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December 25-29th Storm Disco


Chicago Storm

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AREA FORECAST DISCUSSION  

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL  

1214 PM CST SUN DEC 27 2015  

   

UPDATE  

 

1113 AM CST  

 

HAVE NOT MADE ANY CHANGES YET TO THE HEADLINES FOR MONDAY. DO  

ANTICIPATE UPGRADING THE WATCHES TO WARNINGS AND ISSUING  

SOME SORT OF WINTER ADVISORY HEADLINE SOUTH OF THE CURRENT WATCH.  

WE HOPE TO HAVE UPDATED HEADLINES OUT BY ABOUT 2PM CST. THIS  

CONTINUES TO BE AN EXTREMELY CHALLENGING FORECAST WITH PLENTY OF  

LINGERING UNCERTAINTY. FORECAST IS VERY DEPENDENT ON TEMPERATURE  

TRENDS AT THE SURFACE AND ALOFT...WHICH WILL IMPACT HOW MUCH  

PRECIPITATION FALLS IN WHAT TYPE. CONSIDERING HOW STRONG THE EAST  

WINDS WILL BE...GUSTING TO 45-50 MPH...IT WILL NOT TAKE MUCH ICE  

ACCRETION ON TREES AND POWERLINES TO CAUSE HUGE PROBLEMS. WINDS  

LOOK TO BE EVEN STRONGER ONTO THE ILLINOIS SHORE...WITH GUSTS UP  

TO 60 MPH OR SO. IN ADDITION TO LARGE BATTERING WAVES CAUSING  

POTENTIALLY SIGNIFICANT LAKESHORE FLOODING...THE WINDS COULD BE  

STRONG ENOUGH TO CAUSE MINOR WIND DAMAGE THEMSELVES. DID A QUICK  

COMPARISON TO THE HALLOWEEN 2014 WIND AND LAKESHORE FLOODING  

EVENT...AND THE MINOR LIMITING FACTOR TOMORROW WILL BE SHORTER  

FETCH DUE TO EAST WIND DIRECTION ON MONDAY VS. THE DUE NORTH WINDS  

IN THE HALLOWEEN '14 EVENT. WILL STILL IN ALL LIKELIHOOD BE  

ISSUING A LAKESHORE FLOOD WARNING TOMORROW FOR COOK AND LAKE IL.  

 

IN THE NEAR TERM...DESPITE LOW INVERSION HEIGHTS...THE LONG FETCH  

OF NORTH-NORTHEAST WINDS AND SOME LOW LEVEL CONVERGENCE AND LIFT HAS  

RESULTED IN FAIRLY WIDESPREAD LAKE EFFECT SHRA. ABOUT AN HOUR  

AGO...THERE WERE EVEN A FEW 35 DBZ ECHOES IN THE ACTIVITY...WHICH  

HAVE COME DOWN SOME SINCE. HOWEVER...STARTING TO SEE AN UPTICK IN  

COVERAGE OF ECHOES AGAIN AS OF THIS WRITING. ADJUSTED POPS UPWARD  

TO ACCOUNT FOR THIS ACTIVITY...WHILE LOWERING TO SLIGHT CHANCE OR  

LESS IN THE FAR SOUTHERN CWA WITH MUCH OF THE LIGHT RAIN STAYING  

SOUTH THROUGH EARLY EVENING.  

 

RC/IZZI  

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Cold air wraps around the low on the EURO pretty quickly...

 

ecmwf_T850_ncus_3.png

 

If the WRF ARW or NMM have got a handle on this then it doesn't get above freezing until 6pm Monday here.

 

Large pool of really low dewpoints and temps in southern Ontario.

 

wrf-arw_Td2m_ncus_44.png

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DVN with a little update...

 

 
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1213 PM CST SUN DEC 27 2015

.UPDATE...
ISSUED AT 1136 AM CST SUN DEC 27 2015

MAIN FORECAST FOCUS CONTINUES TO BE DETAILS OF PRECIPITATION
TYPE/TRENDS/AMOUNTS FOR TONIGHT THROUGH MONDAY. HAVE CONTINUED
WINTER STORM WATCH WITH ADDITIONAL HEADLINES UNDER CONSIDERATION
FOR AFTERNOON ISSUANCE. SYNOPTIC SCALE MODELS HAVE CONVERGED ON
SIMILAR TIMING FOR PRECIPITATION ONSET NEAR OR SHORTLY AFTER
MIDNIGHT TONIGHT IN THE SOUTHERN COUNTIES. AFTER INITIAL LOOK...AM
INCLINED TO THINK HEAVIEST ICE ACCUMULATIONS WILL BE A BIT FARTHER
NORTH THAN CURRENT FORECAST...WHICH WOULD BULLSEYE AREAS NEAR THE
INTERSTATE 80 CORRIDOR. COMBINATION OF ICE/SLEET/SNOW AND WINDS
GUSTING TO 45 MPH MEANS DOWNED LIMBS AND POWER LINES AND
ASSOCIATED POWER OUTAGES ARE STILL A BIG CONCERN. PRECIPITATION
INTENSITY MAY LEAD TO MORE ROAD SURFACE RUNOFF THAN ACTUAL ICE
ACCUMULATION AT TIMES...BUT PERIODS OF SIGNIFICANT ICING ARE STILL
EXPECTED. THERE MAY BE A RATHER SHARP CUTOFF FOR SNOWFALL
ACCUMULATIONS TONIGHT AS THE COLDER AIR WORKS IN...WITH THE HIGHER
TOTALS ACROSS THE NORTHWEST THIRD OF THE FORECAST AREA.
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Certainly seems reasonable based on the model trends. If rates stay lighter, could be catastrophic in areas.

 

Was just thinking if the east/northeast dry flow cuts back on the intensity of the precipitation, that could be a scenario - for awhile at least.

Of course usually freezing rain does not fall when the atmosphere is struggling to saturate.

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This setup would be so much more interesting without 3 major strikes against ice; heavy precip rates, heavy winds, super marginal surface temps after a month of record warmth.

 

 

It'll be interesting to see if high winds have an impact on the ice buildup.  Strongest winds look to lag the onset of precip a little.

 

Since you mentioned the negatives, a couple positives are that we are in late December and have a very strong surface high to the north/east that only slowly retreats (LOT mentioned near-record low level easterly flow).

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This setup would be so much more interesting without 3 major strikes against ice; heavy precip rates, heavy winds, super marginal surface temps after a month of record warmth.

 

I think the ice threat at ground level will be pretty marginal given the recent warmth/heavy rates/marginal temps.  However, elevated objects such as trees/power lines/etc will have significant glazing where the heaviest freezing rain falls.  Even with heavy rates the drops will split up and mist down on lower branches and glaze up.

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I think the ice threat at ground level will be pretty marginal given the recent warmth/heavy rates/marginal temps.  However, elevated objects such as trees/power lines/etc will have significant glazing where the heaviest freezing rain falls.  Even with heavy rates the drops will split up and mist down on lower branches and glaze up.

 

 

Ground level may not be bad but one thing to remember is that many areas will start as sleet.  If a base of sleet gets put down, could make things slippery as it changes to zr.

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The trees are definitely the most in danger of getting glazed over. And with all the wind events we've had in the last two months, some branches have probably been cracked and weakened already. I've lost more tree branches, then I have in any singular severe thunderstorm over the last 6 weeks.

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Ground level may not be bad but one thing to remember is that many areas will start as sleet.  If a base of sleet gets put down, could make things slippery as it changes to zr.

Good point.  Yeah should develop a nice base of sleet before the primary freezing rain band moves north.  Wouldn't be surprised if we see a good inch of sleet here before the glazing really gets going.  

 

La Crosse sits in a good spot on clown maps...we'll see... 

Man it's a tough forecast for La Crosse.  Some models keep you all snow, while others give you a sleet fest before a relatively short period of snow to finish things off.  Hopefully the 00z runs clear things up a bit for you guys in or near the main snow band.

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