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April 6-10th Severe Potential


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Can't get the model data to completely load on my phone :(

Obviously several days out timing is leaving something on the table but that's generally the case this far out. Looks like either Wednesday or Thursday will have some potential. Could definitely split the days as mentioned above but we are about at the point of the year were even systems with blah timing produce some cashable storms and photo opportunities.

I don't like okc and ict both under the gun. Lots of people...

Will check the models tomorrow when I am at the PC.

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00z still looking stout... 500s appear a bit stronger... Capping looks like less of an issue and the target may have fallen back west slightly. Surface winds don't really back until 00z but that's okay.

Sent from my iPad

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00z still looking stout... 500s appear a bit stronger... Capping looks like less of an issue and the target may have fallen back west slightly. Surface winds don't really back until 00z but that's okay.

Sent from my iPad

 

I'd be really concerned for the OKC metro (perhaps Wichita as well) with the 00z GFS' idea, with the dryline essentially uncapped at 21z with storms firing and then with rapidly strengthening low level shear by 00z as capping strengthens and keeps storms discrete. If we see that dryline positioned west of I-35, trouble is likely in the making.

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New Euro is crazy, I'd call it something close to everything falling into place to maximize the potential of this trough. Even convects along the DL Tuesday (which I'll believe when it happens, literally). With its solution, it's easy to imagine both Wed and Thu being called "significant" when it's all said and done. I'm still plenty nervous and I think the practical outcome is highly sensitive to somewhat-subtle details, but it's got to be the best an early April system has looked inside of 96-120 h for several years out here.

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New D4-8 outlook, unsurprisingly the only thing preventing them from upgrading to 30% at this juncture for Wed is the uncertainty in storm coverage. Increasingly strong language being used though, no surprise given the general ramp up in solutions since yesterday.

 

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0358 AM CDT SUN APR 05 2015

VALID 081200Z - 131200Z

...DISCUSSION...
APPRECIABLE SPREAD -- EVEN MORE THAN 24 HOURS PRIOR -- IS EVIDENT
AMONGST THE MEDIUM-RANGE MODELS THIS FORECAST...WITH THE GFS
SHIFTING THE WRN TROUGH INTO THE PLAINS FASTER AND WITH MORE OF A
POSITIVE TILT...WHILE THE UKMET AND PARTICULARLY THE ECMWF DEPICT A
SLOWER AND MORE NEUTRAL TO NEGATIVE TILT PROGRESSION. AS A RESULT
OF THESE DIFFERENCES -- AND THE ASSOCIATED VARIANCES IN SURFACE
FEATURE LOCATIONS IN THE DAY 4-5 TIME FRAME...SPECIFICS OF THE
SEVERE WEATHER FORECAST WITH RESPECT TO TIMING/LOCATION REMAIN
DIFFICULT TO ASCERTAIN.

DESPITE TIMING DIFFERENCES WITH RESPECT TO THE MAIN UPPER
LOW/TROUGH...CONFIDENCE HAS INCREASED THIS FORECAST WITH RESPECT TO
SEVERE RISK FOR DAY 4 /WED 4-8/ ACROSS CENTRAL AND ERN OK/ERN KS/MO.
ALL MODELS INDICATE MID-LEVEL HEIGHT FALLS ACROSS THIS AREA...AND
AT LEAST HINTS OF A SUBTLE/EMBEDDED WAVE CROSSING THE REGION NEAR
PEAK HEATING. ATTM...EXPECT RESULTING UVV TO BE SUFFICIENT ATOP THE
EWD-MIXING DRYLINE TO PERMIT CAP WEAKENING SUFFICIENT TO YIELD
ISOLATED TO SCATTERED STORM DEVELOPMENT BY LATE AFTERNOON. WITH A
VERY MOIST BOUNDARY LAYER AHEAD OF THE DRYLINE TOPPED BY STEEP LAPSE
RATES...AND A KINEMATIC ENVIRONMENT FEATURING FLOW THAT VEERS
SUBSTANTIALLY AND INCREASES STEADILY WITH HEIGHT...SHEAR WILL FAVOR
LONG-LIVED SUPERCELLS AND ATTENDANT RISK FOR VERY LARGE
HAIL...DAMAGING WINDS...AND TORNADOES. GIVEN UNCERTAINTY DUE TO
STORM COVERAGE...WILL MAINTAIN ONLY 15% PROBABILITY AREA ATTM --
DESPITE SIGNIFICANT SEVERE WEATHER POTENTIAL WITH ANY STORM THAT
DOES DEVELOP.

THE LIKELIHOOD FOR MORE WIDESPREAD STORMS -- BUT WITH GREATER
UNCERTAINTY IN TERMS OF TIMING AND AREA -- EXISTS DAY 5 /THU 4-9/.
DEEPENING OF THE SURFACE LOW IN THE KS/NEB/IA VICINITY AND ADVANCE
OF A TRAILING COLD FRONT INTO THE CENTRAL/SRN PLAINS WILL FACILITATE
A BROAD ZONE OF STORM INITIATION...GIVEN THE MOIST/FAVORABLY
UNSTABLE AIRMASS EXPECTED. WITH STRONGER FLOW ALOFT AS COMPARED TO
DAY 4 GIVEN PROGRESSION OF THE MAIN MID-LEVEL JET STREAK INTO THE
CENTRAL STATES...SUPERCELL STORMS AND ASSOCIATED RISK FOR VERY LARGE
HAIL...DAMAGING WINDS...AND TORNADOES CAN BE EXPECTED.

MODELS CONTINUE TO DIVERGE DAY 6 AND BEYOND...AND GIVEN THE
INCREASING SPREAD IN SOLUTIONS BETWEEN THEM...LOW CONFIDENCE EXISTS
WITH RESPECT TO EVOLUTION OF SEVERE RISK THROUGH THE SECOND HALF OF
THE PERIOD. THUS...LOW PREDICTABILITY PRECLUDES ATTEMPTS TO
HIGHLIGHT THREAT AREAS BEYOND DAY 5.

..GOSS.. 04/05/2015
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We're in the NAM range now, and it is quite impressive to say the least. Diffluent flow over central KS... also under the left exit region of the jet streak... I don't see capping being an issue on Wednesday. While I don't love the NAM at hour 84... its hard not to take notice when it agrees with everything else... I see little that's wrong with the Wednesday setup at this point.

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It's down to Wednesday being the only nice looking chase worthy day to me. Gonna try to be out there.

I'm not writing Thursday off yet chase wise, but I agree it looks like Wednesday is the day.  I'm still holding out hope for something Thursday that would be chase worthy on the way back home if I go for Wednesday. 

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I'm not writing Thursday off yet chase wise, but I agree it looks like Wednesday is the day.  I'm still holding out hope for something Thursday that would be chase worthy on the way back home if I go for Wednesday. 

I agree too early to kick Thursday do the curb.  I think it could definitely be potent in AR.  Eastern OK looks possible as well but at this point it would be a lunchtime type event in eastern OK.  Not impossible or unheard of but the atmosphere is likely to be worked over from Wednesday.  Being this early in April I'm not sure how readily the atmosphere can recover?  If it were late afternoon, it would seem to be no problem but a 11am to 1pm?  that's early...

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is it just me, or am I the only one noticing the inverse troughs on the NAM and GFS near i-29 that mysteriously don't appear at all on the Canadian Global between t+72 and t+96? I'm awaiting the Euro now. I know those would screw up the mix a bit, especially on the moisture flux and dynamics sides.

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is it just me, or am I the only one noticing the inverse troughs on the NAM and GFS near i-29 that mysteriously don't appear at all on the Canadian Global between t+72 and t+96? I'm awaiting the Euro now. I know those would screw up the mix a bit, especially on the moisture flux and dynamics sides.

 

I may be referring to a different feature than you... but the only inverted surface trough that I'm seeing is roughly associated with the warm front.

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18z NAM looks pretty darn good for Weds but I will say I don't like the weakness the winds above H5. Quite weak at upper levels would lead to believe HP mode but we'll see. I know some have thrown out 4/14/12 and just for reference 250-300mb winds on the 0z raobs that evening at OUN/LMN are around 80-90kts where the NAM is progging 35-40kts.

 

Isolated convective signal at the triple point with great parameters in place. 

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18z NAM looks pretty darn good for Weds but I will say I don't like the weakness the winds above H5. Quite weak at upper levels would lead to believe HP mode but we'll see. I know some have thrown out 4/14/12 and just for reference 250-300mb winds on the 0z raobs that evening at OUN/LMN are around 80-90kts where the NAM is progging 35-40kts.

 

GFS has significantly stronger flow aloft there with what seems to be a broader left exit region of the subtropical jet.

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18z NAM looks pretty darn good for Weds but I will say I don't like the weakness the winds above H5. Quite weak at upper levels would lead to believe HP mode but we'll see. I know some have thrown out 4/14/12 and just for reference 250-300mb winds on the 0z raobs that evening at OUN/LMN are around 80-90kts where the NAM is progging 35-40kts.

 

This is definitely a concern I share, but these things can be so finicky and hard to nail down. One (crude, optimistic) analog I've been thinking of is 2004-05-29. Several chasers I know chose to stay in OK that day specifically because the jet max was S of I-40, so they feared HP mode up the dryline and closer to the triple point in KS. They were treated to a lovely HP beast that produced a dozen tornadoes across W OK -- approximately none of which were photogenic, and few of which were even visible. Meanwhile, Harper Co. put on the show of the decade for the southern Plains beneath ~60 kt at H25 and ~35 kt at H5.

 

Anecdotal, and probably more the exception than the rule. I'd certainly like to see a greater increase in flow speed with height between H5 and H25. Like that day, though, the best difluence on Wed is N whereas the strongest upper flow is S.

 

Of course, this all assumes the progressive timing of the trough stays on track. I'm as excited as anyone, but I'm trying to keep in perspective that only 48 hours ago, the consensus timing was 12-18 hours slower -- and that oftentimes there's a slowing trend as these systems come ashore. It's fortunate that the ECMWF has been rock solid in initiating along the DL for days now, and that its timing hasn't wavered too much. But obviously, we're not out of the woods yet as far as a heartbreaking cap bust is concerned.

 

Impressed to see another significant southern stream wave on tap for next weekend, as Andy mentioned last night. Pending diurnal timing and adequate recovery of moisture, we might have another shot at something impressive right away... perhaps even over areas of TX that haven't been able to buy favorable synoptic setups for years.

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I agree - Wednesday seems to have the bigger potential over Thursday. Any ideas why analogues are so aggressive for Thursday when instability seems to clearly be lacking, at least on the GFS? Granted, it is only model, but still.

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18z NAM looks pretty darn good for Weds but I will say I don't like the weakness the winds above H5. Quite weak at upper levels would lead to believe HP mode but we'll see. I know some have thrown out 4/14/12 and just for reference 250-300mb winds on the 0z raobs that evening at OUN/LMN are around 80-90kts where the NAM is progging 35-40kts.

 

Isolated convective signal at the triple point with great parameters in place. 

 

The good news is that weak winds above H5 is not as much as a deal breaker as high LCLs or VBV wind profiles are. If I recall correctly both Pilger from last year and 6/17/10 were prolific tornado events with fairly weak winds above H5.

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I agree - Wednesday seems to have the bigger potential over Thursday. Any ideas why analogues are so aggressive for Thursday when instability seems to clearly be lacking, at least on the GFS? Granted, it is only model, but still.

 

wednesday is looking more like a mesoscale day for sure.

 

but when it comes to thursday, if the models are close on the timing, what you lose in thermodynamic buoyancy you get back in not only shear, but also pure synoptic forcing (frontal lift and a vigorous vortmax  resulting from the upper air low synching rather well)  which can over-ride most of the mesoscale thermodynamic buoyancy issues.

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wednesday is looking more like a mesoscale day for sure.

 

but when it comes to thursday, if the models are close on the timing, what you lose in thermodynamic buoyancy you get back in not only shear, but also pure synoptic forcing (frontal lift and a vigorous vortmax  resulting from the upper air low synching rather well)  which can over-ride most of the mesoscale thermodynamic buoyancy issues.

 

How so?

 

Everything I'm seeing is indicating that Wednesday will be driven heavily by the synoptic side, particularly the timing of the synoptic scale trough.

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The 00z NAM is pretty eye popping verbatim. 

 

There's been a clear and steady slowing trend with the progression of the upper trough, though, from the 12z run this morning to tonight's 00z run. Whether it means anything, being the NAM beyond H+48 and a synoptic-scale feature upstream of the CONUS, is questionable. But I'm nervously keeping an eye on whether that trend occurs with the GFS or Euro.

 

I will say that the lack of explicit QPF on the NAM down the dryline doesn't bother me at this stage, given the BMJ convective scheme is known to struggle in this scenario. If anyone gets nervous about that, just know that it showed a cap bust along the length of the dryline the night before this. :lol:

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