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February 21st - 23rd Winter Storm Part 2


Powerball

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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
711 PM CST THU FEB 21 2013

.MESOSCALE DISCUSSION...
711 PM CST

TRICKY SNOWFALL FORECAST FOR TONIGHT CONTINUES TO EVOLVE. GOES
IMAGERY AND REGIONAL RADAR MOSAIC THIS EVENING SHOWS LEAD SHORTWAVE
AND ITS ASSOCIATED SLUG OF HEAVIER PRECIPITATION CONTINUING TO PUSH
EASTWARD INTO INDIANA AND KENTUCKY. THE LEADING EDGE OF THE SNOW
CONTINUES TO GET EATEN AWAY BY THE PRONOUNCED LOW LEVEL DRY AIR THAT
IS GETTING SATURATED FROM TOP DOWN. PROGRESSION OF ACARS SOUNDINGS
OUT OF MDW FROM 20Z THROUGH NOW SHOWS THAT THE COLUMN IS INDEED
QUICKLY SATURATING...SO START TIME OF THE SNOW STILL LOOKS TO BE
GENERALLY ON TARGET. AS THE TOP DOWN SATURATION OCCURS COULD SEE A
BRIEF PERIOD OF GRAUPEL OR SLEET AT THE ONSET OF THE PRECIP EVEN AS
FAR NORTH OF THE WI BORDER...BUT A QUICK TRANSITION TO SNOW SHOULD
OCCUR THIS EVENING.

OF NOTE AND SOME CONCERN REGARDING FORECAST SNOWFALL IS THE
PRONOUNCED MID LEVEL DRY INTRUSION QUICKLY SPREADING NORTHEAST INTO
SOUTHWESTERN ILLINOIS THIS EVENING. RUC/WRF-NAM SEEM TO HAVE THE
GENERAL TRENDS DECENTLY HANDLED WITH THIS DRY INTRUSION LIKELY TO
CONTINUE RAPIDLY SPREADING NORTHEAST...LIKELY REACHING OUR SOUTHERN
MOST CWA BETWEEN 03-05Z.

THE NORTHWARD PROGRESSION OF THE DRY INTRUSION MAY ULTIMATELY BEGIN
TO SLOW DOWN SOME OVERNIGHT AS WATER VAPOR SHOWS A VERY WELL DEFINED
VORTICITY MAX PIVOTING EAST-NORTHEASTWARD INTO WESTERN MISSOURI
EARLY THIS EVENING. AS THIS FEATURE PIVOTS COUNTER-CLOCKWISE AROUND
THE LARGE UPPER LOW MODELS SUGGEST SOME RAMPING UP OF UPWARD
VERTICAL VELOCITIES OVERNIGHT AND SOMEWHAT OF A FILLING IN OF THE
BAND OF STEADIER/HEAVIER PRECIPITATION OVERNIGHT...PARTICULARLY OVER
NORTHERN PORTIONS OF THE CWA. RUC/WRF-NAM BOTH SUGGEST THAT WE WILL
LOSE SATURATION IN THE CRITICAL -12 TO -18C LAYER EVEN OVER FAR
NORTHERN PORTIONS OF THE CWA BY 09-10Z LEAVING LOWER CLOUD VOID OF
ICE NUCLEI NECESSARY FOR SNOW.

WOULD EXPECT A TRANSITION TO DRIZZLE/FREEZING DRIZZLE AS THE DRY
INTRUSION OVERTAKES THE AREA...HOWEVER GIVEN THE SOMEWHAT STEEPER
LAPSE RATES IN THE DRY INTRUSION AND WEAKER STABILITY WOULD
ANTICIPATE THE DRIZZLE TO BE PUNCTUATED WITH AT LEAST SOME SHOWERY
SNOW AT TIMES THROUGH LATE TONIGHT AND POSSIBLY INTO FRIDAY MORNING.

THE TIME PERIOD OF POTENTIAL SNOWFALL IS LOOKING LIKE ITS
GETTING PINCHED A SMIDGE ON THE FRONT END BY THE DRY AIR AND
PROBABLY A BIT MORE ON THE BACK END BY RAPIDLY ENCROACHING DRY
INTRUSION...SO THE DURATION OF HEAVIER SNOW LOOKS TO BE FAIRLY SHORT
BUT COULD STILL BE INTENSE ENOUGH TO REACH GOING FORECAST SNOW
AMOUNTS...SO AT THIS TIME NOT PLANNING ANY BIG OVERHAULS TO THE SNOW
AMOUNT FORECAST BUT WILL BE REFINING GRIDS THIS EVENING TO TWEAK
TIMING AND INTRODUCE FREEZING DRIZZLE INTO EVEN NORTH CENTRAL
ILLINOIS LATE TONIGHT. SHOULD THE ANTICIPATED RE-DEVELOPMENT AND
WESTWARD FILLING IN OF THE PRECIP BAND NOT TAKE PLACE AS ROBUSTLY
AS MODELS SUGGEST THEN SNOW TOTALS COULD END UP BEING MUCH CLOSER
TO THE LOWER END OF THE FORECAST RANGE.

IZZI

 

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Went from sleet back to all snow here..

 

   MESOSCALE DISCUSSION 0197   NWS STORM PREDICTION CENTER NORMAN OK   0746 PM CST THU FEB 21 2013      AREAS AFFECTED...NRN IL TO SRN IND      CONCERNING...WINTER MIXED PRECIPITATION       VALID 220146Z - 220545Z      SUMMARY...MODERATE TO LOCALLY HEAVY SNOW WILL SPREAD ACROSS CNTRL   INTO NRN IL AND PORTIONS OF NRN IND LATE THIS EVENING WITH SNOW   RATES GENERALLY LESS THAN ONE INCH PER HOUR.  A MIX OF SLEET AND   FREEZING RAIN IS EXPECTED ACROSS MUCH OF CNTRL INTO SRN IND.      DISCUSSION...NRN PLUME OF WARM CONVEYOR BELT IS SPREADING NORTH   ACROSS IL/IND WHILE THE MAIN CORRIDOR OF WARM ADVECTION GRADUALLY   SHIFTS EAST INTO THE LOWER OH VALLEY.  SIGNIFICANT WARMING IS   EXPECTED TO RESULT IN A SNOW TO SLEET TO FREEZING RAIN EVENT ACROSS   CNTRL/SRN IND AS INTENSE LLJ FOCUSES ACROSS THIS REGION LATER THIS   EVENING.  LATEST OBSERVATIONAL TRENDS SUGGEST THIS IS OCCURRING WITH   NUMEROUS REPORTS OF SLEET AND FREEZING RAIN NOW REPORTED ACROSS THIS   REGION.      SLEET/SNOW LINE MAY ULTIMATELY ESTABLISH ITSELF FROM NEAR CMI IN   ECNTRL IL TO LAF TO FWA OVER IND.  MODERATE TO LOCALLY HEAVY SNOW IS   EXPECTED TO DEVELOP/SPREAD NWD ACROSS IL AND NWRN IND WHERE HALF   INCH TO PERHAPS ONE INCH PER HOUR RATES MAY BE OBSERVED FOR A FEW   HOURS.  THIS WARM ADVECTION BAND OF PRECIPITATION WILL GRADUALLY   SHIFT NORTH TOWARD SRN WI/LOWER MI AFTER MIDNIGHT WHERE PROFILES   WILL BE SUFFICIENTLY COOL FOR SNOW MAINTENANCE.
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GRR and DTX might be spot on with this storm system.

I feel 1-2" is a good forecast, but may be overdone. At this point an inch or less would seem most likely with drizzle being the main player.

Pessimism is one thing, and it is certainly NO stranger to this board, but less than an inch with mostly drizzle? Goes 100% against model and radar trends.
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Watching the radar returns get eaten up by the dry air for the moment. 

 

Still thinking we are going to get less than 2" down this way.  Feels like it.  The bands of snow are dying just to my SW.  A few flurries are blowing around out there now, but for the moment, it doesn't look all that impressive.

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Watching the radar returns get eaten up by the dry air for the moment. 

 

Still thinking we are going to get less than 2" down this way.  Feels like it.  The bands of snow are dying just to my SW.  A few flurries are blowing around out there now, but for the moment, it doesn't look all that impressive.

Was about to post the same thing. This band is getting demolished.

 

Got the special teams unit on the field, running the play clock down for the punt...

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Watching the radar returns get eaten up by the dry air for the moment. 

 

Still thinking we are going to get less than 2" down this way.  Feels like it.  The bands of snow are dying just to my SW.  A few flurries are blowing around out there now, but for the moment, it doesn't look all that impressive.

 

 

Was about to post the same thing. This band is getting demolished.

 

Got the special teams unit on the field, running the play clock down for the punt...

 

We knew the band would get obliterated as it pushed NE but it's even worse than I had expected for those further SW.  Counting on this secondary vort max to swing through and perk things up seems like fools gold.

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