Jun 28, 2018 0600 UTC Day 1 Convective Outlook
Updated: Thu Jun 28 05:58:24 UTC 2018 (20180628 1200Z Day 1 shapefile | 20180628 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180628 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 69,789 483,606 Bismarck, ND...Grand Forks, ND...Minot, ND...Mandan, ND...Dickinson, ND...
SLIGHT 118,738 1,094,319 Billings, MT...Fargo, ND...Moorhead, MN...Aberdeen, SD...West Fargo, ND...
MARGINAL 352,599 52,699,105 New York, NY...Memphis, TN...Nashville, TN...Atlanta, GA...St. Louis, MO...
Probabilistic Tornado Graphic
20180628 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
5 % 48,983 295,731 Bismarck, ND...Minot, ND...Mandan, ND...Dickinson, ND...Williston, ND...
2 % 145,699 6,466,785 Worcester, MA...Springfield, MA...New Haven, CT...Hartford, CT...Waterbury, CT...
Probabilistic Damaging Wind Graphic
20180628 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
SIG SEVERE 48,790 342,454 Bismarck, ND...Minot, ND...Mandan, ND...Dickinson, ND...Jamestown, ND...
30 % 55,121 450,254 Bismarck, ND...Grand Forks, ND...Minot, ND...Mandan, ND...Dickinson, ND...
15 % 133,027 1,126,976 Billings, MT...Fargo, ND...Moorhead, MN...Aberdeen, SD...West Fargo, ND...
5 % 351,131 52,271,029 New York, NY...Memphis, TN...Nashville, TN...Atlanta, GA...St. Louis, MO...
Probabilistic Large Hail Graphic
20180628 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 49,095 190,223 Minot, ND...Dickinson, ND...Williston, ND...Miles City, MT...Glendive, MT...
30 % 27,647 136,696 Minot, ND...Dickinson, ND...Glendive, MT...Sidney, MT...
15 % 100,162 537,375 Billings, MT...Bismarck, ND...Mandan, ND...Sheridan, WY...Jamestown, ND...
5 % 249,318 11,127,974 Memphis, TN...Nashville, TN...St. Louis, MO...Huntsville, AL...Clarksville, TN...
   SPC AC 280558

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Thu Jun 28 2018

   Valid 281200Z - 291200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   THE NORTHERN PLAINS...

   ...SUMMARY...
   Severe thunderstorms are expected across parts of the northern
   Plains Thursday afternoon into Thursday night. The primary threat
   will be damaging winds, but large hail and perhaps a couple
   tornadoes will be possible as well. Elsewhere, isolated
   strong/severe storms will be possible from the mid Mississippi
   Valley to the Southeast, as well as over parts of the Northeast.

   ...Synopsis...
   Pertinent features for this convective outlook will generally be
   situated around the periphery of an expansive mid-level ridge
   anchored over the central Plains. Although 500mb height tendencies
   will be neutral/slightly positive across the northern Plains
   initially (owing to lower-level warm advection), heights will
   gradually fall through Thursday night with the approach of an
   upstream trough over the Pacific Northwest. Farther east, a compact
   impulse will cross the Hudson Valley and southern/central New
   England through the afternoon. Meanwhile, a series of
   low-amplitude/convectively augmented impulses will drop southeast
   from the mid Mississippi Valley to the Southeast through the period.

   ...Northern Plains...
   In response to continued warm advection over Montana and the
   Dakotas, a warm front will lift northward towards the Canadian
   border through the day. Meanwhile, a cold front will begin to
   accelerate southeast over central Montana during the evening hours.
   Between these two surface features, southeasterly flow will
   transport mid/upper 60s dew points over the western Dakotas and into
   eastern Montana. Closer to the trough / cooler temperatures aloft,
   convection should initiate near/ahead of the cold front over the
   higher terrain of Montana. Here, steep mid-level lapse rates and
   strong effective shear will likely yield a few supercells and/or
   bowing segments, capable of large hail and damaging winds during the
   afternoon and evening.

   Farther east, warmer temperatures aloft and relatively neutral
   height tendencies should keep convective coverage more sparse
   through the afternoon hours. However, convergence near the warm
   front and amplifying large-scale ascent will likely promote a rapid
   increase in coverage through the evening and early overnight over
   eastern Montana and western North Dakota. Storms should rapidly
   become severe, owing to strong buoyancy characterized by MLCAPE
   values of 3000-3500+ J/kg. Organized by veering flow with height,
   initial cells will likely be supercellular, capable of very large
   hail, damaging winds, and a couple tornadoes. Through the
   evening/overnight, though, upscale growth into one or more
   eastward-accelerating convective systems is anticipated, with a
   swath of damaging winds possible. At present, uncertainty regarding
   the timing/location of such upscale growth precludes an upgrade to
   moderate risk.

   ...Mid Mississippi Valley to the Southeast...
   Severe potential will be highly dependent on initial convective
   organization/evolution over the mid Mississippi Valley this morning.
   Aided by steep mid-level lapse rates and sufficient effective shear
   around 25-35 kt, a few storms this morning will be capable of
   isolated large hail and damaging winds near the mid Mississippi
   Valley. Some potential exists for a small convective complex to
   develop and spread southeast during the morning/afternoon hours,
   with an attendant damaging wind potential. Related MCVs may also
   focus convective/gusty wind potential across the Tennessee Valley
   and Southeast within a warm/moist, but relatively weak flow regime,
   during the afternoon. A slight risk could be introduced in later
   outlooks, pending greater confidence in the location of any focusing
   mechanisms.

   ...Northeast...
   A warm front will lift northeast across New England this morning,
   with weak instability/surface-based buoyancy spreading northeastward
   in tandem. Warm advection should yield a few showers/thunderstorms
   through the morning hours, and a threat may exist for a brief
   tornado or localized damaging gusts, owing to enhanced low-level
   shear and moist/neutral boundary-layer profiles. A few stronger
   storms may also develop through mid-day/afternoon, as the main
   shortwave impulse crosses the region and offers some focus for
   stronger convection along a surface trough.

   ..Picca/Nauslar.. 06/28/2018

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