Prognostic Meteorological Discussion
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FXUS02 KWBC 301558
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EDT SAT MAY 30 2015

VALID 12Z TUE JUN 02 2015 - 12Z SAT JUN 06 2015

...PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT...

LATEST GUIDANCE MAINTAINS SOME SIMILAR THEMES REGARDING THE LARGE
SCALE PATTERN THAT SHOULD INVOLVE DEVELOPMENT OF AN ANOMALOUSLY
AMPLIFIED WRN/SWRN US TROUGH NEAR 120W AND A BROAD MEAN RIDGE
DOWNSTREAM. OVER CANADA...MEAN RIDGING SHOULD PREVAIL OVER WRN
AREAS WITH A MEAN TROUGH SETTLING IN WELL EWD. UNCERTAINTIES
WITHIN THE WRN CONUS TROUGH PERSIST AND CONTINUED RUN TO RUN
ISSUES WITH THE HANDLING OF FEATURES OVER THE ERN/SERN STATES
SUGGEST LOWER THAN AVERAGE FORECAST PREDICTABILITY OVERALL AT
MEDIUM-RANGE TIME SCALES.

ACCORDINGLY...THE WPC MEDIUM RANGE PRODUCT SUITE HAS BEEN
PRIMARILY DERIVED FROM A BLEND OF THE 00 UTC GEFS MEAN AND 00 UTC
ECMWF ENSEMBLE MEAN. PLACED MORE WEIGHTING ON THE ECMWF ENSEMBLE
MEAN THAT OFFERS BETTER CONTINUITY.

THERE HAS BEEN A RECENT TREND TO DEVELOP A MORE AMPLIFIED PATTERN
FED INTO THE WRN US AND WATER VAPOR IMAGERY CERTAINTY SHOWS SOME
SUPPORT UPSTREAM OVER THE PACIFIC. THE WPC SOLUTION IS WELL ON THE
MORE AMPLIFIED SIDE OF THE FULL ENVELOP OF GUIDANCE...BUT NOT
QUITE AS STRONG AS THE DEEP/CLOSED 00 UTC ECMWF GIVEN LINGERING
UNCERTAINTY/UPSTREAM COMPLEXITY AND CONTINUITY.

MEANWHILE...THE FCST HAS BECOME INCREASINGLY UNCERTAIN AND
COMPLICATED ACROSS THE SRN TIER. THROUGH YESTERDAY...
GFS/GEFS-BASED SOLNS HAD BEEN PERSISTENT IN CLOSING OFF AN UPR LOW
NEAR THE LWR MS VLY WHILE ECMWF/ECMWF MEAN RUNS AS WELL AS CMC/CMC
MEAN SOLNS WERE TRENDING MORE OPEN AND PROGRESSIVE WITH THE ENERGY
OVER THE PAST DAY.  GFS/GEFS PERSISTENCE AND SLOW MOVING NATURE OF
SRN TIER FLOW ALOFT OFFERED SOME ALLOWANCE FOR THE GFS SCENARIO.
HOWEVER THE 00Z GFS/GEFS MEAN HAVE TRENDED MORE PROGRESSIVE THUS
LOWERING THE POTENTIAL FOR A WWD SOLN AND NOW THE 06 UTC GFS/GEFS
HAVE ALLOWED A SIGNIFICANT RUN TO RUN CHANGE WITH A MORE NWD
SYSTEM EMPHASIS/SHIFT.

THEN THERE IS THE FURTHER COMPLICATION OF HOW THIS FEATURE MAY
INTERACT WITH ONE OR MORE IMPULSES THAT MAY FLOW NNEWD FROM THE
WRN CARIBBEAN OR VICINITY... AND WHAT KIND OF SFC EVOLUTION WILL
RESULT. FOR NOW PREFER A CONSERVATIVE APPROACH WITH A BROAD SFC
TROUGH AS IT REMAINS TO BE SEEN WHETHER MID LVL ENERGY WILL EVOLVE
IN SUCH A WAY AS TO SUPPORT A WELL DEFINED SFC SYSTEM.  STILL ALSO
NOTE THAT GEFS/ECMWF ENSEMBLE PROBS OF COMBINED HIGH RH/LOW WIND
SHEAR ARE FAIRLY LOW FROM THE SERN GULF NEWD...DEFINING A THREAT.


...SENSIBLE WEATHER HIGHLIGHTS/THREATS...

EXPECT EPISODES OF RAIN/THUNDERSTORMS FROM THE N-CENTRAL
INTERMOUNTAIN WEST/ROCKIES THROUGH THE NRN HALF OF THE PLAINS/MS
VALLEY WHERE SOME LOCALLY HEAVY TO EXCESSIVE AMOUNTS ARE POSSIBLE.
LOW PREDICTABILITY OF IMPORTANT SHORTWAVE DETAILS MEANS IT WILL
LIKELY TAKE UNTIL THE SHORT RANGE TIME FRAME TO PINPOINT THE MOST
FAVORABLE LOCATIONS FOR HEAVIEST RNFL. CONSULT SPC OUTLOOKS FOR
INFO REGARDING SEVERE POTENTIAL. THE SOUTHEAST/FL SHOULD BE
ANOTHER REGION LIKELY TO SEE ENHANCED MOISTURE/RAINFALL...AT LEAST
WITH SOMEWHAT HIGHER CONFIDENCE THAN THE EXACT SURFACE/ALOFT
EVOLUTION. RECENT TRENDS TOWARD SOME PROGRESSION OF SRN TIER
ENERGY YIELD LESS POTENTIAL FOR SIGNIFICANT RAINFALL OVER THE
LOWER MS VALLEY. MEANWHILE RECENT TRENDS ALOFT TOWARD
AMPLIFICATION ALLOW MORE MOISTURE INTO THE NORTHEAST EARLY NEXT
WEEK WITH CLOSER SURFACE SYSTEM PASSAGE.

MEANWHILE...THE NHC IS ALSO MONITORING EARLY SEASON HURRICANE
ANDRES WELL OFFSHORE OVER THE TROPICAL ERN PACIFIC NEAR 13.7N
115.3W AS OF 15 UTC.

RAUSCH/SCHICHTEL

$$




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