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Christmas Grinch Storm Part 2


Chicago Storm

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Off the LOT Facebook page a few minutes ago:

 

Quick update. one of our reliable forecast models which had been a hold out, is now on board with the potential for heavy snowfall over at least portions of the region Wednesday. It is looking increasingly likely that travel could become EXTREMELY difficult in or very near our region Christmas Eve. If the remainder of computer model guidance looks as ominous when it comes in later this evening, then a winter storm watch would likely be posted later tonight for portions of the region for Wednesday's storm.

 

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AREA FORECAST DISCUSSION  

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL  

850 PM CST MON DEC 22 2014  

   

UPDATE  

 

850 PM CST  

 

NO CHANGES PLANNED TO FORECAST FOR TONIGHT AS UPPER LOW TO OUR  

WEST CONTINUES TO DUMBBELL SLOWLY NORTHEAST FROM THE CORN BELT  

TOWARD WISCONSIN. ASSOCIATED SFC LOW OVER SOUTHERN IOWA WILL MOVE  

NORTHEAST IN CONCERT WITH THE UPPER LOW AND DRAG A WARM FRONT  

NORTH ACROSS THE CWA OVERNIGHT INTO EARLY TUESDAY MORNING. THE  

RESULT DRIZZLE AND FOG OVERNIGHT PUNCTUATED WITH PERIODS OF RAIN  

ALONG WITH SLOWLY RISING TEMPS AS THE DIFFUSE WARM FRONT LIFTS  

SLOWLY NORTH. TRENDS IN THE GRIDS ALREADY HAVE A GOOD HANDLE ON  

THIS AND NO CHANGES ARE PLANNED.  

 

OF MUCH GREATER CONCERN CONTINUES TO BE THE POTENTIAL FOR A WINTER  

STORM AFFECTING PORTIONS OF THE REGION WEDNESDAY...CHRISTMAS EVE  

DAY. THE 00Z WRF-NAM IS TRICKLING IN AND APPEARS TO HAVE FINALLY  

CAVED IN AND JOINED THE CAMP OF WHAT THE REMAINDER OF THE GLOBAL  

MODELS HAD SHOWN ON WITH THE 12Z RUNS. LACK OF RUN-TO-RUN  

CONSISTENCY AND HIGH DEGREE OF VARIABILITY BETWEEN VARIOUS MODELS  

HAS MADE THIS A CHALLENGING SYSTEM TO FORECAST FOR...HOWEVER THE  

12Z GLOBAL MODELS CAME INTO MUCH BETTER AGREEMENT AND NOW THE 00Z  

WRF-NAM SEEMS TO HAVE JOINED THAT CAMP WHICH COULD POSE A  

SIGNIFICANT WINTER STORM THREAT TO A POTENTIALLY LARGE PORTION OF  

OUR CWA WEDNESDAY.  

 

THE EXPLOSIVE DEEPENING OF THE SYSTEM PROGGED IN THE MODELS WITH  

500MB...ALONG WITH AMPLE MOISTURE...AND ELEVATED INSTABILITY ALL  

LEAVE ME VERY CONCERNED THAT WE COULD BE LOOKING AT A VERY HEAVY  

AND WET SNOW AFFECTING THE REGION WEDNESDAY. THE NEGATIVE MID-  

LEVEL THETA-E LAPSE RATES AND LAPSE RATES GREATER THAN 6C/KM FROM  

600-300MB POINT TOWARD THE POTENTIAL FOR UPRIGHT CONVECTION WITHIN  

THE DEFORMATION BAND. THERMAL PROFILES IN THE MODELS ARE MARGINAL  

FOR SNOW...ESPECIALLY DOWN LOW...HOWEVER GIVEN THE EXTREMELY  

IMPRESSIVE DYNAMICS SHOWN IN THE LATEST GUIDANCE WOULD ANTICIPATE  

STRONG ASCENT TO OVERWHELM IN MARGINAL WARMTH DOWN LOW AND LIKELY  

ALLOW FOR HEAVY WET SNOW IN THE DEFO BAND.  

 

NOT UNCOMMON FOR RAPIDLY DEEPENING SYSTEMS TO TRACK A BIT FARTHER  

WEST THAN MODELS FORECAST...WHICH COULD PUSH THE HEAVY SNOW BAND  

FARTHER WEST IN OUR CWA WITH MORE OF A MIX EAST. THE STRONG  

FRONTOGENETIC FORCING AND WEAK INSTABILITY WOULD FAVOR A RATHER  

NARROW BUT INTENSE BAND OF PRECIPITATION...MAKING THE PLACEMENT OF  

ANY HEAVY SNOW BAND VERY DIFFICULT TO PINPOINT.  

 

AM RELUCTANT TO MAKE ANY WHOLE SALE CHANGES TO THE 4TH PERIOD OF  

THE FORECAST ON AN EVEN SHIFT FOLLOWING A QUICK GLANCE AT THE  

LATEST NAM...HOWEVER IF THE 00Z GLOBAL GUIDANCE COMES IN LOOKING  

SIMILAR TO THEIR 12Z RUNS AND ANYTHING LIKE THE 00Z WRF-NAM THEN  

THE MIDNIGHT SHIFT WILL PROBABLY NEED TO CONSIDER WINTER STORM  

WATCH FOR AT LEAST PORTIONS OF THE AREA. WHILE IT LOOKS TO BE A  

VERY HIGH WATER CONTENT SNOWFALL...THE CONVECTIVE ALLOWING MODELS  

ARE SPITTING OUT QPF VALUES THAT COULD SUPPORT 6+ INCHES OF SNOW  

EVEN WITH SNOW:LIQUID RATIOS AS LOW AS 7-8:1. WILL UPDATE THE SPS  

AND HIT THINGS HARDER IN THAT PRODUCT FOR NOW.  

 

IZZI  

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I said before (and held firm on it) that this would be Chicago's storm.

 

These type of bombing lows coming of the gulf almost always produce nicely there. Given the dynamics and amount of moisture associated with the storm, the marginal temps shouldn't be as big as a detriment as some thought.

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