ACUS11 KWNS 180834
SWOMCD
SPC MCD 180833
MAZ000-CTZ000-NYZ000-NHZ000-VTZ000-NJZ000-PAZ000-181430-
MESOSCALE DISCUSSION 0030
NWS STORM PREDICTION CENTER NORMAN OK
0233 AM CST TUE JAN 18 2011
AREAS AFFECTED...NERN PA...NRN NJ...SERN HALF OF NY INCLUDING LONG
ISLAND...CT...WRN MA AND SRN VT
CONCERNING...WINTER MIXED PRECIPITATION
VALID 180833Z - 181430Z
PRECIPITATION WILL TRANSITION FROM SNOW TO SLEET AND EVENTUALLY
PREDOMINATELY FREEZING RAIN ACROSS NERN PA...NRN NJ...LONG ISLAND
AND NWD TO S CENTRAL NY AND LOWER HUDSON VALLEY /BGM TO POU/ BETWEEN
09-12Z. SIMILAR TRANSITION IN WINTRY PRECIPITATION IS EXPECTED NWD
INTO ERN NY...CT...WRN MA AND SRN VT BETWEEN 12-15Z.
THE GREATEST FREEZING RAIN RATES /0.05-0.10 INCH PER HR/ AND AREA TO
RECEIVE PREDOMINATELY FREEZING RAIN IS EXPECTED TO EXTEND FROM NERN
PA/FAR NWRN NJ NWD INTO NY AND SWRN NEW ENGLAND. FREEZING RAIN
RATES WILL TEND TO BE LESS WITH ERN EXTENT ACROSS LONG ISLAND...WITH
PRECIPITATION CHANGING TO RAIN OVER NERN NJ...THE EXTREME SRN
PORTION OF THE LOWER HUDSON VALLEY...LONG ISLAND AND COASTAL CT AS
SURFACE TEMPERATURES RISE ABOVE 32 F AFTER 12Z.
HEIGHT FALLS ATTENDANT TO EWD PROGRESSION OF A LONGWAVE TROUGH INTO
THE ERN STATES AND EMBEDDED SHORTWAVE TROUGHS TRACKING NEWD FROM THE
OH VALLEY AND SRN ATLANTIC COAST WILL SUPPORT A STRENGTHENING /50-60
KT/ SLY LLJ FROM COASTAL MID ATLANTIC STATES TO THE LOWER HUDSON/CT
RIVER VALLEYS BY 12-15Z. STRONG LOW LEVEL WAA IN THE 800-900 MB
LAYER ALONG THE LLJ WITH TEMPERATURES RISING ABOVE 0 C WILL PROMOTE
A PTYPE CHANGE FROM SNOW TO BRIEFLY SLEET AND THEN FREEZING RAIN...
GIVEN SUB FREEZING SURFACE TEMPERATURES. PERSISTENT AND INCREASING
LOW LEVEL WAA WILL SUPPORT SURFACE TEMPERATURES RISING ABOVE 32 F
FROM NERN NJ THROUGH LONG ISLAND TO COASTAL CT AFTER 12Z PER TRENDS
FURTHER S ACROSS CENTRAL/SRN NJ. N/NELY SURFACE WINDS FROM SRN NEW
ENGLAND INTO ERN PA SUGGEST SUB FREEZING SURFACE TEMPERATURES SHOULD
BE MAINTAINED ASIDE FROM THE AFOREMENTIONED AREAS CLOSER TO THE
COAST. MEANWHILE...FARTHER N FROM UCA-GFL...VERTICAL THERMAL
STRATIFICATION PER FORECAST SOUNDINGS SUGGEST THIS AREA WILL BE TOO
FAR N FOR STRONGER LOW LEVEL WAA TO BOOST THE 800-900 MB LAYER ABOVE
0 C. THUS...SNOW SHOULD MIX WITH SLEET...BUT NOT CHANGE OVER TO
FREEZING RAIN. AN INCREASE IN PW VALUES WILL HOWEVER SUPPORT AN
INCREASE IN SNOW/SLEET RATES WITHIN REGION OF ISENTROPIC ASCENT/WAA.
..PETERS.. 01/18/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...BOX...BTV...OKX...ALY...PHI...BGM...CTP...
LAT...LON 43467510 43377398 43287254 41907210 40867216 40387400
41007602 41327676 41867673 43207552 43467510
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