Heavy Snow in VA, Freezing Rain in East NC
Posted by JAC on 1/30/2010, 5:29 am


MESOSCALE DISCUSSION 0090
  NWS STORM PREDICTION CENTER NORMAN OK
  0256 AM CST SAT JAN 30 2010
 
  AREAS AFFECTED...SOUTHERN PORTIONS OF WV/VA
 
  CONCERNING...HEAVY SNOW
 
  VALID 300856Z - 301330Z
 
  MODERATE TO HEAVY SNOW APPEARS LIKELY TO CONTINUE TO DEVELOP
  NORTH-NORTHEASTWARD THROUGH THE EARLY MORNING HOURS ACROSS SOUTHERN
  WV AND MUCH OF SOUTHERN VA. SNOWFALL RATES MAY EXCEED 1 IN/HR FOR
  SEVERAL HOURS DURATION.
 
  WATER VAPOR IMAGERY REFLECTS A POSITIVELY TILTED/INCREASINGLY OPEN
  UPPER TROUGH NEARING THE LOWER-MIDDLE MS RIVER VALLEY EARLY THIS
  MORNING...WITH IMPLIED ASCENT ATTRIBUTABLE TO A STRONG/COUPLED UPPER
  JET AND LOW LEVEL WARM ADVECTION/ISENTROPIC LIFT REGIME...LIKELY TO
  YIELD INCREASING PRECIPITATION RATES ACROSS MUCH OF THE CENTRAL
  APPALACHIANS VICINITY. THIS WILL BE IN THE FORM OF MODERATE/HEAVY
  SNOW ACROSS SOUTHERN WV/VA THIS MORNING WHERE 20S F SURFACE
  TEMPERATURES CURRENTLY RESIDE. WITH A NORTHEASTWARD SURGING DRY SLOT
  OVER THE TN VALLEY ALSO NOTED PER WATER VAPOR IMAGERY...NUMERICAL
  GUIDANCE IMPLIES THAT STEEPENING LAPSE RATES ALOFT AND A COMBINATION
  OF WEAK UPRIGHT/SLANTWISE INSTABILITY COULD POTENTIALLY CONTRIBUTE
  TO ENHANCED SNOW RATES ON THE MESOSCALE. ACCORDINGLY...06Z RUC
  SOUNDINGS REFLECT WEAK POTENTIAL INSTABILITY/UPRIGHT CAPE BASED
  AROUND 600 MB IN MULTIPLE FORECAST SOUNDINGS ACROSS SOUTHERN VA
  LATER THIS MORNING. SIMILAR TO A COLD/WELL-SATURATED 06Z GSO
  OBSERVED RAOB...THE AFOREMENTIONED RUC SOUNDINGS SUGGEST INCREASING
  DEEP LAYER OMEGA COINCIDENT WITH A FAVORABLE DENDRITIC GROWTH
  ZONE...ATOP AN INCREASINGLY SATURATED ISOTHERMAL 2-3 KM AND WEDGE
  REINFORCED WELL-BELOW FREEZING LOWEST 1 KM. ALL THIS IMPLIES A
  NORTH-NORTHEASTWARD EXPANSION OF MODERATE TO HEAVY SNOW ACROSS MUCH
  OF SOUTHERN VA THROUGH 12Z-15Z...WITH EMBEDDED 1+ IN/HR RATES A
  DISTINCT POSSIBILITY.
 
  ..GUYER.. 01/30/2010
 










MESOSCALE DISCUSSION 0089
  NWS STORM PREDICTION CENTER NORMAN OK
  0116 AM CST SAT JAN 30 2010
 
  AREAS AFFECTED...COASTAL PLAIN OF ERN NC AND NE SC
 
  CONCERNING...FREEZING RAIN
 
  VALID 300716Z - 301215Z
 
  THE THREAT OF FREEZING RAIN WILL INCREASE ACROSS THE COASTAL PLAIN
  OF ERN NC AND NERN SC. RATES OF .05 TO .10 INCH PER HR WILL BE
  POSSIBLE THROUGH 12Z.
 
  LATEST WATER VAPOR IMAGERY DEPICTS A MID-LEVEL VORT MAX
  TRANSITIONING EASTWARD TOWARDS THE MID-MS VALLEY...WITH A 850 MB
  CYCLONE LOCATED OVER NRN AL. BROAD AREA OF MOIST ASCENT IS EVIDENT
  ACROSS ERN AL/GA THROUGH WRN NC...CONFIRMED BY SWATH OF
  PRECIPITATION EVIDENT ON MOSAIC RADAR IMAGERY. 07Z SUBJECTIVE
  ANALYSIS PLACES THE SFC FREEZING LINE FROM NEAR HAMLET NC TO NEAR
  MOREHEAD CITY NC. DRIER AIR IS FOUND FARTHER S INTO NERN SC...WITH
  SFC T-TD SPREADS OF 10-15 DEGREES COMMON.
 
  AS THE LOW LEVEL CYCLONE CONTINUES TO TRANSITION EASTWARD...WIND
  SPEEDS ABOVE THE SFC COLD DOME /APPROX ABOVE 900 MB/ WILL INCREASE
  SIGNIFICANTLY. MODEL FORECAST SOUNDINGS INDICATE A STRONGLY VEERED
  PROFILE...IMPLYING A DEVELOPING WAA REGIME...WITH SIGNIFICANT
  MOISTURE TRANSPORT NORTHWARD OCCURRING. AS WA/MOIST ADVECTION
  BECOMES COUPLED WITH INCREASING SYNOPTIC SCALE ASCENT WITH THE
  APPROACHING VORT MAX...AN EXPANSION OF PRECIPITATION OVER THE AREA
  IS EXPECTED.
 
  PRECIP TYPE FORECAST WILL BE CHALLENGING AS THE VERTICAL TEMPERATURE
  PROFILE FLUCTUATES WITH TIME. WET-BULB COOLING WILL CAUSE THE SFC
  FREEZING LINE TO SHIFT SOUTHWARD...AND BECOME ORIENTED NEARLY
  PARALLEL TO THE COAST. VERTICAL TEMPERATURE PROFILE WILL BECOME
  FAVORABLE FOR FZRA WITH INCREASING LOW LEVEL WAA. RATES OF .05 TO
  .10 PER HOUR...WITH LOCALLY HIGHER AMOUNTS POSSIBLE...WILL BECOME
  LIKELY AS THE MORNING PROGRESSES.
 
  ..ROGERS/SMITH.. 01/30/2010
 
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Major Winter Storm: OK to VA - JAC, 1/28/2010, 7:04 am
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