Area Forecast Discussion
Issued by NWS Grand Forks, ND

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000
FXUS63 KFGF 311444
AFDFGF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND FORKS ND
944 AM CDT SUN AUG 31 2014

.UPDATE...
ISSUED AT 944 AM CDT SUN AUG 31 2014

CURRENT RADAR IMAGERY INDICATES SHOWERS (ISOLD THUNDER) MAINLY
ACROSS NORTHEAST NORTH DAKOTA...JUST AHEAD OF THE 850MB LOW WHERE
WARM AIR ADVECTION IS MAXIMIZED. ANTICIPATE THAT THIS FORCING WILL
PROPAGATE E/NE THROUGH THE MORNING AND EARLY AFTERNOON HOURS (AS
UPPER WAVE PROPAGATES IN THIS DIRECTION). ADJUSTED POPS/WX
ACCORDINGLY (RAISED POP VALUES TO NEAR 100% WHERE THIS STRONGER
FORCING IS EXPECTED...AND LOWERED POP VALUES TO 10%-20% FOR OTHER
AREAS).

SPC HAS SHIFTED THE SLIGHT RISK EASTWARD FOR THIS
AFTERNOON...WHICH MOST NEWER GUIDANCE SUPPORTS. IN FACT...MOST
GUIDANCE SUGGESTS THAT THE BEST RISK FOR SEVERE STORMS WILL BE
WELL SOUTH OF THE FA...AND THAT ANY NORTHERN DEVELOPMENT WILL BE
EAST OF THIS FA. WILL BE WATCHING TO SEE HOW INSTABILITY SETS
UP (WHERE ANY CLEARING MIGHT OCCUR)...AND EXACTLY HOW QUICKLY THE
SFC TROUGH SHIFTS EAST THIS AFTERNOON. THUNDER AND STRONG THUNDER
PROBABILITIES FOR THIS AFTERNOON APPEAR QUITE LOW...BUT SHOULD
KNOW MORE BY THE 100PM UPDATE.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 330 AM CDT SUN AUG 31 2014

FOR THE NEXT 6 TO 12 HOURS THE MAIN CONCERN IS THE CONVECTION AND
RISK FOR SEVERE. AS OF 08Z A LINE OF TSRA EXTENDED FROM
KDVL...KS32 TO KGWR MOVG EAST 35 KTS. THIS LINE IS MOVING INTO AN
AREA OF INCREASINGLY STABLE AIR AND APPEARS TO BE OUTRUNNING THE
LOWER LEVEL FORCING. THE NAM12 AND GFS40 HAD BEEN INCREASING THE
BULK 0-6KM SHEAR TO NEAR 50KTS IN THE DEVILS LAKE BASIN...WHICH
DOES NOT YET APPEAR TO BE THE CASE. HAVE TRIED TO TIME THE TSRA
ACROSS THE CWFA THIS FIRST 12 HOURS BLENDING INHERITED FCST AND
HRRR/NAM/WRF MODEL MOVEMENT.

THE FIRST WAVE ASSOCIATED WITH CONVECTION MOVES EAST BY
18Z...WITH SECOND FAST WAVE MOVING INTO WY AS OF 08Z. AS THE UPPER
WAVES ARE PROGRESSIVE AND THE SYNOPTIC SCALE MODELS ARE IN FAIR
AGREEMENT WITH THE HIGH-RES MODELS...HAVE TRENDED THE BULK OF THE
TSRA/RASH OVER THE EASTERN HALF CWFA BY 00Z. MAY HAVE HELD ON TO
POPS TOO LONG POST 18Z...BUT THIS IS DIFFICULT TO ASCERTAIN ATTM.
THE FCST PRESENCE OF THE LOW LEVEL BOUNDARY AND INSTABILITY 18Z-
00Z ARGUES FOR HOLDING ONTO POPS.

SECOND SHORT WAVE FORECAST TO MOVE ACROSS THE SOUTHERN HALF OF
THE FA 00Z TO 06Z MONDAY SO HAVE HELD ON TO CHC POPS THROUGH 06Z
THEN ENDED RAIN RISK FOR MONDAY. HIGH TEMPERATURES TODAY WILL BE
HIGHLY DEPENDENT ON THE CLOUD COVER...THICKNESSES ARE HIGH ENOUGH
OVER THE SOUTH TO SUPPORT UPPER 70S TO LOWER 80S. HAVE USED THE
LOCAL BIAS CORRECTED TEMPERATURE MODEL FOR TODAY - TUESDAY AS IT
SEEMS TO HAVE SUPERIOR SKILL OF LATE.

.LONG TERM...(MONDAY NIGHT THROUGH SATURDAY)
ISSUED AT 330 AM CDT SUN AUG 31 2014

FLOW ALOFT TURNS FLAT WEST-NORTHWEST BEHIND SECOND WAVE BUT
HEIGHTS DO NOT FALL APPRECIABLY. THE NEXT SHORTWAVE AND ASSOCIATED
SURFACE REFLECTION IMPACTS THE SOUTHERN CWFA MONDAY NIGHT. MODELS
SUGGEST NEXT WAVE FOR TUESDAY FOCUSED MORE ALONG AND NORTH OF THE
HIGHWAY 2 CORRIDOR FOR TUESDAY AFTERNOON AND EVENING...WITH ONLY
CHC POPS.

WEDNESDAY THROUGH SATURDAY...THE NEXT UPPER TROUGH WILL MOVE INTO
THE NORTHERN ROCKIES AT THE START OF THE PERIOD...THEN MOVING OFF
INTO MANITOBA BY THURSDAY. THE SFC LOW WILL MOVE BY TO OUR SOUTH AND
WE SHOULD SEE PLENTY OF PRECIP WITH A BOUNDARY NEARBY...ALTHOUGH THE
MODELS DIFFER ON EXACT TIMING AND PLACEMENT OF THE LOW. WILL
CONTINUE TO KEEP FAIRLY HIGH POPS FOR WEDNESDAY NIGHT AND SOME
LINGERING IN THE EST INTO THURSDAY AS A COLD FRONT COMES THROUGH.
SFC HIGH PRESSURE BUILDING IN FOR THE END OF THE PERIOD WILL BRING
DRY CONDITIONS AND COOLER TEMPERATURES. THE ECMWF AND GFS START TO
DIVERGE BY SATURDAY...SO KEPT ALLBLEND POPS FOR THE TIME BEING.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 636 AM CDT SUN AUG 31 2014

TYPICAL MIXTURE OF VFR/MVFR/IFR CIGS FOUND IN THE PRESENCE OF TSRA
AND SHRA AS AREA OF CONVECTION MOVES NORTHEAST 30 TO 35 KTS. SFC
LOW AND ASSOC WNDSHFT FCST TO MOVE TO KGFK...KFAR LINE 19Z TO
20Z...REACHING KBJI AROUND 010200Z. AFTER INITIAL CONVECTION MOVES
NORTHEAST TAF SITES...EXPCT VFR CIGS AND VSBY.


&&

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

$$

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






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