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May 15-20 Severe Threat

MattPetrulli

By MattPetrulli,
in Central/Western States

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yoda

yoda

Posted
Posted 
Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1139 AM CDT Thu May 18 2017

   Valid 181630Z - 191200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHWESTERN AND CENTRAL KANSAS SOUTH INTO NORTHWEST OKLAHOMA...

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE SOUTHERN TWO-THIRDS OF KANSAS AND INTO WESTERN AND NORTHERN
   OKLAHOMA...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   HIGH AND MDT RISK AREAS...AND EXTENDING EAST TO FAR WESTERN MISSOURI
   AND SOUTH INTO CENTRAL TEXAS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS A BROAD
   SWATH OF THE CENTRAL AND SOUTHERN PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
   GREAT LAKES VICINITY EAST-NORTHEAST TO WESTERN NEW ENGLAND...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   CENTRAL AND SOUTHERN PLAINS SURROUNDING HIGHER-RISK AREAS...AND
   EAST-NORTHEAST ACROSS THE MIDWEST AND INTO NEW ENGLAND SURROUNDING
   HIGHER-RISK AREAS...

   ...SUMMARY...
   An outbreak of severe thunderstorms with tornadoes, very large hail
   and wind damage is expected to develop across parts of the southern
   and central Plains from this afternoon into this evening and
   overnight.  Some strong, long-lived tornadoes are expected, along
   with hail to near 4 inches in diameter, over parts of Kansas and
   Oklahoma.  Large hail, tornadoes and wind damage also will be
   possible outside of these areas across parts of the southern and
   central Plains.  Locally damaging gusts and sporadic hail also are
   expected across parts of the lower Great Lakes region to western New
   England this afternoon and early evening.

   ...Synopsis...
   A large upper low centered over Utah this morning and comprised of
   two smaller centers of upper circulation -- one moving
   east-northeast over southwest Colorado and the other moving
   south-southwest across northeast Nevada and western Utah -- is
   forecast to weaken overall while making very slow eastward progress
   today.  With large-scale/broad upper troughing surrounding this
   feature affecting roughly the western half of the country, dowstream
   ridging will largely prevail over the east.  The exception will be
   across the Great Lakes and into New England, where low-amplitude
   northern-stream short-wave troughing will progress eastward with
   time, north of the southern-stream ridge.

   At the surface, a low over the upper Great Lakes this morning is
   forecast to move/develop eastward through southeast Canada --
   crossing the Ottawa and St. Lawrence Valleys through tonight.  A
   trailing cold front will become increasingly west-to-east oriented
   across the Midwest/Ohio Valley region, as the low moves quickly
   eastward, while some northward retreat of the front may occur into
   Kansas as a southern Plains lee low strengthens ahead of western
   U.S. upper troughing.  Continued northward advection of low-level
   moisture across the southern Plains and into parts of Kansas will
   support development of widespread strong-to-severe storms near this
   front, and near and ahead of a dryline extending southward across
   Texas and Oklahoma.  As a result, a broad, potentially high-end,
   all-hazards outbreak of severe weather is expected this afternoon.

   ...Central and southern Plains...
   A complex -- but likely higher-end -- severe weather outbreak is
   expected to evolve this afternoon and evening, near and south of a
   warm front moving slowly northward into Kansas and east of a dryline
   mixing slowly eastward across the southern High Plains.  Very moist
   low-level air continues streaming northward ahead of the developing
   lee low over the High Plains, which combined with strong heating and
   very steep lapse rates aloft within the elevated mixed layer will
   result in strong destabilization, with mixed-layer CAPE into the
   3000 to 4000 J/kg range expected by late afternoon.  Along with
   initiation near the warm front and southward along the dryline mid
   afternoon, CAMs as well as to some degree operational model runs
   continue to strongly suggest a secondary area of convective
   development across parts of central Texas, ahead of the dryline. 
   Cellular initial development in all areas will rapidly
   organize/become supercellular, with attendant risk for very large
   hail and locally damaging winds.  In addition, with low-level flow
   likely to remain backed near the frontal zone and southward across
   western and central Oklahoma, a very favorable low-level wind field
   (0-1 km shear in excess of 40 kt and helicity in excess of 300
   m2/s2) suggests that right-moving supercells will be favored, and
   capable of producing strong/damaging tornadoes.

   With time, guidance suggests upscale growth of convection -- both
   across Texas with storms spreading eastward across central and north
   Texas through the evening, and across the Kansas/Oklahoma area where
   one or more northeastward-surging, bowing bands of storms are
   indicated.  Given the degree of CAPE, dry air aloft, and strong
   shear, an organized/widespread damaging wind risk is also apparent. 
   Greatest overall combined risk appears to remain across Kansas and
   the northwest half of Oklahoma, though expansion of the ENH risk
   area (to include all severe hazards) is being introduced southward
   to central Texas at this time.  

   Risk should continue through the evening and into the overnight
   hours, with bands of storms spreading east into parts of Missouri
   and Arkansas, but with likelihood for some continued redevelopment
   of storms across western portions of the risk area near the dryline,
   as large-scale ascent persists ahead of the slowly advancing western
   upper trough.
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jojo762

jojo762

Posted
Posted
3 minutes ago, 1900hurricane said:

The cell that tried firing near Snyder, TX looks like it's dying out.

Indicative of an unfavorable/hostile environment, currently, for significant convective development. Good sign, still just 17Z though. 

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hlcater

hlcater

Posted
Posted
4 minutes ago, yoda said:

It doesn't say whether it will be PDS or not... but I am guessing it will be when it is issued

Not so sure about that. While the environment here is favorable, no doubt about it, along with high instability, the VWPs here aren't nearly as good as the ones that are forecast to be present over NW OK and KS later today. Despite this, tornadoes are definitely possible in this area, hence the watch. I think large hail due to steep lapse rates and RFD damaging wind will probably be the greatest threat, but tornado potential will need to be watched as well. I don't have time to check mesoanalysis and forecast soundings, hence the lack of concrete numbers, I just know that conditions in this ballpark are forecast to be in place.

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jojo762

jojo762

Posted
Posted
1 minute ago, OceanStWx said:

Former student intern here at GYX. Clearly having more fun than we are now.

Loaded gun with a stout cap, looks good, and that wind profile will obviously improve bigly here in a few hours. 

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Quincy

Quincy

Posted
Posted
15 minutes ago, Amped said:

With that much cape there's bound to be a lot of HP cells. Not the safest day to be chasing.

Chaser behavior/traffic/etc. has become increasingly problematic in recent weeks as well with threats in Oklahoma and immediately adjacent areas. Combine that with such a significant threat zone relatively close to OKC and there's more evidence to support your bolded statement above. 

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Superstorm93

Superstorm93

Posted
Posted 
 Some forecast soundings
   indicate a deep-layer wind profile marginally supportive of a few
   left splits with initial warm sector development east of the dry
   line this afternoon. Cell mergers/interference would preclude a
   higher-end severe threat. However, as low-level hodographs enlargen
   (with greater clockwise looping) late this afternoon into this
   evening, cyclonically rotating supercells may become favored, with a
   greater eastward component of movement. Any such discrete cell would
   possess a threat for tornadoes (which could be strong), very large
   hail, and damaging winds.
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