April 27-29 Severe Threat

[Stebo]

I thought I heard that the area around the bootheel is ok but don't quote me on that.

It is, from Poplar Bluff to Cape Girardeau to New Madrid, that triangle i mostly farms and flat.

[Thunder Road]

Monday on the NAM in central/southern IL looks very interesting.

Sups and tors if that verifies.

 

Yeah, 3000 J/kg CAPE with that kind of VWP could be big.  

 

You can see at 18z Mon the NAM has the SLP in NW Iowa, whereas the GFS has it way back near Pierre, SD.  At 500 mb, the cutoff Low off the Northeast coast isn't as deep on the NAM (looks like a 3-4 dam difference), so heights between it and our system don't build as much (the 570 dam contour is particularly useful in this case), and hence, the 500 mb center gets farther east before the surface Low starts occluding.

 

It's the extended range NAM so my first inclination is to just toss it.  But it could happen though.  A 3-4 dam difference over the ocean 78 hours out really isn't all that significant when you think about it...

[cyclone77]

Really not much new to add to all of the above.  18z GFS gets the cape up over 2000j/kg around the St. Louis area Monday afternoon.  Southeast MO and southern IL are looking pretty jacked if destabilization takes place as well as advertised.

[Thunder Road]

0z NAM was a weiner deflater

 

Still though, it's only the NAM

[Hoosier]

Main forum thread:

 

http://www.americanwx.com/bb/index.php/topic/43501-april-26th-29th-significant-severe-potential/

 

 

Going to leave this one here for localized chatter/questions but the bulk of the discussion should go in the thread in the main forum.

[ilstormchaser]

I am keeping a close eye on far Western Illinois for early tomorrow afternoon near the warm front. The NAM has been consistent with likely supercell development over that general area the last several runs. I am liking the I-72 corridor near Quincy. This might be a nice "sleeper" area for tomorrow that chasers are overlooking. 

[Thunder Road]

I'm going to keep posting here since I'm only concerned with central IL for chasing purposes, and leave the main thread for discussion by the more-knowledgeable-than-me folk

 

AFDs time.  LOT:

THE OTHER MORE SIGNIFICANT CONCERN WOULD BE FOR A BETTER POTENTIAL
FOR MORE ROBUST SURFACE BASED CONVECTIVE ACTIVITY MONDAY AFTERNOON
AND EVENING...PARTICULARLY ACROSS THE SOUTHERN HALF OF MY AREA.
GUIDANCE INDICATES THAT A PIECE OF MID LEVEL ENERGY WILL ROTATE
NORTHEASTWARD ACROSS THE MID MISSISSIPPI VALLEY...ALONG THE EASTERN
PERIPHERY OF THE MID/UPPER LEVEL VORTEX. THIS LOOKS TO INTERACT WITH
THE MOIST UNSTABLE ATMOSPHERE TO THE SOUTH OF THE WARM
FRONT...LEADING TO ANOTHER PERIOD OF CONVECTIVE ACTIVITY MONDAY
AFTERNOON AND EVENING...AND THESE STORMS COULD BE STRONG TO
SEVERE...ESPECIALLY WITHIN AND NEAR THE WARM SECTOR...WHICH COULD
INCLUDE MY SOUTHERN AREAS SOUTH OF INTERSTATE 80. THIS POSSIBILITY
WILL NEED TO BE MONITORED.

ILX:

Monday there should be convection ongoing early in the morning,
but then a break in the convection from late morning-early
afternoon could result in rapidly increasing instability by late
after non. Strong wind shear - especially east of I-55, will be
favorable for another round of strong to severe storms from Monday
afternoon through early Monday night. The best parameters for
severe storms are south of a SPI-MTO-Paris line Monday. The
tornado parameters are not clear cut on the models at this time,
but the threat can not be ruled out, especially in southeast IL.

[IWXwx]

 

I'm going to keep posting here since I'm only concerned with central IL for chasing purposes, and leave the main thread for discussion by the more-knowledgeable-than-me folk

 

 

 

Keep us "locals" posted here if you decided to chase and hopefully cyclone will post here too as well as the main thread.

[RCNYILWX]

I'm going to eastern KS/W MO tomorrow/later today and might chase again on Monday if I'm not called into work. The 00z 4km NAM was very interesting all the way up to I-80 in IL and IN.

[Stebo]

I'm going to eastern KS/W MO tomorrow/later today and might chase again on Monday if I'm not called into work. The 00z 4km NAM was very interesting all the way up to I-80 in IL and IN.

30 probs for Northern IL on the new Day 2 with mention of tornadoes. Looks pretty impressive up that way along the warm front.

[Thunder Road]

NAM and GFS today have both trended farther north with the warm front, putting Chicago (or at least its southern burbs) in the warm sector.  Climo suggests the front will hang up around I-80, especially due to the lake, but let's see.

 

My two concerns about Monday in central IL are:

 

1) relatively weak 850-700 mb winds (possibly as low as 25 kts by 0z)

2) backing aloft, generally above 500 mb, but the farther north you go the messier the wind profile gets.  There are places close to the WF that are literally a VBVBV, if there even is such a thing.

 

That said, this still looks like a set-up with a lot of chase potential, and the relatively clear warm sector and high-but-not-too-high bases (both by Midwest standards anyway) are very enticing.

[Hoosier]

NAM and GFS today have both trended farther north with the warm front, putting Chicago (or at least its southern burbs) in the warm sector.  Climo suggests the front will hang up around I-80, especially due to the lake, but let's see.

 

My two concerns about Monday in central IL are:

 

1) relatively weak 850-700 mb winds (possibly as low as 25 kts by 0z)

2) backing aloft, generally above 500 mb, but the farther north you go the messier the wind profile gets.  There are places close to the WF that are literally a VBVBV, if there even is such a thing.

 

That said, this still looks like a set-up with a lot of chase potential, and the relatively clear warm sector and high-but-not-too-high bases (both by Midwest standards anyway) are very enticing.

 

 

Some concerns as you said but potential is there.  I'll be interested to see how prolific the IA/NE is on Sunday as a similar environment may occur downstream on Monday, albeit with less shear.

[Brewers]

Contemplating whether I want to head down to Illinois on Monday since I don't work. Might be riding solo since my chaser partner is not as lucky.

[Thunder Road]

I mean, who wouldn't love this hodo?

 

 

(NW of Peoria at 18z Mon)

 

 

Before the SPC Day 2 came out I was liking Champaign-Effingham, but now they have my curiosity piqued by the placement of their 30%.  Still though, with hodos like that farther north, I'm not ready to jump on the SPC bandwagon just yet.

[Thunder Road]

Morning AFDs

 

ILX:

SHORT TERM...Today and tomorrow...
Severe weather potential on both days though tomorrow looks like
more of an effective widespread threat. For today, low still out
to the SW...and cold front that has passed through the region will
get disintegrated and slowly overtaken by developing warm frontal
feature to the south. Mid level front already showing more
distinctive in the 00z soundings for the region. Extent of high
temperatures will depend greatly on position of developing surface
boundary. Still some discrepancies about how far north the warm
temps will get, though most of central Illinois forecast to get
into the 70s with plenty of shower and thunderstorm activity as
the deepening trof pushes plenty of energy out over the region.
Best activity for this afternoon in the south/southwestern
portions of ILX CWA, but dependent highly on location of front
when the afternoon heating maximizes. Though the instability may
be less than tomorrow...and the shear is directional but
weak...the boundary in place and pockets of dry air in the mid
levels upstream will keep the threat for severe winds and isolated
tornadoes. Tomorrow, however, most of the FA is in the warm
sector with increasingly southerly component to the sfc winds.
Temps warming in concert with increased RH from todays
rain...resulting in incredibly unstable air in place prior to the
cold fropa in the afternoon. Deep shear limited in forecast
soundings, and 0-3km helicity in the 100-150 m2/s2 range by noon.
All of that being said, the dry air threat out there, and
mesoscale shifts in the region just all point to a troublesome
atmosphere. Too much in flux...with a very unstable airmass.
Severe threat for Monday a bit more concerning for severe winds,
and tornadic threat for the afternoon hours with the dryline
interaction with 3000-4000 J/kg CAPE.

LOT:

MONDAY...
MORNING RAIN AND EMBEDDED CONVECTION IS LIKELY WHICH IS EXPECTED TO
SHIFT NORTHWARD. THE SURFACE LOW ON A COMPOSITE OF THE NAM/GFS/EC
IS 988MB NOT FAR WEST OF OMAHA BY MID-AFTERNOON. THE SURFACE WARM
FRONT ON ALL THESE GUIDANCE MEMBERS IS EXPECTED TO BE MOVING
NORTHWARD INTO THE SOUTHERN FORECAST AREA DURING THE DAY MONDAY
AND LIKELY DIABATICALLY ENHANCED WITH THE CLOUDS/RAIN NORTH OF
THIS FEATURE. THIS LOOKS TO BE A POTENTIAL RIPE FOCUS FOR SEVERE
CONVECTION AS THE NEXT MID-LEVEL SPEED MAX ROTATES OVER EASTERN
IA/MO/CTRL AND NRN IL DURING MONDAY AFTERNOON INTO EVENING. MODEL
WIND AND INSTABILITY PROFILES ARE CERTAINLY SUPPORTIVE OF
SUPERCELLS GIVEN THE WARM FRONT PLACEMENT. THE POTENTIAL WOULD
EXIST FOR TORNADOES AND LARGE HAIL WITH THESE STORMS IF THEY CAN
DEVELOP. THERE OBVIOUSLY IS QUITE A BIT OF CONVECTION EXPECTED
WITH THIS SYSTEM THROUGH THE NEXT 24-30 HOURS AND THAT WILL
INFLUENCE MODEL SOLUTIONS GREATLY GIVEN THE MASSIVE AMOUNTS OF
LATENT HEAT RELEASE THE MODELS ARE DEPICTING AND PROPAGATING THE
OVER THESE UPCOMING PERIODS. SO WHILE HAVE NOT GOT TOO PRECISE WITH
THE WARM FRONT DEPICTION IN THE FORECAST...CONTINUE TO TIGHTEN THE
TEMPERATURE GRADIENT WITH UPPER 40S/LOWER 50S FORECAST ALONG PARTS
OF THE NORTHEAST IL LAKE SHORE...TO NEAR 80 IN THE SOUTHERN
FORECAST AREA...THOUGH LIKELY AM NOT TIGHT ENOUGH WITH THIS
AND IT WILL FURTHER BE REFINED AS CONFIDENCE ON EXACT PLACEMENT
GROWS. ALSO HAVE ADDED TEMPORAL RESOLUTION TO POPS TO INDICATE
MORNING AND LATE AFTERNOON/EVE BEING THE BEST TIMES. CIPS BEST
ANALOG MATCHES FOR THIS SOMEWHAT ATYPICAL SYNOPTIC SETUP THIS TIME
OF YEAR DO INDICATE SEVERE WEATHER POTENTIAL WITH A HANDFUL OF
TORNADOES ACROSS NW/NC/CTRL IL. WILL HIGHLIGHT FURTHER IN THE
HWO.

[Brewers]

While the weak wind profiles had worried me all along, the 12z NAM is concerning, 0-6km shear is only 20-25kts at best and not to mention hodos are a mess. Obviously going to wait until the rest of the 12z data, but I might sit this one out.

[RCNYILWX]

Decided to call off chasing out in western MO today so now hoping to go tomorrow in IL if I'm not called into work. The wind profile is very veer-back-veer but if it can improve a bit, won't need the entire hodo to be perfect since any sups that can form would likely be low topped. The proximity to the warm front would enhance low level helicity and also the 6z NAM was showing absolutely extreme values of 0-3 km CAPE over the 30% area on the order of 200-500 j/kg.

Hadn't looked at the 12z NAM but if deep shear values verify that low, that would make tomorrow a no go in terms of chasing likely.

[Brewers]

Decided to call off chasing out in western MO today so now hoping to go tomorrow in IL if I'm not called into work. The wind profile is very veer-back-veer but if it can improve a bit, won't need the entire hodo to be perfect since any sups that can form would likely be low topped. The proximity to the warm front would enhance low level helicity and also the 6z NAM was showing absolutely extreme values of 0-3 km CAPE over the 30% area on the order of 200-500 j/kg.

Hadn't looked at the 12z NAM but if deep shear values verify that low, that would make tomorrow a no go in terms of chasing likely.

 

These cold core lows usually entice me, since you can generally get something decent out of what seems like marginal conditions. You seemed a bit more optimistic, although I'm not quite sure anymore...

[Hoosier]

Wind profile a little messy but nice turning in the low levels.  This might work.

 

 

[RCNYILWX]

Wind profile a little messy but nice turning in the low levels. This might work.

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That's a very nice sounding for low topped supercell tor potential. The good low level turning you noted plus substantial 0-3 km CAPE and low LCL heights.

Starting to think that IN might be a better play tomorrow near the warm front because while wind profiles are still a bit messy the midlevel jet punches into central IN creating more favorable deep layer shear.

[Hoosier]

That's a very nice sounding for low topped supercell tor potential. The good low level turning you noted plus substantial 0-3 km CAPE and low LCL heights.

Starting to think that IN might be a better play tomorrow near the warm front because while wind profiles are still a bit messy the midlevel jet punches into central IN creating more favorable deep layer shear.

 

 

SREF sigtor ingredients have had higher probs in E IL and IN tomorrow, possibly due to the better shear. 

[RCNYILWX]

SREF sigtor ingredients have had higher probs in E IL and IN tomorrow, possibly due to the better shear.

That would make sense because the deep layer shear is pretty marginal back farther west. Low level shear and helicity magnitude was also good on the sounding you posted. Interested to read how SPC handles the new D2 in a few minutes given the trends today.

[Brewers]

Highest probs remain in the same locations for the new day 2 outlook, however they added a hatched area as well.

[RCNYILWX]

Highest probs remain in the same locations for the new day 2 outlook, however they added a hatched area as well.

They did expand the 30% east a bit into IN if I'm not mistaken. But overall no big changes aside from adding the hatched area.

[Thunder Road]

Highest probs remain in the same locations for the new day 2 outlook, however they added a hatched area as well.

 

The 30% was (rightfully so) pulled southeastward a bit.

 

I'm still not sure how much I agree with how far NW it goes.  We'll see what the people in charge of chasing want to do, but if I had to take a stab at it, I'd head for Champaign/Urbana by 19z or so.  Nice set of roads emanating outward from there to head any direction.

[Brewers]

Yup, you guys are correct with the eastward shift into Indiana. Regardless of the better parameters shifting to the E, I might test my luck farther NW, over NC IL, since I really don't feel like driving through Chicago.

[Thunder Road]

NMM/ARW and SPC WRF all have decent convection coverage, but all are struggling to pop off anything discrete.  Just a big complex rolling through N IL.

[Thunder Road]

15z SREF.  Slight bump up in STI, I think:

 

 

 

 

Edit:  Better representation in the STP, which now pops a 2 contour up to ~Peoria, as well as the Supercell Composite, which gets a 3 contour up to I-80 at 18z and Lake Michigan by 21z:

 

http://www.spc.noaa.gov/exper/sref/frames.php?run=latest

[Central Illinois]

ILX on board with severe weather along the dry line starting early afternoon tomorrow

Sent from my SM-G900V using Tapatalk

[Thunder Road]

We're meeting at 7 a.m. to pick a target.  Most of us are thinking Effingham attm.