Prognostic Meteorological Discussion
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FXUS02 KWBC 231506
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1106 AM EDT WED JUL 23 2014

VALID 12Z SAT JUL 26 2014 - 12Z WED JUL 30 2014

...OVERVIEW AND MODEL GUIDANCE...

THERE ARE NO SIGNIFICANT CHANGES TO THE MEDIUM RANGE GUIDANCE AS A
LARGE SCALE PATTERN CHANGE CONTINUES TO UNFOLD WITH AN
INCREASINGLY AMPLIFIED WESTERN RIDGE/EASTERN TROUGH LOOKING QUITE
LIKELY.  DURING THIS PERIOD...500 MB HEIGHT ANOMALIES APPROACH 3
STDEVS BELOW NORMAL ACROSS THE OHIO VALLEY/APPALACHIANS WHILE
ACROSS THE WEST...STDEVS PEAK ABOUT 1.5 TO 2 ABOVE NORMAL. IN THE
EAST...THIS REPRESENTS ANOTHER UNUSUAL OUTBREAK OF RELATIVELY COOL
AIR DURING A MONTH THAT OFTEN FEATURES THE HIGHEST TEMPERATURES OF
THE YEAR.  HOWEVER...OUT WEST...A CONTINUING THREAT OF DROUGHT AS
WELL AS SOME ISOLATED ELEVATED CONVECTION INCREASING THE DANGER OF
FIRE WEATHER.

AS NOTED IN PREVIOUS DISCUSSIONS...THERE IS STILL QUITE A BIT OF
UNCERTAINTY WITHIN THIS RELATIVELY CONFIDENT FORECAST IN THE
EVOLUTION OF THE MESOSCALE DETAILS OF FRONTAL TIMING/LOCATION AND
ANY WEAK WAVES OF LOW PRESSURE ASSOCIATED WITH THE LEADING EDGES
OF COOL AIR IMPULSES.  FOR EXAMPLE...ON DAYS 3 AND 4/SATURDAY AND
SUNDAY...THERE IS QUITE A BIT OF COMPLEXITY WITH THE EVOLUTION OF
FEATURES ACROSS THE UPPER MISSISSIPPI VALLEY...MIDWEST INTO THE
NORTHEAST.  AS ONE PRIMARY AREA OF LOW PRESSURE BECOMES MORE
ORGANIZED BY DAY 5/MONDAY...THAT COMPLEXITY SEEMS TO DIMINISH AS
THE FRONT NEARS AND PASSES THE EAST COAST ON DAYS 6 AND 7/TUESDAY
AND WEDNESDAY.

LATER IN THE FORECAST...THE OPERATIONAL RUNS APPEAR TO DEVIATE
MORE FROM THEIR RESPECTIVE MEANS WITH THE LATEST 06Z GFS/00Z ECMWF
RUNNING SLOWER THAN THE MEANS.  AS A RESULT...HAVE USED A BLEND OF
ALL FOR DAYS 6 AND 7 TO HAVE SOME SORT OF INTERMEDIATE SOLUTION
BETWEEN THE MEANS AND THE OPERATIONAL RUNS.  WHILE THIS MOSTLY
AFFECTS THE LOCATION OF LOW PRESSURE NORTHEAST OVER QUEBEC...IT
REALLY ONLY MEANS JUST SLIGHT DIFFERENCES IN THE POSITION OF THE
PRIMARY COLD FRONT AS IT NEARS AND CROSSES THE EAST COAST.

...SENSIBLE WEATHER HIGHLIGHTS...

COOLER AIR WILL SPREAD SEWD FROM THE NORTH CENTRAL STATES ACROSS
MUCH OF THE EAST DURING THE PERIOD... LEAVING MUCH OF THE EASTERN
HALF OF THE NATION WITH BELOW AVERAGE READINGS BY THE MIDDLE OF
NEXT WEEK.  IN GENERAL...MAX TEMPS SHOULD BE SOMEWHAT FARTHER
BELOW NORMAL THAN THE MINS THOUGH IN MOST CASES LIKELY NOT AS
EXTREME AS WITH THE PREVIOUS COOL AIR OUTBREAK...ESPECIALLY OVER
THE MIDWEST.  AHEAD OF THIS COOLING TREND...ONE OR MORE SFC
LOWS/FRONTAL SYSTEMS WILL SUPPORT AREAS OF SHOWERS/TSTMS OVER THE
ERN THIRD OF THE NATION FROM THE WEEKEND INTO EARLY NEXT WEEK...
SETTLING TOWARD THE SE/GULF COAST THEREAFTER.  SOME LINGERING
SHOWERS MAY CONTINUE FOR A TIME IN THE VICINITY OF THE GREAT LAKES
NEAR THE CORE OF THE UPPER TROUGH.  MEANWHILE LOW LEVEL UPSLOPE
FLOW BEHIND THE TRAILING PART OF THE MAIN SFC FRONT MAY INCREASE
POTENTIAL FOR LOCALLY HEAVY RAIN OVER PORTIONS OF COLORADO/NEW
MEXICO INTO THE SOUTHERN PLAINS LATE IN THE FORECAST.  OVER THE
INTERIOR WEST... TEMPS SHOULD BE ABOVE NORMAL WITH ONLY SCATTERED
CONVECTION...INCREASING THE LIKELIHOOD FOR WILDFIRES.

KOCIN

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