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Short-Term Severe/Flooding Discussion


Quincy
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So sorry to hear about SE Texas... again!!! Can't get a break.

Meanwhile, the Front Range and adjacent Plains are having a sudden hail-fest, after training hailstorms (yes) last night up the I-76 corridor. Today we have a couple of almost-tornadoes near Hudson and Keenesburg and baseball sized hail in the densely populated South Metro area. 2 inch hail at my house, 3 inch hail only 2 miles in both directions. Not home to provide pics, but there are plenty on Twitter if you like broken windshields. Yikes.

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BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Brownsville TX
1045 AM CDT WED JUN 20 2018

...FLASH FLOOD EMERGENCY FOR SOUTHEAST HIDALGO COUNTY...

The National Weather Service in Brownsville has extended the

* Flash Flood Warning for...
  Southeastern Hidalgo County in Deep South Texas...

* Until 215 PM CDT.

* At 1037 AM CDT, Doppler radar indicated heavy rain from
  thunderstorms has fallen across the warning area. The radar
  estimates 4 to 9 inches of rain has fallen across the warning
  area. Flash flooding is already occurring. Hidalgo County
  Emergency Management reported multiple vehicles submerged under
  water in the warning area earlier this morning and most of the
  frontage roads along I-2 remain flooded.

  This is a FLASH FLOOD EMERGENCY for southeast Hidalgo county.
  This is a PARTICULARLY DANGEROUS SITUATION. SEEK HIGHER GROUND NOW!

* Some locations that will experience flooding include...
  Edinburg, Mission, Pharr, San Juan, Alamo, Donna, Hidalgo, Elsa,
  Palmhurst and North McAllen.
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BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Brownsville TX
1012 AM CDT WED JUN 20 2018

...FLASH FLOOD EMERGENCY FOR Southeastern Hidalgo and Northwestern
Cameron Counties...

The National Weather Service in Brownsville has extended the

* Flash Flood Warning for...
  Southeastern Hidalgo County in Deep South Texas...
  Northwestern Cameron County in Deep South Texas...

* Until 130 PM CDT.

* At 1008 AM CDT, Doppler radar indicated thunderstorms producing
  heavy rain across the warned area. Flash flooding is already
  occurring. Doppler radar and local observations have measured
  accumulated rainfall of up to 15 inches in the warned area.

  This is a FLASH FLOOD EMERGENCY for Southeastern Hidalgo and
  Northwestern Cameron Counties. This is a PARTICULARLY DANGEROUS
  SITUATION. SEEK HIGHER GROUND NOW!

* Some locations that will experience flooding include...
  Harlingen, Weslaco, San Benito, Mercedes, La Feria, Progreso,
  Edcouch, Santa Rosa, Rio Hondo and La Villa.
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Surprised no one is talking about this severe threat in the southern plains. SPC just added a moderate risk area for parts of KS/OK/TX.

Quote

Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1244 PM CDT Sat Jun 23 2018 Valid 241200Z - 251200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF SOUTHERN KANSAS INTO NORTHWEST OKLAHOMA...

...SUMMARY... Significant severe storms capable of destructive winds, very large hail and a few tornadoes are possible on Sunday across much of Kansas, northern Oklahoma and into the eastern Texas Panhandle. A few severe storms are also possible from Missouri toward Tennessee and Kentucky.

...Central/Southern Plains to Mid-Missouri Valley... A shortwave trough will migrate across the Plains, bringing a band of 40-50 kt southwesterly midlevel flow across the region. At the surface, rich low level moisture (dewpoints upper 60s to low 70s) will be in place ahead of a southeastward advancing cold front. Additionally, a dryline will extend southward from a surface low over the TX Panhandle. Convection will likely be ongoing across parts of NE at the beginning of the period. Further south, some cloud debris is possible from overnight convection in the Day 1 period, but the airmass across KS into OK should experience strong heating. As such, an extremely unstable airmass will evolve by afternoon. There is some uncertainty regarding convective evolution, with the NAM forecast continuing to be an outlier compared to other deterministic and hi-res guidance. Expect that one or more clusters will develop across NE along the front and track east/southeast through the morning. Additional storms will then develop southward along the front across western KS, as well as across the OK/TX Panhandles in the vicinity of the surface low/triple point. 40+ kt deep layer shear coupled with very steep lapse rates will favor initial supercells capable of very large hail and damaging winds. Cells likely will not stay discrete long and quick upscale growth is expected. The strength of deep layer shear and degree of instability will support widespread damaging winds, with many significant wind gusts possible. Any cell that can remain discrete will pose a tornado threat initially given high-quality low level moisture (mean mixing rations around 17 g/kg) and favorable low level shear. Additionally, embedded mesovortex circulations are possible once upscale growth occurs. One or more bowing segments are expected to track east/southeast across KS and northern OK overnight, with strong wind potential being maintained due to increasing 40-50 kt southwesterly low level jet. Additional strong to severe storm are possible in warm advection across MO into IA. A very unstable and moist airmass will be in place, though deep layer shear will remain more modest. Still, steep low level lapse rates and high PW values could result in scattered strong wind gusts

. ...Portions of the mid-Mo Valley into KY/TX Vicinity... A weak lead shortwave impulse will track eastward across the region during the afternoon. This will provide enough deep layer shear and forcing some organized cells capable of strong wind gusts. Lapse rates will remain poor in spite of moderate instability, limiting large hail potential.

...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 45% SIG - Moderate Hail: 30% SIG - Enhanced

..Leitman/Smith.. 06/23/2018

 

day2otlk_1730.gif

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Seems to me that CAMs, especially the HRRR, have been a bit (way) too slow with the severe MCS currently raging over NC OK. Could bode well for later severe prospects, but the festering convection tailing the MCS and the developing complex over NW KS/E CO has me still concerned.  

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Outflow is surging south across the Texas panhandle and should reach I-40 in the Amarillo vicinity shortly. Would have to guess that most areas east of US-83 are game over for anything significant. It's unclear if the panhandle outflow will be detrimental, period, or if the atmosphere can recover and use the boundary as a focal point late this afternoon. 

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Yesterday was terrible, today is terrible, tomorrow will be terrible, and I’m sure Tuesday will find a way to fall apart across northern Illinois. Just an absolutely miserable severe season. MCS washout galore. 

Curious to see how far east the current severe storms over western KS can maintain their severe levels. 

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On 6/24/2018 at 7:29 PM, jojo762 said:

Yesterday was terrible, today is terrible, tomorrow will be terrible, and I’m sure Tuesday will find a way to fall apart across northern Illinois. Just an absolutely miserable severe season. MCS washout galore. 

Curious to see how far east the current severe storms over western KS can maintain their severe levels. 

Boy did you ever call it. Despite 3 tornado reports, all were brief and all unwarned except the last which was based on a law enforcement report.

I've forgotten what a supercell radar signature looks like.

worst-spring-ever.jpg

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Depends what model you prefer for Thursday. NAM’s low-level wind fields are wholly unimpressive, and would just simply not get the job done. S/W timing is a bit early too, yet the NAM does not convect until ~19-21Z, for some reason. GFS shows a similar timing and convects by before 15Z, and continues to through much of the afternoon before a large MCS forms by evening. NAM also shows an eventual MCS. Storm mode seems like an obvious caveat, as per usual in the summer. Very strong instability will be in place, which lends some credence to the idea of a slop fest... however, low-level winds, and really the entire column in general, are very impressive on the GFS, even before 00Z. Looks like a day where a few tornadoes are possible, possibly even a strong one *IF* the GFS is right, which I’m not sure I’m buying it’s stock right now. Models have been abysmal lately, especially CAMs.

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Latest HRRR renditions, in addition to most of the SPC HREF members, throw a bit of an additional wrench/caveat into the threat later today. You guessed it... Morning convection — perhaps persisting into the early afternoon, as indicated in a couple CAM solutions — downstream of the current enhanced risk area. This, of course, would prove to be quite detrimental to what would otherwise be an impressively moist boundary-layer (with surface dew points well into the upper 60s to low 70s)... In addition, numerous CAM solutions — aside from the 00z NSSL-WRF, which tends to carry more weight in my book — do not develop storms until either nearly 23z OR even later, mostly in eastern Montana/Wyoming with next to no development further east along the warm front in North Dakota, where conditions will be admittedly more favorable for low-level mesocyclones.

Not looking too great. However if the NSSL-WRF verifies, we could be looking at a fairly interesting day. But going off a consensus amongst the CAMs (which, keep in mind have not even doing too stellar lately)... appears to be an hour or two of discrete/semi-discrete activity (in a less favorable environment, than if it were further east/along the warm front) before eventual upscale growth into a rather large MCS or two. 

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1 hour ago, CheeselandSkies said:

MDT risk incoming per activity loop graphic. Site says 13Z was issued 15 minutes ago but nothing else has updated.

Looks like a do over for the last North Dakota moderate risk, plus this is a bit farther south. While this has early day convection like that day, today's morning convection is exiting the area along a warm front and should have little to no negative affect on the environment, based on timing and observational tends. 

Cautiously optimistic that there could be a few tornadoes today and possibly a strong one given the degree of instability coupled with substantial deep layer shear. Storms interacting with the outflow reinforced warm frontal boundary in western to central ND should pose the greatest supercell tornado risk. The threat for a potentially significant MCS increases tonight in the same general area. 

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8 minutes ago, Quincy said:

Looks like a do over for the last North Dakota moderate risk, plus this is a bit farther south. While this has early day convection like that day, today's morning convection is exiting the area along a warm front and should have little to no negative affect on the environment, based on timing and observational tends. 

Cautiously optimistic that there could be a few tornadoes today and possibly a strong one given the degree of instability coupled with substantial deep layer shear. Storms interacting with the outflow reinforced warm frontal boundary in western to central ND should pose the greatest supercell tornado risk. The threat for a potentially significant MCS increases tonight in the same general area. 

About time that happened at least once in 2018.

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1 hour ago, CheeselandSkies said:

Tornado probs slashed back to 5% at 1630Z without explanation. Marginal wind probs expanded into WI, just barely touching Madison.

Low-level shear may be on the lower end of the spectrum, but with 5000 J/kg MLCAPE, 50-60kts of deep layer shear and >100 m2/s2 0-1km SRH, the downgrade seems a bit odd. It doesn't help that convection allowing models have been inconsistent for the eastern portion of the threat zone, but the potential for intense supercells seems unusually high (given local climatology) for eastern Montana into western North Dakota. I'd think very large to possibly giant hail may be the biggest threat, but even with modest low-level shear, the thermodynamic profile alone coupled with more than adequate deep layer shear suggests an "enhanced" tornado threat. 

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I have to suspect low-level shear wasn't much if any better in SW WI on Tuesday, with much less impressive instability parameters. Sometimes the atmosphere just behaves oddly and things happen on such a small scale they can't be resolved by any model. How many times have we seen big honking supercells struggle to produce tornadoes because the dewpoint was 2 degrees too low, or the RFD too wet, or not enough 0-1km SRH, while those teeny little thundershowers spun them up like nobody's business?

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