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November 20-21 Early Season Snowstorm Part 2


Hoosier

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LOT...

SHORT TERM FOCUS IS ON UPCOMING HEAVY SNOW EVENT TONIGHT INTO

SATURDAY...AND THEN ON VERY COLD CONDITIONS SATURDAY NIGHT.

FIRST OFF...THE CHANGES TO FORECAST ARE AS FOLLOWS...

1) IT APPEARS THAT THE SWATH OF HEAVY SNOW LOOKS TO BE A BIT MORE

BROADLY FOCUSED...AND ALSO SLIGHTLY FARTHER SOUTH THAN IN

PREVIOUS FORECAST AND 2) HAVE INCLUDED WILL COUNTY IN THE WINTER

STORM WARNING...MAINLY FOR NORTHERN PORTIONS.

FOR THE DETAILS...

A BAND OF HEAVY SNOW HAS SET UP ACROSS PORTIONS OF SOUTH

DAKOTA AND IOWA THIS AFTERNOON AHEAD OF OUR INCOMING SYSTEM. THIS

REGION IS IN A FOCUS AREA OF 850-700 MB FRONTOGENESIS THAT HAS

ORGANIZED OVER A NARROW SWATH. SATURATION AND COOLING FROM THE TOP

DOWN HAS RESULTED IN A QUICK MOISTENING OF THE LOWER LEVELS IN

IOWA WHERE DEWPOINTS QUICKLY JUMP FROM THE LOW TEENS TO THE MID

20S. THIS PROCESS WILL OCCUR IN OUR AREA TONIGHT...BUT RIGHT NOW

IT IS VERY DRY.

THE MESOSCALE PROCESS GOING ON IN IOWA IS NOT WHAT IS EXPECTED TO

BRING OUR AREA-WIDE HEAVY SNOWFALL...BUT A PORTION OF THIS

ELEVATED FGEN AXIS WILL SLIDE INTO NORTHERN ILLINOIS THIS EVENING

AND TONIGHT AND LEAD TO A BAND OF SNOW ACROSS THE NORTHERN TIER

INITIALLY. THE STRENGTH OF THE FGEN ALONG THE 700 MB BAROCLINIC

ZONE IS SOMEWHAT TRANSIENT AND DOES NOT LOOK TO BE AS STRONG AS IT

IS IN IOWA. UPSTREAM OBSERVATIONS HAVE ALSO SHOWN A VERY SHORT

PERIOD OF RAIN/SLEET THAN VERY QUICKLY CHANGING TO SNOW IF NOT

GOING RIGHT TO SNOW ONCE THE ATMOSPHERE SATURATES.

THEN TONIGHT INTO SATURDAY MORNING...THEN THE SURFACE LOW WILL

PASS FROM SOUTH OF ST LOUIS BAY DAYBREAK SATURDAY...THEN TO SOUTH

OF FORT WAYNE BY MIDDAY. THIS WILL ALLOW THE BAROCLINIC ZONE TO

PIVOT OVER THE AREA. THIS COMBINED WITH VERY STRONG Q-VECTOR

FORCING FROM THE UPPER WAVE CONTINUES TO SUGGEST A PERIOD OF VERY

MODERATE TO VERY HEAVY SNOWFALL OVERNIGHT INTO SATURDAY MORNING.

ENSEMBLE GUIDANCE FROM THE GEFS/SREF CONTINUE TO PAINT A PICTURE

OF A WEST-EAST ORIENTED SWATH OF HEAVY SNOW WHICH WILL FOCUS FROM

LEE/OGLE/NORTHERN LASALLE COUNTIES EASTWARD TO DEKALB/KANE/WESTERN

DUPAGE COUNTIES. THE FGEN BANDING POTENTIAL COULD STRENGTHEN INTO

THE MORNING AS COLDER AIR STARTS TO WRAP INTO NORTHWEST ILLINOIS.

THE BIGGEST QUESTION MARK THEN BECOMES HOW MUCH DOES THE WARM

PAVEMENT LIMIT THE ACCUMS...AND WHERE THIS CUTOFF OCCURS...WHICH

CREATES SOME FORECAST UNCERTAINTY AS TO WHERE THIS SHARP

GRADIENT OCCURS IN COOK COUNTY. QPF NUMBERS ARE CONSISTENT AND

HIGH...AND SUPPORT HEAVY SNOWFALL EVEN INTO CHICAGO...BUT EXPECT

ACCUM RATES WILL DROP OFF SIGNIFICANTLY FROM OHARE EAST TO THE

LAKE. THINGS WILL WIND DOWN CONSIDERABLY THROUGH THE AFTERNOON

FROM WEST TO EAST...THOUGH STILL SOME LIGHT SNOW ONGOING.

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LOT...

SHORT TERM FOCUS IS ON UPCOMING HEAVY SNOW EVENT TONIGHT INTO

SATURDAY...AND THEN ON VERY COLD CONDITIONS SATURDAY NIGHT.

FIRST OFF...THE CHANGES TO FORECAST ARE AS FOLLOWS...

1) IT APPEARS THAT THE SWATH OF HEAVY SNOW LOOKS TO BE A BIT MORE

BROADLY FOCUSED...AND ALSO SLIGHTLY FARTHER SOUTH THAN IN

PREVIOUS FORECAST AND 2) HAVE INCLUDED WILL COUNTY IN THE WINTER

STORM WARNING...MAINLY FOR NORTHERN PORTIONS.

FOR THE DETAILS...

A BAND OF HEAVY SNOW HAS SET UP ACROSS PORTIONS OF SOUTH

DAKOTA AND IOWA THIS AFTERNOON AHEAD OF OUR INCOMING SYSTEM. THIS

REGION IS IN A FOCUS AREA OF 850-700 MB FRONTOGENESIS THAT HAS

ORGANIZED OVER A NARROW SWATH. SATURATION AND COOLING FROM THE TOP

DOWN HAS RESULTED IN A QUICK MOISTENING OF THE LOWER LEVELS IN

IOWA WHERE DEWPOINTS QUICKLY JUMP FROM THE LOW TEENS TO THE MID

20S. THIS PROCESS WILL OCCUR IN OUR AREA TONIGHT...BUT RIGHT NOW

IT IS VERY DRY.

THE MESOSCALE PROCESS GOING ON IN IOWA IS NOT WHAT IS EXPECTED TO

BRING OUR AREA-WIDE HEAVY SNOWFALL...BUT A PORTION OF THIS

ELEVATED FGEN AXIS WILL SLIDE INTO NORTHERN ILLINOIS THIS EVENING

AND TONIGHT AND LEAD TO A BAND OF SNOW ACROSS THE NORTHERN TIER

INITIALLY. THE STRENGTH OF THE FGEN ALONG THE 700 MB BAROCLINIC

ZONE IS SOMEWHAT TRANSIENT AND DOES NOT LOOK TO BE AS STRONG AS IT

IS IN IOWA. UPSTREAM OBSERVATIONS HAVE ALSO SHOWN A VERY SHORT

PERIOD OF RAIN/SLEET THAN VERY QUICKLY CHANGING TO SNOW IF NOT

GOING RIGHT TO SNOW ONCE THE ATMOSPHERE SATURATES.

THEN TONIGHT INTO SATURDAY MORNING...THEN THE SURFACE LOW WILL

PASS FROM SOUTH OF ST LOUIS BAY DAYBREAK SATURDAY...THEN TO SOUTH

OF FORT WAYNE BY MIDDAY. THIS WILL ALLOW THE BAROCLINIC ZONE TO

PIVOT OVER THE AREA. THIS COMBINED WITH VERY STRONG Q-VECTOR

FORCING FROM THE UPPER WAVE CONTINUES TO SUGGEST A PERIOD OF VERY

MODERATE TO VERY HEAVY SNOWFALL OVERNIGHT INTO SATURDAY MORNING.

ENSEMBLE GUIDANCE FROM THE GEFS/SREF CONTINUE TO PAINT A PICTURE

OF A WEST-EAST ORIENTED SWATH OF HEAVY SNOW WHICH WILL FOCUS FROM

LEE/OGLE/NORTHERN LASALLE COUNTIES EASTWARD TO DEKALB/KANE/WESTERN

DUPAGE COUNTIES. THE FGEN BANDING POTENTIAL COULD STRENGTHEN INTO

THE MORNING AS COLDER AIR STARTS TO WRAP INTO NORTHWEST ILLINOIS.

THE BIGGEST QUESTION MARK THEN BECOMES HOW MUCH DOES THE WARM

PAVEMENT LIMIT THE ACCUMS...AND WHERE THIS CUTOFF OCCURS...WHICH

CREATES SOME FORECAST UNCERTAINTY AS TO WHERE THIS SHARP

GRADIENT OCCURS IN COOK COUNTY. QPF NUMBERS ARE CONSISTENT AND

HIGH...AND SUPPORT HEAVY SNOWFALL EVEN INTO CHICAGO...BUT EXPECT

ACCUM RATES WILL DROP OFF SIGNIFICANTLY FROM OHARE EAST TO THE

LAKE. THINGS WILL WIND DOWN CONSIDERABLY THROUGH THE AFTERNOON

FROM WEST TO EAST...THOUGH STILL SOME LIGHT SNOW ONGOING.

 

Good write-up.

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Fabert updates his graphic, going with 2-3", that's a pretty bold call for him, given the circumstances. Let's see what happens.

Poor alek didn't want anymore snow, now he staring down the barrel of a top 5 November snowstorm :lol:

 

ILX going with none for I-72.... a inch for bloomington and 1-3 north of that....yikes! most models have that entire area in a 2-6" band

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Snow just started here about 5 minutes ago.  With the exception of a few trees in my neighborhood, all of the trees are bare.  Did not start as rain, just snow.  Temp at 32F.

 

 

Most trees around here are bare/nearly bare, but I actually have one that has almost a full amount of leaves.  Not sure how it will fare.

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ILX going with none for I-72.... a inch for bloomington and 1-3 north of that....yikes! most models have that entire area in a 2-6" band

I'm going to be happy if I just see some flakes here. Not expected anything to stick in Springfield. Good luck to everyone else. Also, first post. Hi everyone!

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The drive to ORD at 5am should be fun....thankfully there will not be anyone out.

 

It has widespread 2-3" across Chicagoland by 11z except for the immediate lakefront and a few 4" spots in Lake/McHenry 

 

attachicon.gifhrrr_ref_chicago_16.png

I don't buy the rain it is showing here, it is 44/14 here with the dew point ticking down a bit in the last hour. We are going to be closer to freezing than these NW models NAM/NAM4/HRRR are thinking.

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DTX harps on the "mainly grassy areas" accumulation factor a bunch in their forecast, which may explain the high end advisory as opposed to a watch. That and the still relatively uncertain location of the pivot point.

I think it is a bad move, low end warning criteria, first storm of the year, high impact/short duration. The other issue is the secondary band that forms and moves over Detroit that all models are honing in on, that won't affect GRR's CWA outside of a couple counties, so DTX should have gone warning while GRR went advisory even if it looked silly.

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