Winter Storm and Winter Weather in Delaware, February 25 to 26, 2007

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
925 AM EST SUN FEB 25 2007

LATEST ACAR SOUNDINGS FROM THE IAD AREA AND POINTS WWD SUPPORT GFS
MODEL FCST SOUNDINGS. OVER THE LAST COUPLE OF HOURS THEY WERE
SHOWING THE WARM LAYER EVAP OR DYNAMIC COOLING. THIS IS A SIM
PROCESS WE ARE EXPECTING TO OCR HERE LATER TDY ONCE PCPN INTENSITY
INCREASES. IMPRESSIVE LLJ OVR THE APLCHNS IS HELPING PCPN ADVECT NWD
EASIER THAN EWD ATTM, BUT THE GFS (AND TO TOO MUCH OF AN EXTENT THE
WRF-NMM) HAD THIS. PPCN STILL EXPECTED TO OVERSPREAD OUR CWA THIS
AFTN.

NO CHGS TO ADVYS OR WRNGS ATTM. WE DID REMOVE THE FREEZING RAIN FROM
THE DELMARVA ZONES, BUT ADDED SLEET. WANT TO SEE HOW THE SNOW PART
PLAYS OUT BEFORE WE DROP THE ADVY. ONLY OTHER CHG WAS TO UP ACCUMS A
BIT IN OCEAN/MONMOUTH AND WE/LL SEE WHAT THE REST OF THE 12Z MODEL
RUNS DO. THE SREF ENSEMBLE MEAN KEEPS 32F RIGHT THRU PHL/I95 THRU
THE NIGHT SO THIS IS THE DESTINY OF THIS EVENT, THIS LOCN WILL BE ON
THE FENCE THRUT AND THE SNOW PART IN THE SERN PART OF THE WRNG AREA
IS HIGHLY DEPENDENT ON A FRONT END LOADING.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 11 AM EST
     MONDAY FOR PAZ054-055-060>062-067>071.

NJ...WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 5 PM EST
     MONDAY FOR NJZ001-007>010-012-015.

     WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO MIDNIGHT
     EST TONIGHT FOR NJZ021-022-027.

     WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 PM EST
     MONDAY FOR NJZ013-014-020-026.

     WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 11 AM EST
     MONDAY FOR NJZ016>019.

DE...WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 11 AM EST
     MONDAY FOR DEZ001.

     WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 7 PM EST
     THIS EVENING FOR DEZ002.

MD...WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 11 AM EST
     MONDAY FOR MDZ008.

     WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 7 PM EST
     THIS EVENING FOR MDZ012-015-019-020.

MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 12 PM EST
     MONDAY FOR ANZ450>455.

&&

GIGI

PREV AFD ************************************************************

.SHORT TERM /TODAY THROUGH MONDAY/...
AS A CONTINUATION TO THE PROCESS, WINTER STORM WARNINGS HAVE NOW
BEEN ISSUED TO REPLACE THE PREVIOUSLY ISSUED WATCHES. ALSO, WINTER
WEATHER ADVISORIES HAVE BEEN ISSUED FOR THE REST OF THE AREA WITH
THE EXCEPTION OF SUSSEX COUNTY DE, CAPE MAY NJ AND COASTAL ATLC
COUNTY.

AS OF WRITING THIS...PCPN HAD ADVANCED THROUGH WV AND WAS MOVING
INTO N CENTRAL VA. SNOW WAS ALSO STARTING TO BREAK OUT OVER THE VA
MTNS WHILE RAIN WAS OBS TO THE SE. EVEN SO, THIS WAS GENERALLY
EXPECTED AS THE COLDER IS REMAINS FARTHER N/E.

AS THE LOW PRESSURE SYSTEM AND ITS ASSOCIATED FRONTAL SYSTEM MOVE
BY TO THE SOUTH TODAY, PCPN WILL SPREAD ACROSS THE REGION.
FORECAST SOUNDINGS AND DIFFERENTIAL THICKNESSES ALL INDICATE
MOSTLY SNOW TODAY EXCEPT IN DELMARVA AND EXTREME SOUTHERN NJ WHERE
SOME RAIN WILL MIX IN. THE PCPN SHOULD BEGIN THIS MORNING SOUTH
AND SPREAD NE THROUGH THE ENTIRE AREA BY EVENING. TEMPERATURES
SHOULD START MOVE ABOVE FREEZING BEFORE THE PCPN STARTS OVER MOST
AREAS BUT ONCE ANY SNOW BEGINS, THE TEMP WILL DROP TO FREEZING OR
BELOW WITH THE EXCEPTION OF THE SOUTHERN COAST, SUSSEX DE AND CAPE
MAY NJ. THEREFORE FOR THOSE AREAS NO WINTER WEATHER HEADLINES ARE
NEEDED.

TONIGHT...AN AREA OF STRONG VVS MOVES THROUGH EARLY THIS EVENING
AND IS ASSOCIATED WITH SOME CONDITIONAL SYMETRIC INSTABILITY,
MAINLY OVER THE CENTRAL AND SOUTHERN AREAS. THEREFORE, SNOW MAY
BECOME HEAVY FOR A TIME EARLY THIS EVENING AND EVEN AN ISOLATED
TSTM CANNOT BE RULED OUT. THEN BEHIND IT SNOW, FREEZING RAIN AND
SLEET CONTINUE IN MOST AREAS AND ICING IS EXPECTED. MODEL
SOUNDINGS LOOK TOO COLD FOR FREEZING PCPN EXTREME NORTH.

OVER THE AREAS WHERE THE ADVISORIES HAVE BEEN ISSUED, ENOUGH WARM
AIR SHOULD WORK ITS WAY IN FROM THE OCEAN CHANGING PCPN TO RAIN
TEMPORARILY. HOWEVER, LATE AT NIGHT, ONCE THE LOW REDEVELOPS OFF THE
COAST, COLDER AIR WILL RETURN CHANGING THE PCPN BACK TO SNOW SLEET
AND FREEZING RAIN.

ON MONDAY...THE LOW PULLS AWAY BUT, MOISTURE IS LEFT IN ITS WAKE
AS ISENTROPIC LIFT CONTINUES FROM PHL NORTH AND EAST. THIS MEANS
SOME SNOW WILL CONTINUE INTO THE THE DAY. IT COULD LAST THROUGHOUT
THE DAY OVER NRN NJ, SO THE WINTER STORM WARNING THAT WAS ISSUED FOR
THERE IS IN EFFECT THROUGH ALL OF MONDAY.

ON MONDAY NIGHT, SOMEWHAT DRIER AIR FINALLY MOVES OVER THE AREA.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/... FAIR WEATHER WILL
PERSIST FOR THE MIDDLE PART OF NEXT WEEK AS WE WILL BE ON THE
SOUTHERN PERIPHERY OF A LARGE HIGH PRESSURE THAT WILL BE LOCATED
IN EASTERN CANADA. THERE MAY BE A FEW SHOWERS LATE MONDAY INTO
EARLY TUESDAY, ESPECIALLY NORTH, AS THE FRONTAL BOUNDARY THAT
MOVES THROUGH LATE SUNDAY NIGHT INTO MONDAY CONTINUES TO SLOWLY
DISSOLVE. WITH RIDGING IN THE UPPER LEVELS, WARMER AIR WILL BE
ALLOWED TO SLOWLY FILTER IN FOR THE LATTER PART OF THE WEEK AHEAD
OF THE NEXT STORM SYSTEM APPROACHING FROM THE WEST. THE BEST
CHANCE OF PRECIPITATION IN THE EXTENDED IS SLATED FOR THE FRIDAY
INTO EARLY SATURDAY TIME PERIOD AS AN OCCLUDED FRONT ASSOCIATED
WITH A LOW PRESSURE NEAR THE GREAT LAKES MOVES ACROSS THE AREA.
TEMPERATURES SHOULD BE WARM ENOUGH TO KEEP PRECIP ALL RAIN DURING
THE DAY FRIDAY, BUT AFTER MIDNIGHT WHEN THE FRONT MOVES THROUGH,
WE COULD GET A MIXTURE.

&&

.AVIATION...
THIS TAF FORECAST WILL BE ONE OF TRANSITIONING...FIRST TRANSITIONING
FROM VFR CEILINGS TO IFR BY THE END OF THE PERIOD. OVERRUNNING
PRECIPITATION WILL BE SLOW TO ADVANCE INTO THE AREA, AS THE LOWEST
LEVELS WILL NEED TO MOISTEN UP SOMEWHAT BEFORE SNOW BEGINS IN
EARNEST THIS AFTERNOON AT OUR TAF SITES. ONCE SNOW BEGINS, CEILINGS
AND VISIBILITIES SHOULD LOWER RAPIDLY INTO THE IFR CATEGORY, AND TO
LOW IFR THIS EVENING. PRECIPITATION TYPE WILL BE PROBLEMATIC, AS
WARMER AIR ON AN EASTERLY FLOW TRIES TO SHUNT THE COLDEST AIR
WESTWARD. FURTHER TRANSITIONING OCCURS AS SNOW WAS BLENDED TO A
MIXTURE OF SNOW AND SLEET, AND THEN MIXING WITH FREEZING RAIN AT THE
CENTRAL TAF SITES. SOUTH AND EAST, FOR MIV AND ABE, RAIN SHOULD
ENTER THE PICTURE BEFORE 06Z AS 1000-850 HPA THICKNESSES RISE ABOVE
1305, AND 850 HPA TEMPERATURES RISE JUST ABOVE ZERO DEGREES C. THE
1305 1000-850 HPA THICKNESS LINE MIGRATES TO ABOUT PHL BEFORE
RETURNING MONDAY MORNING, GIVING CREDENCE TO THE MIXED-TYPE
PRECIPITATION.

WINDS SHOULD BE FAIRLY LIGHT AT THE SURFACE, WITH NOT A GREAT DEAL
OF INCREASE OFF THE SURFACE. ONE EXCEPTION MAY BE AT 925 HPA BY
ABOUT 06Z, WHEN THE SOUTHEASTERN TAF SITES MAY BE BRUSHED BY THE
TIGHTER GRADIENT TO THE NORTHWEST OF THE SURFACE LOW. LOW LEVEL WIND
SHEAR MAY BE IN EVIDENCE FOR A BRIEF TIME, AND LATER FORECASTERS MAY
WISH TO WATCH FOR THIS IF CONFIDENCE GROWS.

&&

.MARINE...
A SMALL CRAFT ADVISORY WAS ISSUED FROM MIDNIGHT TONIGHT TO NOON
MONDAY, AS WINDS BUILD A BIT AND SEAS RESPOND. THE DAYSHIFT SAW
THIS, AND LATER GUIDANCE VALIDATES THIS IDEA. THE WINDS, AS
MENTIONED ABOVE, SHOULD BE STRONGEST SOUTH IN THE PROXIMITY OF THE
LOW, BUT GUSTS COULD REACH 25 KNOTS EVEN NORTH. WAVEWATCH BUILDS
SEAS TO THE 5 OR 6 FOOT CATEGORY LATE TONIGHT INTO MONDAY MORNING,
UNTIL THE LOW PASSES TO THE EAST OF THE AREA, AND THIS IS REASONABLE
AND ACCEPTED.

&&

.TIDES...
TIDES SHOULD NOT BE A PROBLEM TONIGHT AND MONDAY, AS THE POSITIVE
ANOMALIES ARE FORECAST TO REMAIN AT OR BELOW 1.5 FEET ABOVE NORMAL.
ALSO, EFFECTS SHOULD BE LESS THAN DRAMATIC SINCE FULL MOON IS ABOUT
A WEEK AWAY, AND THE COASTAL LOW IS NOT TERRIBLY STRONG AND HAS A
FAIRLY BRIEF IMPACT.

&&

SHORT TERM...STAUBER
LONG TERM...TFG
AVIATION/MARINE/TIDES... /