SPC AC 270545

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1245 AM CDT Sat Jun 27 2020

   Valid 271200Z - 281200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL APPALACHIANS EASTWARD TO NEAR THE NEW JERSEY COAST AND
   VICINITY OF NEW YORK CITY...

   ...SUMMARY...
   Severe thunderstorms associated with damaging wind gusts and hail
   will be possible today across parts of the central Appalachians
   eastward to New Jersey and far southwestern New England. Marginally
   severe storms will be possible in parts of the central, southeast
   and northwestern states this afternoon.

   ...Central Appalachians To New Jersey and Far Southwest New
   England...
   At the start of the period, a linear MCS should be ongoing in parts
   of the central Appalachians from northeast Pennsylvania into
   southern New York. Wind damage will be possible along the leading
   edge of this convective line as it moves eastward across southern
   New England this morning. In the wake of this feature, a moist
   airmass will exist across the central Appalachians with surface
   dewpoints in the mid 60s F. In response, pockets of moderate
   instability are expected to develop by afternoon across parts of the
   Upper Ohio Valley eastward to the vicinity of New York City. An
   outflow boundary from the morning MCS should be present across the
   area. This boundary will likely be a focus for convective
   development. Additional convection should initiate off of terrain
   features in the central Appalachians. By mid to late afternoon,
   scattered thunderstorms are forecast to develop from eastern Ohio
   eastward to near the New Jersey coast and Long Island. RAP forecast
   soundings along this corridor at 21Z show unidirectional wind
   profiles from the west-southwest with speed shear in the mid-levels
   and steep low-level lapse rates. This environment should be enough
   for damaging wind gusts with the more organized multicell line
   segments. For this outlook, have left the slight risk area similar
   to the previous outlook. This is mainly due to uncertainties with
   the forecast which include the location of the outflow boundary and
   resulting distribution of instability.

   ...Central Plains/Mid Mississippi Valley/Southern Great Lakes/Ohio
   Valley...
   An upper-level ridge will move slowly eastward from the central
   Plains into the lower Missouri Valley today. Further west, a
   shortwave trough will move into the central High Plains. Beneath
   these two features, a moist airmass should exist with surface
   dewpoints generally ranging from the lower 60s F in the west-central
   Kansas to near 70 in the lower Missouri Valley. As surface heating
   takes place during the day, moderate to strong instability is
   expected to develop across much of central Plains eastward into the
   Lower Missouri Valley. Although convection should remain isolated
   during the day, a few thunderstorms could form along pre-existing
   boundaries in areas that destabilize the most. These storms may have
   a marginal wind damage threat. This threat is expected to continue
   into early evening as a 40 to 50 kt low-level jet strengthens across
   the region.

   Further west into eastern Colorado, convection is expected to
   develop in the higher terrain of central Colorado. These storms will
   move eastward into the central High Plains during the afternoon just
   ahead of a subtle shortwave trough. Although instability in eastern
   Colorado should be relatively weak, lapse rates will be very steep.
   This along with deep-layer shear of 30 to 40 kt should be enough for
   semi-organized multicells with hail and a few marginally severe wind
   gusts.

   ...Southeast...
   A very moist airmass will be in place across the Gulf Coast States
   today with surface dewpoints mostly in the upper 60s and lower 70s
   F. In response to surface heating, moderate to strong instability is
   expected to develop across much of the moist sector by afternoon
   from far east Texas eastward into Alabama. Some models suggest
   MLCAPE will peak near or above 3000 J/kg across parts of the
   Southeast. This magnitude of instability combined with steep
   low-level lapse approaching or exceeding 8.0 C/km should be enough
   for an isolated wind damage threat with the stronger pulse storms or
   multicells.

   ...Northern Rockies/Northern High Plains...
   An upper-level trough will dig southeastward into the Pacific
   Northwest today. West to southwest mid-level flow will be in place
   ahead of the trough across much of the northern Rockies and northern
   High Plains. As the upper-level trough approaches the northern
   Rockies this afternoon, scattered thunderstorms are expected to
   develop in the higher terrain of western and central Montana. These
   storms will move eastward into the lower elevations across central
   and eastern Montana late this afternoon into early evening. Although
   instability should be relatively weak, steep lapse rates and
   moderate deep-layer shear may be enough for a marginal severe
   threat.

   ..Broyles/Bentley.. 06/27/2020

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z