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000
FXUS63 KFGF 172352
AFDFGF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND FORKS ND
652 PM CDT FRI MAY 17 2013

.UPDATE...
ISSUED AT 652 PM CDT FRI MAY 17 2013

ADJUSTED POPS ALONG THE CANADIAN BORDER FOR THE NEXT FEW HOURS TO
ACCOUNT FOR THE WEAK SHOWERS/SPRINKLES DEVELOPING IN THAT AREA.
HOWEVER...THE MAIN PRECIP IS WELL TO OUR SOUTH...SO KEPT THE HIGH
POPS RESERVED FOR AFTER MIDNIGHT AS THE GOING FORECAST HAS.
TWEAKED CLOUDS TO INCLUDE CLEARING IN OUR SOUTHWESTERN COUNTIES
BUT THAT WILL NOT LAST LONG AS BLOW OFF FROM CONVECTION FROM OUR
SOUTHWEST BEGINS TO MOVE IN. SHOULD BE TOTALLY CLOUDY AFTER
MIDNIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 330 PM CDT FRI MAY 17 2013

THE MAIN CONCERNS WILL BE HEAVY RAIN AND SEVERE POTENTIAL. 12Z
MODELS IN DECENT AGREEMENT WITH SYNOPTIC FEATURES...BUT STILL
ENOUGH DIFFERENCES THAT CONFIDENCE IS LOW WITH DETAILS.

WEST COAST TROUGH WILL GRADUALLY PROPAGATE EAST WITH MULTIPLE
SHORTWAVES EJECTING INTO THE REGION. HARD TO PINPOINT EXACTLY WHEN
AND WHERE THE BEST THUNDER CHANCES WILL BE...BUT THE MODELS DO
OFFER A COUPLE STRONGER SIGNALS. THE FIRST BEST CHANCE IS TONIGHT
INTO SATURDAY MORNING AS MENTIONED IN THE PREVIOUS AFD (1243PM).
18Z HRRR DOES INDICATE A THUNDERSTORM COMPLEX MOVING INTO THE
SOUTHERN FA AFTER 06Z...ALONG WITH WITH ISOLATED STRONGER STORMS.
THIS COMPLEX SHOULD MOVE THROUGH FAIRLY QUICKLY...WITH UP TO 0.5
INCH AREAL QPF POSSIBLE.

THINKING THERE WILL BE A BRIEF BREAK IN ACTIVITY ON SATURDAY.
SEVERE POTENTIAL WILL DEPEND ON HOW FAR NORTH THE SURFACE WARM
FRONT WILL MAKE IT BY SATURDAY AFTERNOON. THE GEM/GFS BRING THIS
FEATURE MUCH FURTHER NORTH THAN OTHER MODELS (LIKELY BECAUSE THEY
ARE STRONGER WITH A SHORTWAVE INTO SOUTHERN CANADA). AT ANY
RATE...GIVEN THIS TIME OF YEAR WITHOUT EVAPOTRANSPIRATION...THE
NAM SEEMS TO HAVE THE CORRECT IDEA INDICATING MLCAPE 1000-1500
J/KG WITHIN THE WARM SECTOR. THIS INSTABILITY ALONG WITH DEEP
LAYER SHEAR 30-35 KNOTS SHOULD BE ENOUGH FOR LIMITED SEVERE
POTENTIAL WITHIN THE WARM SECTOR AS THE COLD FRONT SLOWLY
PROPAGATES EAST INTO THE EVENING HOURS.

THE BEST CHANCE FOR FLASH FLOODING POTENTIAL WOULD BE SATURDAY
EVENING AND OVERNIGHT ALONG THE SLOW MOVING BOUNDARY. THE BIGGEST
QUESTIONS AT THIS POINT WILL BE THE EXACT LOCATION OF THIS
FEATURE...AND HOW QUICKLY IT WILL MOVE TO THE EAST. NOT ENOUGH
CONFIDENCE FOR A FLASH FLOOD WATCH AT THIS POINT...BUT THERE IS A
SLIGHT RISK FOR FLASH FLOODING ALONG AND EAST OF THE VALLEY.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 330 PM CDT FRI MAY 17 2013

SUNDAY-MONDAY...UPPER LOW WILL CLOSE OFF JUST SOUTH OF THE FA AND
BRING PERIODIC SHOWERS AND THUNDERSTORMS TO THE REGION.
INSTABILITY IS MUCH WEAKER BY THIS TIME...BUT GIVEN HIGH PWATS AN
ADDITIONAL 1-2 INCHES OF RAINFALL IS POSSIBLE (ESPECIALLY THE
SOUTHERN HALF OF THE FA). THIS RAINFALL WOULD OVER A COUPLE DAYS
AND ANY FLOOD THREAT IS DEPENDENT ON WHAT OCCURS SATURDAY/SATURDAY
NIGHT.

MONDAY NIGHT-FRIDAY...12Z GFS/12Z ECMWF IN PRETTY GOOD AGREEMENT
IN SHOWING THE 500 MB LOW OVER EASTERN SD/MN REGION TUESDAY THEN
DRIFTING A BIT SOUTH AND EAST WEDNESDAY AND THEN EAST OF THE AREA
THURSDAY. LOOK FOR A CONTINUED HIGH THREAT FOR SHOWERS
TUESDAY...DIMINISHING ON WEDNESDAY. A 500 MB RIDGE WILL BUILD IN
BEHIND THE LOW FOR THE END OF THE WEEK WITH DRY WEATHER RETURNING.
LOOK FOR TEMPS TO BIT A BIT BELOW NORMAL WITH THE CLOUDS/RAIN TUE-
WED THEN RETURN TO CLOSE TO NORMAL LEVELS BY LATE WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 652 PM CDT FRI MAY 17 2013

VFR CLOUDS WILL CONTINUE OVER MUCH OF THE AREA...BUT SOME MVFR
CEILINGS OVER THE SOUTHEASTERN FORECAST AREA WILL BEGIN TO SPREAD
NORTH AND WEST LATER ON TONIGHT. HAVE KFAR DECREASING TO MVFR
AFTER MIDNIGHT AND THE OTHER SITES MORE TOWARDS MORNING. SHOWERS
AND A FEW THUNDERSTORMS WILL MOVE IN AFTER MIDNIGHT...WITH THE
BEST CONVECTION IN THE SOUTH AROUND KFAR WHILE THE NORTHERN SITES
WILL BE MORE SHOWERY. WINDS WILL SHIFT TO A MORE SOUTHERLY
DIRECTION DURING THE DAY TOMORROW AS A WARM FRONT LIFTS NORTH INTO
THE AREA...ALTHOUGH THERE IS STILL SOME UNCERTAINTY AS TO EXACTLY
WHERE THE BOUNDARY WILL END UP. FOR NOW HAVE IT GOING PAST OUR
NORTHERN TAF SITES BY LATE IN THE PERIOD BUT THE BOUNDARY MAY
STALL OUT AND LEAVE THEM IN EASTERLY WINDS AND MORE RAIN. THINK
THAT THERE SHOULD BE SOME BRIEF IMPROVEMENT TO VFR IN MOST SITES
DURING THE LATE MORNING OR AFTERNOON ALTHOUGH MUCH WILL DEPEND ON
HOW EARLY MORNING CONVECTION PLAYS OUT.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...NONE.
MN...NONE.
&&

$$

UPDATE...JR
SHORT TERM...TG
LONG TERM...TG/RIDDLE
AVIATION...JR