AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 726 AM EDT THU AUG 7 2014 .SYNOPSIS... SHOWERS AND THUNDERSTORMS REDEVELOPING TODAY...SOME OF WHICH MAY BE STRONG TO SEVERE WITH THREATS OF SMALL HAIL AND GUSTY WINDS. HIGH PRESSURE WHICH WILL DOMINATE FOR THE WEEKEND AND EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 AM UPDATE... 11Z WV IMAGERY SHOWS BASE OF ROBUST AND ACUTE SHORTWAVE TROF ALREADY IN WRN NY. SOME WEAK -SHRA ACTIVITY HAS BEEN MONITORED ALL NIGHT LONG MOVING OUT OF ONTARIO/QUEBEC AND JUST NOW SHIFTING INTO FRANKLIN AND CHESHIRE COUNTIES. THIS SPEAKS VOLUMES OF BOTH THE STRENGTH OF THE LIFT ASSOCIATED WITH THE WAVE AND THE INSTABILITY FROM COLD H5 TEMPS...THAT THESE SHOWERS HAVE REMAINED IN TACT DESPITE THE DRY AIR LACK OF DIURNAL HEAT SUPPORT OVERNIGHT. THEREFORE...STILL LIKE THE CHANCE-LIKELY POPS FOR AFTERNOON CONVECTIVE ACTIVITY AND STILL FEEL SMALL HAIL AND GUSTY WINDS ARE WARRANTED. COULD EVEN BE THAT THESE ARE SEEN IN SHOWERS WITHOUT ANY ACTIVE LIGHTNING. THEREFORE...POPS/WX WERE PRETTY MUCH LEFT ALONE THIS MORNING. GIVEN THE CLEAR SKIES ACROSS THE S AND SE...HEATING HAS THE BEST CHANCE TO BE MAXIMIZED THERE. WILL ADJUST TEMPS/DWPTS AND SKIES TO BRING THEM UP TO CURRENT TRENDS. PREVIOUS DISCUSSION... POSITIVELY-TILTED TROUGH PREVAILS ACROSS THE NE-CONUS THROUGH WHICH A STRONG IMPULSE DRAGS H5 -18C AIR SOUTHWARD /-3 TO -4 STANDARD DEVIATIONS...ANOMALOUSLY COLD!/ WHILE YIELDING ENHANCED ASCENT ACROSS THE REGION. SUBSEQUENT STRONG LIFT WITHIN AN UNSTABLE ENVIRONMENT WILL YIELD SCATTERED STRONG TO POTENTIALLY SEVERE STORMS ACROSS S NEW ENGLAND MUCH OF THE DAY. EVALUATING FOR CONVECTION...PUSH OF COLD AIR S PARENT WITH MID-LEVEL DRYING WILL YIELD CONDITIONALLY UNSTABLE H5-7 LAPSE RATES AROUND 7C/KM. AS THE BOUNDARY-LAYER MIXES DRY-ADIABATICALLY UP TO H7... SURFACE-BASED INSTABILITY GROWS TO AROUND 1000 J/KG. WHILE CAPE- PROFILES ARE THIN AS EVIDENCED BY NCAPE VALUES BELOW 0.1...ALSO AN INDICATION OF WEAK PARTICLE ACCELERATIONS...A SIGNIFICANT MAGNITUDE OF INSTABILITY WITHIN THE CAPE PROFILE LIES WITHIN THE BETTER HAIL GROWTH ZONE OF -10 TO -30C ON THE ORDER OF SEVERAL HUNDRED J/KG. SO WHILE UPDRAFTS MAY NOT SUSTAIN FOR LONG PERIODS OF TIME...THEIR VERTICAL EXTENT WILL LIKELY YIELD HAIL WITHIN THE ANOMALOUSLY COLD- AIR ALOFT. AFOREMENTIONED MID-LEVEL DRYING WILL ALSO PROMOTE EVAPORATION AND LOWERING OF FREEZING LEVEL HEIGHTS DOWN TO THE WET-BULB-ZERO WHICH RANGES AROUND 7-8 KFT. AS UPDRAFTS PREVAIL...SUBSEQUENT EVAPORATIVE COOLING THROUGH THE COLUMN WILL YIELD HIGHER DENSITY AIR WITH NEGATIVE BUOYANCY THAT WILL LIKELY ACCELERATE TOWARDS THE SURFACE RESULTING IN STRONG DOWNDRAFTS. DCAPE VALUES DERIVED FROM THE 07.0Z NAM/GFS MODEL SUITE AVERAGE AROUND 1000 J/KG IN SOME LOCATIONS. ALSO WORTHY OF KEEPING IN MIND AN INCREASE IN THE ATMOSPHERIC WIND PROFILE AHEAD OF THE AFOREMENTIONED STRONG IMPULSE WHICH WILL LIKELY BE DRAGGED DOWN TO THE SURFACE. SO TAKING THE DISCUSSION ABOVE IN PERSPECTIVE...EXPECTING AN ACTIVE DAY OF WEATHER BEGINNING IMMEDIATELY AFTER SUNRISE CONTINUING THROUGH THE AFTERNOON. GREATEST CONFIDENCE WITH WRF-MODEL SOLUTIONS AND BELIEVE THE GREATEST THREAT WILL BE ACROSS S/E PORTIONS OF NEW ENGLAND WHERE DAYTIME HEATING AND BUOYANCY/INSTABILITY IS LIKELY TO BE GREATEST. PRESENT WAVE OF FOCUS MOVING INTO THE E GREAT LAKES / UPSTATE NY IS LIKELY TO REACH N/W PORTIONS OF NEW ENGLAND TOO EARLY FOR DAYTIME HEATING TO BE FULLY EFFECTIVE. WILL CONTINUE WITH FORECAST WORDING OF SMALL HAIL AND GUSTY WINDS. YES...STORMS CAN BECOME POTENTIALLY SEVERE SO LONG AS ENOUGH HEAT AND INSTABILITY IS PRESENT WITHIN THE UNSTABLE ENVIRONMENT TO SUSTAIN MOISTURE THROUGH THE UPDRAFT IN THE BETTER HAIL GROWTH ZONES. AGAIN...FEEL SUCH POSSIBILITIES WILL EXIST FOR S/E PORTIONS OF NEW ENGLAND WHERE DAYTIME HEATING IS LIKELY TO BE THE GREATEST AND THERE IS ALSO THE POTENTIAL INTERACTION WITH AN ONSHORE SEA- BREEZE. OTHERWISE...MUCH OF THE ACTIVITY BASED ON THE CONVECTIVE SCHEMES DISCUSSED ABOVE WILL LIKELY BE PULSE-TYPE CONVECTION IN WHERE WHAT GOES UP WILL QUICKLY COME DOWN. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... TONIGHT... ACTIVITY CONCLUDES WITH SUNSET. HIGH PRESSURE BEGINS TO BUILD FROM THE W AS THE MID- TO UPPER-LEVEL TROUGH EXITS THE REGION. ANTICIPATE MOSTLY CLEAR CONDITIONS WITH A SUSTAINED LIGHT NW-FLOW PREVAILED BY A LINGERING SURFACE PRESSURE GRADIENT ACROSS THE REGION. FOR THOSE LOCATIONS WHICH CAN BECOME SHELTERED FROM THE WIND AND EFFECTIVELY RADIATE OUT...LOWS INTO THE UPPER-40S WILL BE POSSIBLE /THIS DURING THE PEAK OF SUMMER WHEN LOWS ARE NORMALLY AROUND THE LOW-60S/. MUCH OF THE REMAINING REGION WILL EXPERIENCE LOW TEMPERATURES BY SUNRISE FRIDAY RANGING AROUND THE MID-50S. SINCE WHEN DID EARLY AUGUST BECOME LATE SEPTEMBER? FRIDAY... DESPITE CYCLONIC FLOW ACROSS THE REGION THROUGH WHICH THURSDAY/S IMPULSE LINGERS PARENT WITH A WEAK MID- TO UPPER-LEVEL JET STREAK... FEEL THE FOCUS OF ANY WEATHER WILL BE ALONG THE N/W-FACING SLOPES OF HIGHER TERRAIN...OTHERWISE EXPECTING A DRY AND QUIET WEATHER DAY WITH THE PRESENCE OF SCATTERED-BROKEN DIURNAL CUMULUS. +10C H85 AIR ACROSS THE REGION WILL MAKE FOR SEASONABLE TEMPERATURES WITH HIGHS AROUND THE UPPER-70S UNDER BREEZY NW-FLOW /SUBSEQUENT OF BOUNDARY- LAYER MIX-DOWN OF FASTER MOMENTUM TO THE SURFACE/. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... OVERVIEW AND MODEL PREFERENCES... 07.00Z MODEL GUIDANCE CONTINUES TO HAVE FAVORABLE AGREEMENT IN THE LONG TERM PATTERN THROUGH AT LEAST EARLY NEXT WEEK. THE BIGGEST ISSUES COME WITH A DEEPENING TROF FOR THE MID PORTION OF NEXT WEEK...AS BOTH OPERATIONAL AND ENSEMBLE GUIDANCE DIFFER ON HOW AMPLIFIED THE FLOW WILL BE BY THIS POINT. WHILE THERE IS AGREEMENT THAT A TRANSITION TO MORE UNSETTLED AND POTENTIAL WET WX WILL OCCUR...THE TIMING EXACT TIMING AND SENSIBLE WX DETAILS WILL HAVE TO BE WORKED OUT. OTHERWISE...THROUGH EARLY NEXT WEEK...A SLOWLY BUILDING RIDGE WITH H5 HEIGHTS AROUND 585DM WILL GRADUALLY BUILD ACROSS THE REGION...YIELDING SFC HIGH PRES AND MAINLY DRY CONDITIONS. THE OVERALL PATTERN ALSO FAVORS A WEAK TROF IN THE FLOW EQUATORWARD OF THE RIDGE...WHICH KEEPS MOST OF THE SUBTROPICAL HEAT AND HUMIDITY TO THE S. THEREFORE...LOOKS LIKE A PLEASANT PATTERN OF MAINLY DRY WX AND NEAR SEASONABLE TEMPERATURES. DETAILS... FRI NIGHT... FINAL VORT MAX WILL BE SLIDING THROUGH THE BASE OF ROBUST SHORTWAVE TROF JUST E OF SRN NEW ENGLAND FRI EVENING. THIS WILL LEAD TO A RAPIDLY DIMINISHING TREND IN ANY LEFTOVER SHOWERS FROM PEAK HEATING. THEREFORE...EXPECT GRADUAL CLEARING EVERYWHERE THROUGH THE NIGHT. WITH THIS CLEARING AND A SLACKENING PRES GRADIENT...MIN TEMPS MAY MAKE A RUN TO NEAR 50F IN THE NORMALLY COOLER VALLEYS OF NW MA AND SRN NH. WARMER AT THE NORMAL URBAN AREAS. SAT THROUGH MON... RIDGE OF HIGH PRES WILL BE MOVING ACROSS THE AREA THROUGH THE PERIOD...PROVIDING DRY WX THROUGHOUT. H85 TEMPS AROUND +12 TO +14C SUGGESTS...WITH FULL MIXING HIGHS SHOULD REACH TO EITHER SIDE OF 80 DEGREES. COOLER NEAR THE COAST WITH SEA BREEZES THANKS TO A WEAK PRES GRADIENT. OVERNIGHT MINS FALL BACK INTO THE LOW 50S IN THE NW INTERIOR TO AROUND 60 NEAR THE COASTLINES. DWPTS MAINLY IN THE MID 50S TO AROUND 60 SUGGESTS MOSTLY LOW HUMIDITY. TUE... A TRANSITIONAL PERIOD WITH HIGH PRES SLIDING TO THE E...ALLOWING FOR RETURN FLOW AND INCREASING HEAT/HUMIDITY. A COLD FRONT LOOKS TO TRY TO APPROACH TO THE N AND W AS A TROF DEEPENS AROUND THE GREAT LAKES. AT THIS POINT IT DOES APPEAR ENOUGH SUBSIDENCE WILL REMAIN AS THE HIGH EXITS TO PREVENT MAINTAIN A MOSTLY DRY FORECAST. HIGHS LOOK TO POTENTIAL INCH A BIT ABOVE NORMAL. WED AND THU... AS MENTIONED ABOVE...THERE ARE SOME DIFFERENCES HERE REGARDING THE DEPTH AND ORIENTATION OF A TROF MOVING OVER FROM THE GREAT LAKES REGION. THE GFS IS THE MOST AMPLIFIED AND CARRIES A SLOW MOVING LOW PRES ACROSS THE REGION WHILE THE ECMWF PUSHES A COLD FRONT THROUGH EARLY WED. WILL PUT MORE WEIGHT ON THE ECMWF GIVEN ITS BEEN MORE PERSISTENT AND HAS MORE SUPPORT FROM ENSEMBLES. THEREFORE...EXPECT WET AND UNSETTLED CONDITIONS BY WED...WITH THE POSSIBILITY OF A RETURN OF DRY WX BY THU.
Posted on: Thu, 07 Aug 2014 14:04:07 +0000
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