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andyhb

May 7th-9th Severe Weather Episodes

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HRRRx has been steadfast this morning in advertising several storms initiating along the dryline, but only about two of them surviving in the long term, with a lot of space between them. The somewhat muted UH magnitude from most of the CAMs today is a little concerning, and makes me think the potential for long-track sigtors is tempered a bit, albeit far from zero. Still, I think at least a couple reasonably nice tornadoes are a pretty good bet in the 5-8pm time frame. Hopefully, when it comes to storm choice today, all of us heading out can choose wisely!

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HRRRx has been steadfast this morning in advertising several storms initiating along the dryline, but only about two of them surviving in the long term, with a lot of space between them. The somewhat muted UH magnitude from most of the CAMs today is a little concerning, and makes me think the potential for long-track sigtors is tempered a bit, albeit far from zero. Still, I think at least a couple reasonably nice tornadoes are a pretty good bet in the 5-8pm time frame. Hopefully, when it comes to storm choice today, all of us heading out can choose wisely!

 

12z NSSL WRF is also rather anemic. Oklahoma sees some cells initiate, but as you mentioned they don't last very long at all. Also, the mean updraft strength is surprisingly low. 

 

http://wrf.nssl.noaa.gov//newsite/index.php?model=nssl&dom=ICT&field=updrft&hr=00&date=16050812

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Btw, OUN is doing a special sounding around 18Z. Should provide at least some insight into LLVL moisture quality... LLVL moisture quality will be better over SW OK though...

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The high res models suggest only modest low level helicity across the threat zone until about 00z as the low level jet expands west and strengthens. That is probably another factor in the weak UH signal with some of the CAMs.

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Predictable amount--according to most of the models-- of moisture return into OK. Pretty juicy for 18z compared to what most expected.current.TDEW.grad.png

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MESOSCALE DISCUSSION 0556 NWS STORM PREDICTION CENTER NORMAN OK 0118 PM CDT SUN MAY 08 2016

AREAS AFFECTED...PORTIONS OF N TX AND WRN OK

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 081818Z - 082015Z

PROBABILITY OF WATCH ISSUANCE...95 PERCENT

SUMMARY...STORMS ARE EXPECTED TO INITIATE ALONG THE DRYLINE ACROSS SW OK BY 21Z. ADDITIONAL STORM WILL DEVELOP OVER NW OK AND MOVE INTO S-CNTRL KS AS WELL. VERY LARGE HAIL...A FEW TORNADOES AND DAMAGING WIND GUSTS WILL BE POSSIBLE AND A TORNADO WATCH WILL LIKELY BE NEEDED IN THE NEXT 1-2 HOURS.

DISCUSSION...LOW LEVEL CUMULUS FIELD CONTINUES TO EXPEND FROM NEAR THE RED RIVER THROUGH WESTERN OK THIS AFTERNOON. THE NATURE OF THE CU SUGGESTS INHIBITION STILL EXISTS. BUT EXPECT INITIATION BY THE 20-21Z TIME FRAME ACROSS WESTERN N TX INTO SOUTHWEST OK WHERE HEATING HAS BEEN STRONGEST AND TEMPS ARE IN THE LOW 80S AS OF 18Z. SURFACE DEWPOINTS ARE HOVERING IN THE 62-66 DEG F RANGE ACROSS MUCH OF THE MCD AREA EXCEPT PORTIONS OF FAR NW OK INTO S-CNTRL KS WHERE UPPER 50S AND LOW 60S WERE NOTED...RESULTING IN MUCAPE RANGING FROM 1000-2000 J/KG. DEEP LAYER SHEAR PROFILES WILL FAVOR SUPERCELLS. MIDLEVEL LAPSE RATES GREATER THAN 7.5 DEG C/KM PER OBJECTIVE ANALYSIS WILL SUPPORT VERY LARGE HAIL /SOME BIGGER THAN 2 INCHES/. SPEED SHEAR IN THE LOWEST 1-2 KM IS CURRENTLY UNIMPRESSIVE BUT SHOULD IMPROVE IN THE 22-00Z TIME FRAME IN VICINITY OF THE BULGING DRYLINE. AS SUCH...A FEW HOURS OF INCREASED TORNADO POTENTIAL WITH ISOLATED DISCRETE CONVECTION WILL EXIST ACROSS SW OK.

ADDITIONAL STORMS ARE EXPECTED TO DEVELOP LATER THIS AFTERNOON ACROSS NW OK AND MOVE INTO S-CNTRL KS. THESE STORMS WILL EXIST IN A SIMILAR BACKGROUND ENVIRONMENT AS THOSE FURTHER S OVER SW OK...BUT QUALITY OF LOW LEVEL MOISTURE AND INSTABILITY DIMINISHES INTO S-CNTRL KS WHERE ONGOING SHOWERS AND THUNDERSTORMS HAVE PERSISTED MOST OF THE DAY. STORM COVERAGE AND INTENSITY IS A BIT MORE UNCERTAIN IN THIS AREA...THOUGH A WATCH WILL LIKELY BE NEEDED LATER THIS AFTERNOON AS WELL.

..LEITMAN/HART.. 05/08/2016

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SBCAPE as of 18Z. NAM may not be far off showing values of 3000+J/KG later on.

sbcp_sf.gif?1462732030890

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I totally forgot I had OK Mesonet and West TX Mesonet placefiles that I could use in GRLevel3. It appears the dryline is from Spearman TX to Big Spring TX down to that storm next to Ft. Stockton. North of Spearman, there is a not-so-dry airmass, i.e. cold air mass.

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FWIW, Texas Tech's 12Z 3KM WRF model develops numerous storms along the dryline in KS/OK at 23Z then kills most of them off, and shows a dominate supercell moving toward OKC metro thereafter... That same supercell's UH track on the TTU-WRF is also eh like most of the other hi-res guidance. 

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Dewpoints seem to be falling into place. Maybe another degree or two. I have seen talk about how 2 or 3 degrees in dewpoints could escalate the situation quite a bit, why is that?

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Dewpoints seem to be falling into place. Maybe another degree or two. I have seen talk about how 2 or 3 degrees in dewpoints could escalate the situation quite a bit, why is that?

dewpoint/moisture significantly affects instability profile. Alps lowers LCL which is crucial for tornadoes

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18z OUN sounding...

16ae97a66259c4277761d2cf848c34c8.jpg

Pretty good BL moisture, especially when you think that DPs are a bit higher in SW/W OK... That huge cap does not surprise me too much, it is likely quite a bit weaker in W/SW OK where SFC temps are either near or into the 80s.

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The morning crapvection and general cloud cover will probably be the undoing of a higher-end day. CINH will kill most or all of the storms at some point into the warm sector, probably a decent bit W of 35. What we need to root for is initiation as late as possible so that SRH is maximized during the storms' relatively short mature phases. Obviously there's always the chance that a cell goes bonkers and is able to plow through a capped environment on the strength of its established VPPGF, but in general, I see storm longevity being the biggest limiting factor. The strong midlevel flow is a double edged sword...

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Moisture return into Kansas is not bad either with P28 up to 63F now, but I do agree with a generally limited window for most storms. One or two longer-lived cells remain possible, posing the most significant severe risk.

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Cap should deteriorate some later on too, its not like that will stick throughout the entire evening. Reference 18Z RAP soundings, they initialized comparably well to the 18Z OUN sounding, it shows the cap being much less strong by 00Z. You are right though, most storms will probably die off.

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17z HRRR shows some significant storms as soon as 21z near Woodward, Frederick/Snyder OK, Ashland/Coldwater KS

 

The 18z HRRR has a UH signature near Frederick between 21-22z that is probably the strongest I have seen on any run today. As multiple others have noted, however, the strong UH signature is relatively short-lived.

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Set up shop in Clinton for now with the option to head south on Highway 183. We'll see what happens.. At least we have some clearing in place here. I was starting to get annoyed at the cloud cover to the east.

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Set up shop in Clinton for now with the option to head south on Highway 183. We'll see what happens.. At least we have some clearing in place here. I was starting to get annoyed at the cloud cover to the east.

We just left there to go south on 183. We decided to commit.

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Set up shop in Clinton for now with the option to head south on Highway 183. We'll see what happens.. At least we have some clearing in place here. I was starting to get annoyed at the cloud cover to the east.

At least a few of us sitting at the Shell on 183 South of Clinton right now

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66-67 F Tds are beginning to materialize along the Red River, and we're likely going to see CI in SW OK where the best low level shear should exist by 23-00z... so two of the biggest caveats out of the way. But widespread cloud cover and cool sfc temps extending as far west as Weatherford and Lawton could counteract much of that progress, in terms of the setup as a whole. Just beyond frustrating if it turns out we can't sustain mature storms today, after working out the other issues. Gonna be a nail biter.

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Looks like the SPC is going to hold off a bit on the watch issuance to assure initiation.

Well, as of 1930Z, there is not much in the way of agitated CI along or east of the DL. Those incoming clouds over the TX panhandle/ N TX would appear to indicate the presence of better forcing though.

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