Jul 17, 2018 2000 UTC Day 1 Convective Outlook
Updated: Tue Jul 17 20:00:20 UTC 2018 (20180717 2000Z Day 1 shapefile | 20180717 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180717 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 77,537 27,442,944 New York, NY...Philadelphia, PA...Boston, MA...Jersey City, NJ...Providence, RI...
MARGINAL 367,207 37,791,587 Baltimore, MD...Denver, CO...Washington, DC...Oklahoma City, OK...Virginia Beach, VA...
Probabilistic Tornado Graphic
20180717 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
2 % 52,811 4,755,639 Worcester, MA...Fort Collins, CO...Hartford, CT...Thornton, CO...Cambridge, MA...
Probabilistic Damaging Wind Graphic
20180717 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
15 % 76,689 27,424,182 New York, NY...Philadelphia, PA...Boston, MA...Jersey City, NJ...Providence, RI...
5 % 357,968 37,809,304 Baltimore, MD...Denver, CO...Washington, DC...Oklahoma City, OK...Virginia Beach, VA...
Probabilistic Large Hail Graphic
20180717 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
15 % 59,320 627,376 Greeley, CO...Cheyenne, WY...Casper, WY...Laramie, WY...Gillette, WY...
5 % 168,730 5,627,004 Denver, CO...Colorado Springs, CO...Wichita, KS...Aurora, CO...Lakewood, CO...
   SPC AC 172000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Tue Jul 17 2018

   Valid 172000Z - 181200Z


   Severe thunderstorms capable of damaging winds are possible over the
   Northeast States through early evening. Scattered severe storms are
   also expected across parts of the central High Plains during the
   late afternoon and evening.

   The Marginal and Slight Risks have been trimmed in the immediate
   wake of the leading line of convection across portions of the
   Northeast. Some redevelopment is occurring further west along the
   cold front where some pockets of heating have allowed for moderate
   destabilization, and a Marginal Risk has been maintained for the
   cold frontal convection into early evening. 

   ...Southern Plains into the Ozarks...
   Some expansion of the Marginal Risk has been included across
   portions of AR, downstream of an intensifying cluster of convection
   across far northeast OK/northwest AR. Confidence is decreasing in
   redevelopment along an outflow boundary further west across OK, but
   a conditional risk remains and no change has been made to the severe
   probabilities in this area. 

   ...Central/Northern High Plains...
   Minor adjustments to the severe probabilities have been made across
   portions of the central/northern High Plains, but the previous
   forecast reasoning remains valid. See the previous discussion below
   for more information.

   ..Dean/Peters.. 07/17/2018

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Jul 17 2018/

   ...Northeast States/southern New England...
   Bands of east/northeastward-moving storms continue to intensify at
   midday from eastern PA/southeast NY into southern New England within
   a warm conveyor and zone of differential heating in advance of an
   eastward-moving cold front. Weak mid-level lapse rates and modest
   strength effective shear of 20-30 kt are still expected to limit the
   overall magnitude of today's severe. However, steep low-level lapse
   rates and ample moisture content will nonetheless contribute to some
   severe risk. Damaging winds including scattered downed trees will be
   the most common hazard before storms weaken and/or move offshore by
   early evening. Reference Mesoscale Discussions 1064/1065 for
   additional details.

   ...Central High Plains...
   Weak height falls and a moderate strengthening of west-northwesterly
   winds aloft will occur across the region in advance of a shortwave
   trough progressing from eastern ID/southern MT into WY. 30-40 kt
   500-mb westerlies attendant to this feature will overspread much of
   WY with mid-to-late afternoon storm initiation expected off the
   higher terrain. In the presence of MLCAPE ranging from 1000-2000
   J/kg, speed shear through the cloud-bearing layer should be
   sufficient for supercells with large hail and isolated severe gusts
   being the primary hazards. Some upscale growth may occur this
   evening with storms spreading southeastward across the region with a
   continued damaging wind/sporadic hail risk.

   ...KS/OK to the Ozarks/ArkLaTex...
   The remnants of an overnight weakening MCS continue to spread
   southeastward over southeast KS at midday. The related MCV may help
   semi-focus afternoon-intensifying thunderstorms across eastern OK
   into parts of the Ozarks and ArkLaTex. Microburts capable of
   localized damaging winds are possible through the afternoon.

   Farther west/northwest across portions of northern OK/far southern
   KS, MCS-related outflow may gradually stall and modify across the
   region this afternoon with a hot/well-mixed air mass to its south.
   Although overall forcing will be weak, at least some severe risk,
   including the possibility of a few transient supercells, may exist
   particularly along the corridor of modified outflow presuming storms
   redevelop. This region will be reevaluated this afternoon for any
   need of a Slight Risk upgrade.