May 18, 2017 2000 UTC Day 1 Convective Outlook
Updated: Thu May 18 19:45:03 UTC 2017 (20170518 2000Z Day 1 shapefile | 20170518 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Public Severe Weather Outlook

The SPC is forecasting ...Outbreak of tornadoes and severe thunderstorms expected over parts of the central and southern Plains this afternoon and tonight....   Please read the latest public statement about this event.  View What is a Watch? clip.

Categorical Graphic
20170518 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
HIGH 24,321 909,140 Wichita, KS...Enid, OK...Hutchinson, KS...Dodge City, KS...Derby, KS...
MODERATE 27,938 618,718 Salina, KS...Stillwater, OK...Emporia, KS...Ponca City, OK...Yukon, OK...
ENHANCED 97,549 12,153,914 Dallas, TX...Fort Worth, TX...Oklahoma City, OK...Kansas City, MO...Tulsa, OK...
SLIGHT 172,116 11,558,582 Buffalo, NY...Rochester, NY...Springfield, MO...Syracuse, NY...Waco, TX...
MARGINAL 244,892 24,666,414 San Antonio, TX...Columbus, OH...Austin, TX...Cleveland, OH...Omaha, NE...
Probabilistic Tornado Graphic
20170518 2000 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SIG SEVERE 62,481 2,783,457 Oklahoma City, OK...Wichita, KS...Norman, OK...Lawton, OK...Edmond, OK...
30 % 24,330 904,275 Wichita, KS...Enid, OK...Hutchinson, KS...Dodge City, KS...Derby, KS...
15 % 27,587 619,550 Salina, KS...Stillwater, OK...Emporia, KS...Ponca City, OK...Yukon, OK...
10 % 24,906 1,740,541 Oklahoma City, OK...Norman, OK...Wichita Falls, TX...Lawton, OK...Edmond, OK...
5 % 65,615 5,495,430 Fort Worth, TX...Kansas City, MO...Tulsa, OK...Overland Park, KS...Kansas City, KS...
2 % 184,814 16,396,677 Dallas, TX...Arlington, TX...Buffalo, NY...Plano, TX...Garland, TX...
Probabilistic Damaging Wind Graphic
20170518 2000 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SIG SEVERE 50,569 2,760,539 Oklahoma City, OK...Wichita, KS...Topeka, KS...Edmond, OK...Midwest City, OK...
30 % 138,338 13,619,105 Dallas, TX...Fort Worth, TX...Oklahoma City, OK...Tulsa, OK...Arlington, TX...
15 % 164,768 11,447,991 Kansas City, MO...Buffalo, NY...Rochester, NY...Springfield, MO...Syracuse, NY...
5 % 244,293 23,641,289 San Antonio, TX...Columbus, OH...Austin, TX...Cleveland, OH...St. Louis, MO...
Probabilistic Large Hail Graphic
20170518 2000 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SIG SEVERE 104,814 4,242,391 Oklahoma City, OK...Wichita, KS...Abilene, TX...Norman, OK...Wichita Falls, TX...
45 % 37,552 1,161,411 Wichita, KS...Enid, OK...Salina, KS...Hutchinson, KS...Dodge City, KS...
30 % 99,205 10,543,923 Dallas, TX...Fort Worth, TX...Oklahoma City, OK...Tulsa, OK...Arlington, TX...
15 % 184,688 13,487,627 Kansas City, MO...Buffalo, NY...Rochester, NY...Overland Park, KS...Springfield, MO...
5 % 244,426 24,648,416 San Antonio, TX...Columbus, OH...Austin, TX...Cleveland, OH...Omaha, NE...
   SPC AC 181945

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0245 PM CDT Thu May 18 2017

   Valid 182000Z - 191200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON
   ACROSS PARTS OF NORTHWESTERN OKLAHOMA INTO SOUTHWESTERN AND SOUTH
   CENTRAL KANSAS...

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS
   SURROUNDING AREAS OF WESTERN OKLAHOMA AND CENTRAL/SOUTHERN KANSAS...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
   SURROUNDING AREAS OF THE SOUTH CENTRAL PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SURROUNDING
   AREAS OF THE CENTRAL AND SOUTHERN PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON AND EVENING ACROSS THE LOWER GREAT LAKES REGION INTO
   PORTIONS OF WESTERN NEW ENGLAND...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   PLAINS SLIGHT RISK AREA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   LOWER GREAT LAKES SLIGHT RISK AREA...AS FAR WEST AS THE UPPER OHIO
   VALLEY AND EASTWARD ACROSS NORTHERN NEW ENGLAND...

   ...SUMMARY...
   An outbreak of severe thunderstorms is now underway across parts of
   the south central high Plains.  A few long-lived supercell storms
   capable of producing very large hail and strong tornadoes are
   expected to continue to develop into early evening, before perhaps
   consolidating into one or two organizing clusters with increasing
   damaging wind potential.

   ...20Z Outlook Update...

   ...Central and southern Plains...
   Severe storms have initiated along the dryline across northwest
   Texas through western Oklahoma, as an initial short wave impulse
   begins pivoting northeast of the southern Rockies.  As this feature
   shifts into the central Plains, toward the mid Missouri Valley
   through the remainder of the period, discrete storm development is
   expected to continue through late afternoon, generally becoming
   focused near a developing surface frontal wave, across northwest
   Oklahoma into southwestern/south central Kansas.  A subsequent
   upscale growth into one or two organizing mesoscale convective
   systems appears possible along the frontal zone across
   central/eastern Kansas, southward into parts of northern/western
   Oklahoma.  This will be supported by the difluent upper regime
   downstream of a broad mid-level closed low slowly redeveloping
   across the southern Great Basin, toward the Colorado Rockies, as
   another short wave impulse digs to the west and south of the Four
   Corners region.

   Categorical and probabilistic lines have generally remained
   unchanged, except to account for ongoing destabilization which has
   occurred as far west as the eastern Texas Panhandle.

   ...Ohio Valley into New England...
   The environment is at least conditionally supportive of
   thunderstorms capable of producing severe winds and hail, across a
   sizable pre-frontal corridor across the region.  This is generally
   well south of the remnants of the short wave impulse emerging from
   the Plains yesterday, and now accelerating east northeast of Lake
   Huron into Quebec.  However, a belt of seasonably strong (40-50 kt
   deep layer mean) flow to the south of this feature will enhance
   widely scattered storm development which has initiated across parts
   of the upper Ohio Valley and to the lee of the lower Great Lakes,
   aided by the lake breeze, and perhaps a weak perturbation or two on
   the southern fringe of the westerlies.

   Categorical and probabilistic lines have been adjust to account for
   the eastward progression of the aforementioned short wave impulse.

   ..Kerr.. 05/18/2017

   .PREV DISCUSSION... /ISSUED 1139 AM CDT Thu May 18 2017/

   ...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.

   ...Lower Great Lakes vicinity into portions of New England...
   Showers and scattered thunderstorms are forecast to increase this
   afternoon, from the Midwest/Ohio Valley area east-northeast across
   the lower Great Lakes and into parts of New England.  A moist
   boundary-layer airmass in place (upper 50s to low- to mid-60s) will
   continue to heat/destabilize this afternoon, permitting storms to
   form both along the advancing cold front, as well as along
   pre-frontal confluence bands and lake-breeze boundaries.  While
   somewhat modest west-southwesterly flow aloft is expected over much
   of the Ohio Valley area, limiting severe risk to some degree,
   stronger deep-layer west-southwesterlies centered in the vicinity of
   the international border suggest potential for greater storm
   organization and possibly upscale growth into one or more
   clusters/bands, which will be capable of producing locally damaging
   winds and hail.  Coverage of storms -- and thus severe risk -- will
   diminish gradually through mid to late evening, as the boundary
   layer diurnally stabilizes.

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