Jun 20, 2018 0600 UTC Day 1 Convective Outlook
Updated: Wed Jun 20 05:40:44 UTC 2018 (20180620 1200Z Day 1 shapefile | 20180620 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180620 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 419,691 48,173,104 Dallas, TX...Columbus, OH...Fort Worth, TX...Portland, OR...Kansas City, MO...
Probabilistic Tornado Graphic
20180620 1200 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 % 31,093 2,192,544 Omaha, NE...Des Moines, IA...Cedar Rapids, IA...Iowa City, IA...Council Bluffs, IA...
Probabilistic Damaging Wind Graphic
20180620 1200 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
5 % 420,008 48,311,118 Dallas, TX...Columbus, OH...Fort Worth, TX...Portland, OR...Kansas City, MO...
Probabilistic Large Hail Graphic
20180620 1200 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
5 % 179,543 12,885,073 Portland, OR...Kansas City, MO...Omaha, NE...Tulsa, OK...Des Moines, IA...
   SPC AC 200540

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1240 AM CDT Wed Jun 20 2018

   Valid 201200Z - 211200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE PACIFIC NW AND FROM THE SOUTHERN PLAINS TO THE MID ATLANTIC...

   ...SUMMARY...
   Scattered strong thunderstorms, possibly severe, are expected to
   develop from portions of the southern Plains/Mid-Mississippi Valley
   to the Middle Atlantic. Other strong/severe storms are possible
   across parts of the Pacific Northwest.

   ...Southern Plains/Mid MS Valley...

   Early-morning water-vapor imagery depicts a well-defined short-wave
   trough over the central High Plains ejecting east in line with
   latest model guidance. This feature is forecast to shift into the
   eastern part of the central Plains by 18z then drift into the MS
   Valley by the end of the period. Considerable amount of convection
   has evolved over NE/KS ahead of this feature at 05z and an expansive
   MCS should propagate southeast and weaken toward daybreak. In all
   likelihood this complex of storms will be more disruptive than late
   evening guidance , and CAM solutions suggest. For this reason have
   shunted 5% severe probs to a position where convective outflow is
   most likely to exist by 18z. If the air mass over IA is not
   overturned by early afternoon there is some concern that a few
   supercells could evolve immediately ahead of the upper low. This 
   area will be favorably sheared for perhaps a few weak tornadoes and
   a SLGT risk may be needed if buoyancy is adequate. However,
   confidence is low regarding this scenario given that the leading
   edge of the MCS is already into western IA. Otherwise, strong
   boundary-layer heating is expected to aid convection along the
   remnant outflow/front by mid-late afternoon. Hail/wind are the
   primary threats.


   ...OH Valley/Middle Atlantic...

   Remnant convective debris field will drift across the OH Valley
   early in the period. Heating along the leading edge of this activity
   is expected to result in destabilization necessary for renewed
   thunderstorm development. Isolated strong wind gusts could accompany
   convection that develops ahead of this disturbance from southern OH
   into the Middle Atlantic.

   ...Pacific Northwest...

   Exit region of a strong mid-level speed max will advance into
   northern CA/OR during the afternoon ahead of a short-wave trough off
   the Northwest Coast. Cool 500mb temperatures and steep lapse rates
   will ensure sufficient buoyancy for robust convection as
   temperatures warm. 20/00z NAM is a bit too aggressive with surface
   dew points/instability across this region but isolated severe
   thunderstorms are nonetheless expected due to favorable dynamics and
   aforementioned lapse rates.

   ..Darrow/Squitieri.. 06/20/2018

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