071  
FXUS02 KWBC 201602  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1202 PM EDT FRI OCT 20 2017  
 
VALID 12Z MON OCT 23 2017 - 12Z FRI OCT 27 2017  
   
..OVERVIEW
 
 
GUIDANCE IS SHOWING A HIGHER DEGREE OF VARIABILITY AS THE EASTERN  
U.S. RIDGE IS FORECAST TO BE REPLACED BY WAVES OF ENERGETIC HIGH  
AMPLITUDE TROUGHS NEXT WEEK AS WE HEAD DEEPER INTO FALL.  
CYCLOGENESIS APPEARS LIKELY FROM THE EASTERN GULF COAST UP TOWARD  
THE APPALACHIANS AND LOWER GREAT LAKES SOME TIME NEXT TUESDAY.  
THIS SHOULD BE FOLLOWED BY ANOTHER SIGNIFICANT TROUGH DROPPING  
SOUTH FROM WESTERN CANADA INTO THE PLAINS AND THE GREAT LAKES BY  
THE LATTER HALF OF NEXT WEEK.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE FIRST FEATURE OF CONCERN IS THE POTENTIAL FOR CYCLOGENESIS AT  
THE START OF THE MEDIUM-RANGE PERIOD OVER THE EASTERN U.S. MODELS  
ARE INDICATING THAT A FRONTAL WAVE APPROACHING THE SOUTHEAST U.S  
EARLY NEXT WEEK WILL AMPLIFY AS AN ENERGETIC UPPER TROUGH  
APPROACHES FROM THE PLAINS. THE ECMWF HAS BECOME MORE AGGRESSIVE  
WITH THE RATE OF CYCLOGENESIS FOR THE LAST COUPLE OF RUNS WHEREAS  
THE GFS HAS BEEN QUITE CONSISTENTLY INDICATING A LATER ONSET OF  
THE CYCLOGENESIS. DESPITE THIS DIFFERENCE...BOTH MODELS ARE  
INDICATING A STRONG COLD FRONT MOVING ACROSS AND OFF THE EAST  
COAST BY WEDNESDAY.  
 
MEANWHILE...MODELS ARE INDICATING THE NEXT SIGNIFICANT UPPER  
TROUGH ACROSS WESTERN CANADA SHOULD BE DIPPING INTO THE NORTHWEST  
AND NORTHERN U.S. DURING LATTER HALF OF NEXT WEEK. MODELS HAVE  
TRENDED TOWARD A MORE AMPLIFIED SOLUTION WITH THE COLD AIR MASS  
REACHING FARTHER SOUTH INTO THE PLAINS LATE NEXT WEEK. THERE IS  
STILL A HIGH DEGREE A UNCERTAINTY ON WHETHER A CYCLONE WILL  
DEVELOP ALONG THE FRONT FROM THE CANADIAN BORDER AND HEADING  
FARTHER INTO CANADA.  
 
NOTE ALSO THAT THE EXTRATROPICAL TRANSITIONS TYPHOON LAN MAY LEAD  
TO DOWNSTREAM ADJUSTMENTS IN THE CONUS THAT ARE STILL NOT YET  
APPARENT.  
 
THE UPDATED FORECAST INCORPORATES A COMPROMISE BETWEEN THE 00Z  
ECMWF AND THE 06Z GFS. THE BLEND INCREASES EMPHASIS OF THE  
ENSEMBLE MEANS LATE IN THE PERIOD GIVEN THEIR RELATIVE AGREEMENT  
VERSUS THE SPREAD OF OPERATIONAL RUNS.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
MULTIPLE AREAS OF HEAVY RAINFALL ARE POSSIBLE TO THE EAST OF THE  
MS RIVER AS A WAVY FRONT GRADUALLY PROGRESSES ACROSS THE EASTERN  
STATES. FLOW AHEAD OF AN INITIAL MS VALLEY UPPER TROUGH/LOW  
SHOULD SUPPORT AN AXIS OF HEAVIEST ACTIVITY FROM THE EAST-CENTRAL  
GULF COAST NORTHWARD EARLY IN THE WEEK WITH ATLANTIC INFLOW  
EVENTUALLY SUPPORTING ENHANCED AMOUNTS OVER THE NORTHEAST MID-LATE  
WEEK AS THE FRONT CONTINUES ONWARD. DETAILS/TIMING OF INDIVIDUAL  
FEATURES ALOFT ARE STILL UNRESOLVED, TEMPERING CONFIDENCE IN  
SPECIFICS OF EXACTLY WHERE/WHEN HEAVIEST RAINFALL WILL OCCUR.  
TOWARD FRI ANOTHER AREA OF PRECIP MAY DEVELOP WITH ANOTHER FRONT  
REACHING THE EAST-CENTRAL U.S.. MEANWHILE AN AREA OF MOSTLY LIGHT  
PRECIP SHOULD EXTEND FROM THE NORTHWEST INTO THE CENTRAL  
ROCKIES/HIGH PLAINS AROUND WED-THU.  
 
THE AMPLIFIED PATTERN ALOFT WILL LEAD TO SOME SIGNIFICANT  
TEMPERATURE ANOMALIES. LOCATIONS OVER CALIFORNIA AND THE  
SOUTHWEST/GREAT BASIN MAY SEE ONE OR MORE DAYS WITH HIGHS OF  
10-20F ABOVE NORMAL WITH A FEW DAILY RECORDS BEING CHALLENGED.  
THIS HEAT ALONG WITH DRY/GUSTY WINDS ASSOCIATED WITH OFFSHORE  
GRADIENTS WILL LIKELY ENHANCE WILDFIRE DANGER ONCE AGAIN. A VERY  
BRIEF EPISODE OF WARMTH MAY OCCUR OVER THE NORTHERN-CENTRAL PLAINS  
AROUND MIDWEEK. THE EASTERN U.S. WILL ALSO BE QUITE WARM AT THE  
START OF THE WEEK BEFORE FRONTAL PASSAGE, BUT THEN TREND BELOW  
NORMAL WITH A DAY OR TWO OF MINUS 5-15F ANOMALIES BY WED-THU.  
 
KONG/RAUSCH  
 

 
 
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