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April 8-10 Severe threat


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LOT and the posters i respect all sound bullish but this one sure smells like a warm front bust for NE Illinois, especially Chicago proper on north towards Geos. But what do i know and we'll find out soon enough, everything looks dope if things can come together.

 

12z 4km NAM suggesting the warm front doesn't pass Kenosha. 

 

Showing a nice line starting near you.

 

nam4km_ref_ncus_12.png

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Wow the line in Southern Ohio has an RIJ with it and is shaping up nicely. Might be turning into a full fledged derecho

 

I'm downstream from it and I've been keeping my eye on that MCS this morning in Ohio. That thing has turned into a pretty potent line and continues to strengthen as it pushes into more unstable atmosphere. SPC seems to think it'll continue to strengthen through the afternoon as well.

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12z 4km NAM suggesting the warm front doesn't pass Kenosha. 

 

Showing a nice line starting near you.

 

nam4km_ref_ncus_12.png

 

 

How about that one single discrete cell over top of my house though. Way out ahead of everything.  :whistle:

 

Like IWXwx said, the nocturnal event that the NAM has is concerning, to say the least. I would guess a decent chunk of IN will go under enhanced during the 1730z run of the SPC. 

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Here is a little something to excite the Indiana and Michigan posters as you wake up this morning. Discreet convection still ongoing at 03Z on the 06Z 4km NAM. 

attachicon.gifnam4km_ref_uv10m_ncus_15.png

Both NAMs keep that stuff on the cold front discrete into Michigan after dark. That is very concerning especially since the instability gets drawn north and doesn't wane until Midnight.

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We're slowly running out of time for things to go haywire at the synoptic scale to throw a wrench into this event.  I think the synoptic ingredients are now well more than likely to be there for a tornado outbreak across IL/wrn IN/far srn WI tomorrow afternoon and evening.  The mesoscale details, however, are far from settled.  I know there's some concerns about morning convection, and that's valid, but I think the advection of lapse rates into the area will likely lead to rapid and better-than-sufficient destabilization, even if the convection takes awhile to clear out in the morning.  What that convection might aid in doing, however, is leaving the sfc winds backed and low-level veering enhanced by limited boundary layer mixing to a shorter window of the day.

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IZZI update...

 

 

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1140 AM CDT WED APR 8 2015

.UPDATE...
1140 AM CDT

LOW CONFIDENCE IN DETAILING THE TIMING OF BETTER CONVECTIVE
CHANCES THE NEXT 18-24 HOURS...THOUGH AT LEAST PERIODIC BOUTS OF
STRONG TO POSSIBLY SEVERE THUNDERSTORMS APPEAR FAIRLY. STRONG
QUASI-STATIONARY FRONT CURRENTLY RESIDES FROM JUST EAST OF QUINCY
TO NEAR LAFAYETTE LATE THIS MORNING. HAVE SEEN SOME TENDENCY FOR
THE FRONT TO INCH NORTHWARD INTO OUR SOUTHERN CWA TO THE EAST OF A
WEAK SFC LOW BETWEEN SPI/PIA. A WEAKENING/LOOSELY ORGANIZED
STRATIFORM LEADING MCS OVER MISSOURI HAS BEEN SLOWLY PROPAGATING
EASTWARD TOWARD ILLINOIS WITH ITS DENSE CIRRUS SHIELD ALSO
SPREADING EAST AND LIKELY TO SLOW HEATING/DESTABILIZATION ALONG
THE WARM FRONT. MODIFYING ILX SOUNDING FOR CURRENT OBS JUST TO THE
SOUTH OF THE WARM FRONT SUGGESTS CINH IS WEAKENING...THOUGH MOST
LIKELY SCENARIO WOULD SUGGEST THAT THERE WILL BE ENOUGH INHIBITION
TO PREVENT CONVECTION FROM FIRING ON ALONG THE WARM FRONT THIS
AFTERNOON...IF IT DOES DEVELOP SEVERE THREAT WOULD BE VERY REAL
GIVEN THE SHEAR/INSTABILITY. MORE PROBABLE SCENARIO WOULD BE FOR
MO/IA MCS TO RE-INTENSIFY THIS EVENING AS IT MOVES EAST INTO
ILLINOIS LATE THIS AFTERNOON AND THIS EVENING. VERY STEEP MID
LEVEL LAPSE RATES AND RESULTANT ELEVATED INSTABILITY ALONG WITH
STRONG EFFECTIVE SHEAR SUPPORTS A THREAT OF HAIL WITH THE STRONGER
STORMS TONIGHT AND POTENTIALLY WIND DAMAGE SHOULD ORGANIZED COLD
POOL DEVELOP. HEAVY RAINFALL IS ALSO A THREAT GIVEN THE
UNSEASONABLY HIGH PWATS THOUGH DUE TO THE ANTECEDENT DRY
CONDITIONS NOT PLANNING ANY SORT OF HYDRO HEADLINES.

CONFIDENCE REMAINS LOW IN EVOLUTION OF CONVECTION TONIGHT INTO
TOMORROW MORNING WHICH LENDS ITSELF TO UNCERTAINTY AS TO THE
MAGNITUDE OF THE SEVERE WEATHER THREAT THURSDAY AFTERNOON AND
EVENING. MODELS CONTINUE TO SHOW A PLUME OF VERY STEEP MID LEVEL
LAPSE RATES ADVECTING NORTHEAST INTO THE AREA THURSDAY AFTERNOON
AND GIVEN THE STRENGTH OF THE CYCLONE WOULD SUSPECT THE WARM FRONT
WILL BE ABLE TO BLAST NORTH ACROSS THE AREA PLACING MOST OF THE
CWA IN THE WARM SECTOR. ASSUMING THE PLUME OF STEEP LAPSE RATES
ARRIVE AS FORECAST AND ARE NOT DISTURBANCE BY EARLY DAY
CONVECTION AND THAT CONVECTION OR DEBRIS CLOUDINESS DOESNT
CONTAMINATE THE WARM SECTOR...THEN KINEMATIC FIELDS WOULD BE VERY
FAVORABLE FOR SEVERE THUNDERSTORMS...INCLUDING SUPERCELLS
POTENTIALLY WITH TORNADO THREAT. STILL MANY CONVECTIVE AND
MESOSCALE DETAILS TO WORK OUT BUT SYNOPTIC PATTERN CONTINUES TO
LOOK FAVORABLE FOR A POTENTIAL HIGHER END SEVERE EVENT IN THE
REGION LATE THURS AFTERNOON AND EVENING.

IZZI
 

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Just looking more deeply at the 4km NAM for tomorrow, I really do believe if there are storms on the warm front in Michigan they have a very good potential to be tornadic. 0-1km helicity of 300m^2/s^2 with 0-3km helicity of 450m^2/s^2 combine that with over 1500 J/kg SBCAPE along and south of the warm front feeding into the area. It really sets up for a volatile atmosphere.

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We're slowly running out of time for things to go haywire at the synoptic scale to throw a wrench into this event.  I think the synoptic ingredients are now well more than likely to be there for a tornado outbreak across IL/wrn IN/far srn WI tomorrow afternoon and evening.  The mesoscale details, however, are far from settled.  I know there's some concerns about morning convection, and that's valid, but I think the advection of lapse rates into the area will likely lead to rapid and better-than-sufficient destabilization, even if the convection takes awhile to clear out in the morning.  What that convection might aid in doing, however, is leaving the sfc winds backed and low-level veering enhanced by limited boundary layer mixing to a shorter window of the day.

 

 

thanks for dropping by the old 'hood

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I bolded their reasoning for taking out the hatched area:

 

 

...GREAT LAKES/OHIO VALLEY INTO SOUTHEASTERN PLAINS...
   MODEL OUTPUT IS SUGGESTIVE THAT DEEPER/RICHER BOUNDARY LAYER
   MOISTENING MAY BE CONFINED TO A RELATIVELY NARROW CORRIDOR IN
   ADVANCE OF THE COLD FRONT.  AND CONSIDERABLE CONVECTIVE ACTIVITY MAY
   BE ONGOING IN THE WARM SECTOR ACROSS PARTS OF THE MIDDLE MISSISSIPPI
   AND OHIO VALLEYS AT THE OUTSET OF THE PERIOD.  BY 12Z THURSDAY...IT
   ALSO APPEARS THAT THERE MAY BE CONSIDERABLE STABILIZATION OF THE
   BROAD AREA OF STEEP MID-LEVEL LAPSE RATES NOW PRESENT ACROSS THE
   PLAINS INTO THE VICINITY OF THE APPALACHIANS.  THESE FACTORS...AMONG
   OTHERS...MAY BE LIMITING FACTORS TO A POTENTIALLY MORE SUBSTANTIVE
   SEVERE WEATHER RISK FOR THIS PERIOD.

   STILL...GIVEN THE LARGE-SCALE FORCING AND STRENGTH OF DEEP LAYER
   FLOW/SHEAR...INCLUDING A RATHER BROAD AREA OF 40-50 KT SOUTH
   SOUTHWESTERLY 850 MB FLOW DURING THE DAY...THE ENVIRONMENT WILL BE
   CONDUCIVE TO ORGANIZED CONVECTIVE DEVELOPMENT...INCLUDING
   SUPERCELLS.  AND POCKETS OF STRONGER DESTABILIZATION COULD YIELD
   SCATTERED AREAS WITH POTENTIAL FOR INTENSE SUPERCELLS CAPABLE OF
   PRODUCING A STRONG TORNADO OR TWO...IN ADDITION TO VERY LARGE HAIL.
   IT IS POSSIBLE THAT ONE OF THESE AREAS COULD DEVELOP NEAR THE WARM
   FRONT...IN THE VICINITY OF THE SURFACE LOW...ACROSS PARTS OF
   NORTHERN ILLINOIS...INCLUDING THE CHICAGO METRO AREA...
   DURING THE MIDDAY AND AFTERNOON HOURS.  ANOTHER COULD DEVELOP NEAR
   THE COLD FRONT/DRY LINE INTERSECTION...ACROSS PARTS OF THE OZARK
   PLATEAU AND ARKLATEX REGION DURING THE LATE AFTERNOON AND EVENING.
   HOWEVER...TOO MUCH UNCERTAINTY CURRENTLY EXISTS CONCERNING COVERAGE
   AND AREA TO SUPPORT 10 PERCENT SIGNIFICANT SEVERE WEATHER
   PROBABILITIES AT THE PRESENT TIME.

 

Basically what I am gathering is they think there is potential for higher end severe they are just unsure on location at this time. Once the mesoscale details are resolved tomorrow, I think the hatching will be reintroduced.

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I bolded their reasoning for taking out the hatched area:

Basically what I am gathering is they think there is potential for higher end severe they are just unsure on location at this time. Once the mesoscale details are resolved tomorrow, I think the hatching will be reintroduced.

Hatching would have made it a moderate risk, so it makes sense.
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