May 26, 2017 1300 UTC Day 1 Convective Outlook
Updated: Fri May 26 12:55:08 UTC 2017 (20170526 1300Z Day 1 shapefile | 20170526 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170526 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 81,313 1,278,065 Fort Collins, CO...Greeley, CO...Longmont, CO...Loveland, CO...Cheyenne, WY...
MARGINAL 233,452 20,788,209 Indianapolis, IN...Denver, CO...Kansas City, MO...Colorado Springs, CO...Wichita, KS...
Probabilistic Tornado Graphic
20170526 1300 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 % 71,405 1,327,886 Aurora, CO...Greeley, CO...Cheyenne, WY...Parker, CO...Brighton, CO...
Probabilistic Damaging Wind Graphic
20170526 1300 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 % 81,374 1,237,590 Fort Collins, CO...Greeley, CO...Longmont, CO...Loveland, CO...Cheyenne, WY...
5 % 234,316 20,913,024 Indianapolis, IN...Denver, CO...Kansas City, MO...Colorado Springs, CO...Wichita, KS...
Probabilistic Large Hail Graphic
20170526 1300 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 % 81,401 1,237,601 Fort Collins, CO...Greeley, CO...Longmont, CO...Loveland, CO...Cheyenne, WY...
5 % 234,288 20,913,012 Indianapolis, IN...Denver, CO...Kansas City, MO...Colorado Springs, CO...Wichita, KS...
   SPC AC 261255

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Fri May 26 2017

   Valid 261300Z - 271200Z



   Several severe thunderstorms with hail and damaging gusts are
   expected over the central High Plains.  Isolated damaging gusts and
   hail are possible from there eastward to parts of the Ohio Valley.

   In mid/upper levels, the cyclone associated with several days of
   severe weather from the central to eastern U.S. finally will exit
   the Northeast today.  In its wake, and downstream from a positively
   tilted, complex trough over the northern Great Basin/northern
   Rockies region, expect a broad fetch of zonal to west-southwesterly
   flow aloft.  Embedded within that flow is an MCV -- now apparent in
   satellite and radar composites over the MO/IA border region, with an
   associated shortwave trough over northern MO.  This feature should
   track east-northeastward across southern WI and northern IL,
   reaching southern Lake Michigan around 00Z, then weakening and
   crossing lower MI overnight.  In the West, a basal shortwave trough
   is evident in moisture-channel imagery over southern ID and northern
   NV.  The northern part of this feature will move faster than the
   rest, leading to an increasingly elongated and positively tilted
   perturbation with time.  By 00Z, this trough should extend from
   northwestern WY to northern NV.  By 12Z it should stretch from the
   Black Hills to central UT and eastern NV. 

   At the surface, a complex pattern was evident in the 11Z analysis, 
   with the main features being:
   *  A weak low over north-central OK
   *  Weak cold front from that low southwestward across the southern
   TX Panhandle
   *  Stationary/warm front from that low northeastward to northern MO
   then eastward across south-central IL
   *  Outflow boundary interrupting the latter front over northern MO
   *  Stronger cold front from western MN to northwestern KS, to a weak
   low over southeastern CO. 

   In response to the action of the MCV, a weak low should develop this
   afternoon, farther northeast along the southern front, over
   northeastern MO or western IL, tracking eastward toward
   north-central IN.  The southern front will stall and weaken over the
   southern High Plains, as will the northern one over eastern CO. 
   Still, upslope flow is expected, related to these boundaries and
   low-level troughing over the Front Range area.

   ...Central High Plains...
   Only minor adjustments are made to the outlook to reflect
   most-probable zones for convective development and motion this
   afternoon and evening, with strong MLCINH imparting lower confidence
   in initiation southward through the southern High Plains.  Widely
   scattered to locally scattered thunderstorms are expected to develop
   this afternoon with heating of higher elevations in the western part
   of the outlook, from eastern WY southward over eastern CO to the
   Raton Mesa area.  The main concerns will be large hail and locally
   severe gusts, aided by a well-mixed subcloud layer.  A tornado
   cannot be ruled out.

   The upslope component will aid low-level lift, storm-relative
   boundary-layer flow and vertical shear.  Sufficient deep shear will
   exist across this corridor (i.e., effective-shear magnitudes of
   45-60 kt and effective SRH potentially exceeding 200 J/kg) to
   support both discrete supercells and -- where storm mode gets
   relatively dense and clustered to organize a cold pool -- bow-echo
   development.  Activity should move eastward for several hours into
   this evening across portions of western KS and southwestern NE,
   ultimately weakening below severe levels as it encounters
   progressively deeper, more stable boundary layer.  However, widely
   scattered thunderstorms may persist farther eastward across KS
   tonight with elevated inflow from a 40-45-kt southerly LLJ.

   ....Mid-Mississippi and Ohio Valley regions...
   Widely scattered to scattered thunderstorms are expected to develop
   today near and south of the frontal zone, offering isolated,
   sporadic damaging gusts and severe hail.  Multicellular modes should
   predominate, although some supercell structures are possible,
   especially near the front.  Mesoscale outflow or
   differential-heating boundaries related to morning clouds and precip
   may be important to focusing development this afternoon, especially
   given the weak low-level lift otherwise evident and presence of some
   EML air aloft.  Surface dew points in the 50s to mid 60s F should
   support MLCAPE 1000-2000 J/kg where enough surface heating can

   A channel of relatively maximized midlevel flow, typically found
   south (equatorward) of the MCV, has been evident in VAD wind
   profiles this morning.  This is related to perturbation of the
   mesoscale height gradient by the MCV, and should proceed
   east-northeastward apace with it through the day.  Such a track
   would result in enhanced deep shear with a westerly to southwesterly
   vector orientation, spreading over parts of the corridor from the
   mid Mississippi Valley across central/northern IL to Indiana.  

   A complex of thunderstorms may organize across parts of
   central/northern IL.  Uncertainties remain over the organization of
   any such MCS, as well as the amount (if any) of surface-based
   buoyancy available, given:
   1.  Its progged position north of the warm front, and
   2.  Cloud debris from ongoing precip across MO, which extends
   farther south than most overnight high-res guidance has been
   While a small area within the bulbous part of the marginal risk may
   need larger wind probabilities, these will be deferred to a later
   outlook due to the destabilization concerns.

   ..Edwards/Goss.. 05/26/2017