350  
FXUS02 KWBC 131939  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
338 PM EDT SAT AUG 13 2022  
 
VALID 12Z TUE AUG 16 2022 - 12Z SAT AUG 20 2022  
 
...THREAT OF A NOR'EASTER INCREASING ACROSS NEW ENGLAND  
WEDNESDAY-THURSDAY AS A TROPICAL DISTURBANCE LIKELY MOVES WEST  
INTO NORTHERN MEXICO...  
 
...MONSOONAL MOISTURE/RAINFALL THREAT CONTINUES FOR THE SOUTHWEST  
AND SOUTH-CENTRAL GREAT BASIN/ROCKIES NEXT WEEK...  
 
...HEAVY RAIN/FLASH FLOODING POSSIBLE ACROSS THE MID-LOWER  
MISSISSIPPI VALLEY TUESDAY-THURSDAY...  
 
...EXCESSIVE HEAT THREAT ACROSS THE SOUTH CENTRAL PLAINS TO  
REFOCUS IN EARNEST OVER INTERIOR CALIFORNIA AND BROADLY ACROSS THE  
NORTHWEST NEXT WEEK...  
 
   
..OVERVIEW
 
 
THE THREAT OF A NOR'EASTER APPEARS TO BE INCREASING ACROSS NEW  
ENGLAND NEXT WEDNESDAY-THURSDAY AS MODELS ARE IN INCREASING  
AGREEMENT FOR CYCLOGENESIS TO OCCUR OFF THE NEW ENGLAND COAST  
UNDER A SLOW-MOVING UPPER TROUGH/LOW. MEANWHILE, A PERSISTENT  
UPPER RIDGE WITH EMBEDDED SHORTWAVE IMPULSES WILL ALSO CONTINUE TO  
SUPPORT WIDESPREAD MONSOONAL MOISTURE STREAMING UNDERNEATH INTO A  
WET AND UNSETTLED SOUTHWEST AND SOUTH-CENTRAL GREAT BASIN/ROCKIES  
NEXT WEEK. THE DOWNSTREAM DIGGING OF SHORTWAVES/HEIGHT FALLS TO  
THE LEE OF THE RIDGE WILL PERIODICALLY REINFORCE UPPER DIFFLUENT  
FLOW OVER THE CENTRAL U.S. BEFORE FEEDING INTO A SLOW-TO-DEPART  
CLOSED LOW OVER THE NORTHEASTERN U.S. ACROSS THE RIO GRANDE  
VALLEY, DEEP TROPICAL MOISTURE ASSOCIATED WITH A TROPICAL  
DISTURBANCE COULD FUEL HEAVY RAINFALL/RUNOFF ISSUES ON TUESDAY.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL SOLUTIONS HAVE CONTINUED TO INDICATE THE GREATEST  
UNCERTAINTY/VARIABILITY TO BE FOCUSED ACROSS THE NORTHEASTERN  
PORTION OF THE COUNTRY WHERE A BROAD AND AMPLIFIED UPPER  
TROUGH/LOW IS FORECAST TO LINGER AS THE MEDIUM-RANGE PERIOD BEGINS  
NEXT TUESDAY. IN PARTICULAR, RECENT MODEL RUNS HAVE INDICATED AN  
INCREASING THREAT OF A LOW PRESSURE SYSTEM TO FORM AND INTENSIFY  
RAPIDLY AHEAD OF THE UPPER TROUGH/LOW AND IMPACT PORTIONS OF NEW  
ENGLAND MIDWEEK. THE GFS HAS BEEN TRENDING TOWARD A MORE  
AMPLIFIED SOLUTION WITH EACH NEW RUN SINCE YESTERDAY, TAKING THE  
CENTER OF THE CYCLONE CLOSER AND CLOSER TO, AND EVENTUALLY OVER  
NEW ENGLAND WITH THIS MORNING'S RUN. THE ECMWF HAS BEEN THE  
WEAKEST AND FARTHEST EAST GUIDANCE BUT THE MOST RECENT RUN (12Z)  
IS MAKING AN ABRUPT SWITCH TO INDICATE A RATHER ROBUST NOR'EASTER  
FOR MID-AUGUST TO BE CENTERED NEAR SOUTHEASTERN NEW ENGLAND NEXT  
THURSDAY. THIS SCENARIO IS SUPPORTED BY THE 12Z UKMET, WHICH IS  
MAKING A SIMILAR ABRUPT SWITCH TOWARD A MUCH AMPLIFIED SOLUTION AS  
WELL. THE CANADIAN MODEL, WHICH HAS BEEN IN BETWEEN THE GFS AND  
ECMWF SOLUTIONS, CONTINUES TO MAINTAIN A NORTHEASTWARD TRACK JUST  
OFF THE NEW ENGLAND COAST.  
 
ELSEWHERE ACROSS THE MID-SOUTH, THERE CONTINUES TO BE WEST-TO-EAST  
TIMING DIFFERENCES REGARDING THE POTENTIALLY HEAVY RAINFALL AXIS  
AHEAD OF A FRONTAL WAVE AS IT MOVES ACROSS THE MID TO LOWER  
MISSISSIPPI VALLEY BY MIDWEEK. THEREAFTER, THE GEFS TENDS TO KEEP  
THE RAIN AXIS FARTHER NORTH ACROSS THE DEEP SOUTH THAN THE EC/EC  
MEAN. MEANWHILE, MODELS ARE GENERALLY IN GOOD AGREEMENT FOR THE  
HEAVY RAINS ASSOCIATED WITH A TROPICAL DISTURBANCE TO MOVE  
WESTWARD AND LARGELY INTO NORTHERN MEXICO BY NEXT TUESDAY.  
 
THE WPC MEDIUM-RANGE FORECASTS WERE COMPOSED BASED ON A CONSENSUS  
OF 40% FROM THE 06Z GFS/GEFS, 40% FROM THE 00Z EC/EC MEAN, AND 20%  
FROM THE 00Z CMC/CMC MEAN, TOGETHER WITH THE 13Z NBM,  
TRANSITIONING TO MOSTLY A CONSENSUS OF THE ENSEMBLE MEANS BY DAY 7.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
PORTIONS OF THE WEST HAVE SEEN PERSISTENT MONSOONAL MOISTURE OVER  
THE PAST COUPLE OF MONTHS, AND NEXT WEEK WILL CONTINUE THAT  
PATTERN AS ANOMALOUSLY HIGH MOISTURE STREAMS INTO THE SOUTHWEST,  
GREAT BASIN, AND ROCKIES IN CONJUNCTION WITH SMALL-SCALE SHORTWAVE  
ENERGY TO PRODUCE RAIN AND THUNDERSTORMS, PARTICULARLY IN THE  
AFTERNOON AND EVENING HOURS. WPC EXPERIMENTAL SLIGHT RISKS OF  
EXCESSIVE RAINFALL ARE IN PLACE FOR THE SOUTH-CENTRAL ROCKIES FOR  
EARLY-MID NEXT WEEK, WHERE THERE IS A VIABLE GUIDANCE SIGNAL FOR  
HEAVY CONVECTIVE RAINFALL ROOTED BY DIGGING SHORTWAVE ENERGY/UPPER  
DIFFLUENCE AND TERRAIN LIFT.  
 
THERE ARE INCREASING CHANCES FOR ORGANIZED CLUSTERS OF CONVECTION  
WITH HEAVY DOWNPOURS TO SPREAD THROUGH EASTERN PORTIONS OF THE  
CENTRAL/SOUTHERN PLAINS AND ESPECIALLY INTO THE MID-LOWER  
MISSISSIPPI VALLEY AS NEXT WEEK PROGRESSES. THERE IS A WPC SLIGHT  
RISK OF EXCESSIVE RAINFALL IN PLACE ACROSS CENTRAL-SOUTHERN  
MISSOURI AND NORTHERN ARKANSAS TUESDAY INTO WEDNESDAY. ELSEWHERE,  
THE GULF COAST AND INTO FLORIDA COULD SEE SCATTERED STORMS WITH A  
MOIST AIRMASS AND FRONTAL BOUNDARIES. A FRONTAL WAVE EXPECTED TO  
TRACK ACROSS THE MID-ATLANTIC TO THE NORTHEAST TO FOCUS SOME  
ORGANIZED RAINS. AN AREA OF ENHANCED RAINFALL IS ALSO FORECAST  
OVER THE LOWER MISSISSIPPI VALLEY BY WEDNESDAY-THURSDAY ON THE  
TRAILING PORTION OF THE FRONT AHEAD OF ANOTHER WAVE OVER THE  
SOUTHERN PLAINS. MEANWHILE, THE THREAT OF A MULTI-DAY RAIN AND  
WIND EVENT IS INCREASING FOR MUCH OF THE COASTAL NORTHEAST, FROM  
NEW JERSEY UP TO MAINE THROUGH MID-WEEK AS MODEL SOLUTIONS ARE  
CONVERGING TOWARD COASTAL CYCLOGENESIS AHEAD OF A CLOSED UPPER  
LOW. PERIODS OF HEAVY RAIN ARE ALSO A DISTINCT POSSIBILITY OVER  
PORTIONS OF NEW ENGLAND GIVEN THAT THE CYCLOGENESIS COULD BE  
RATHER RAPID AND ROBUST.  
 
THE NATIONAL HURRICANE CENTER (NHC) CONTINUES TO MONITOR A  
TROPICAL DISTURBANCE OVER THE NORTHWEST GULF OF MEXICO FOR ANY  
SIGNS OF TROPICAL CYCLOGENESIS. A MAIN THREAT BY MEDIUM RANGE  
TIME SCALES MAY BE FOR SLOW TRACKING AND DEEP TROPICAL MOISTURE  
FUELING HEAVY RAINFALL/RUNOFF ISSUES UP THE RIO GRANDE VALLEY AND  
ACROSS NORTHERN MEXICO ALONG WITH ANY SUBSEQUENT MOISTURE  
INFLUENCE INTO THE MONSOONAL FETCH INTO THE SOUTHWEST, ALL  
CONTINGENT ON UNCERTAIN DEVELOPMENT.  
 
AS THE UPPER RIDGE EXPANDS OVER THE WEST/NORTHWEST NEXT WEEK,  
EXPECT A HEAT WAVE WITH DAYTIME AND OVERNIGHT TEMPERATURE 10-20F  
ABOVE NORMAL. THESE TEMPERATURES ARE LIKELY TO PRODUCE SOME LOCAL  
RECORD VALUES, ESPECIALLY FOR HOT OVERNIGHT CONDITIONS. MEANWHILE,  
BELOW NORMAL HIGHS ARE EXPECTED IN THE EAST-CENTRAL U.S. BEHIND  
THE COLD FRONT, WITH THE MOST PERSISTENT COOLER THAN AVERAGE  
WEATHER IN THE OHIO AND TENNESSEE VALLEYS TOWARD THE MID-ATLANTIC.  
GIVEN THE RAINFALL AND CLOUDINESS OVER THE SOUTHWEST AND  
SOUTH-CENTRAL GREAT BASIN/ROCKIES, HIGHS ARE LIKELY TO REMAIN  
SEVERAL DEGREES BELOW NORMAL.  
 
KONG/SCHICHTEL  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE  
AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 

 
 
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