EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1143 AM EDT TUE OCT 10 2017 VALID 12Z FRI OCT 13 2017 - 12Z TUE OCT 17 2017 ...OVERVIEW... SOME ATMOSPHERIC SHUFFLING IS FORECAST TO OCCUR OVER THE NEXT WEEK, RESULTING IN A FLATTENING OF THE UPPER PATTERN AFTER AN INITIAL SYSTEM PUSHES OUT OF THE CENTRAL STATES AND OFF THE EAST COAST BY EARLY NEXT WEEK. THIS WILL LEAD TO A COOLER PERIOD BY NEXT WEEK IN THE EAST, BUT ONLY BACK TO MORE TYPICAL VALUES FOR MID-OCTOBER. THE NORTHWESTERN PORTION OF THE LOWER 48 INTO THE PLAINS WILL SEE SEVERAL DAYS OF NEAR TO BELOW AVERAGE TEMPERATURES. ...GUIDANCE EVALUATION/PREFERENCES... WHILE A GENERAL MODEL BLEND SHOULD SUFFICE TO START THE PERIOD, DIFFERENCES APPEAR BY THE WEEKEND REGARDING THE UPPER TROUGH EXITING THE CENTRAL ROCKIES. THE 00Z ECMWF AND MANY OF THE ECMWF ENSEMBLE MEMBERS WERE SLOWER THAN THE GFS/UKMET/CANADIAN AND MOST OF THE GEFS/CMC ENSEMBLE MEMBERS. TREND IN THE ENSEMBLES HAS BEEN SOMEWHAT QUICKER BUT NOT ENTIRELY CONSISTENT. ECMWF MAY BE EXHIBITING ITS SLOW BIAS WITH DIGGING FEATURES SO A BLENDED POSITION IN BETWEEN THE QUICKER/SLOWER CAMPS SEEMED REASONABLE BY SATURDAY. AS THE SYSTEM CONTINUES TO PUSH EASTWARD, 00Z ECMWF CONTINUED TO LAG BEHIND THE OTHER MODELS AND MOST ENSEMBLES AS IT WRAPPED UP THE SYSTEM THROUGH WI AND THE U.P. OF MI WHILE THE ENSEMBLE CONSENSUS WAS FARTHER EAST, BUT NOT AS FAR EAST/QUICK AS THE 00Z/06Z GFS. THE 00Z UKMET/CANADIAN FELL IN BETWEEN AND NEAR THE 06Z GEFS/00Z ECMWF ENSEMBLE MEAN OVERLAP, WHICH WAS A GOOD MIDDLE GROUND POSITION AND NOT TOO FAR FROM CONTINUITY. BY NEXT MON/TUE, ENSEMBLES GENERALLY FAVORED A POSITION IN BETWEEN THE 00Z ECMWF AND 06Z GFS AS THE SFC LOW LIFTS THROUGH ONTARIO/QUEBEC AND PUSHES THE WARM FRONT BACK THROUGH MAINE. FRONT SHOULD BE OFFSHORE MOST OF THE EAST COAST BY NEXT TUESDAY EXCEPT FOR FLORIDA. FARTHER UPSTREAM STRONG JET BETWEEN ALASKA AND HAWAI'I BY NEXT WEEK SUGGESTS A LOT OF UNCERTAINTY IN SYSTEM TIMING INTO BRITISH COLUMBIA AND ALSO WASHINGTON. DETERMINISTIC MODELS ARE OF LITTLE USE FOR SPECIFICS BUT HAVE BEEN MOSTLY CONSISTENT IN BRINGING A WAVE INTO BC NEXT WEEK WHILE KEEPING THE SFC BOUNDARY NEAR THE US/CANADIAN BORDER. FINALLY, AN UPPER LOW INITIALLY OVER THE BAHAMAS WILL SLOWLY WEAKEN AS THE UPPER RIDGE TO ITS NORTH GETS SQUEEZED IN A NE-SW DIRECTION. A TROPICAL WAVE IS FORECAST TO MOVE THROUGH THE SUNSHINE STATE AND BRING AN INCREASED CHANCE OF SHOWERS TO MOST OF THE STATE, ESPECIALLY SOUTH OF THE PANHANDLE. FRACASSO ...WEATHER HIGHLIGHTS/THREATS... MODELS/ENSEMBLE CONTINUE TO HINT AT THE POTENTIAL FOR A ROUND OF HEAVY CONVECTION ACROSS THE MIDWEST FRI-SUN AS A AN UPPER SHORTWAVE APPROACHES AND THE ASSOCIATED SURFACE FRONT MOVES INTO THE REGION AND THEN STALLS WHILE ADDITIONAL WAVES DEVELOP ALONG IT. DEVELOPMENT OF A HEALTHY LOW-LEVEL JET SHOULD TRANSPORT SUFFICIENT MOISTURE/INSTABILITY NORTHWARD INTO THE FRONT TO SUPPORT CONVECTION WITH POTENTIALLY HEAVY RAINFALL. DESPITE THE UNCERTAINTY AMONG DETERMINISTIC GUIDANCE SURROUNDING THE MASS FIELDS, THE ECMWF/GEFS ENSEMBLES HAVE BEEN STEADFAST AND REMARKABLY SIMILAR IN THEIR DEPICTION OF A BAND OF HEAVY RAINFALL ALONG/JUST NORTH OF THE FRONT. FARTHER SOUTH, THE FLORIDA PENINSULA WILL REMAIN WET THROUGH THE PERIOD. THE TAIL END OF A WEAKENING FRONTAL BOUNDARY ALONG WITH AN ELONGATED TROUGH/EASTERLY WAVE MOVING FROM THE BAHAMAS ACROSS THE FL PENINSULA WILL SUPPORT SCATTERED TO NUMEROUS SHOWERS AND STORMS FRI-SUN. BY EARLY NEXT WEEK ANOTHER SURFACE FRONT WILL PUSH INTO THE PENINSULA BRINGING A CONTINUATION OF WET CONDITIONS. THE PACIFIC NORTHWEST WILL SEE THE POTENTIAL FOR PRECIPITATION SAT-SUN AS A SURFACE FRONT LINGERS TO THE NORTH. DRY CONDITIONS WILL PREVAIL FOR MOST OF THE NORTHWEST ON MON BEFORE ANOTHER FRONT APPROACHES BY TUE. UPPER RIDGING AND WARM SOUTHERLY FLOW AHEAD OF THE FRONTAL SYSTEM CROSSING THE CENTRAL/EASTERN U.S. WILL SUPPORT WELL ABOVE AVERAGE TEMPERATURES THROUGH MUCH OF THE MEDIUM RANGE. HIGHS RANGING FROM 5 TO 15 DEG F ABOVE AVERAGE ARE EXPECTED ACROSS MUCH OF THE CENTRAL/EASTERN US FRI-SUN. RECORD WARM MINIMUM TEMPERATURES ARE EXPECTED AHEAD OF THE FRONT THIS WEEKEND INTO MONDAY. THE ONE EXCEPTION WILL BE PORTIONS OF THE MID-ATLANTIC EAST OF THE APPALACHIANS ON FRIDAY WHERE EASTERLY FLOW OFF THE ATLANTIC WILL SUPPORT CLOUDS AND PERHAPS A FEW SHOWERS RESULTING IN COOLER TEMPERATURES NEAR SEASONAL NORMAL VALUES. AS THE COLD FRONT SWEEPS EAST BY EARLY NEXT WEEK EXPECT DROPPING TEMPERATURES IN ITS WAKE, ALTHOUGH HIGHS WILL REMAIN NEAR OR JUST ABOVE AVERAGE. ACROSS THE WEST TROUGHING AND PRECIPITATION WILL SUPPORT BELOW AVERAGE TEMPERATURES FRI-SUN, WITH HIGHS 5 TO 15 DEG F BELOW NORMAL. TEMPERATURES WILL MODERATE SOME BY EARLY NEXT WEEK AS CONDITIONS BRIEFLY DRY OUT AND WEAK UPPER RIDGING BUILDS IN. RYAN