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BrandonC_TX

April 29-May 1 Severe Weather

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SPC has introduced an outlined area for Day 6:

day6prob.gif.7bc9c76941426167c0d9ad250ac6151d.gif

The GFS-based models have quite a moist airmass over the warm sector (mid-60s to lower-70s dewpoints), but upper level support, in terms of the jet stream winds, seems a little lacking except across northern OK and southern KS from what I can tell (0z FV3 has the warm sector well into KS, while the 0z regular GFS keeps KS in the cool sector).

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ECMWF has a great background pattern. That far out mesoscale details are not SPC's concern; but, surging CF is stopped in OK and reverses north as a WF. LLJ becomes robust and backed toward 00Z. Wind fields are strong with gradual turning with height through 500 mb. The 200/300 mb level is lighter; however, target area is under the right rear/entrance quad of a departing jet max. That's an area of lift too.

Way too early to look at forecast soundings. However one can infer from the constant press charts that the hodo is good on the ECMWF. Of course that could change. The CF could surge. It could be capped. Low levels could veer off. So 15% is better than 30% attm. While not a travel day IMHO it could be good for local chasers. 

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24 minutes ago, nrgjeff said:

ECMWF has a great background pattern. That far out mesoscale details are not SPC's concern; but, surging CF is stopped in OK and reverses north as a WF. LLJ becomes robust and backed toward 00Z. Wind fields are strong with gradual turning with height through 500 mb. The 200/300 mb level is lighter; however, target area is under the right rear/entrance quad of a departing jet max. That's an area of lift too.

Way too early to look at forecast soundings. However one can infer from the constant press charts that the hodo is good on the ECMWF. Of course that could change. The CF could surge. It could be capped. Low levels could veer off. So 15% is better than 30% attm. While not a travel day IMHO it could be good for local chasers. 

Thanks for the summary. Appreciate it. Haven't had much time to dig I to things besides briefly looking at GFS. Nice to see the pattern turning around. Hopefully this continues into May

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There are some indications that plentiful early-day storms will be ongoing across parts of the region, but at the very least, severe thunderstorm potential will exist on the south/east fringes of these early-day storms.

From SPC outlook today re: the 30th. Painfully familiar 

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ECMWF went to the dogs today. CF surge on MCS. LLJ off in the Ozarks jungle. Upper dynamics are timed poorly. I'm checking out for the weekend.

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2 minutes ago, andyhb said:

Lovely start to May, not.

Just stupid.

Is this #2019ing? 

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1 hour ago, andyhb said:

Lovely start to May, not.

Just stupid.

At least mid-May looks “good.”

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Unbelievable. Seems like every yr it is getting later and later to see any decent Plains setups. Anymore outbreaks are happening in less favorable chase terrain. Just would be nice to have a normal tornado season in classic Tornado Alley. The last several years have been plagued with poorly timed waves or just garbage wind profiles plagued with weaknesses and VBV. Miss those days of bowling balls slamming into a warm sector. To be dealing with crashing cold fronts in late April is ridiculous. Hoping this yr will pull a 2013 and turn around real quick by mid to late May

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And now SPC has a Day 4 30% risk area out for North Texas (including DFW) and southern Oklahoma.  Starting to wonder if this might be a significant event for someone in or near the DFW area.


day4prob.gif.b0df564748fa32c6c6ae6c8d242212a1.gif

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06Z GFS depicts a highly volatile setup across much of western and southwestern Oklahoma by 00Z Wednesday (7pm Tuesday). Impressive boundary layer moisture (in the upper sixties to low seventies), upper-end thermodynamics with CAPE values approaching or exceeding 3000-4000J/Kg, the wind profile clearly favors supercells with veering and strengthening with height producing 45-55kt of effective vertical shear and effective helicities of 250-350m2/s2... Perhaps most importantly from a perspective of maintaining discrete convection, background CIN is on the order of -20 to -40, which is certainly breakable but also enough to limit storm coverage. From a tornado perspective, low-level CAPE is on the upper-end of what you would want (hope) to see and critical angles are *ideal* for stream-wise vorticity ingestion into the mesocyclone (near 90), in addition LCLs are certainly manageable. 

Precip field on this run would generally indicate supercells along the dryline at/by 00Z... with a lot of prefrontal junk in eastern OK at 00Z as well. Early/mid afternoon crapvection is clearly a lesser issue the last couple runs on the GFS. Going to be a game of wait and see, as per usual. 

Of course of all that is taking a singular model run verbatim, so do that at your own risk while also considering the usual caveats at this forecast hours, and the obvious caveats with this setup. 

 

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54 minutes ago, jojo762 said:

06Z GFS depicts a highly volatile setup across much of western and southwestern Oklahoma by 00Z Wednesday (7pm Tuesday). Impressive boundary layer moisture (in the upper sixties to low seventies), upper-end thermodynamics with CAPE values approaching or exceeding 3000-4000J/Kg, the wind profile clearly favors supercells with veering and strengthening with height producing 45-55kt of effective vertical shear and effective helicities of 250-350m2/s2... Perhaps most importantly from a perspective of maintaining discrete convection, background CIN is on the order of -20 to -40, which is certainly breakable but also enough to limit storm coverage. From a tornado perspective, low-level CAPE is on the upper-end of what you would want (hope) to see and critical angles are *ideal* for stream-wise vorticity ingestion into the mesocyclone (near 90), in addition LCLs are certainly manageable. 

Precip field on this run would generally indicator supercells along the dryline at/by 00Z... with a lot of prefrontal junk in eastern OK at 00Z as well. Early/mid afternoon crapvection is clearly a lesser issue the last couple runs on the GFS. Going to be a game of wait and see, as per usual. 

Of course of all that is taking a singular model run verbatim, so do that at your own risk while also considering the usual caveats at this forecast hours, and the obvious caveats with this setup. 

 

Nice to see maybe not all hope is lost. I haven’t had a chance to look at the Euro though.

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8 minutes ago, WhiteoutWX said:

Nice to see maybe not all hope is lost. I haven’t had a chance to look at the Euro though.

00Z Euro couldn’t possibly be any different than what the GFS is showing. Basically a non-zero severe threat on the euro. 

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GFS is pretty much the only model showing this. NAM and Euro both push the front very south which makes sense given the seasonally cold air mass in the Plains with that high pressure. GFS tends to underestimate cold frontal surges. But SPC must be giving some credence to it because if they were following anything close to the other models, OK would pretty much be out of this

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The NAM looks in between the Euro and GFS. I think the Big difference between the GFS/Euro is how much morning convection there is. Euro has a lot through the morning which helps to propagate the front further south. Hard to know from this range which is more likely. 

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All I know is if the front is as far south as the Euro/NAM project (albeit they have been shifting north a bit), the threat is pretty much cooked. The LLJ axis to the E might get interesting though if there isn't a large amount of antecedent convection.

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D2 shifted the threat even further north. Slight risk barely crosses the red river and stops just west of Illinois

Screenshot_20190429-005401_Chrome.jpg

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SPC mentions strong tornadoes possible:

”Initial storm development will probably be accompanied by a risk for very large hail, with an increasing risk for potential damaging wind gusts in subsequent upscale convective growth.  However, in any lingering discrete storm development, the risk for tornadoes could increase by Tuesday evening, with a strong tornado or two possible, before boundary layer instability wanes later Tuesday evening.”

 

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Tuesday is not the debacle progged a few days ago. It's not great; but, I think it can be salvaged for those already in the Plains. No travel plans for me. The strong tornadoes but 5% seems like a disconnect on first read. However, they are right. Who knows where the boundaries will intersect?

Warm front might produce in Missouri, state motto Show Me (tornadoes). However another Missouri solution is an MCS rolling down I-70 and overturning the atmosphere. Given the less than ideal terrain, I would look elsewhere. Exceptions might be local KC/STL chasers or vacationers approaching from the Midwest.

Another potential chase target is farther south from SE Kansas into Oklahoma. SE KS terrain is not ideal, but do able. Oklahoma of course crowds factor in. Morning MCS farther north should drop an outflow boundary. Separate from the cold front would be ideal for chasing concerns. Dry line like feature is forecast to come out in Oklahoma. Perhaps look for the intersecting boundaries. Some progs have the CF surging, but not super cold north side. That could work as the east-west boundary intersecting DL; but, I'd prefer a separate outflow boundary.

Wednesday may also go; but, that will depend on Tuesday. Since Tuesday depends on Monday night, I'll leave it with Tuesday.

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I've updated the title to account for the Slight risk for today (April 29) in Texas as well as the broad Slight risk on Wednesday (May 1) as well.  Where I'm at (DFW) seems like our highest risk is going to be Wednesday, per the SPC outlook, unless something drastically changes for tomorrow.

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This is one of the CAM forecasts tomorrow (01z).  There should be a mess of cells in the northern area, centered on the Springfield MO area, and there may be some discrete cells in the southern area. Even with the large amount of cells in the northern area, the SRH may be above 400 m2/s2. This may lead to a greater tornado/hail/wind risk farther north. More chase-able tornadic storms may be farther south. It does not appear there will be a dryline pushing into the north Texas area, and drylines usually make for better chase conditions.

eL4YprT.png

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The southern jet originating from Mexico is going to add a few unknown variables into the coming days. Models handled extremely poorly with that element in events earlier this winter.

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Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Tue Apr 30 2019

   Valid 301200Z - 011200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE OK/TX
   RED RIVER VICINITY NORTHEASTWARD INTO SOUTHWESTERN MISSOURI...

   ...SUMMARY...
   Severe thunderstorms are possible in a corridor across parts of the
   southern Plains northeastward toward Illinois/Indiana Tuesday
   afternoon into Tuesday night.  This will include a risk for large
   hail, locally damaging wind gusts and a few tornadoes.

   ...Synopsis...
   Large-scale troughing will persist across the Western U.S. today.  A
   lead wave - currently over the Lower Colorado River Valley - will
   open up while ejecting northeastward through the central
   Rockies/Plains, eventually reaching Wisconsin/Illinois by the end of
   the forecast period.  A second trough will amplify southeastward
   from the Pacific Northwest into Wyoming.  A ridge will extend from
   the Great Lakes southward across the Southeast.

   At the surface, a couple of lows will organize in response to the
   ejecting mid-level shortwave - one across Colorado and another
   across the central Plains/Mid-Missouri Valley.  A nearly stationary
   front will extend from the Texas South Plains north-northeastward
   into eastern Kansas, then transition to a warm front across central
   Illinois/Indiana.  Plains portions of this front will oscillate
   northwestward to southeastward today, with those oscillations tied
   to trends in convection in that general vicinity.  South and east of
   the front, southerly low-level flow will maintain a moist and
   buoyant low-level airmass characterized by near 70s F dewpoints.  

   ...Texas northeastward to Illinois/Indiana...
   Early morning convection should be ongoing at the start of the
   period along an axis from the Texas South Plains northeastward to
   eastern Kansas and southern Iowa - mostly along and north of the
   stationary front that should be located from northwest Texas to near
   Kansas City.  Some of these storms may migrate east of the front and
   become surface based, with an attendant risk of isolated damaging
   wind gusts and a brief tornado given strong low-level shear profiles
   and sufficient buoyancy.  30-40 kt southerly 850mb flow may
   encourage northward retreat of this boundary during the morning,
   though the eventual afternoon position of this front will ultimately
   depend on the extent of elevated convection that can develop from
   northwest Texas into northern Oklahoma.

   Over the course of the day, bands of convection are expected to
   organize along an axis from west-central Texas through central
   Oklahoma and into southeastern Missouri very near and just ahead of
   the eventual position of the front.  Pre-frontal convection may also
   evolve from western Arkansas northeastward to central lllinois -
   particularly from mid-morning through the afternoon.  This
   convection may struggle against weak inhibition with southern
   extent, although point forecast soundings indicate a mostly uncapped
   airmass with strong instability and shear across central Illinois
   and adjacent areas of eastern Missouri during the afternoon. Mixed
   convective modes (linear and supercellular) are expected given the
   shear/instability parameter space within the warm sector (1500 J/kg
   MLCAPE across MO/IL increasing to near 4000 J/kg southward across
   west Texas).  At this time, the greatest tornado risk appears
   concentrated across north Texas, eastern Oklahoma, and into central
   Illinois beneath the low-level jet axis where shear profiles will be
   strongest.  A northward-moving warm front across central IL/IN may
   also provide impetus for updraft rotation/tornadogenesis pending
   favorable convective interactions.  Farther southwest across
   west-central Texas, low-level wind fields are expected to be a bit
   less favorable for tornadoes, though steeper lapse rates and
   sufficient deep shear will support large (perhaps significant) hail
   and damaging wind gusts.

   A lingering uncertainty revolves around the northward retreat of the
   surface boundary this afternoon across Oklahoma.  A more
   westward/northwestward position of this boundary is possible pending
   evolution of early-morning convection, and this may result in a
   higher afternoon and evening severe threat than currently depicted
   in this outlook.  This area will be monitored for possible upgrade
   later today.

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I'm starting to wonder if storms could form earlier in the day (about 5-6 hours from now) over north-central Texas given the recent HRRR runs showing discrete activity around that time.  RAP is depicting the same thing pretty much.

EDIT: interestingly enough SPC just downgraded most of DFW to a marginal risk.

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Latest run of HRRR and the 12z WRF-ARW now showing some agreement on discrete activity in Eastern OK by 18z. Previous runs had a more congealed QLCS look vs the more discrete activity it's currently showing. I wonder if we'll see a MOD for Eastern OK with the next D1 update from the SPC.

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Days like this are pretty humbling from a model perspective. This thing can fizzle out or quietly sneak up and produce some discrete cells that could drop some tornadoes. Models in the last 48 hours have shown both possible modes, but we won't know which way the day is leaning until at least lunch time today.

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Several tornadoes, some probably significant appear probable today across the eastern half of Oklahoma. Yes there will be A LOT of cells with a myriad of storm modes existing. But intense supercell structures, even if transient, appear likely. Degree of low-level moisture, instability, and wind fields will strongly favor  intense mesocyclones.

Mix of discrete/semi-discrete supercells and clusters gradually transitioning to more linear modes appear probable. 

FWIW, 09Z calibrated SREF pops a 30% and 45% tornado risk across southern OK later today... which is, uh impressive.

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