AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 945 PM EDT SUN APR 17 2011 .SYNOPSIS... HIGH PRESSURE WILL BRING MAINLY DRY WEATHER MONDAY AFTERNOON. UNSETTLED WEATHER MAY RETURN MONDAY NIGHT THROUGH WEDNESDAY...BRINGING PERIODS OF CLOUDS AND SHOWERS. A COLD FRONT WILL PUSH THROUGH WEDNESDAY NIGHT...BRINGING DRIER BUT COOLER CONDITIONS FOR THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... STRONG SHORTWAVE WITH COLD POOL ALOFT WORKING INTO SOUTHERN NEW ENGLAND THIS EVENING. DESPITE THE LOSS OF DAYTIME HEATING...500 MB TEMPERATURES BELOW -30C AND STEEP MID LEVEL LAPSE RATES IN EXCESS OF 7.5 C/KM WILL ALLOW SCATTERED SHOWERS TO WORK ACROSS SOUTHERN NEW ENGLAND DURING THE FIRST PART OF THE OVERNIGHT HOURS. WILL RUN WITH CHANCE TO LIKELY POPS TO COVER THIS ACTIVITY. TOTAL TOTALS APPROACHING 60 HAVE RESULTED IN ENOUGH INSTABILITY FOR A FEW LIGHTNING STRIKES ACROSS PORTIONS OF NEW YORK THIS EVENING. ITS POSSIBLE THAT A WE SEE AN ISOLATED RUMBLE OR TWO ACROSS OUR REGION. CERTAINLY NOT EXPECTING ANYTHING WIDESPREAD...BUT WILL LEAVE IN A SLIGHT CHANCE OF THUNDER ACROSS PARTS OF RHODE ISLAND/SOUTHEAST MA WHERE THERE IS A BIT BETTER INSTABILITY. ANY OF THE SHOWERS WILL ALSO HAVE THE POTENTIAL TO BRING BRIEF 30 TO 40 MPH WIND GUSTS. WE SHOULD SEE THE ACTIVITY COME TO AN END SHORTLY AFTER 6Z. AS FOR LOW TEMPERATURES...WENT A BIT MILDER THAN GUIDANCE WITH CLOUDS FOR AT LEAST PART OF THE NIGHT AND WINDS NOT DECOUPLING. LOWS SHOULD MAINLY BE IN THE 30S...TO THE LOWER TO MIDDLE 40S IN DOWNTOWN BOSTON/PROVIDENCE. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... MONDAY...WEAK HIGH PRESSURE WILL TEMPORARILY BUILD ACROSS THE REGION. COLD AIR ADVECTION WILL QUICKLY DIMINISH...AND WITH ABUNDANT SUNSHINE THIS WILL ALLOW FOR SOME REBOUND IN TEMPERATURE DURING THE AFTERNOON...WELL INTO THE 50S. HOWEVER GIVEN FAST PROGRESSIVE FLOW ALOFT...CLOUDS WILL ALREADY BE ON THE INCREASE LATE MONDAY AFTERNOON...AS THE NEXT SHORT WAVE DISTURBANCE APPROACHES FROM THE WEST. MONDAY NIGHT... A WARM FRONT WILL SET UP CLOSE TO THE AREA...WHILE A WEAK WAVE OF LOW PRESSURE FORMS ALONG THE FRONT. THE APPROACHING SHORT WAVE IS EXPECTED TO SHEAR OUT IN FAST PROGRESSIVE FLOW. HOWEVER DO NOTE AN APPROACHING LOW LEVEL SOUTHWESTERLY JET 50-55 KT ATTEMPTING TO INTERSECT WITH A DEVELOPING H85 THERMAL RIBBON. SOME QUESTIONS REMAIN WHERE THE BEST LIFTING FOCUS WILL BE. HAVE CHANCE POPS ADVERTISED. && .LONG TERM /TUESDAY THROUGH SUNDAY/... TUESDAY... COLD FRONT STALLS SOUTH OF NEW ENGLAND. NAM AND GFS SHOW AN AREA OF RAIN MOVING ALONG THE NORTHERN SIDE OF THE FRONT. THE GFS SHOWS A QUICK BURST OF RAIN THAT STARTS BY MIDDAY AND ENDS BY EVENING...WHILE THE NAM SHOWS STEADY INCREASE THROUGH THE DAY. ISENTROPIC FIELDS ARE NOT IMPRESSIVE. A 30 KNOT JET MAX AT 850 MB DOES MOVE THROUGH DURING THE DAY AS DOES A TEMPORARY INCREASE IN FRONTOGENESIS. THIS COULD BE PICKING UP ON A WEAK DISTURBANCE SURFING ALONG THE FRONT GENERATING A PERIOD OF RAIN OR SHOWERS. NOT A LOT OF CONFIDENCE IN THIS...BUT ENOUGH TO MENTION CHANCE POPS WITH HIGHEST VALUES IN THE SOUTH. CLOUDS AND A NORTH-TURNING-NORTHEAST SURFACE FLOW SHOULD KEEP TEMPS ON THE COOL SIDE OF NORMAL. NORMAL IS 55-60. WE USED A BLEND OF MOS TO GENERATE TEMPS. TUESDAY NIGHT-WEDNESDAY... SHORTWAVE ALOFT MOVES ONSHORE ON THE PACIFIC COAST MONDAY. THE SHORTWAVE PICKS UP A SURFACE LOW OVER THE PLAINS TUESDAY AND DRIVES IT INTO THE GREAT LAKES WEDNESDAY. SOUTHWEST WINDS AHEAD OF THE LOW AT 950-850 MB PRODUCE INCREASED ISENTROPIC LIFT AS THEY RIDE OVER THE TOP OF THE COOLER MARINE EAST SURFACE FLOW OVER NEW ENGLAND. THIS SHOULD SUPPORT INCREASED CHANCE OF RAIN TUESDAY NIGHT INTO WEDNESDAY. THE STRONGEST WINDS ALOFT AND RESULTING LIFT ARE FORECAST TO MOVE THROUGH THE EASTERN LAKES AND ALONG THE CANADIAN BORDER. THEREFORE EXPECT HIGHEST POPS TO OUR NORTH ESPECIALLY ON WEDNESDAY. SOME QUESTION AMONG THE MODELS AS TO HOW SOON/LATE THE WARM FRONT MOVES THROUGH SOUTHERN NEW ENGLAND. THE NORTHERN TRACK OF THE SURFACE LOW WOULD SUGGEST IT WILL HAPPEN AT SOME POINT...THE GFS SHOWS THE WIND SHIFT WEDNESDAY NIGHT BETWEEN 00Z AND 06Z WHILE THE NAM LIFTS IT THROUGH DURING WEDNESDAY AFTERNOON. THE 12Z GGEM IS CLOSE TO THE NAM. THIS HAS IMPLICATIONS FOR PCPN BEING EITHER A STEADY RAIN OR SHOWERY...AND IMPLICATIONS FOR MAX TEMP WITH COOLER VALUES IN THE MARINE FLOW NORTH OF THE WARM FRONT AND WARMER VALUES IN THE SOUTHWEST FLOW TO THE SOUTH. WE WENT WITH THE COOLER FRONTAL TIMING SIMILAR TO THE GFS. FOR TEMPERATURE WE USED A BLEND OF MOS WITH VALUES 50-55...THIS IS ABOUT 5F WARMER THAN THE COLDEST GUIDANCE VALUES. IF THE WARM FRONT MOVE NORTH OF US BY MID AFTERNOON THEN THE ACTUAL VALUES WILL BE 10-15 DEGREES HIGHER THAN OUR FORECAST. GFS AND GGEM MOVE THE LOW MOVES THROUGH QUEBEC WEDNESDAY NIGHT...AND THE NAM HINTS AT A SIMILAR TRACK PAST THE END OF ITS RUN. THE 12Z ECMWF DIFFERS BY BRINGING THE LOW ACROSS NEW ENGLAND. CURRENTLY FAVOR THE MORE NORTHERLY TRACK...WHICH WOULD SWING A COLD FRONT ACROSS NEW ENGLAND OVERNIGHT. STABILITY INDICES SHOW A POTENTIAL FOR THUNDER WITH TOTALS AROUND 50 AND MID LEVEL LAPSE RATES AT 6.5 TO 7.0C PER KM. THURSDAY... SURFACE LOW MOVES OFF TO THE NORTHEAST WHILE THE UPPER TROUGH MOVES ACROSS NEW ENGLAND. THIS WOULD MEAN LINGERING CLOUDS...ESPECIALLY DURING THE MORNING...WITH A CLEARING TREND IN THE AFTERNOON AS THE UPPER TROUGH MOVES OFF. INCREASING SUNSHINE AND COLD ADVECTION ALOFT WILL AID IN DEEPER MIXING THAT SHOULD REACH 850 MB. WINDS AT THAT LEVEL ARE FORECAST AT 35 TO 40 KNOTS ON THE GFS AND 30-35 KNOTS ON THE ECMWF. TEMPS ARE A BLEND OF HPC AND GMOS VALUES. FRIDAY... HIGH PRESSURE IN PLACE. FAIR WEATHER WITH LIGHT WINDS. TEMPS ARE A BLEND OF HPC AND GMOS VALUES. SATURDAY AND SUNDAY... LOW PRESSURE MOVES OUT OF THE PLAINS SATURDAY. THE GFS MOVES IT THROUGH THE GREAT LAKES SATURDAY...PUSHING A WARM FRONT THROUGH NEW ENGLAND SATURDAY NIGHT AND A COLD FRONT SUNDAY MORNING. THE 12Z ECMWF MOISTURE FIELDS INDICATE UNSETTLED WEATHER...BUT THE PRESSURE FIELDS ARE MUCH MORE VAGUE THAT THE GFS. ENOUGH CONSENSUS TO GO WITH CHANCE POPS FOR BOTH DAYS BUT LOW CONFIDENCE IN THE DETAILS AT THIS TIME. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT MEDIUM...30 PERCENT TO 60 PERCENT HIGH...GREATER THAN 60 PERCENT TONIGHT...MEDIUM TO HIGH CONFIDENCE IN MAINLY VFR CONDITIONS. SCATTERED SHOWERS MAY RESULT IN ISOLATED BRIEF MVFR CONDITIONS. LOW PROBABILITY OF AN ISOLATED RUMBLE OF THUNDER ACROSS RHODE ISLAND/SOUTHEAST MA. SOUTHWEST WIND GUSTS OF 20 TO 25 KNOTS ARE EXPECTED AT TIMES. HOWEVER...BRIEF WIND GUSTS OVER 30 KNOTS ARE POSSIBLE IN ANY SHOWER. MONDAY...VFR. WSW WINDS GUSTING TO 25 KT IN THE MORNING. MONDAY NIGHT...VFR EARLY...THEN POCKETS OF MVFR AFT 06Z AS SCATTERED SHOWERS AND FOG PATCHES DEVELOP OVERNIGHT. KBOS TERMINAL...MEDIUM TO HIGH CONFIDENCE IN TAF. VFR. A FEW PASSING SHOWERS ARE EXPECTED THIS EVENING...BUT PROBABLY WILL NOT HAVE MUCH IMPACT ON THE CEILINGS/VISIBILITIES OR IT WOULD BE VERY SHORT LIVED. OUTLOOK...TUESDAY THROUGH FRIDAY... TUESDAY...VARIABLE CONDITIONS WITH A VFR BASELINE BUT PERIODS OF MVFR CEILINGS AND MVFR-IFR VSBYS IN RAIN OR SHOWERS. LOW CONFIDENCE. TUESDAY NIGHT-WEDNESDAY...CONDITIONS LOWERING TUESDAY NIGHT MVFR/IFR CEILINGS AND VSBYS IN RAIN/SHOWERS/FOG DURING THE OVERNIGHT AND ON WEDNESDAY. SUFFICIENT INSTABILITY FOR SCATTERED EMBEDDED THUNDERSTORMS WEDNESDAY AFTERNOON AND NIGHT. EAST WINDS DURING THE DAY SHIFTING TO SOUTH BRIEFLY WEDNESDAY NIGHT...THEN SOUTHWEST OVERNIGHT. MEDIUM CONFIDENCE. THURSDAY-FRIDAY...CONDITIONS IMPROVING TO VFR. WEST WINDS INCREASING THURSDAY WITH GUSTS AROUND 35 KNOTS...DIMINISHING THURSDAY EVENING. LIGHT WINDS FRIDAY. MEDIUM CONFIDENCE. && .MARINE... TONIGHT...SMALL CRAFT ADVISORY FOR ALL WATERS WITH SOUTHWEST WIND GUSTS OF 25 TO 30 KNOTS. BRIEF ISOLATED 35 KNOT GUSTS ARE POSSIBLE IN ANY SHOWER OVERNIGHT. MONDAY...SMALL CRAFT ADVISORIES WILL REMAIN WITH SW WINDS GUSTING TO 25 KT AND HAZARDOUS SEAS REMAINING ACROSS THE OUTER COASTAL WATERS DUE TO LEFTOVER SWELL. MONDAY NIGHT...SMALL CRAFT ADVISORIES WILL LIKELY CONTINUE FOR HAZARDOUS SEAS ACROSS THE OUTER WATERS. OUTLOOK...TUESDAY THROUGH FRIDAY... TUESDAY...LINGERING 5-7 FOOT SEAS ESPECIALLY ON THE SOUTHERN OUTER WATERS. TUESDAY NIGHT-WEDNESDAY...WINDS AND SEAS BELOW SMALL CRAFT LEVELS TUESDAY NIGHT AND WEDNESDAY. WINDS AND SEAS INCREASE WEDNESDAY NIGHT WITH A COLD FRONT CROSSING THE WATERS...WIND SHOULD REACH 25-30 KNOTS AND SEAS 5-9 FEET ESPECIALLY ON THE SOUTHERN OUTER WATERS. SCATTERED THUNDERSTORMS WEDNESDAY AFTERNOON AND EVENING. THURSDAY...WEST WINDS INCREASING TO 30-35 KNOTS. LOW TO MEDIUM CHANCE THESE MAY REACH GALE FORCE FOR A FEW HOURS DURING THE DAY. SEAS WILL REMAIN 5-10 FEET. FRIDAY...WINDS AND SEAS BELOW SMALL CRAFT LEVELS. && .HYDROLOGY... A FLOOD WARNING CONTINUES FOR THE CONNECTICUT RIVER AT NORTHAMPTON...THOMPSONVILLE...HARTFORD AND MIDDLETOWN. THESE LOCATIONS ARE EXPECTED TO REMAIN IN MINOR FLOOD UNTIL FURTHER NOTICE. MIDDLETOWN MAY EXPERIENCE MODERATE FLOOD STAGE BY MONDAY NIGHT. SEE FLSBOX FOR DETAILS. THE AREAL FLOOD WARNING FOR THE WILLIMANTIC RIVER IN COVENTRY HAS BEEN REPLACED WITH A FLOOD ADVISORY. THE RIVER REMAINS ABOVE FLOOD STAGE BUT HAS ALREADY CRESTED AND WAS FALLING. THE RIVER SHOULD DROP BELOW FLOOD STAGE SOMETIME MONDAY MORNING. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT MONDAY FOR ANZ230>234-236- 251. SMALL CRAFT ADVISORY UNTIL 4 AM EDT TUESDAY FOR ANZ235-237-250- 254>256. && $$