SPC AC 280557

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CDT Sun Jun 28 2020

   Valid 281200Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   OHIO VALLEY...SOUTHERN APPALACHIANS...MID MISSOURI VALLEY...NORTHERN
   HIGH PLAINS...SOUTHEAST NEW YORK AND SOUTHERN NEW ENGLAND...

   ...SUMMARY...
   Severe thunderstorms with wind damage, isolated large hail and a
   tornado or two will be possible this afternoon and evening in parts
   of the mid Missouri Valley. Wind damage and hail may also occur this
   afternoon and evening across parts of the northern High Plains, in
   southern New York, southern New England and from the Ohio Valley
   into the southern Appalachians.

   ...Ohio Valley into the Southern Appalachians...
   A subtle shortwave trough will move east-southeastward across the
   southern Appalachian Mountains today. Scattered thunderstorms will
   likely be ongoing at the start of the period ahead of the trough
   over the Ohio Valley. This convection is forecast to move
   east-southeastward from central Kentucky late this morning into
   western North Carolina by late afternoon. Forecast soundings in the
   18Z to 21Z timeframe along the track of the MCS show surface
   dewpoints from the mid 60s to the lower 70s F with MLCAPE reaching
   the 1500 to 2000 J/kg range. In addition, wind profiles are forecast
   to be veered to the west-southwest at low-levels with unidirectional
   westerly flow in the mid-levels. The wind profile could be favorable
   for damaging wind gusts with the stronger multicell line segments,
   especially as low-level lapse rates become steep in the afternoon.
   The main uncertainty with this forecast is instability. The greatest
   chance for severe storms will be in areas that remain unaffected by
   morning convective outflow. But any line segment that can persist
   and move into an area with moderate instability may become efficient
   at producing damaging wind gusts.

   ...Mid Missouri Valley...
   A subtle shortwave trough will move northeastward across the mid
   Missouri Valley and northern Plains today. At the surface, a
   corridor of maximized low-level moisture will remain from the mid
   Mississippi Valley extending northwestward into the mid Missouri
   Valley. Surface dewpoints along this corridor should be in the lower
   to mid 70s F, contributing to extreme destabilization by afternoon.
   The RAP is forecasting MLCAPE to peak above 5500 J/kg in eastern
   Nebraska with a tight instability gradient across western Iowa.
   Low-level convergence is forecast to become maximized in far
   northeast Nebraska by 00Z/Monday which will help with convective
   initiation. Thunderstorms are expected to develop during the early
   evening and move eastward across central and northern Iowa. In
   addition to the extreme instability, RAP forecast soundings in
   western Iowa at 00Z have 0-3 km shear near 30 kt with some
   directional shear in the low-levels. This environment should be
   favorable for severe storms as cell coverage increases during the
   early to mid evening. Wind damage, isolated large hail, and perhaps
   a tornado or two will be possible with supercells and organized
   multicells.

   ...Northern High Plains...
   An upper-level low will move slowly across the Intermountain West
   today as south-southwesterly mid-level flow remains over the
   northern High Plains. At the surface, a moist airmass will be in
   place across the northern Plains with a surface trough in the
   western Dakotas. Surface dewpoints to the west of the surface trough
   in eastern Montana should be from the mid 60s to lower 60s F. In
   response, SBCAPE may peak in the 1000 to 1500 J/kg range by late
   afternoon. Thunderstorms are expected to initiate in the higher
   terrain of northern Wyoming and spread north-northeastward into the
   northern High Plains during the evening. The exit region of a
   mid-level jet will overspread the northern High Plains, creating
   moderate to strong deep-layer shear. At 00Z/Monday, RAP forecast
   soundings near and to the east of Billings have 0-6 km shear near 60
   kt with strong directional shear in the low-levels. This will be
   favorable for supercells with storms that remain discrete. Isolated
   large hail and wind damage will be the primary threats.

   ...Mid-Atlantic to New England...
   An upper-level low will remain in place across Quebec today as an
   upper-level trough moves slowly eastward across the Northeast. At
   the surface, a moist airmass will be in place from far southeastern
   New York into southern New England. Surface dewpoints in southern
   New England should be in the upper 60s to near 70 F, resulting in
   moderate instability by afternoon. The strongest instability should
   be located from a surface low in New Jersey northeastward into
   Connecticut and Massachusetts. As low-level convergence increases to
   the north of the surface low, thunderstorms should develop around
   midday and move eastward toward the thermal axis. The moderate
   instability, steep low-level lapse rates and 0-6 km shear near 30 kt
   should be sufficient for damaging wind gusts. The greatest wind
   damage potential will likely be associated with the leading edge of
   the more organized multicell line segments.

   ..Broyles/Bentley.. 06/28/2020

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