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Chicago Storm

April 24-30th Severe Potential

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Guys, FYI, there's really nothing that shows a sudden increase in skill when a trough in question comes onshore. The discussion of sampling really doesn't have much significance

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The noticeable VBV in the 18Z GFS at 00Z-- mainly in KS-- would be kind of concerning for storm mode. From 18Z GFS at 7pm tuesday @ICT. One thing I did find cool with this sounding was the SARS having both the 7pm OUN 1999/5/3 sounding, and ICT 8pm 1999/5/3 sounding.

post-7962-0-17441300-1461371400_thumb.pn

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I am almost always a lurker but I wanted to comment about the false notion that there is a dramatic change once the trough comes ashore. It has been discussed many times in the Mid-Atlantic forum but to recap DTK's statement on this topic is that both the North and Southern Hemisphere have very similar model verification even though the southern hemisphere has less upper air samplings and observations in general. So I wouldn't expect a sudden increase in skill on Monday.

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The noticeable VBV in the 18Z GFS at 00Z-- mainly in KS-- would be kind of concerning for storm mode.

 

The trough is getting too amplified on this run of the GFS (also to do with the ridge out ahead shortening the wavelengths) and encouraging more meridional flow at 500 mb. The Euro and CMC (and the UKmet from what I've seen of it) do not have this as an issue. Note that the bulk shear values are pretty unimpressive too. The Euro had 50-65 kts of 0-6 km shear across the dryline in OK at 00z, whereas the 12z/18z GFS barely had/has 40 kts.

 

Probably worth noting that the GFS' 500 mb mid-range verification recently has been pretty abysmal (Sam AKA OKpowdah was mentioning earlier on Twitter that the CMC even has been outperforming it in this department). Something closer to the Euro or especially the CMC at 500 mb has higher end risk written all over it for pretty much the length of the dryline.

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The noticeable VBV in the 18Z GFS at 00Z-- mainly in KS-- would be kind of concerning for storm mode. From 18Z GFS at 7pm tuesday @ICT. One thing I did find cool with this sounding was the SARS having both the 7pm OUN 1999/5/3 sounding, and ICT 8pm 1999/5/3 sounding.

Excellent length and curve to the hodograph until you get to that somewhat subtle backing so hopefully that wouldn't cause a significant issue in storm mode if something closer to the GFS verifies.

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The 0z NAM increased shear over the dryline on Sunday, now 50-55kts. Clicking soundings and you're getting say a 77/64 environment at 0z that evening with CI occuring in a fairly nice environment favorable for a slow moving ESE big boy or two with increasing tornado potential as LCL's lower even more + the LLJ ramping up nicely after 0z. 

 

Doesn't scream something big but I love these nice little sleeper looking days from a chasing standpoint. I'd definitely be chasing if I lived in the area.

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I know nam isn't in its good range yet but it goes out to 12z Tues. Has the trough at a neutral tilt and seems to have a euro'ish SFC low position. But only can take that with a grain of salt. If it waits to go negative tilt longer that could delay upper jet from reaching the best thermodynamics.

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Sunday looking pretty decent if a supercell can initiate over north-central Oklahoma. Nice directional shear, leading to a nice'ish hodograph, and moderate instability. Even if a storm does form and does not produce a tornado, it would have pretty incredible structure. 

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The 0z NAM increased shear over the dryline on Sunday, now 50-55kts.

 

GFS getting up to near 50 kts. Good deep layer moisture and a lot of turning in the lowest 2 km. Fairly breakable cap from Central OK northward to the KS/OK border.

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I am almost always a lurker but I wanted to comment about the false notion that there is a dramatic change once the trough comes ashore. It has been discussed many times in the Mid-Atlantic forum but to recap DTK's statement on this topic is that both the North and Southern Hemisphere have very similar model verification even though the southern hemisphere has less upper air samplings and observations in general. So I wouldn't expect a sudden increase in skill on Monday.

 

Yeah, I've seen dtk mention that more than once. He also mentioned that the special soundings that were ordered in advance of the east coast blizzard had little if any significant impact on the forecast. I have to be honest, I can't remember the last time I've seen a material change in the location of the height and wind fields immediately after the upper air stations sampled a wave. I'm sure it's happened, but not frequently enough for me to notice anyway. There's just so many sources of data now including aircraft soundings which I've been reading are being equipped with instruments that are as good as or even superior to the RAOBs in many cases. 

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Well, there's your poor run to run consistency for the GFS for Tuesday. Very high amplitude compared to basically everything else, although the triple point still looks quite favorable.

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Well, there's your poor run to run consistency for the GFS for Tuesday. Very high amplitude compared to basically everything else, although the triple point still looks quite favorable.

Deep-Layer Shear on the 00Z GFS is non-existent, or may as well not exist, being only ~30kts across the main threat area at 00Z.

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Fully agree with OKpowdah, andy, and others regarding the overhyping of "wait for it to come onshore." With today's data assimilation systems, it isn't going to make a big difference.

 

Watching the 00z GFS come in for Tuesday - my biggest concern remains the increasingly meridional nature of the upper flow on the east side of the low. The two main issues this presents are (1) VBV, and/or (2) the possibility that storm-relative flow in the upper levels is quite weak. But no setup is going to look perfect from 96 hours out. Now that the consensus seems to be shifting away from the progressive idea of ejecting the wave way early in the day, this is still the most ominous I-35 event modeled at this stage since 14 April 2012. I'd say the caveats for Tuesday don't look any worse right now than they did four days before that.

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Meanwhile the GFS goes and tries to show perhaps the best W KS setup since 2008 on Friday.

No joke... Sounding is from around DDC at 7pm on Friday. Saturday also continuing to look impressive.

post-7962-0-49883000-1461386225_thumb.pn

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Deep-Layer Shear on the 00Z GFS is non-existent, or may as well not exist, being only ~30kts across the main threat area at 00Z.

 

The GFS is probably underestimating the backing of surface winds, which would have a significant impact in this regard. With 40-60 kt flow at H5 overspreading the dryline and adjacent warm sector as depicted on this run, I strongly doubt bulk shear would be 30 kt. Even so, the kinematic profiles above H5 on this run are certainly less than ideal for an historic outbreak.

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It looks like the mid level jet streak might be better positioned across the warm sector on Wednesday. I can find some interesting soundings for Wednesday as well...at least according to the 0Z GFS.

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Fully agree with OKpowdah, andy, and others regarding the overhyping of "wait for it to come onshore." With today's data assimilation systems, it isn't going to make a big difference.

 

Watching the 00z GFS come in for Tuesday - my biggest concern remains the increasingly meridional nature of the upper flow on the east side of the low. The two main issues this presents are (1) VBV, and/or (2) the possibility that storm-relative flow in the upper levels is quite weak. But no setup is going to look perfect from 96 hours out. Now that the consensus seems to be shifting away from the progressive idea of ejecting the wave way early in the day, this is still the most ominous I-35 event modeled at this stage since 14 April 2012. I'd say the caveats for Tuesday don't look any worse right now than they did four days before that.

Personally I do not remember there being very many problems whatsoever with 4/14/12 four days in advance, even looking back at the thread, nobody seemed to see any potential issues with anything relating to the setup. Then it went on the next day to be a D3 MDT.

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The GFS is probably underestimating the backing of surface winds, which would have a significant impact in this regard. With 40-60 kt flow at H5 overspreading the dryline and adjacent warm sector as depicted on this run, I strongly doubt bulk shear would be 30 kt. Even so, the kinematic profiles above H5 on this run are certainly less than ideal for an historic outbreak.

 

I have to wonder if it is mixing the dryline too far E (as it very, very often does) on Tuesday. That would mean you might still get better mid/upper level winds overlapping it on Tuesday if it was closer to the TX/OK border.

 

That's also partly a symptom of it not seeing the ageostrophic/isallobaric low level response very well.

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Yeah, I've seen dtk mention that more than once. He also mentioned that the special soundings that were ordered in advance of the east coast blizzard had little if any significant impact on the forecast. I have to be honest, I can't remember the last time I've seen a material change in the location of the height and wind fields immediately after the upper air stations sampled a wave. I'm sure it's happened, but not frequently enough for me to notice anyway. There's just so many sources of data now including aircraft soundings which I've been reading are being equipped with instruments that are as good as or even superior to the RAOBs in many cases. 

Yeah I cant remember either it probably does happen but for synoptic scale features its more subtle like a small change in the tilt of the trough rather than a dramatic shift from the run before its better sampled to the after like a lot of people expect. I feel like this idea that extra soundings or sampling will drastically increase model skill comes from the past when less data was assimilated and adding a few extra RAOBs did actually increase skill. As you said there is so much data from many different sources especially aircraft and satellites its hard to get dramatic changes that aren't in the long range which is good. Model verification at medium range is really amazing and really shows how much NWP has improved over the last decade. 

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..THERE IS A SLGT RISK OF SVR TSTMS FROM WESTERN IA  
PARTS OF  
EASTERN NEB AND NORTHWEST MO THROUGH EASTERN KS TO NORTH-CENTRAL  
OK...  
 
...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLGT RISK AREA  
FROM EASTERN SD AND SOUTHERN MN INTO A SMALL PART OF ADJACENT WI TO  
WESTERN AND CENTRAL OK...  
   
..SUMMARY
 
 
STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE SUNDAY AFTERNOON AND  
EVENING ACROSS PARTS OF OKLAHOMA AND EASTERN KANSAS INTO THE MIDDLE  
MISSOURI VALLEY TO SOUTHERN MINNESOTA.  
   
..SYNOPSIS
 
 
A MID- TO UPPER-LEVEL TROUGH...CURRENTLY MOVING INTO THE WESTERN  
STATES PER WATER-VAPOR IMAGERY...IS EXPECTED TO REACH THE HIGH  
PLAINS FROM EASTERN WY TO EASTERN NM BY 12Z SUNDAY. A CLOSED LOW AT  
THE NORTHERN PORTION OF THIS TROUGH WILL MOVE SLOWLY TO THE EAST  
FROM WY INTO SD/NEB...WHILE THE SOUTHWARD-EXTENDING SHORTWAVE TROUGH  
LOSES AMPLITUDE TRACKING ACROSS THE CENTRAL PLAINS TO THE MID MS  
VALLEY. A COMPACT CLOSED LOW/SHORTWAVE TROUGH MOVING ACROSS  
SOUTHERN BAJA FRIDAY EVENING IS EXPECTED TO PROGRESS EASTWARD  
THROUGH SOUTH TX SUNDAY MORNING AND THEN ACROSS THE NORTHWEST GULF  
OF MEXICO. MEANWHILE...THE NEXT UPSTREAM PACIFIC TROUGH WILL MOVE  
INLAND AND AMPLIFY ACROSS THE WESTERN STATES SUNDAY AND SUNDAY  
NIGHT.  
 
AT THE SURFACE...AN AREA OF LOW PRESSURE ATTENDANT TO THE WY CLOSED  
LOW WILL GRADUALLY WEAKEN AS IT TRACKS ACROSS SD INTO SOUTHWEST MN  
BY 12Z MONDAY ALONG A QUASISTATIONARY BOUNDARY. MODELS DIFFER SOME  
WITH THE PLACEMENT OF THIS BOUNDARY...THOUGH GENERAL AGREEMENT  
SUGGESTS IT SHOULD EXTEND FROM EAST-CENTRAL SD THROUGH SOUTHERN MN  
TO CENTRAL WI AND CENTRAL LOWER MI. IN ADDITION TO THE LIKELIHOOD  
FOR CONVECTIVE DEVELOPMENT IN VICINITY OF THE AFOREMENTIONED  
WEST-EAST ORIENTED BOUNDARY...STRONG TO SEVERE STORMS WILL BE MORE  
LIKELY ALONG AND EAST OF A DRY LINE EXTENDING SOUTHWARD THROUGH  
EASTERN NEB...CENTRAL KS TO WRN OK/TX PANHANDLE BORDER TO TX BIG  
BEND BY MID AFTERNOON SUNDAY.  
 
...PORTIONS OF SOUTHERN/CENTRAL PLAINS TO MID MO VALLEY AND SOUTHERN  
MN...  
THE PRESENCE OF LOW-LEVEL OFFSHORE FLOW INTO THE GULF OF MEXICO AS A  
LARGE AREA OF HIGH PRESSURE ADVANCES ACROSS THE EASTERN U.S. TODAY  
INTO SUNDAY WILL RESULT IN A RELATIVELY NARROW PLUME OF MOISTURE  
RETURN ACROSS THE WARM SECTOR ON SUNDAY. SOUTHERLY LOW-LEVEL WINDS  
LOCATED EAST OF THE DRY LINE WILL TRANSPORT SURFACE DEW POINTS IN  
THE MID-UPPER 50S INTO PARTS OF SOUTHERN MN AND SOUTHWEST WI...WHILE  
VALUES NEAR 60 F SHOULD EXTEND INTO WESTERN/CENTRAL OK BY LATE  
SUNDAY AFTERNOON. STEEP MIDLEVEL LAPSE RATES EXPECTED TO BE ALREADY  
PRESENT ACROSS THE CATEGORY 1 AND 2 SEVERE RISK AREAS AT 12Z SUNDAY  
COMBINED WITH THE POLEWARD MOISTENING AND SURFACE HEATING WILL  
RESULT IN MODERATE INSTABILITY.  
 
SHOWERS AND THUNDERSTORMS SHOULD BE ONGOING AT 12Z SUNDAY NEAR AND  
NORTH OF THE SURFACE LOW AND QUASISTATIONARY BOUNDARY...WITHIN  
STRONG LOW-LEVEL WARM ADVECTION AND WEAK HEIGHT FALLS AHEAD OF THE  
HIGH PLAINS TROUGH. CLOUDINESS ATTENDANT TO THIS ACTIVITY MAY LIMIT  
DESTABILIZATION WITH NORTHWARD EXTENT ACROSS EASTERN SD TO  
WEST-CENTRAL/SOUTHWEST WI...WITH A LOWER PROBABILITY FOR STRONG TO  
SEVERE STORMS SUNDAY AFTERNOON AND EVENING.  
 
A GREATER LIKELIHOOD FOR STRONG TO SEVERE STORMS WILL BE FOUND  
ACROSS THE SLIGHT RISK AREA...WHERE MODERATE INSTABILITY COMBINED  
WITH VERTICALLY VEERING WINDS /INCLUDING 50-60-KT SOUTHWESTERLY  
500-MB WINDS/ WILL RESULT IN STRONG TO SEVERE STORM DEVELOPMENT  
SUNDAY AFTERNOON. EFFECTIVE BULK SHEAR OF 35-45 KT WITH AN  
ORTHOGONAL ORIENTATION TO THE DRY LINE SUGGESTS DISCRETE SUPERCELLS  
CAN BE EXPECTED WITH ALL SEVERE HAZARDS.
WEAKER TO NEUTRAL HEIGHT  
FALLS INTO OK MAY TEND TO LIMIT THE COVERAGE OF STORMS. 

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12Z NAM likes the Triple point and warm front at 84 hours for having the best environment.

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12Z NAM coming in now, at 7pm LI's just to the west of I35 corridor are -10 to -14.  There are still some differences between upper air features and surface features that are a bit concerning.  

Triple point is looking pretty potent up in central KS as well.

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NAM would keep highest tornado threat over the triple point, SC/C KS, and C OK along the dryline. Trough is a bit slow still.

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NAM with 5k CAPE. Probably overdoing CAPE a bit though, with pockets of 70+ DP's. Sharp DL though, which I like.

b65e841683b0e535c9fc217ef0254e98.jpg

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