MESOSCALE DISCUSSION 0110
   NWS STORM PREDICTION CENTER NORMAN OK
   1125 PM CST SAT FEB 19 2011
   
   AREAS AFFECTED...PARTS OF NRN NEB/SRN SD EWD TO SWRN MN/EXTREME NWRN
   IA
   
   CONCERNING...WINTER MIXED PRECIPITATION 
   
   VALID 200525Z - 201030Z
   
   WINTRY PRECIPITATION IS EXPECTED TO DEVELOP NEWD ACROSS NORTH
   CENTRAL NEB/SOUTH CENTRAL SD BETWEEN 06-09Z...AND THEN EWD INTO SWRN
   MN AND FAR NWRN IA MAINLY AFTER 09Z.  WEAK ELEVATED INSTABILITY WILL
   SUPPORT THE POTENTIAL FOR TSTMS WHICH WILL INCREASE THE RATE OF
   FREEZING RAIN AND SLEET.  FREEZING RAIN WITH RATES 0.15 INCH PER 3
   HOUR SHOULD REMAIN CONFINED TO A 50 MILE WIDE CORRIDOR EXTENDING
   FROM LOGAN COUNTY NEB TO TURNER COUNTY SD AND THEN EWD INTO FAR NWRN
   IA AND ADJACENT COUNTIES IN SWRN MN.  MODELS SUGGEST AN AREA
   EXTENDING 60-80 MILES NORTH OF THE FREEZING RAIN SHOULD CONSIST OF
   PREDOMINANTLY SLEET FROM THE ONSET OF PRECIPITATION THROUGH AT LEAST
   12Z.  HEAVY SLEET RATES WILL BE POSSIBLE...ESPECIALLY WITH ANY TSTMS
   THAT DEVELOP.
   
   SURFACE THETA/THETAE ANALYSES INDICATED A BAROCLINIC ZONE EXTENDING
   EWD FROM SERN WY INTO CENTRAL NEB...THEN NEWD TO SWRN/SRN MN AND FAR
   NWRN/NRN IA.  MODELS MAINTAIN THIS BOUNDARY POSITION THROUGH
   12Z...WITH THIS FEATURE GENERALLY COINCIDENT WITH THE SURFACE
   FREEZING LINE.  AS SUCH...THIS BOUNDARY WILL BE THE SRN EXTENT OF
   THE FREEZING RAIN THREAT THROUGH THE OVERNIGHT PERIOD.  PERSISTENT/
   EXPANDING AREA OF LIGHTNING ACROSS ERN CO AND COOLING CLOUD TOPS PER
   IR SATELLITE IMAGERY OVER ERN CO INTO WRN/CENTRAL NEB ARE LIKELY
   INDICATIVE OF THE STRONG DEEP LAYER ASCENT SPREADING NEWD TONIGHT
   PER A LEAD SHORTWAVE TROUGH OVER CENTRAL CO.  AIR MASS MOISTENING IS
   UNDERWAY ACROSS THE DISCUSSION AREA ATTENDANT TO INCREASING WAA
   REGIME ALONG NOSE OF STRENGTHENING SRN-CENTRAL PLAINS LLJ AND WITHIN
   EXIT REGION OF STRONG SWLY UPPER LEVEL JET NOSING INTO THE CENTRAL
   PLAINS.
   
   PRECIPITATION RATES...ALTHOUGH GENERALLY LIGHT AT THE ONSET ACROSS
   SWRN/CENTRAL NEB...ARE EXPECTED TO INCREASE OVERNIGHT INTO EARLY
   SUNDAY MORNING AS DEEP LAYER ASCENT BECOMES MAXIMIZED ACROSS THE
   DISCUSSION AREA PER AFOREMENTIONED EVOLUTION OF MASS FIELDS. 
   FORECAST SOUNDINGS WITHIN THE EXPECTED FREEZING RAIN CORRIDOR
   SUGGEST A 3-4 DEGREE MAXIMUM INCREASE ABOVE 0 C IN THE 850-700 MB
   LAYER THROUGH 12Z.  THIS WILL BE MORE THAN SUFFICIENT TO SUPPORT
   FREEZING RAIN...GIVEN SUB-FREEZING SURFACE TEMPERATURES.  FARTHER
   N...VERTICAL THERMAL PROFILES SUPPORT MAINLY SLEET.  BY 12Z...AN
   INCREASE IN LOW LEVEL CAA WILL BE DEVELOPING FROM WNW-ESE ACROSS
   WRN-CENTRAL NEB AS A SURFACE LOW MOVES INTO FAR SWRN NEB/NWRN KS. 
   THIS TREND MAY SUPPORT A TRANSITION FROM SLEET TO SNOW ACROSS
   CENTRAL SD.
   
   ..PETERS.. 02/20/2011
   
   
   ATTN...WFO...MPX...DMX...FSD...OAX...ABR...LBF...UNR...
   
   LAT...LON   44369813 44429670 44309533 44039439 43659354 43169350
               42989432 43149591 42679727 42219805 41539972 41560119
               42200150 42860171 44049959 44369813