Prognostic Meteorological Discussion
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000 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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