May 16, 2018 0730 UTC Day 3 Severe Thunderstorm Outlook
Updated: Wed May 16 07:29:38 UTC 2018 (20180516 0730Z Day 3 shapefile | 20180516 0730Z Day 3 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180516 0730 UTC Day 3 Outlook Graphic
Day 3 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 88,660 1,386,358 Aurora, CO...Fort Collins, CO...Greeley, CO...Grand Island, NE...Parker, CO...
MARGINAL 104,091 3,507,902 Denver, CO...Lakewood, CO...Thornton, CO...Westminster, CO...Arvada, CO...
Probabilistic Graphic
20180516 0730 UTC Day Probabilitic Graphic
Probability of severe weather within 25 miles of a point.
Hatched Area: 10% or greater probability of significant severe within 25 miles of a point.
Day 3 Prob. Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 89,458 1,584,017 Aurora, CO...Fort Collins, CO...Greeley, CO...Loveland, CO...Grand Island, NE...
5 % 103,853 3,322,589 Denver, CO...Lakewood, CO...Thornton, CO...Westminster, CO...Arvada, CO...
   SPC AC 160729

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0229 AM CDT Wed May 16 2018

   Valid 181200Z - 191200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON
   AND EVENING NEAR THE FRONT RANGE OF THE ROCKIES INTO PARTS OF THE
   CENTRAL PLAINS...

   ...SUMMARY...
   Severe thunderstorms are possible near the Front Range of the
   Rockies eastward into parts of the central Plains late Friday
   afternoon and evening.

   ...Synopsis...
   The mid-latitude westerlies emanating from the Pacific will remain
   split through this period and beyond, as large-scale blocking
   persists near the Pacific coast.  It appears that this will include
   the evolution of an increasingly prominent high at a bit higher
   latitude than the previous one, becoming centered near the Canadian
   Rockies, inland of the British Columbia coast.  Within the
   downstream northern branch, at least a couple of significant short
   wave troughs are forecast to remain progressive, one well east of
   the Canadian Maritimes, the other across and east of the Canadian
   Prairies.  The lead wave is expected to be accompanied by a surface
   front through much of the Northeast and Ohio Valley, which should
   stall and may begin gradually returning northward as subtropical
   ridging centered over the Atlantic builds northward across the
   northern Mid Atlantic and southern New England.  The upstream wave
   is expected to be accompanied by another cold front, which may
   advance southward through much of the northern Plains and portions
   of the northern intermountain region by late Friday night.

   Preceding the latter front, outflow from convection late Thursday
   and Thursday night may stall and weaken across the southern Nebraska
   into northeast Colorado vicinity during the day Friday.  This is
   expected to occur as a sub-1000 mb low forms within lee surface
   troughing over southeast Colorado by Friday afternoon.  The
   low-level cyclogenesis is forecast as perhaps the main short wave
   impulse emerges from larger-scale southern branch troughing
   initially over the Southwest.  Associated southeasterly/southerly
   low-level flow across much of the central Plains probably will
   maintain at least modest boundary layer moisture.  Seasonably high
   moisture content, though, will generally remain confined to a plume
   ahead of remnant mid/upper troughing east of the Mississippi Valley
   through the Caribbean, particularly across the southern/mid Atlantic
   Seaboard, on the western periphery of the subtropical ridge.

   ...Front Range of Rockies into central Plains...
   Given at least modest moisture (surface dew points in the mid 50s to
   lower 60s F) east of the dryline across southwestern Kansas, and
   near/north of the remnant outflow boundary, or nose of stronger
   surface heating/deeper boundary layer mixing across the southern
   into central High Plains, moderately large CAPE appears possible by
   peak heating in the presence of steep lapse rates.  Resultant
   thermodynamic profiles likely will support a severe hail/wind threat
   with any thunderstorm development.  Storms are expected to initiate
   by late Friday afternoon aided by orographic forcing and lift
   associated with the approaching mid-level impulse.  Guidance
   continues to suggest that this may be accompanied by a belt of 30-40
   kt mid-level flow nosing across the southern Rockies, which seems
   likely to be sufficient to support organized convective development,
   including supercells at least initially.

   There appears at least some risk for tornadoes, particularly across
   parts of northeastern Colorado.  However, these may tend to be
   mostly short-lived and relatively weak, barring better than
   currently anticipated moisture.  Storms could eventually
   consolidate/grow upscale into an organizing convective system with
   mainly a continuing severe wind risk into Friday evening, generally
   across parts of northern Kansas/adjacent southern Nebraska.

   ..Kerr.. 05/16/2018

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