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2/18/14 Clipper OBS Thread


dryslot

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MESOSCALE DISCUSSION 0112
NWS STORM PREDICTION CENTER NORMAN OK
1214 PM CST TUE FEB 18 2014

AREAS AFFECTED...PARTS OF CT/RI/MA TO SOUTHERN/EASTERN NH AND
SOUTHWEST MAINE

CONCERNING...HEAVY SNOW

VALID 181814Z - 182315Z

SUMMARY...MODERATE TO HEAVY SNOW WITH RATES REACHING 1-2 IN/HR WILL
STEADILY DEVELOP NORTHEASTWARD ACROSS SOUTHERN NEW ENGLAND THIS
AFTERNOON/EARLY EVENING...ESPECIALLY WITHIN A CORRIDOR FROM
EAST-CENTRAL MA TO SOUTHERN/EASTERN NH AND SOUTHWEST/COASTAL MAINE.

DISCUSSION...17Z SURFACE ANALYSIS FEATURES A DEEPENING SURFACE LOW
ROUGHLY 75 MILES OFF THE COAST OF LONG ISLAND/SOUTHERN NEW
ENGLAND...WITH 3+ MB/2-HR PRESSURE FALLS MAXIMIZED ALONG COASTAL NEW
ENGLAND. AS THE NEAR-COASTAL CYCLONE CONTINUES TO
DEEPEN...DPVA/STRONG WARM ADVECTION WILL CONTRIBUTE TO INCREASING
UVV/PRECIPITATION RATES /AND A GENERAL SOUTHWEST TO NORTHEAST
ADVANCEMENT THEREOF/ THROUGH THE AFTERNOON/EARLY
EVENING...ESPECIALLY IN AREAS ROUGHLY WITHIN 50-80 MILES OF THE
COAST. SUCH A SCENARIO IS GENERALLY CONSISTENT WITH GUIDANCE SUCH AS
MULTI-RUN HRRR AND THE 12Z WRF-NSSL.

INCREASING UVV/SATURATION ASIDE...UPSTREAM OBSERVED 12Z SOUNDINGS
FROM ABERDEEN PROVING GROUND /KAPG/ AND WALLOPS ISLAND /KWAL/
SAMPLED A PLUME OF STEEP MID-LEVEL LAPSE RATES AND EVEN SOME WEAK
ELEVATED BUOYANCY. ATTENDANT TO THE CYCLONE...LIKELY DOWNSTREAM
ADVECTION/PROXIMITY OF THESE RELATIVELY STEEP LAPSE RATES/VERY WEAK
BUOYANCY LEADS FURTHER CREDENCE TO THE POTENTIAL FOR HEAVIER SNOW
INCLUDING 1-2 IN/HR RATES. FOR INSTANCE...12Z NAM FORECAST SOUNDINGS
INDICATE RELATIVELY STEEP LAPSE RATES BETWEEN 800-600 MB ACROSS THE
REGION THIS AFTERNOON...WHICH SHOULD BE VERTICALLY COLLOCATED WITH A
SATURATED DENDRITIC LAYER FOR A MULTI-HOUR DURATION.

..GUYER.. 02/18/2014


ATTN...WFO...GYX...BOX...

LAT...LON 44586932 44226916 43747016 42947101 42287134 41877193
42337248 43137191 44217116 44586932

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