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Mesoscale Discussion 91
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   MESOSCALE DISCUSSION 0091
   NWS STORM PREDICTION CENTER NORMAN OK
   0644 AM CST FRI FEB 05 2016

   AREAS AFFECTED...LONG ISLAND INCLUDING NEW YORK CITY/CT/RI/MA

   CONCERNING...HEAVY SNOW 

   VALID 051244Z - 051845Z

   SUMMARY...SNOWFALL RATES TO AROUND 1 INCH PER HOUR ARE FORECAST TO
   OCCUR...AT TIMES...ACROSS LONG ISLAND THROUGH SOUTHERN NEW ENGLAND
   THIS MORNING INTO THE EARLY AFTERNOON.

   DISCUSSION...TRENDS IN EARLY MORNING SURFACE OBSERVATIONS SHOWED
   MOST LOCATIONS ACROSS SOUTHERN NEW ENGLAND TO LONG ISLAND HAVE
   TRANSITIONED TO SNOW AS THE PRIMARY PRECIPITATION TYPE...WITH THE
   EXCEPTION BEING ACROSS SOUTHEAST MA WHERE THE PTYPE REMAINS RAIN.
   COOLING WET-BULB TEMPERATURES TO LESS THAN 32 F WILL CONTINUE TO
   OCCUR THIS MORNING FROM NORTHWEST TO SOUTHEAST.  MEANWHILE...THE
   VERTICAL THERMAL PROFILE WILL UNDERGO FURTHER COOLING AS LOW-LEVEL
   COLD AIR ADVECTION INCREASES WITHIN STRENGTHENING NORTHERLY
   LOW-LEVEL WINDS LOCATED TO THE NORTHWEST TO NORTH OF THE DEEPENING
   OFFSHORE SURFACE LOW.  THE SURFACE LOW...NOW LOCATED OFF THE
   SOUTHEAST VA COAST...IS FORECAST TO TRACK NORTHEAST...REACHING
   40N/70W BY 18Z...WHILE DEEPENING 4-5-MB PER 6 HOURS DURING THIS
   PERIOD.  THESE PROCESSES WILL OCCUR AS INCREASING UPWARD VERTICAL
   MOTION SPREADS ACROSS THE DISCUSSION AREA WITH THE APPROACH OF A
   NEGATIVELY TILTED MIDLEVEL SHORTWAVE TROUGH...CURRENTLY LOCATED OVER
   VA/NC.  JET COUPLING ALOFT WILL BECOME MORE PRONOUNCED TODAY AS
   WELL...ENHANCING UPWARD VERTICAL MOTION.  

   FORECAST SOUNDINGS SUGGEST VERTICAL MOTION WITHIN A MOIST DENDRITIC
   GROWTH ZONE WILL SUPPORT THE POTENTIAL FOR HEAVIER SNOWFALL RATES
   /AROUND 1 INCH PER HOUR/...ESPECIALLY AS AFOREMENTIONED VERTICAL
   MOTION INCREASES THIS MORNING TO EARLY AFTERNOON ACROSS THE
   DISCUSSION AREA.  LIGHTNING HAS BEEN DETECTED NEAR AN OFFSHORE
   BAROCLINIC ZONE...SOUTHEAST OF LONG ISLAND...WHILE SOME INTRACLOUD
   LIGHTNING WAS OBSERVED AT 1130Z IN VICINITY OF NYC.  LOW COVERAGE OF
   LIGHTNING WILL REMAIN POSSIBLE WITHIN THE DEVELOPING HEAVIER
   SNOWFALL...AS THE 12Z WALLOPS ISLAND SOUNDING SHOWED VERY WEAK
   INSTABILITY ROOTED AROUND 700-MB AND FORECAST SOUNDINGS ALSO SHOW
   SIMILARLY VERY WEAK INSTABILITY ROOTED BETWEEN 600-700 MB INTO
   SOUTHERN NEW ENGLAND TODAY.

   ..PETERS.. 02/05/2016


   ATTN...WFO...GYX...BOX...OKX...ALY...PHI...

   LAT...LON   40577428 42097380 42707281 43047144 42687081 41897081
               41537092 40977179 40697277 40467344 40577428 

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Page last modified: February 05, 2016
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