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Severe Potential: April 22-25, 2015


andyhb

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Anyone have any new thoughts on Friday's setup? I see the 0z NAM does not get more than 1750 CAPE in east OK, also not convecting. I personally just don't believe this solution so much, given the amount of dynamics associated with this storm. It almost wants to point to Wichita, KS being the spot, with higher CAPE values located there and seems to initiate IIRC.

Not real impressed with Friday just yet. I'm still concerned about moisture return among other things. Hopefully the picture will become a little more clear by tomorrow, but it's likely we won't really know how things are going to shake out until Friday morning.

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Anyone have any new thoughts on Friday's setup? I see the 0z NAM does not get more than 1750 CAPE in east OK, also not convecting. I personally just don't believe this solution so much, given the amount of dynamics associated with this storm. It almost wants to point to Wichita, KS being the spot, with higher CAPE values located there and seems to initiate IIRC. 

 

All of the models blow up crapvection in TX very early and block off moisture transport and destabilization to area further north. The most likely areas IMO for interesting stuff on Friday will be on the boundaries of that crapvection (in TX) and the areas furthest from it (in KS). Incidentally that is also where the ENH risk areas are.

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The ceiling is certainly high for east-central to southeastern Kansas, but there are some red flags as well. Crapvection, lackluster instability, storm mode, etc. The dynamics are certainly there. The NAM has a strong LLJ screaming through from after 00z to 03z SAT. 50-60+ knot at 850mb and even 40-45+ knots down to 925mb.

The NAM model reflectivities tend to favor storms firing in central Kansas early in the day and congealing to an MCS toward evening. That could further complicate the "chaseable" tornado potential, but it may be another 18-24 hours before mesoscale details can bring substantial clarity.

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Really like the 18Z NAM depiction of tomorrow, seemingly perfect timing of the strong H5 jet (at least imo), a moderate/strong S/SSW (40-60kts by 00Z) H85 LLJ, LLVL southerly shear of 30-40kts, all on top of backed SFC flow.. Obviously the wind fields are very conducive to severe storms and even tornadoes, some which could be strong/intense, nevertheless all that is juxtaposed to SBCAPE/MUCAPE of 1500-2000J/KG along the DL and even the WF across EC KS. Also, it has begun to show several dryline supercells developing between 21-00Z across SE KS/NE OK (the area with the highest severe/tornado parameters). This run of the NAM seems to have backed off of the idea of a deteremental impact by morning convection imo... Thoughts? Of course this is only one run, but seeing as to how we are with 24-30 hours of the event it seemed like a good step in the right direction, as far as significant SVR potential.

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Great discussion from TOP regarding tomorrow:

LONG TERM

(FRIDAY NIGHT THROUGH THURSDAY)

ISSUED AT 329 PM CDT THU APR 23 2015

FRIDAY AFTERNOON INTO THE OVERNIGHT PRESENTS A COMPLICATED WEATHER SCENARIO WITH A LIKELIHOOD OF SEVERE WEATHER IN THE AREA, AND A POTENTIAL FOR A FEW SIGNIFICANT SEVERE EVENTS.

THE PRIMARY FORECAST QUESTIONS THROUGH THIS PERIOD WILL BE 1) HOW FAR NORTH DOES THE WARM SECTOR SURGE? 2) HOW BROAD EAST/WEST WILL THE UNSTABLE WARM SECTOR BE? 3) HOW MUCH AND HOW SOON WILL THE BOUNDARY LAYER STABILIZE BY MID TO LATE EVENING?

IN TERMS OF THE QUESTIONS ABOVE, VARIOUS MODEL GUIDANCE ARE GENERALLY IN THE SAME BALLPARK REGARDING HOW FAR NORTH THE WARM SECTOR WILL SURGE, BUT THE NORTHERN EDGE OF THE SURFACE BASED INSTABILITY RANGES FROM SOMEWHERE NEAR THE NEBRASKA BORDER (GFS) TO A COUNCIL GROVE TO LAWRENCE LINE (NAM/NMM). THE REST OF GUIDANCE IS IN BETWEEN, AND FRANKLY THE ECMWF RENDITION OF THE SURFACE LOW AND WARM FRONT TRACK LOOKS TO BE QUITE REASONABLE, WITH THE WARM SECTOR COMING AS FAR NORTH AS MINNEAPOLIS TO MANHATTAN TO HOLTON LINE. MOST INDICATIONS ARE ALSO THAT THE WARM SECTOR WILL NOT BE PARTICULARLY BROAD EAST/WEST, AND THIS *MAY* BE ABLE TO LIMIT THE POTENTIAL FOR LONG TRACK SEVERE STORMS A BIT AS THE INDIVIDUAL STORM FORWARD SPEED (40+ MPH) SHOULD BE FASTER THAN THE SYSTEM AS A WHOLE, AND THEY COULD MOVE TOWARD LESS UNSTABLE AIR WITH TIME. IN TERMS OF EVENING STABILIZATION, ALL INDICATIONS POINT TO AN UNSTABLE WARM SECTOR AIRMASS THROUGH APPROXIMATELY 8-11 PM BEFORE BECOMING INCREASINGLY STABLE. THIS IS NOT ENTIRELY FOR SURE AS THE SURFACE LOW WILL TRACK DIRECTLY ACROSS THE AREA AFTER MIDNIGHT, BUT IT DOES SEEM LIKELY THAT CINH WILL INCREASE AND THE TORNADO THREAT DECREASE BY LATE EVENING.

THE RELATIVE CERTAINTIES IN THIS FORECAST ARE FOLLOWING 1) THUNDERSTORMS WILL DEVELOP AND MOVE ACROSS THE FORECAST AREA. 2) WIND SHEAR PARAMETERS ARE VERY IMPRESSIVE AND WILL SUPPORT STORM ORGANIZATION. 3) THE COMBINATION OF STEEP LAPSE RATES AND STRONG SHEAR WILL SUPPORT LARGE HAIL (SOME VERY LARGE) IN STORMS BOTH NORTH AND SOUTH OF THE FRONT.

THE REST OF THE DETAILS ARE FUZZIER BUT IMPORTANT. DAMAGING WIND

POTENTIAL DOES NOT APPEAR TO BE A HUGE THREAT GIVEN LOW LCL HEIGHTS, BUT THE POTENTIAL FOR SOME UPSCALE GROWTH BY MID/LATE EVENING AND VERY STRONG AMBIENT WIND FIELDS SUGGEST THAT A WIND THREAT COULD DEVELOP. THE POTENTIAL FOR TORNADOES IS CONDITIONAL, BUT VERY PRESENT. A WORST CASE SCENARIO WOULD BE IF CELLS CAN REMAIN SEMI-DISCRETE OR MOVE EAST OF THE MAIN CLUSTER OF CONVECTION AS ANY ISOLATED SUPERCELL IN THE WARM SECTOR WOULD HAVE FULL ACCESS TO 30+ KTS OF 0-1 KM WIND SHEAR UNDERNEATH A STRONG MID LEVEL STEERING FLOW (60 KTS AT 500 HPA) AND EXHAUST JET ALOFT (130 KTS AT 250 HPA). THERE WOULD SEEM TO BE A PRIMARY WINDOW OF OPPORTUNITY BETWEEN 6 PM AND 10 PM FOR TORNADO POTENTIAL, ESPECIALLY WITH ANY ISOLATED SUPERCELLS, AS THE LOW LEVEL JET RAPIDLY INTENSIFIES DURING THIS PERIOD BUT INHIBITION IS SLOW TO INCREASE. THE TAKE AWAY MESSAGE IS THAT THE POTENTIAL EXISTS FOR ALL MODES OF SEVERE WEATHER, AND WHILE THERE ARE COMPLICATING FACTORS, IT WILL BE IMPORTANT TO PREPARE FOR A FEW SIGNIFICANT SEVERE STORMS.

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The fact that as of this Thursday evening there is deep rich moisture across much of TX with little appreciable convection bodes well for advection of that moisture northward hopefully without contamination tomorrow. SE KS, NE OK and western MO need to be especially mindful of forecasts tomorrow given the current parameters.  We'll see what tonight's runs indicate.

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Not sure we're going to get off that easily. Storms are firing up and down the lee side of the NE Mexican mountains as we speak. The HRRR has been fairly consistent in developing these storms into a big MCS which could linger in the coastal areas until after sunrise. It is worth noting that the HRRR has been overzealous with initiating storms down there lately (and traditionally too), but anything close to that type of solution would have big implications on what goes down tomorrow.

 

southplains_loop.gif

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Not sure if this thread should be moved, but the 00z NAM slowed down for tomorrow and is really looking nasty for Saturday east of the MS Valley. 4 km follows suit on the latter.

 

That TX target tomorrow has my attention, considering you won't have a nuclear cap down there like you usually do in May or June.

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Not sure if this thread should be moved, but the 00z NAM slowed down for tomorrow and is really looking nasty for Saturday east of the MS Valley. 4 km follows suit on the latter.

 

That TX target tomorrow has my attention, considering you won't have a nuclear cap down there like you usually do in May or June.

 

Yeah 00Z NAM looks very impressive for both Friday and Saturday. I've been watching the Texas target very closely (planning to chase) and the trends are pretty promising. It's also worth mentioning that the SREFs have been rock solid with respect to the southern end of the threat area ever since it came into forecast range.

 

And wow at that shear out east for Saturday!

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Yeah 00Z NAM looks very impressive for both Friday and Saturday. I've been watching the Texas target very closely (planning to chase) and the trends are pretty promising. It's also worth mentioning that the SREFs have been rock solid with respect to the southern end of the threat area ever since it came into forecast range.

 

Things have been slowing down this year within the last 36 hours, it ended up causing problems with the setup on 4/8. This time, it might work in the opposite direction particularly for tomorrow.

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Things have been slowing down this year within the last 36 hours, it ended up causing problems with the setup on 4/8. This time, it might work in the opposite direction particularly for tomorrow.

I'd like to hear your thoughts on Saturday and particularly why MS, AL, TN look like the bigger threat than KY. I personally was thinking of planning just east of the surface low in KY where surface flow may tend to back some. That worries me in the warm sector further south that we have more southwesterly surface flow. It does however to seem to be a trend though in Dixie Alley that speed shear can compensate for lack of directional shear.

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I'm actually feeling pretty good about central/south-central Kansas. SPC WRF further backs up the area of focusing on just ahead of the surface low, near the triple point HRRR trends for prior cloud-cover are also encouraging.

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I'd like to hear your thoughts on Saturday and particularly why MS, AL, TN look like the bigger threat than KY. I personally was thinking of planning just east of the surface low in KY where surface flow may tend to back some. That worries me in the warm sector further south that we have more southwesterly surface flow. It does however to seem to be a trend though in Dixie Alley that speed shear can compensate for lack of directional shear.

 

You answered your own question heh. In the SE, you can easily have SW surface winds and still get significant setups, given that the moisture trajectories still come out of the Gulf. Low level hodographs still show plenty of curvature with the forecast soundings, and deep layer shear overall is obviously very strong. I do think that the area near the low in the Ohio Valley/KY also has good potential though, you tend to see a dominant storm or two track near the triple point in these kinds of situations, with more southerly/backed near-surface flow.

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I'd like to hear your thoughts on Saturday and particularly why MS, AL, TN look like the bigger threat than KY. I personally was thinking of planning just east of the surface low in KY where surface flow may tend to back some. That worries me in the warm sector further south that we have more southwesterly surface flow. It does however to seem to be a trend though in Dixie Alley that speed shear can compensate for lack of directional shear.

The southwesterly surface winds wouldn't be a deal breaker in this case.  I've become rather intrigued by Saturday. 

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You answered your own question heh. In the SE, you can easily have SW surface winds and still get significant setups, given that the moisture trajectories still come out of the Gulf. Low level hodographs still show plenty of curvature with the forecast soundings, and deep layer shear overall is obviously very strong. I do think that the area near the low in the Ohio Valley/KY also has good potential though, you tend to see a dominant storm or two track near the triple point in these kinds of situations, with more southerly/backed near-surface flow.

Ha I kind of knew the answer I just wanted to discuss it. Still uncertain of where I'd like to play on Saturday but I'll 100% be chasing because it's the weekend and I'm off work. Only issue is if I'm heading for AL, I'll definitely need to leave tomorrow night.

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I'm entirely confused by Dr. Forbes holding onto a TOR:CON of 6 for SE KS, and a 5 for NE KS. Obviously he knows more than me, and probably more than anyone else on this board but it doesn't make much sense...

Makes perfect sense to me, SE KS should be more unstable than NE KS, and the risk in NE KS is a bit more conditional depending how far north the warm front gets.
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30% sig-hatched added for KY and TN in the D2, mentions of strong tornadoes and a possible upgrade in risk in future outlooks (basically what I expected considering the 00z guidance). A bit surprised that it didn't get extended further south into AL/MS, although I suppose storm coverage further south is still a question.

 

D1 has two 10% hatched tornado areas for KS and E TX/Arklatex.

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