AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 425 PM EDT MON APR 18 2011 .SYNOPSIS... UNSETTLED WEATHER WILL RETURN TONIGHT THROUGH WEDNESDAY...BRINGING CLOUDS AND OCCASIONAL RAIN. A COLD FRONT WILL SWING THROUGH WEDNESDAY NIGHT. HIGH PRESSURE WILL BRING DRY BUT COOL CONDITIONS FROM THURSDAY THROUGH FRIDAY NIGHT. ANOTHER STORM MOVING OUT OF THE PLAINS WILL BRING MORE UNSETTLED WEATHER FOR MUCH OF THE WEEKEND. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... DOPPLER RADAR MOSAIC INDICATES SCATTERED SHOWERS MOVING IN FROM NEW YORK STATE COURTESY OF A SHORT WAVE DISTURBANCE AND WEAK WAVE OF SURFACE LOW PRESSURE TRAVELING ALONG A DEVELOPING WARM FRONT. A SOUTHWESTERLY 925 MB 45-50 KT LOW LEVEL JET IS EXPECTED TO ADVANCE THIS EVENING...AND ATTEMPT TO INTERSECT WITH A DEVELOPING H85 THERMAL RIBBON THIS EVENING. HOWEVER SURFACE TO H85 MOISTURE CONVERGENCE REMAINS RATHER MODEST WITH UNIDIRECTIONAL VERTICAL WIND FIELDS. CURRENT DEWPOINT DEPRESSION SPREADS ARE ALSO AVERAGING 25 TO 30 DEGREES. THUS WITH THE LACK OF DEEP RH THE PRECIPITATION IS GENERALLY EXPECTED TO FALL AS LIGHT SHOWERS OR SPRINKLES THIS EVENING BEFORE THE SHORT WAVE HEADS EAST OF THE AREA AFTER MIDNIGHT. LEANED TOWARDS THE LIGHTER QPF OF THE NAM. MAINTAINED CHANCE POPS FOR MEASURABLE PRECIPITATION TONIGHT...THEN DIMINISH POPS BY DAYBREAK AS THE SHORT WAVE EJECTS EAST OF THE AREA. THIS WILL ALLOW THE FRONTAL BOUNDARY TO SHIFT SOUTH. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... TUESDAY...CLOUDS ARE EXPECTED TO PREVAIL...BUT AS HIGH PRESSURE ATTEMPTS TO BUILD SOUTH...EXPECT A LULL IN PRECIPITATION THROUGH AT LEAST MIDDAY. LIGHT ONSHORE FLOW WILL DEVELOP ALONG THE COAST. TRIED TO REFLECT A TREND IN DROPPING HOURLY TEMPERATURES ALONG THE COAST DURING THE AFTERNOON. LATER IN THE AFTERNOON WARM AIR ADVECTION IS EXPECTED TO REDEVELOP PRIMARILY ACROSS THE SOUTHWESTERN ZONES AS THE NEXT WAVE OF LOW PRESSURE ADVANCES FROM PENNSYLVANIA. RH CROSS SECTIONS WILL BECOME INCREASINGLY MOIST WITH TIME GIVEN INCREASING WARM AIR ADVECTION AND ONSHORE FLOW. THUS HAVE LIKELY POPS MENTIONED ACROSS THE SOUTHWESTERN ZONES...TRENDING DOWN TO CHANCE ACROSS THE NORTHEAST. TUESDAY NIGHT...MAIN THRUST OF WARM AIR ADVECTION OCCURS WITH THE ADVANCEMENT OF A 40 KT SW H85 JET AND THE WARM FRONT. ONSHORE FLOW CONTINUES AS WELL. MAIN FOCUS OF FOR LIFT WILL OCCUR ACROSS THE WESTERN ZONES AS A 25-30 KT SE LOW LEVEL JET PROVIDES INCREASING LOW LEVEL MOISTURE CONVERGENCE. THUS HAVE LIKELY TO SOME CATEGORICAL POPS SREADING ACROSS THE AREA OVERNIGHT. PREFERRED THE SLOWER NAM TIMING. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... WEDNESDAY... FIRST QUESTION IS THE TIMING OF WARM FRONT PASSAGE...IF ANY. THE NAM KEEPS THE WARM FRONT SOUTH OF NEW ENGLAND THROUGH 18Z...THEN MOVES IT NORTH INTO AT LEAST SOUTHEAST MASS BY 00Z. THE GFS IS MORE PROGRESSIVE WITH SOUTHWEST FLOW TO THE SOUTH COAST BY 18Z AND TO ALL OF SOUTHERN NEW ENGLAND BY 00Z. THE 12Z ECMWF IS MOST PROGRESSIVE WITH SOUTHWEST FLOW TO THE NH BORDER BY 18Z. BASED ON THE UPPER FLOW AND WITH HIGH PRESSURE OVER QUEBEC/MARITIMES...WE FAVOR THE SLOWER NAM SOLUTION. TEMPERATURES ARE DRAWN FROM THE MET MOS VALUES. STRONGEST 850 MB WINDS...50 TO 75 KNOTS...ARE FORECAST TO MOVE ACROSS NORTHERN NEW ENGLAND WEDNESDAY. NO SURPRISE THAT THIS IS WHERE THE STRONGEST ISENTROPIC LIFT IS FORECAST. MUCH LIGHTER LIFT IS FORECAST ACROSS SOUTHERN NEW ENGLAND. HOWEVER LIFT OF 10 MB/HOUR IS FORECAST TO MOVE ACROSS NORTHWEST MASS/SOUTHWEST NH DURING THE MORNING...SO THIS PART OF OUR FORECAST AREA WILL HAVE THE BEST CHANCE OF RAIN IN OUR AREA. SATURATION CONTINUES THROUGH THE DAY AT 290K /ROUGHLY 900 MB/ BUT DRYING AT HIGHER LEVELS. WITH THIS IN MIND...WE USED LIKELY POPS SOUTH AND CATEGORICAL POPS NORTH. SECOND QUESTION IS TIMING OF COLD FROPA WEDNESDAY NIGHT. THE NAM BRINGS A WIND SHIFT FROM SOUTH TO WEST BETWEEN 06Z AND 12Z. NAM BRINGS TOTALS OF 45 TO 50 NORTH ACROSS OUR AREA DURING THE MORNING/MIDDAY BUT WITH VERY STABLE LI VALUES AND NO FORECAST CAPE. THIS MAY MEAN ELEVATED CONVECTION...OR POSSIBLY CONVECTION IF WE BREAK INTO THE WARM SECTOR. THESE VALUES THEN DIMINISH WEDNESDAY NIGHT. HAVE INCLUDED A CHANCE OF THUNDER IN THE FORECAST. THURSDAY... SUPPORTING UPPER LOW MOVES PAST WITH PVA AND A -24C COLD POOL. THIS SHOULD SUPPORT DIURNAL CLOUDS AND WIDELY SCATTERED SHOWERS. WEST FLOW AND COLD ADVECTION SHOULD ALLOW FOR DEEPER MIXING. 850 MB TEMPS OF -3C TO -5C SHOULD SUPPORT MAX TEMPS IN THE 50S...ESPECIALLY THE LOW TO MID 50S. WINDS AT 850 MB ARE FORECAST AT 30 TO 40 KNOTS...HIGHER IF THE NAM HAS A SAY...AND LAPSE RATES FAVOR MOST OF THIS MIXING TO THE SURFACE IN AFTERNOON GUSTS. FRIDAY... HIGH PRESSURE MOVES OVERHEAD. THIS SHOULD BE A FAIR DAY WITH LIGHT WIND. DEWPOINTS IN THE 20S AND LIGHT WIND SHOULD ALLOW MORNING TEMPS TO START COOL...IN THE UPPER 20S TO MID 30S. ONSHORE WINDS WILL KEEP THE COASTAL AREAS COOL DURING THE DAY...WITH UPPER TEMPS OF -1C TO -3C SUPPORTING MAX TEMPS IN THE 50S. INCREASING HIGH LEVEL MOISTURE WILL MEAN INCREASING HIGH CLOUDS ESPECIALLY IN THE AFTERNOON AND EVENING. FRIDAY NIGHT-SATURDAY... SOUTHERN STREAM SHORTWAVE KICKS A SURFACE LOW OUT OF THE PLAINS AND INTO THE GREAT LAKES BY SATURDAY. THIS IS A SIMILAR TRACK TO THE LAST STORM AND TO THE PROJECTED WEDNESDAY STORM. PER THE 12Z ECMWF...INCREASING ISENTROPIC LIFT IS EXPECTED TO REACH THE CONNECTICUT VALLEY LATER FRIDAY NIGHT WITH THE BEST LIFT CROSSING NEW ENGLAND SATURDAY MORNING. THE GFS IS ABOUT 6 HOURS FASTER WITH THIS LIFT. ALL THIS WILL MEAN INCREASING/THICKENING CLOUDS WITH CHANCE POPS FOR RAIN IN WESTERN AREAS LATE FRIDAY NIGHT AND ACROSS ALL AREAS ON SATURDAY. A COLD FRONT THEN SWINGS THROUGH SATURDAY NIGHT. THE VARIOUS TIMINGS WOULD BRING IT THROUGH AROUND 06Z. THIS WILL MEAN CHANCE POPS FOR SHOWERS...THEN DRYING TOWARD MORNING. SUNDAY-MONDAY... BOTH THE GFS AND ECMWF BUILD HIGH PRESSURE OVER THE NORTHEAST USA SUNDAY MORNING...THEN MOVE IT EAST IN THE AFTERNOON. THE SATURDAY NIGHT FRONT STALLS JUST SOUTH OF THE REGION...A LOW PRESSURE WAVE MOVES ALONG THE FRONT LATE SUNDAY/SUNDAY NIGHT. THIS WOULD BRING A CHANCE OF RAIN/SHOWERS BACK TO OUR AREA LATE SUNDAY AND SUNDAY NIGHT...TAPERING OFF MONDAY. LOW CONFIDENCE AT THIS TIME. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT MEDIUM...30 PERCENT TO 60 PERCENT HIGH...GREATER THAN 60 PERCENT TONIGHT...VFR PREVAILING...A FEW POCKETS OF MVFR CEILINGS AND VSBYS POSSIBLE DUE TO SCATTERED SHOWERS. TUESDAY...VFR PREVAILING NORTH OF THE PIKE...AREAS OF MVFR CEILINGS AND VSBYS DEVELOPING SOUTH WITH SHOWERS DURING THE AFTERNOON. LOCALIZED IFR CEILINGS POSSIBLE IN CONNECTICUT AND RHODE ISLAND AFT 21Z. TUESDAY NIGHT...VFR PREVAILING NORTHEAST...MVFR WITH AREAS OF IFR CEILINGS SOUTH AND SOUTHWEST. SHOWERS BECOMING MORE WIDESPREAD OVERNIGHT ALONG WITH FOG PATCHES. KBOS TERMINAL...MEDIUM TO HIGH CONFIDENCE IN VFR TONIGHT AND TUESDAY. EXPECT VFR CONDITIONS TO DOMINATE...BUT A PERIOD OR TWO OF MVFR CEILINGS ARE POSSIBLE WITH THE BEST CHANCE TUESDAY AFTERNOON AND NIGHT. OUTLOOK...WEDNESDAY THROUGH SATURDAY... WEDNESDAY...MVFR/IFR EXPECTED IN LOW CEILINGS AND RAIN/FOG. SCATTERED THUNDERSTORMS POSSIBLE IN THE AFTERNOON/EVENING. EAST WIND DURING THE DAY BECOMES WEST OVERNIGHT. MEDIUM CONFIDENCE. THURSDAY...VFR CONDITIONS. WEST WINDS AT SUSTAINED 20 KNOTS AND GUSTS 35 TO 40 KNOTS DURING THE DAY. MEDIUM TO HIGH CONFIDENCE. FRIDAY...VFR. HIGH CONFIDENCE. SATURDAY...CONDITIONS LOWERING TO MVFR/IFR IN LOW CEILINGS/RAIN/FOG. MEDIUM CONFIDENCE. && .MARINE... TONIGHT...SMALL CRAFT ADVISORIES REMAIN POSTED ACROSS PORTIONS OF THE COASTAL WATERS MAINLY DUE TO HAZARDOUS SEAS...LEFTOVER SWELL. TUESDAY...SMALL CRAFT ADVISORIES HAVE BEEN EXTENDED INTO THE AFTERNOON ACROSS THE SOUTHEASTERN WATERS DUE TO LEFTOVER HAZARDOUS SEAS. LIGHT EAST FLOW DEVELOPING. TUESDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS SHOULD BE EXTENDED OVERNIGH AS ENE WINDS GUST NEAR 25 KT ACROSS THE SE WATERS APPROACHING DAYBREAK WEDNESDAY. OUTLOOK...WEDNESDAY THROUGH SATURDAY... WEDNESDAY...WINDS JUST BELOW SMALL CRAFT LEVELS...BUT SEAS AT 5 TO 8 FEET ESPECIALLY ON THE OUTER WATERS. EAST WINDS DURING THE DAY WITH SOUTH WINDS ON THE SOUTHERN OUTER WATERS...ALL SHIFTING TO WEST WEDNESDAY NIGHT AS A COLD FRONT MOVES THROUGH. THURSDAY...WEST WINDS NEAR GALE FORCE DURING THE DAY...DIMINISHING IN THE EVENING. SEAS 5 TO 8 FEET ESPECIALLY ON THE OUTER WATERS...DIMINISHING LATE. FRIDAY...WINDS AND SEAS BELOW SMALL CRAFT LEVELS. SATURDAY...SOUTH WINDS INCREASING TO SMALL CRAFT ADVISORY SPEEDS. SEAS BUILDING TO 5 TO 8 FEET. && .HYDROLOGY... THE HEAVY RAINFALL FROM THIS PAST WEEKEND ALONG WITH RECENT SNOWMELT FROM NORTHERN NEW ENGLAND HAS CONTINUED TO CAUSE RIVER RISES ALONG SOME OF THE MAINSTEM RIVERS AND TRIBUTARIES. MINOR FLOODING CONTINUES ALONG PORTIONS OF THE CONNECTICUT RIVER. A FLOOD WARNING CONTINUES FOR THE CONNECTICUT RIVER AT NORTHAMPTON...THOMPSONVILLE AND HARTFORD. THESE LOCATIONS ARE EXPECTED TO REMAIN IN MINOR FLOOD THROUGH AT LEAST THURSDAY....AND PERHAPS LONGER. THE CONNECTICUT RIVER AT MIDDLETOWN MAY BRIEFLY GO INTO LOW END MODERATE FLOODING THIS EVENING. QPF AMOUNTS TONIGHT ARE EXPECTED TO TOTAL LESS THAN 0.10 INCH. QPF AMOUNTS TUESDAY THROUGH TUESDAY NIGHT ARE EXPECTED TO RANGE FROM 0.10 INCH OR LESS NORTHEAST...UP TO 0.33 INCH SOUTHWEST. THIS IS NOT EXPECTED TO HAVE A SIGNIFICANT IMPACT ON RIVER STAGES. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ230>234-236-251. SMALL CRAFT ADVISORY UNTIL 5 PM EDT TUESDAY FOR ANZ235-237- 254>256. SMALL CRAFT ADVISORY UNTIL 7 AM EDT TUESDAY FOR ANZ250. && $$ SYNOPSIS...WTB/STRAUSS