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Severe threat april 14, Tornado outbreak possible


janetjanet998

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Depending on the exact track of the low, I can see your area getting in on some pseudo cold-core type action mid-late afternoon, though the best chances will probably be a bit to your S. I'm fully expecting some tornado reports inside an ICT-RSL-EMP polygon during the 3-6pm window.

Do you see any chance the dryline moves slower than expected through SW OK allowing early day convection west of I 35?

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Do you see any chance the dryline moves slower than expected through SW OK allowing early day convection west of I 35?

Given the model trends toward the system closing off and stacking earlier, it looks like the dryline should be fairly NW-SE oriented, especially as the day progresses. Because of that, I kind of doubt much in the way of severe convection will occur over SW OK (in the CASA domain, if that's what you're wondering about). Perhaps on the eastern fringes, at best. Farther N, however, I can see places like Enid and Guthrie getting in on the action, since the dryline is almost always a tad slower than the low-resolution models suggest.

Unfortunately (both for chasers and CASA), the severe drought conditions only make it that much more unlikely that the dryline will move substantially slower than expected.

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Another thing I like to look at, especially in regards to regional severe weather as opposed to specific targets, is 0-4km thetae lapse rates and jet level wind speed. Generally speaking 0-4km encompasses the surface to 600 mb layer, and gives you an idea of low/mid level instability. Being able to toggle that with the jet stream gives you an idea of both divergence for lift and speed for shear. Here is an example from the 12z NAM. Values greater than about -4 C/km (red and left on the scale at the top left) are more favorable. You can see the NAM is forecasting some of the best thetae lapse rates I've seen this year, at almost -7 C/km.

Over the top of that you have a strong jet streak, approaching 100 knots. We already know about the forecast shear and intense vertical motions that are going to result from this.

The GFS forecast for thetae lapse rates is a little closer to -4 C/km, and I'm guessing that is mostly due to the fact that is has ongoing precip at 00z that is cutting down on the values.

Nice procedures. I wish I had a good set of severe procedures. I will have to take you up on your offer and contact you about some.

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Unfortunately (both for chasers and CASA), the severe drought conditions only make it that much more unlikely that the dryline will move substantially slower than expected.

Indeed. It's self-sustaining for sure. Sunday night the east side of the CASA domain picked up the first measurable precipitation since at least Feb. 24th. It was entirely unforecasted, as convection in N. TX developed west of the models and moved NE. Obviously I am hoping for a similar westward bust. The drought has me grasping I realize.

There were a number of fire reports today, including a fairly large one in Fletcher. Tomorrow will be dangerous fire weather.

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@ OceanStWX...Oh what I would give for AWIPS laugh.gif

Hopefully the public release for AWIPS II doesn't suffer from any more delays. Anyways...

I'm just glad to see that another dryline wont cross through OK without T-storm development. It's been hard looking at some of the surface maps over the past few weeks...

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE TULSA OK

931 PM CDT WED APR 13 2011

.DISCUSSION...

ATMOSPHERIC STAGE BEING SET FOR WELL ADVERTISED

THUNDEROUS PERFORMANCE LATE THURSDAY AFTERNOON

AND EVENING. SEVERE NOT LIMITED TO LARGE HAIL

AND DAMAGING WIND...BUT ALSO INCLUDES A TORNADO

THREAT GIVEN SHEAR PARAMETERS WHICH PAINT A 180

DEGREE TURNING 0-3KM HODOGRAPH. LATEST 00Z ETA

STAYS WITH DRYLINE CROSSING I-35 AROUND 22Z-23Z

BALLPARK. STAY TUNED.

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Looks like on the NAM, there is a broken line of convection racing out in advance of the main band along the front. I would think broken band with the level of turning winds in the atmosphere would tend to enhance tornado chances further east than shown on the Day 2. Seems like we are not that far from a high risk.

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I'll be chasing tomorrow and from tonight's data, it sure looks like we're going to get some decent activity. One note of caution I'd like to bring up is how the dryline always seems to end up further west then anticipated. Two days I can remember that occurring would be May 10, 2010 (Models had it out east of OKC in the woods and we ended up getting storms firing a good two counties west of OKC) and February 27, 2011 where the models had the dryline east of I-35 (closer to Tulsa in fact) and we ended up chasing supercells almost 70 miles west of the highway. I'm just saying that we've ended up with the dryline further west then models have shown. For that reason, I'm willing to bed the WRF's position of the dryline is accurate. However, the 03Z HRRR seems to be favoring more of an eastern solution by the end of its range. We'll just have to wait and see.

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I'll be chasing tomorrow and from tonight's data, it sure looks like we're going to get some decent activity. One note of caution I'd like to bring up is how the dryline always seems to end up further west then anticipated. Two days I can remember that occurring would be May 10, 2010 (Models had it out east of OKC in the woods and we ended up getting storms firing a good two counties west of OKC) and February 27, 2011 where the models had the dryline east of I-35 (closer to Tulsa in fact) and we ended up chasing supercells almost 70 miles west of the highway. I'm just saying that we've ended up with the dryline further west then models have shown. For that reason, I'm willing to bed the WRF's position of the dryline is accurate. However, the 03Z HRRR seems to be favoring more of an eastern solution by the end of its range. We'll just have to wait and see.

I respectively disagree. Depending on how the trough ultimately unfolds, I think the dryline may even set up further east than currently progged. Drylines tend to mix out east pretty effectively when we have zonal-ish flow rather than meridional flow. Also, the ECM appears to push the DL pretty far east. And, of course... the drought out west. (I do hope it doesn't end up that far east though.)

I do think however initiation will occur ~21Z a little east of I-35. Although the tornado potential initially should be low (I'm a little concerned about LCLs and back-veer-back wind profiles), you guys may be able to get something before the storms move into the woods. I would not be surprised to see two rounds of storms form off the DL.

On another note, the lapse rates look insane... giant hail (3"+) will be a norm in any supercell that develops.

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I respectively disagree. Depending on how the trough ultimately unfolds, I think the dryline may even set up further east than currently progged. Drylines tend to mix out east pretty effectively when we have zonal-ish flow rather than meridional flow. Also, the ECM appears to push the DL pretty far east. And, of course... the drought out west. (I do hope it doesn't end up that far east though.)

I do think however initiation will occur ~21Z a little east of I-35. Although the tornado potential initially should be low (I'm a little concerned about LCLs and back-veer-back wind profiles), you guys may be able to get something before the storms move into the woods. I would not be surprised to see two rounds of storms form off the DL.

On another note, the lapse rates look insane... giant hail (3"+) will be a norm in any supercell that develops.

I pretty much agree with this. LCLs concern me early on (I think the first tornado threat will be up into KS). I don't really see veer-back-veer being a problem. What I do see is likely a major tornado risk around/after sunset. It's really kinda scary.

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I concur with both posts above regarding the LCLs. I think the signficant tornado threat will hold off until near and after sunset, which is about when the helicities go through the roof. I definitely see the back-veer-back profile north of I-40, but when you get away from the closed upper low south of I-40, it's not a problem at all. The NAM seems to show this being less of a problem than the GFS, but this whole problem is really sensitive to how the trough/low evolves during the day tomorrow.

I think we'll see some significant tornadoes tomorrow. If I had to bet on where the storm of the day would be, I'd bet on south of I-40 somewhere around the Mcalester, OK to Mena, AR region. I have a feeling that last storm down the line is the one most likely to beast-out.

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I concur with both posts above regarding the LCLs. I think the signficant tornado threat will hold off until near and after sunset, which is about when the helicities go through the roof. I definitely see the back-veer-back profile north of I-40, but when you get away from the closed upper low south of I-40, it's not a problem at all. The NAM seems to show this being less of a problem than the GFS, but this whole problem is really sensitive to how the trough/low evolves during the day tomorrow.

I think we'll see some significant tornadoes tomorrow. If I had to bet on where the storm of the day would be, I'd bet on south of I-40 somewhere around the Mcalester, OK to Mena, AR region. I have a feeling that last storm down the line is the one most likely to beast-out.

My instinct is that there will be 2 or 3 headline-making supercells tomorrow, and I think the region you named is probably prime. I am also concerned, however, with the state of AR overnight as the storm move east. Could definitely envision tornadoes with any semi-discrete cells or even a line.

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I respectively disagree. Depending on how the trough ultimately unfolds, I think the dryline may even set up further east than currently progged. Drylines tend to mix out east pretty effectively when we have zonal-ish flow rather than meridional flow. Also, the ECM appears to push the DL pretty far east. And, of course... the drought out west. (I do hope it doesn't end up that far east though.)

I do think however initiation will occur ~21Z a little east of I-35. Although the tornado potential initially should be low (I'm a little concerned about LCLs and back-veer-back wind profiles), you guys may be able to get something before the storms move into the woods. I would not be surprised to see two rounds of storms form off the DL.

On another note, the lapse rates look insane... giant hail (3"+) will be a norm in any supercell that develops.

You very well could be correct, I was mainly speaking on experience with previous events. Something to also consider is the severe drought we're in, so that would also validate your view. The SREF also supports it, which actually does peak out some crazy values in SW AR by 10 PM. With a few schedule constants in place, I'm considering being lazy and just playing I-30 tomorrow from NE TX into SW AR as superecells form up the highway. Another option will be US-82 on the river.

EDIT: The HRRR also shows your solution, which does make sense when looking at everything. Oh well, chasing in E. TX is still local enough to be worth it.

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12z NAM= I'll believe it when I see it..eveything in perfect

but talk about a HUGE 2 day outbreak..wow... including over night tonight

old low occludes off (after the 1st low nails eastern KS eastern OK and AR overnight, and a new on forms more southeast for round 2 starting tomorrow morning)

is there even an analog for something like this over 2 days?

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I usually don't post much, because I don't have the knowledge you guys have. I've been reading this thread and looking at forecasts, and I'll be watching carefully tonight. I'm smack in the middle of the mod risk area. Thanks for all of the info you guys put out here. I won't clog up the thread later tonight, but if anything significant happens here I'll post it.

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE TULSA OK

950 AM CDT THU APR 14 2011

...UPDATE...

.DISCUSSION...

OVERALL...THINKING ON THE SEVERE WEATHER TONIGHT HAS NOT CHANGED.

MOISTURE RETURN APPEARS ON SCHEDULE...WITH 60 DEGREE DEW POINTS

ALMOST TO I-40...AND DOUBLE DIGIT 3 HOUR DEW POINT CHANGES ACROSS

A GOOD CHUNK OF CENTRAL AND EASTERN OKLAHOMA. CLOUD COVER IS

ACCOMPANYING THE MOISTURE RETURN...BUT EXPECT THAT THE CLOUDS WILL

BREAK UP DURING THE AFTERNOON HOURS.

12Z NAM HAS COME IN SLIGHTLY QUICKER WITH THE DRYLINE THIS

AFTERNOON/EVENING...BRINGING IT INTO FAR WESTERN PORTIONS OF OSAGE

AND PAWNEE COUNTIES BY 00Z. 12Z RUC IS NOT QUITE THAT FAST...BUT

STILL BRINGS IT JUST EAST OF I-35 BY THAT TIME. BOTH MODELS

SHOWING A COUPLE OF REGIONS OF INITIATION LATE

AFTERNOON/EVENING...THE FIRST BEING NEAR THE KS/OK BORDER...AND

THE SECOND NEAR THE OK/TX BORDER. BEST CHANCE OF THE LATTER WILL

BE AFTER 00Z SO HAVE INCREASED POPS SLIGHTLY FOR SE OK DURING THAT

TIME FRAME. HAVE ALSO INCREASED POPS FROM 21-00Z NORTH OF I-40 AND

WEST OF HIGHWAY 75 TO REFLECT THE SLIGHTLY FASTER DRYLINE

MOVEMENT. WILL ALSO INCREASE THE TORNADO PROBABILITIES FOR THE

NORTH OF I-40 AND WEST OF HIGHWAY 75 REGION WITH INCREASED

CONFIDENCE THAT DISCRETE CONVECTION WILL BE IN THIS REGION DURING

THE LATE AFTERNOON/EVENING HOURS.

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HRRR showing initiation along the dryline by 21z along the I-35 corridor, with, in some cases, 2500-4000 J/kg CAPE and >200 m2/s2 0-1km SRH across E/SE OK.

mref_t5sfc_f09.png

Just going off the actual CRP and DRT balloons, and the magnitude of CINH present, I'd seriously doubt any model that shows convection near or even South of I-10 in Texas.

I am hoping for 18Z soundings

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