILKIN-
WEST OTTER TAIL-EAST OTTER TAIL-WADENA-GRANT-CAVALIER-PEMBINA-
EASTERN WALSH COUNTY-TRAILL-CASS-RANSOM-SARGENT-RICHLAND-
330 PM CDT SUN MAY 23 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN NORTH
DAKOTA...WEST CENTRAL AND NORTHWEST MINNESOTA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO REDEVELOP
ALONG AND SOUTH OF THE HIGHWAY 200 CORRIDOR AFTER MIDNIGHT.
HOWEVER SEVERE WEATHER IS NOT ANTICIPATED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

LOW PRESSURE IS EXPECTED TO LIFT NORTHWARD ACROSS THE WESTERN
DAKOTAS ON MONDAY. OUT AHEAD OF THIS SYSTEM...MOIST AND UNSTABLE
AIR WILL MOVE BACK INTO THE ENTIRE REGION. SCATTERED SHOWERS AND
THUNDERSTORMS WILL CONTINUE THROUGHOUT THE DAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED.

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