AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 355 PM EDT SAT AUG 13 2011 .SYNOPSIS... HIGH PRESSURE WILL MOVE OFFSHORE TONIGHT. LOW PRESSURE WILL BRING LOCALLY HEAVY RAINFALL TO PORTIONS OF SOUTHERN NEW ENGLAND SUNDAY THROUGH MONDAY. WEAK HIGH PRESSURE MOVES IN AROUND MIDWEEK. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... HIGH PRESSURE MOVES OFFSHORE TONIGHT BUT WILL REMAIN CLOSE ENOUGH TO NEW ENGLAND TO KEEP MAINLY DRY WEATHER...ESPECIALLY FOR EASTERN NEW ENGLAND. HOWEVER...AS MID LEVEL TROF AMPLIFIES OVER THE GT LAKES DEEP MOISTURE PLUME AND AREA OF MID LEVEL LIFT WILL APPROACH SNE FROM THE WEST LATE TONIGHT. LOW LEVEL THETA-E RIDGE MOVES INTO FAR W ZONES TOWARD 12Z WITH GOOD MOISTURE TRANSPORT AND SOME ELEVATED INSTABILITY SUGGESTING SHOWERS AND ISOLD TSTMS WILL MOVE INTO THE CT VALLEY AND BERKSHIRES. WE THINK GFS IS TOO AGGRESSIVE WITH PRECIP MOVING INTO E NEW ENG BY 12Z SO WE FOLLOWED A NAM/SREF/ECMWF BLEND WHICH FOCUSES SHOWERS CLOSER TO CT VALLEY INVOF OF MODEST LOW LEVEL JET. POPS INCREASED TO LIKELY ACROSS SW MA AND HFD COUNTY WITH CHC ACROSS REST OF N CT AND W MA. BUT KEPT EASTERN HALF OF NEW ENG DRY. MIN TEMPS MAINLY 60 TO 65 DEGREES. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... SUNDAY... MID LEVEL TROF MOVES SLOWLY EWD FROM GT LAKES WITH SW FLOW ALOFT ADVECTING HIGHER PWAT AIR INTO SNE. HOWEVER...BASED ON LOCATION OF LOW LEVEL THETA-E RIDGE AXIS AND HIGHER KI VALUES WE THINK MORE PERSISENT SHOWERS AND HEAVIER RAINFALL WILL REMAIN FOCUSED OVER W ZONES...MAINLY WEST OF MHT-ORH-IJD WHERE POPS WILL BE IN LIKELY CATEGORY. SOUNDINGS DO SHOW SOME ELEVATED INSTABILITY IN THE WEST SO ISOLD TSTMS POSSIBLE...WITH LOCALLY HEAVY RAINFALL POSSIBLE GIVEN PWATS INCREASING OVER 1.5". THERE IS SOME UNCERTAINTY WITH HOW FAR EAST THE SHOWERS WILL GET DURING SUNDAY BUT WE DO EXPECT A FEW SHOWERS TO SPILL INTO PORTIONS OF EASTERN NEW ENG AND HAVE CHC POPS TO THE I95 CORRIDOR. KEPT DRY FORECAST SE COASTAL MA AND CAPE/ISLANDS. COOLER TEMPS EXPECTED DUE TO CLOUD COVER WITH MAXES AROUND 70 BERKSHIRES TO UPPER 70S COASTAL PLAIN...BUT MORE HUMID WITH DEWPOINTS RISING TO THE LOW AND MID 60S. SUNDAY NIGHT... SECONDARY LOW DEVELOPMENT EXPECTED...MOVING NE FROM MID ATLC COAST. DEEP MOISTURE PLUME AND WEAK ELEVATED INSTABILITY ACROSS SNE SUGGESTS MORE SHOWERS AND ISOLD TSTMS WITH ACTIVITY LIKELY SHIFTING FURTHER EAST FROM CT VALLEY. WE WILL HAVE LIKELY POPS FOR ALL SNE. MILD AND HUMID NIGHT WITH TEMPS IN THE 60S. && .LONG TERM /MONDAY THROUGH SATURDAY/... HIGHLIGHTS... * HEAVY SHOWERS LIKELY SOMETIME SUNDAY EVENING INTO MONDAY * DRY WEATHER EXPECTED FOR THE MIDDLE OF NEXT WEEK DETAILS... SUNDAY NIGHT INTO TUESDAY... 13/00Z GUIDANCE IS COMING INTO BETTER AGREEMENT WITH THE DETAILS OF THIS SYSTEM...BUT THERE ARE STILL SOME DIFFERENCES. 0OZ GFS LOOKS TO BE A BIT TOO FAST TO BRING PRECIPITATION INTO SOUTHERN NEW ENGLAND WITH A HIGH PRESSURE OFF THE EAST COAST. ECMWF IS A BIT SLOWER...BUT THINKING THE 12/21Z SREF HAS THE BEST TIMING OF ALL. NOW THINKING THE BRUNT OF THE RAINFALL STARTS TO OVERSPREAD OUR REGION LATE SUNDAY AFTERNOON INTO SUNDAY NIGHT. THE HEAVIEST RAINFALL SHOULD BE AFTER MIDNIGHT MONDAY INTO MID-MORNING MONDAY. THEREAFTER...GFS AND ECMWF COME INTO BETTER AGREEMENT WITH LOCATION AND TRACK OF A SECONDARY LOW PRESSURE TUESDAY MORNING. ECMWF IS CLOSER TO THE COAST THAN THE GFS. THINKING A BLEND OF THESE TWO GUIDANCE SOURCES IS THE BEST FORECAST AT THIS TIME FOR MONDAY NIGHT INTO TUESDAY. THUS HAVE KEPT A CHANCE OF SHOWERS INT THE FORECAST FOR TUESDAY UNTIL THIS SECONDARY LOW PRESSURE PASSES US BY. WEDNESDAY THROUGH FRIDAY... HIGH PRESSURE WILL SPREAD EASTWARDS ACROSS THE AREA WEDNESDAY... THEN SLOWLY MOVE OUT OF THE AREA LATE THURSDAY. A WEAK WARM FRONT ATTEMPTS TO APPROACH OUR REGION THURSDAY NIGHT INTO FRIDAY. BROUGHT IS A CHANCE OF SHOWERS DURING THIS TIME FRAME...BUT THE TIMING IS STILL SUBJECT TO CHANGE. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT MODERATE...30 PERCENT TO 60 PERCENT HIGH...GREATER THAN 60 PERCENT TONIGHT... HIGH CONFIDENCE VFR. MAY SEE TEMPORARY DECREASE IN MID/HIGH CLOUDS THIS EVENING BEFORE CLOUDS INCREASE AGAIN OVERNIGHT. SHOWERS AND LOWER VFR CIGS WILL LIKELY REACH BDL/BAF TOWARD 12Z. SOME LATE NIGHT PATCHY FOG ALSO POSSIBLE ACROSS INTERIOR TERMINALS. SUNDAY... LOW TO MEDIUM CONFIDENCE. MAY SEE A WIDE RANGE IN CONDITIONS ACROSS THE REGION. CONDITIONS LOWERING TO MVFR/IFR ACROSS CT VALLEY AS SHOWERS AND ISOLD TSTMS OVERSPREAD THE REGION...BUT VFR CIGS EXPECTED TO PERSIST ACROSS EASTERN TERMINALS. GREATEST COVERAGE OF SHOWERS SHOULD BE CONFINED MAINLY WEST OF ORH BUT A FEW SHOWERS MAY SPILL INTO EASTERN NEW ENG. SUNDAY NIGHT... MEDIUM CONFIDENCE. MVFR/IFR CONDITIONS IN SHOWERS AND PATCHY FOG. KBOS TERMINAL... HIGH CONFIDENCE IN TAF. VFR EXPECTED THROUGH THE PERIOD. SEABREEZE WILL GIVE WAY TO SOUTHERLY WIND BY 23Z. OUTLOOK...MONDAY THROUGH WEDNESDAY... MONDAY THROUGH TUESDAY... MODERATE CONFIDENCE FOR MVFR AND IFR CONDITIONS FOR THE TERMINALS DUE TO RAIN...PATCHY FOG AND LOW CLOUDS OVER THE REGION. WEDNESDAY... HIGH CONFIDENCE THAT VFR CONDITIONS WILL PREVAIL. && .MARINE... THROUGH SUNDAY NIGHT... WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT CRITERIA. MAINLY SOUTHERLY WINDS 15 KT OR LESS THROUGH SUNDAY...BECOMING SE SUN NIGHT. SEAS BUILDING TO 2 TO 4 FEET SUN NIGHT. OUTLOOK...MONDAY THROUGH THURSDAY... AS A LOW PRESSURE APPROACHES WINDS AND SEAS WILL INCREASE SUNDAY NIGHT INTO MONDAY. CONFIDENCE IS NOT AS HIGH A SMALL CRAFT ADVISORY WILL BE NEEDED ACROSS ALL OF THE COASTAL WATERS.. THINKING THE OUTER COASTAL WATERS SOUTH OF NEW ENGLAND SOUTH OF NANTUCKET AND EAST OF CAPE COD WILL BE MOST AT RISK SUNDAY NIGHT INTO MONDAY NIGHT. && .HYDROLOGY... LATEST GUIDANCE SUGGESTS THE HEAVIEST RAINFALL ACROSS SNE WILL BE FOCUSED IN THE CT VALLEY AND BERKSHIRES WHERE POTENTIAL EXISTS FOR 1 TO 3 INCHES. THIS RAIN WOULD BRING THE POTENTIAL FOR MINOR POOR-DRAINAGE AND URBAN FLOODING...AND MAY PUSH A FEW SMALL STREAMS TO NEAR BANKFULL LEVELS. AS WITH PREVIOUS HEAVY RAIN EVENTS WE HAVE HAD RECENTLY...THE URBAN AREAS WOULD BE THE MOST VULNERABLE. AT THIS TIME...MORE SUBSTANTIAL RIVERINE FLOODING IS NOT ANTICIPATED. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...KJC