000
FXUS63 KFGF 070213
AFDFGF
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND FORKS ND
856 PM CDT SAT SEP 6 2008
.DISCUSSION...
WE WILL MAKE SOME MINOR ADJUSTMENTS TO TONIGHT/S FCST...MAINLY TO
TIDY UP POPS AND SKY NOW THAT OBS MAKE IT MORE OBVIOUS THAT MUCH
OF THE CONVECTION IS DIURNALLY-INDUCED AND THUS WILL NOT SURVIVE
THE NIGHT. THE MAIN EXCEPTION WILL BE WITH THE BATCH OF -SHRA NOW
ENTERING SE ND...WHICH SHOULD LAST LONGER /DESPITE ITS CONVECTIVE
ORIGINS/ GIVEN MODERATE 500-300 HPA Q-VECTOR CONVERGENCE PER THE
18Z NAM/GFS. OUR CHANCE POPS WILL FOLLOW THIS UPWARD MOTION INTO
NW MN 05-09Z. MODIFYING SFC TEMPS ON THE 00Z BIS/ABR RAOBS
SUGGEST THAT ONCE WE FALL INTO THE MID 50S F /AS MOST SITES ARE
NOW/ THE BUOYANCY WILL BE TOO MARGINAL FOR THUNDER SO THIS WILL
ALSO BE DROPPED FROM THE DATABASE. FURTHER UPSTREAM...SATELLITE
SHOWS A CELLULAR NATURE TO MOST CLOUDS WHICH SUGGESTS AT LEAST
PARTIAL CLEARING SHIFTING SE INTO EASTERN ND JUST AS THE 00Z RUC
SHOWS. THIS WILL BE TEMPERED SOME BY LOW/MID LVL CAA...WHICH DROPS
850-HPA TEMPS DOWN TO +2 C IN THE NW FA BY 12Z. NOT AN IDEAL
RADIATIONAL COOLING SITUATION...BUT EVEN THIS MORNING LANGDON WAS
DOWN TO 38 F...SO WE WILL LOWER TEMPS ABOUT 3 F THERE. THE 18Z NAM
ACTUALLY DROPS THAT AREA TO 35 F.
ONE OTHER ISSUE MAY AGAIN BE PATCHY FOG OR AT LEAST LOWER
CIGS...ESPECIALLY WHERE IT RAINED TDY...AND IN NW MN WHERE MOST
12/18Z MODELS AND THE 00Z RUC ALL DEVELOP IFR CIGS 09-12Z. WE WILL
NOT ADD ANY FOG AT THIS POINT BUT IT IS SOMETHING TO KEEP AN EYE
ON.
.AVIATION...
SCATTERED -SHRA WILL MOVE EAST AT 20KTS INTO NW MN THRU 06Z...
THOUGH IT IS QUESTIONABLE HOW LONG THEY WILL LAST NOW THAT THE SUN
HAS SET. MARGINAL MVFR CIGS/VIS COULD ACCOMPANY THIS ACTIVITY. THE
LOW CONFIDENCE PART OF THE AVIATION FORECAST IS 08-13Z WHEN IFR OR
LOWER CIGS /OR VIS/ ARE POSSIBLE. THIS HAPPENED THE PAST TWO
MORNINGS AND MODEL GUIDANCE SUGGESTS IT WILL AGAIN...AT LEAST AT
KTVF/KBJI. THIS IS HINTED AT IN THE PRESENT TAF SET...BUT UNTIL
CONFIDENCE INCREASES THE FORECAST WILL REMAIN SOMEWHAT OPTIMISTIC.
&&
.PREV DISCUSSION... /ISSUED 339 PM CDT SAT SEP 6 2008/
SHORT TERM...
MAIN FORECAST CHALLENGE IS PRECIPITATION. WHEN LOOKING AT THE LATEST
SURFACE ANALYSIS...AN AREA OF LOW PRESSURE IS CENTERED IN NE MB WITH
A WEAK COLD FRONT THAT EXTENDS E MB TO ALONG A ROX TO DTL LINE. WHEN
COMPARING THE MODELS...THE MODELS REMAIN IN PRETTY GOOD AGREEMENT
FOR THE SHORT TERM...SO ENDED UP USING MODEL COMPROMISE FOR THE
FORECAST. BLENDED THE GFS AND NAM FOR POPS AS THEY DIFFER ON WHAT
PART OF THE CWFA WILL BE MOST AFFECTED BY TONIGHT`S TROF PASSAGE. AS
FAR AS TEMPS...WITH ADJMAVBC STILL DOING PRETTY WELL...USED IT AS
A STARTING POINT AND THEN ADJUSTED FROM THERE.
KMVX CURRENTLY SHOWS TWO AREAS OF CONVECTION...ONE IN THE E AND
ANOTHER IN THE W. E PCPN IS AHEAD AND ALONG OF SURFACE FRONT AND W
PCPN IS ASSOCIATED WITH PUSH OF NEXT WAVE AS SEEN ON WV IN
ASSOCIATION WITH THE 500MB TROF. 500MB TROF IS EXPECTED MOVE THROUGH
THE N PLAINS TONIGHT AND SUN...SO KEPT PCPN IN THE FORECAST. MODELS
DO KEEP SHOWALTERS AT OR BELOW ZERO OVER PARTS OF THE AREA UNTIL 06Z
TONIGHT. WITH OCCASIONAL LTG FOUND IN STORMS THAT HAVE DEVELOPED...
KEPT THUNDER MENTION IN FOR THIS EVENING AND TRANSITIONED TO SHRA
AFTER 06Z.
FOR SUN NIGHT INTO TUE...SURFACE HIGH PRESSURE DOMINATES THE
WEATHER...SO KEPT THE FORECAST DRY. THERE IS A ANOTHER 500MB
TROF THAT MOVES THROUGH ON MON NIGHT...BUT WITH MINIMAL UVV AT
700MB...850MB Q-VECTOR DIVERGENCE INDICATED AND ALSO STABILITY
INDICES ABOVE ZERO...BELIEVE THAT WILL ONLY SEE CLOUDS FROM THIS
TROF PASSAGE AT THIS TIME.
LONG TERM (TUE THROUGH SAT)...
MEDIUM-RANGE MODELS CONTINUE TO DIFFER WITH STRENGTH AND TIMING
OF NEXT PACIFIC SHORT WAVE. 00 UTC CANADIAN AND 12 UTC ECMWF
SOLUTIONS BRIEFLY CUT-OFF WEAK 500 HPA LOW OVER THE CENTRAL
ROCKIES THU MORNING BEFORE EJECTING PRIMARY ENERGY EASTWARD...WHEREAS
GFS IS STRONGER AND MUCH MORE PROGRESSIVE. CURRENT FORECAST
PRIMARILY FOLLOWS HPC GUIDANCE...WHICH FAVORED FASTER GFS. MODEL
CONSENSUS SHOWS BEST CHANCE FOR MEASURABLE PRECIPITATION WED AND
THU OUT AHEAD OF PRIMARY MID-LEVEL WAVE...ALTHOUGH THIS TIME
FRAME MAY BE PUSHED LATER OR EXTENDED IF SLOWER CANADIAN/ECMWF
SOLUTIONS BECOME REALITY. EITHER WAY...TEMPERATURES WILL CONTINUE
TO TREND BELOW SEASONAL NORMALS THROUGH NEXT WEEK.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...NONE.
MN...NONE.
&&
$$
SCHULTZ/NG/ROGERS
