TX Panhandle: 1 to 2"/hr
Posted by JAC on 1/28/2010, 9:24 am


MESOSCALE DISCUSSION 0071
  NWS STORM PREDICTION CENTER NORMAN OK
  0701 AM CST THU JAN 28 2010
 
  AREAS AFFECTED...PORTIONS E-CENTRAL/NERN NM...TX PANHANDLE AND
  SOUTH-PLAINS REGIONS...WRN-CENTRAL OK.
 
  CONCERNING...WINTER MIXED PRECIPITATION
 
  VALID 281301Z - 281800Z
 
  EXTENSIVE AND GROWING PRECIP AREA ACROSS ERN NM...W TX AND SRN OK
  FCST TO MOVE/EXPAND NWD AND NEWD THROUGH 18Z...RESULTING IN SNOW
  RATES 1-2 INCH/HOUR FROM NEAR LVS-SRR LINE NEWD AND EWD ACROSS NRN
  PANHANDLE THROUGH 18Z.  MEANWHILE FREEZING RAIN ALREADY OBSERVED
  INVOF AMA/CVS SHOULD TRANSITION TO AREA OF SLEET THAT EXPANDS IN
  PROGRESSIVELY NARROWER ZONE EWD ACROSS PORTIONS WRN/CENTRAL OK NEAR
  AND JUST NW OKC.  MIXED ZONE OF BOTH SLEET AND FREEZING RAIN WILL
  EXIST FOR MUCH OF REMAINDER MORNING ALONG CORRIDOR FROM E OF CVS
  TOWARD CSM/OKC AREAS...WITH FREEZING RAIN BECOMING PREDOMINANT
  PRECIP TYPE WITH SWD TO SWD-SHIFTING SFC FREEZING LINE.
 
  PRECIP PLUME WILL BE ENHANCED BY STG LOW LEVEL WAA AND MOISTURE
  TRANSPORT REGIME ACCOMPANYING BOTH BROAD/35-45 KT SRN/WARM BRANCH OF
  LLJ OVER SW TX...AND SIMILARLY STRONG BUT SOMEWHAT NARROWER NRN
  BRANCH LLJ ACROSS SWRN OK...SRN PANHANDLE/NRN SOUTH-PLAINS REGION
  AND E-CENTRAL NM.  MID-UPPER WINDS WILL BE STRONGLY MERIDIONAL WITH
  SOME ELY COMPONENT...NE OF SHORTWAVE TROUGH THAT IS EVIDENT IN
  MOISTURE CHANNEL IMAGERY EJECTING NEWD OVER SWRN NM.  12Z AMA RAOB
  SHOWS ROUGHLY 2500 FT DEEP WARM NOSE ABOVE STABLE/POSTFRONTAL
  BOUNDARY LAYER...SUPPORTING FREEZING RAIN AS OBSERVED...BUT SHOULD
  COOL THROUGHOUT REMAINDER MORNING AS TRANSITION OCCURS THROUGH SLEET
  TO SNOW.  12Z OUN SOUNDING...WITHOUT ANY ADVECTION OR DYNAMIC
  COOLING -- WOULD EXPERIENCE WET-BULB CHANGE TO JUST ABOVE FREEZING.
  HOWEVER...CONTINUED CAA AND DRY ADVECTION BENEATH OVERSPREADING
  PRECIP PLUME WILL RESULT IN SEVERAL EFFECTS...
  1. SFC FREEZING LINE WILL CONTINUE TO MIGRATE S ACROSS CENTRAL/SWRN
  OK AND TX SOUTH-PLAINS REGION THROUGH 18Z...REACHING TO NEAR
  ROW-FSI-OKM LINE.
  2. EVAPORATIVE EFFECTS...TO SOME EXTENT AND IN A TOP-DOWN
  FASHION...WILL BE OFFSET BY DOWNWARD-DIRECTED SENSIBLE HEAT FLUXES
  FROM RELATIVELY WARM PRECIP FALLING INTO COLDER AIR.  THIS WILL ACT
  TO COMPACT ISOTHERMS AND COMPRESS LAYER OF STRONGEST STATIC
  STABILITY VERTICALLY.  MAIN UNCERTAINTY ATTM IS TO WHAT EXTENT THIS
  WILL OCCUR...WHICH WILL AFFECT TRANSITION FROM FREEZING RAIN TO
  SLEET IN AND NEAR AFOREMENTIONED TRANSITION ZONE.
 
  ..EDWARDS/JEWELL.. 01/28/2010


 
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Major Winter Storm: OK to VA - JAC, 1/28/2010, 7:04 am
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