SPC Mar 20, 2017 1730 UTC Day 2 Convective Outlook

By Newsroom America Feeds at 20 Mar 2017

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Mon Mar 20 2017 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY AREA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF THE LOWER MISSISSIPPI VALLEY INTO THE CAROLINAS... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE SACRAMENTO VALLEY AREA... ...SUMMARY... A threat for large hail and damaging wind gusts will exist Tuesday from a portion of the lower Mississippi Valley, the Tennessee Valley and Carolinas. ...Synopsis... A synoptic trough will amplify over the eastern half of the U.S. while another trough moves into the West Coast region. At the surface high pressure will build south from the northern Plains into the OH and TN Valleys. A cold front demarcating the leading edge of this airmass will extend from northern OK into the south and east portions of the OH Valley early Tuesday, but will advance slowly south during the day. ...Lower to middle MS and TN valleys and the Carolinas... A cold front should approach northern TN early Tuesday and extend westward into northern OK. Modified continental-polar air with upper 50s to near 60F dewpoints will advect through the pre-frontal warm sector beneath an eastward-expanding plume of 7.5 to 8 C/km mid-level lapse rates. These processes will contribute to moderate instability with mlcape from 1500-2000 j/kg possible as the boundary layer warms during the afternoon. A few storms may be ongoing in vicinity of this boundary with some threat for mainly hail. As the warm sector destabilizes and with the approach of a weak shortwave trough embedded within northwesterly flow, additional storms are expected to develop along the front during the afternoon from southern MO, northern AR into TN and subsequently spread southeast. Wind profiles will remain westerly unidirectional, but mid-level winds will increase with the approach of the shortwave trough with effective bulk shear from 30-40 kt supporting both multicell and a few supercell structures. Storms may eventually consolidate into clusters as they develop southeast with a threat for mainly damaging wind and large hail. Additional storms may develop farther east into the Carolinas later in the afternoon into the evening. ...Sacramento Valley area... Steep mid-level lapse rates supported by cold air aloft accompanying the upper trough will spread inland during the day. Scattered showers will likely be ongoing in this region in association with ascent attending a lead shortwave trough embedded within the synoptic trough. In the wake of this feature some cloud breaks and a general decrease in shower activity is possible which may allow the boundary layer to undergo some destabilization with mlcape to 500 J/kg possible. Additional storms may develop during the afternoon. With surface winds remaining backed to southerly in the valley along with 40 kt sfc-6 km vertical shear, a conditional risk will exist for a few supercells with hail and possibly a couple of tornadoes later in the afternoon into early evening. ..Dial.. 03/20/2017 Read more



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