019
FXUS02 KWBC 051808
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
207 PM EDT WED AUG 05 2009
VALID 12Z SAT AUG 08 2009 - 12Z WED AUG 12 2009
THE LONGWAVE PATTERN THIS MEDIUM RANGE WILL USHER IN A CHANGE FROM
THE WRN RIDGE/ERN TROF PATTERN THAT HAS DOMINATED THE CIRCULATION
OVER THE LOWER 48 STATES MOST OF THE PAST MONTH. AN UPPER LOW NOW
OFF THE NRN CA COAST IS GETTING PICKED UP AND MOVED
ASHORE...BEGINNING AN ENE TREK ACROSS THE COUNTRY. IT WILL PULL A
BUBBLE OF HOT AIR OUT OF THE PLAINS STATES THIS WEEKEND TOWARDS
THE SRN GRT LAKES AND OH VLY MON. BY TUE...IT WILL MOVE THIS HEAT
TO THE ATLANTIC COAST STATES FROM SRN NEW ENG INTO THE CAROLINAS.
THE QUESTION IS HOW LONG WILL THE HEAT WAVE LAST IN THE ERN
STATES. A CONSENSUS OF THE ENSEMBLE MEANS OF THE
GEFS...ECMWF...AND CANADIAN SEEM TO BE THE COURSE OF LEAST REGRET.
THIS CONSENSUS STEERS A MIDDLE COURSE BETWEEN THE WED DAY 7
AMPLIFIED COOL NE TROF SOLUTION...DEFINED BY THE DETERMINISTIC
ECMWF AND A FEW OF ITS ENSEMBLE MEMBERS...AND THE DETERMINISTIC
GFS WHICH IS NEAR THE NRN EDGE (ANTICYCLONIC) SIDE OF THE ENVELOPE
IN DEFINING THE PATTERN OVER THE NERN CONUS DAY 7. I THINK NOW
THAT A RETURN TO MORE NORMAL TEMPS IN THE NORTHEAST NEXT WEEK IS
THE MOST LIKELY OUTCOME.
THE NEW 12Z/05 GFS IS FAIRLY CONSISTENT WITH ITS PREVIOUS 00Z/05
RUN CONCERNING MOST FEATURES ACROSS THE LOWER 48. BY TUE DAY 6
IT BECOMES FLATTER AND FASTER THAN ITS CONTINUITY MOVING ANOTHER
SHORTWAVE ACROSS THE NWRN QUADRANT OF THE LOWER 48. BY DAYS 6-7
THE NEW 12Z/05 GFS CONTINUES TO MOSTLY BE OUT OF PHASE WITH THE
00/05 ECMWF FROM THE NRN PLAINS WWD INTO THE PACIFIC...AND WE WILL
NOT BE INCORPORATING IT INTO THE MIX THIS FORECAST CYCLE. THE
CANADIAN AND UKMET ARE SIMILAR TO THE ECMWF IN KEEPING MOST OF THE
UPPER ENERGY IN THE GULF OF ALASKA/NE PACIFIC DAYS 5-7...HOWEVER
THEY ARE FLATTER THAN THE ECMWF WITH THE TROF THE ECMWF MOVED INTO
THE NERN STATES FOR TUE DAY 6. IN THAT REGARD THEY MAY BE MORE
REASONABLE THAN THE ECMWF SINCE TELECONNECTIONS ON A NEGATIVE
HEIGHT ANOMALY NEAR 45N/135W FAVOR ONLY A FLAT TROF NEAR THE E
COAST OF NOAM.
THE FINAL UPDATED FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7 ARE
BASED ON THE 00Z/05 DETERMINISTIC ECMWF THRU MON DAY 5. BEYOND
THAT TIME...WE BLENDED INCREASING PERCENTAGES OF THE NEWER 00Z/05
ECMWF ENSEMBLE MEAN..USING IT TO REPLACE THE 12Z/04 ECMWF MEAN
THAT HAD BEEN USED IN THE PRE-DAWN UPDATE. THE DETERMINISTIC
00Z/05 ECMWF HAS STRONG CONTINUITY FROM ITS LAST TWO DETERMINISTIC
RUNS...AND ROBUST SUPPORT FROM THE 12Z/04 AND 00Z/05 ECMWF
NSEMBLE MEANS. THE GFS RUNS HAVE NOT BEEN AS CONSISTENT AS THE
ECMWF...AND HAVE BEEN BUCKING PERSISTENCE BY KEEPING THE NE
QUADRANT OF THE LOWER 48 HOT RIGHT INTO THE MIDDLE OF NEXT WEEK.
INDEED...A HOT SPELL SHOULD AFFECT THESE AREAS EARLY NEXT WEEK.
HOWEVER BY TUE/WED DAYS 6-7...THE ENSEMBLE MEANS OF THE
ECMWF...CANADIAN...AND EVEN THE GEFS ARE HINTING OF A RETURN TO
COOLER CONDITIONS ACROSS THE NORTHEASTERN STATES...THOUGH NOT TO
THE EXTENT OF THE DETERMINISTIC ECMWF.
SENSIBLE WEATHER WILL BE LARGELY DETERMINED BY MCS COMPLEXES
DEVELOPING ON THE SRN EDGE OF THE WESTERLIES/MEAN FRONTAL BOUNDARY
AS THEY MOVE AROUND THE PERIPHERY OF THE LARGE WARM ANTICYCLONE
ESTABLISHING ITSELF OVER THE SERN CONUS. WSW DRY FLOW WILL KEEP
MONSOONAL PCPN SPARSE OVER THE INTERMOUNTAIN WEST. SOME MCS
CLUSTERS ROTATING AROUND THE LARGE HIGH OVER THE SERN STATES COULD
GENERATE EXCESSIVE RAINFALL. SOME STRONG CONVECTION IS POSSIBLE IN
THE N CENTRAL PLAINS THIS WEEKEND AS THE WEAKENING YET STILL
STRONG WRN H5 TROF LIFTS ENE ACROSS THE N CENTRAL STATES. ON THE
WARM SIDE OF THE MEAN FRONTAL BOUNDARY...EXPECT SOME OF THE
HOTTEST MOST HUMID DAYS OF THIS SUMMER WITH DIURNAL CONVECTION
SOMEWHAT SUPPRESSED BY ANTICYCLONIC CONDS ALOFT.
FLOOD
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