May 1, 2018 0600 UTC Day 1 Convective Outlook
Updated: Tue May 1 06:00:46 UTC 2018 (20180501 1200Z Day 1 shapefile | 20180501 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180501 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 43,767 1,901,192 Omaha, NE...Lincoln, NE...Council Bluffs, IA...Bellevue, NE...Salina, KS...
SLIGHT 56,335 2,252,044 Des Moines, IA...St. Joseph, MO...Waterloo, IA...Ames, IA...West Des Moines, IA...
MARGINAL 159,668 9,364,043 Wichita, KS...St. Paul, MN...Madison, WI...Rockford, IL...Fort Collins, CO...
Probabilistic Tornado Graphic
20180501 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
SIG SEVERE 20,198 286,414 Salina, KS...Hays, KS...Great Bend, KS...
10 % 20,248 292,186 Salina, KS...Hays, KS...Great Bend, KS...
5 % 41,755 1,945,540 Omaha, NE...Lincoln, NE...Council Bluffs, IA...Bellevue, NE...Manhattan, KS...
2 % 151,040 7,654,479 Wichita, KS...Madison, WI...Des Moines, IA...Rockford, IL...Fort Collins, CO...
Probabilistic Damaging Wind Graphic
20180501 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
30 % 32,827 821,221 Lincoln, NE...Salina, KS...Junction City, KS...Great Bend, KS...Beatrice, NE...
15 % 31,842 1,476,919 Omaha, NE...Council Bluffs, IA...Bellevue, NE...Manhattan, KS...Grand Island, NE...
5 % 144,217 7,280,777 Wichita, KS...Madison, WI...Des Moines, IA...Rockford, IL...Fort Collins, CO...
Probabilistic Large Hail Graphic
20180501 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
SIG SEVERE 43,029 1,536,432 Lincoln, NE...Bellevue, NE...Salina, KS...Hutchinson, KS...Hastings, NE...
30 % 41,230 1,861,497 Omaha, NE...Lincoln, NE...Council Bluffs, IA...Bellevue, NE...Salina, KS...
15 % 57,661 2,274,378 Des Moines, IA...St. Joseph, MO...Waterloo, IA...Ames, IA...West Des Moines, IA...
5 % 157,551 9,049,490 Wichita, KS...St. Paul, MN...Madison, WI...Rockford, IL...Fort Collins, CO...
   SPC AC 010600

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Tue May 01 2018

   Valid 011200Z - 021200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF CENTRAL KS...SOUTHEAST NE...FAR SOUTHWEST IA...AND FAR NORTHWEST
   MO...

   ...SUMMARY...
   Severe storms are expected mainly across north-central Kansas into
   southeast Nebraska Tuesday from late afternoon through evening.
   Large hail, damaging winds, and a few tornadoes are possible.

   ...Synopsis...
   Shortwave trough currently located approximately 400nm off the
   central CA coast is expected to continue southward Tuesday morning
   before turning more southeasterly during the afternoon. The
   trajectory of this shortwave will lead to an overall deepening of
   the parent upper trough, which covers much of the western CONUS.
   Additionally, a modest westward regression of the upper trough is
   anticipated, which will support building heights across the central
   CONUS. 

   The surface pattern at the beginning of the period will likely
   feature a low centered over the MN arrowhead with a cold front
   extending southwestward to another low over north-central KS. This
   frontal zone is not expected to move much throughout the day with
   the second low developing into a well-defined triple-point by the
   afternoon. This triple-point, and the surface features extending
   from it, will serve as the focus for convective development late
   Tuesday afternoon through the evening.

   ...Central Plains into the Upper MS Valley...
   A second day of moisture advection is anticipated as a deepening lee
   surface low  and strong low-level flow persist. Expectation is for
   dewpoints to generally be in the low to mid 60s east of the dryline
   across central KS, with values gradually increasing southward. Warm
   temperatures aloft and weak synoptic forcing for ascent will likely
   keep the warm sector free of convection throughout most of the day.
   Impetus for convective initiation will likely be surface convergence
   near the triple-point and along the cold front and dryline. Recent
   guidance also shows a very subtle shortwave moving into the central
   Plains during the afternoon, which would enhanced lift across the
   region if realized. High-resolution guidance, including the HREF, is
   in good agreement that convection initiation will occur around 21Z
   along the dryline in central KS. 

   With very steep mid-level lapse rates and strong instability in
   place, the airmass will be primed for explosive thunderstorm
   development once convective initiation occurs. An initially discrete
   storm mode is anticipated along the dryline in KS while a clustered
   storm mode is more likely along the cold front from south-central NE
   across IA. Veering wind profiles are anticipated along the dryline,
   with current guidance suggesting effective SRH over 250 m2/s2 and
   effective bulk shear over 50 kt. These wind profiles are more than
   supportive of supercells, and, given the likely discrete initial
   mode, tornadoes. A few strong tornadoes are possible, particularly
   near the triple point where the probability of backed surface winds
   is higher. Very large hail (i.e. greater than 2 inches in diameter)
   is also likely with the storms along the dry line as well as initial
   development farther northeast along the cold front. The hail threat
   will extend into southern WI as the low-level jet supports
   thunderstorms along the frontal zone.

   A Moderate Risk for tornadoes may be warranted in subsequent
   outlooks but the confined nature of the threat and remaining
   uncertainty regarding the location of the triple-point during the
   afternoon as well as the extent of the moisture return merits
   waiting for more confidence before upgrading.

   ...Central High Plains...
   Upslope flow and resulting convergence will support the development
   of thunderstorms during the afternoon across northeast CO and
   adjacent portions of southeast WY and southwest NE Panhandle. Some
   isolated hail is possible with the strongest storms.

   ..Mosier/Dean.. 05/01/2018

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