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May 15-20 Severe Threat


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Also potential mod risk in next update for KS/NE/IA/MO

Quote

   ...KS/NEB/IA/MO...
   Morning water vapor loop shows a deep trough over the western
   states, with a leading shortwave impulse rotating across NM.  12z
   model solutions remain consistent that a cluster of intense
   thunderstorms will develop by mid afternoon over parts of southwest
   KS as this shortwave trough approaches.  Strong heating is occurring
   in this region, with afternoon MLCAPE values over 3000 J/kg and
   minimal cap.  Initial storms will likely be capable of very large
   hail and isolated tornadoes, but it seems likely that rapid upscale
   growth into a fast-moving squall line will occur.  This will enhance
   the risk of damaging winds as storms spread northeastward across
   central/eastern KS and into parts of NE/IA/MO.  If storm-scale
   trends dictate, this area may be considered for an upgrade to MDT
   risk in later updates.

 

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All the CAMs are insistent upon developing a very big isolated supercell down around Midland.  If it persists as it moves off of the dryline, it eventually runs into better low-level shear, albeit not as good as up north.  Still, that could be a hell of a storm with lots of CAPE to work with.

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12z GFS/NAM kicked Thursday up a notch as well. Assuming the forecast convection further south in TX isn't overly detrimental, there's a fairly decent shot that could be a rather significant/widespread severe wx event given the breadth of the warm sector, strong flow aloft and strong backing of the surface winds (among other things).

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33 minutes ago, Jonbo said:

Also potential mod risk in next update for KS/NE/IA/MO

Strong heating is occurring in this region, with afternoon MLCAPE values over 3000 J/kg and minimal cap.



If there's little cap and so much CAPE, does that give these storms a better chance to go linear rather than form discrete SCs?
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5 minutes ago, andyhb said:

12z GFS/NAM kicked Thursday up a notch as well. Assuming the forecast convection further south in TX isn't overly detrimental, there's a fairly decent shot that could be a rather significant/widespread severe wx event given the breadth of the warm sector, strong flow aloft and strong backing of the surface winds (among other things).

Parameter space on both is fairly significant - comparable to today, perhaps a tad better, and over a much larger area. Hard to go wrong in May with seasonable moisture, a favorably timed mid-level jet, a substantial southerly/south-southeasterly low-level jet, and steep lapse rates.

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 Mesoscale Discussion 0730
   NWS Storm Prediction Center Norman OK
   0119 PM CDT Tue May 16 2017

   Areas affected...eastern tx/ok panhandle...western ok

   Concerning...Severe potential...Tornado Watch likely 

   Valid 161819Z - 161915Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe thunderstorms will develop across the eastern TX/OK
   Panhandles over the next few hours.  Tornadoes are expected with
   this activity, along with very large hail and severe wind gusts. 
   Tornado watch will be issued by mid afternoon.

   DISCUSSION...Latest visible satellite imagery suggests large-scale
   forcing for ascent is spreading across the southern Rockies, per
   marked increase in showers and thunderstorms over western/central
   NM.  Downstream, dry line has mixed east and is becoming well
   defined over the TX Panhandle/South Plains region with substantial
   boundary-layer cu immediately east of the dry line.  Towering cu,
   and a few attempts at glaciation, are noted over
   Hutchinson/Hansford/Ochiltree Counties.  There is increasing
   confidence supercells will develop across the eastern TX/OK
   Panhandles by mid afternoon with subsequent movement expected into
   western portions of OK/southwest KS into the evening. Environmental
   conditions appear favorable for tornadoes and very large hail as
   steep lapse rates are evident on 12z soundings and surface dew
   points have now risen into the mid 60s.  Environmental conditions
   appear favorable for a few strong tornadoes.

   ..Darrow/Hart.. 05/16/2017
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1 minute ago, jojo762 said:

 Mesoscale Discussion 0730
   NWS Storm Prediction Center Norman OK
   0119 PM CDT Tue May 16 2017

   Areas affected...eastern tx/ok panhandle...western ok

   Concerning...Severe potential...Tornado Watch likely 

   Valid 161819Z - 161915Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe thunderstorms will develop across the eastern TX/OK
   Panhandles over the next few hours.  Tornadoes are expected with
   this activity, along with very large hail and severe wind gusts. 
   Tornado watch will be issued by mid afternoon.

   DISCUSSION...Latest visible satellite imagery suggests large-scale
   forcing for ascent is spreading across the southern Rockies, per
   marked increase in showers and thunderstorms over western/central
   NM.  Downstream, dry line has mixed east and is becoming well
   defined over the TX Panhandle/South Plains region with substantial
   boundary-layer cu immediately east of the dry line.  Towering cu,
   and a few attempts at glaciation, are noted over
   Hutchinson/Hansford/Ochiltree Counties.  There is increasing
   confidence supercells will develop across the eastern TX/OK
   Panhandles by mid afternoon with subsequent movement expected into
   western portions of OK/southwest KS into the evening. Environmental
   conditions appear favorable for tornadoes and very large hail as
   steep lapse rates are evident on 12z soundings and surface dew
   points have now risen into the mid 60s.  Environmental conditions
   appear favorable for a few strong tornadoes.

   ..Darrow/Hart.. 05/16/2017

Wouldn't be surprised to see this as a higher-end/PDS tornado watch.

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1 minute ago, jojo762 said:

A PDS Watch could be warranted, but given that this should occur over relatively sparsely populated areas, im not sure that they will pull the trigger on that. 

I thought it was only geographical distribution, number, and intensity of storms that determined the PDS watch and not population but I could be wrong.

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3 minutes ago, Upper Level LOL said:

PDS tornado watch out

 

e: yeah I have no idea what Jojo is talking about regarding population

Intensity of storms matters the most. But they prefer to issue them in areas with higher population densities due to the higher probability of destruction. 

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9 minutes ago, jojo762 said:

Intensity of storms matters the most. But they prefer to issue them in areas with higher population densities due to the higher probability of destruction. 

Got a source on that? That doesn't seem to make a lot of sense on first blush. Tornado outbreaks are dangerous regardless population density

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   Mesoscale Discussion 0731
   NWS Storm Prediction Center Norman OK
   0203 PM CDT Tue May 16 2017

   Areas affected...western/central ks

   Concerning...Severe potential...Watch likely 

   Valid 161903Z - 161930Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe thunderstorms are expected to develop across much
   of western and central Kansas this afternoon.  Large hail and
   isolated tornadoes are likely, along with some damaging winds. 
   Tornado watch will be issued shortly.

   DISCUSSION...Higher quality boundary-layer moisture is advecting
   north across the central Plains early this afternoon, per
   deepening/expanding cu field.  Dry line should sharpen and retreat
   slightly over western Kansas over the next few hours and supercells
   are expected to develop beneath agitated mid-level convection
   currently expanding across this region.  It's not entirely clear
   what is causing this mid-level convection but low-level moistening,
   and cooling aloft should minimize CINH such that convection should
   increase and expand northeast into the early evening hours.  Very
   large hail and isolated tornadoes appear likely.

   ..Darrow/Hart.. 05/16/2017

 

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FAST storm motions... Wall cloud on the northern supercell about to enter the OK PH.

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 245 PM CDT
FOR WESTERN BEAVER...EASTERN TEXAS...NORTHEASTERN HANSFORD AND
NORTHWESTERN OCHILTREE COUNTIES...

At 206 PM CDT, a severe thunderstorm was located 10 miles northwest
of Perryton, moving northeast at 50 mph.

HAZARD...Golf ball size hail and 60 mph wind gusts. A wall cloud is 
         also being observed with this storm. 

SOURCE...Radar indicated. 

IMPACT...Minor damage to roofs, siding, and trees is possible. 
         People and animals outdoors will be injured. Expect hail 
         damage to roofs, siding, windows, and vehicles. 

Locations impacted include...
Perryton, Beaver, Tyrone, Forgan, Hardesty, Adams, Farnsworth, Boyd,
Floris, Bryans Corner, Baker, Mocane, Turpin, Balko and Elmwood.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

This thunderstorm is capable of producing all types of severe weather
including extremely large hail, destructive straight line winds and
tornadoes. Move quickly to a safe shelter, such as an interior room,
a bathroom or closet or basement.

&&

A tornado watch remains in effect until 1000 PM CDT for the Panhandle
of Oklahoma...and the Panhandle of Texas.

LAT...LON 3628 10084 3640 10127 3700 10110 3700 10016
TIME...MOT...LOC 1906Z 219DEG 47KT 3649 10096 

TORNADO...POSSIBLE
HAIL...1.75IN
WIND...60MPH
 

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21 minutes ago, jojo762 said:

Intensity of storms matters the most. But they prefer to issue them in areas with higher population densities due to the higher probability of destruction. 

Yeah no Rick Smith in OUN  says this is pretty much false. Population density doesn't really matter at all when they make that call.

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