SPC Mar 7, 2018 1300 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 7 Mar 2018

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0654 AM CST Wed Mar 07 2018 Valid 071300Z - 081200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Isolated thunderstorms are possible across the southern half of Florida into the afternoon, while lightning strikes cannot be ruled out across parts of the Northeast. Severe weather is not expected. ...Synopsis... The upper-air pattern for this outlook will be dominated by a complex/deep-tropospheric cyclone located initially over the upper Great Lakes. A pronounced, basal shortwave trough is evident in moisture-channel imagery from eastern KY across northern GA then curving across central AL and eastern MS. The synoptic 500-mb low should pivot slowly/erratically southeastward across MI through the period, while the shortwave trough ejects northeastward offshore from the MD/VA/NC Tidewater region. By 00Z, the trough should evolve a closed 500-mb low east of NJ and south of Long Island, moving northeastward across the Cape Cod/ACK region to the Gulf of Maine overnight. At the surface, a deeply occluded low was analyzed over southeastern Lower MI, with occluded front southeastward to a deepening triple- point low located east of the Chesapeake Bay mouth. As the aforementioned shortwave trough approaches/closes off, the surface low will deepen considerably, tracking just southeast of the mid/upper-level low and just offshore from Cape Cod. The trailing surface cold front -- analyzed initially from the low across the Atlantic to central FL -- should proceed southeastward down the FL Peninsula, clearing the Keys around 00Z. ...FL... Widely scattered to scattered showers and isolated thunderstorms are expected to occur near the surface cold front and/or a prefrontal convergence zone as they move across the remainder of the peninsula through the afternoon. Convection over this region largely should be disorganized, with only marginal thunder potential, given the layers of weak lapse rates evident in low/middle levels in 12Z RAOBs and forecast soundings. Surface diabatic heating inland may be strong enough to generate weak CAPE briefly extending into upper levels; however, updraft mass continuity will be difficult to maintain because of the stable layers and generally weak lapse rates above the boundary layer. With a narrow corridor of briefly maximized low-level shear possible immediately ahead of the surface front, before too much surface veering occurs this afternoon, a few cells may exhibit weak/transient storm-scale cyclonic shear. Still, any associated severe potential appears too isolated and speculative to introduce unconditional/categorical severe probabilities at this time. ...Northeast... Deep-layer lift will intensify substantially in the 15-8Z time frame, from southeast to northeast across the mid Atlantic, then over portions of southern New England through afternoon. Lightning in this region should be isolated overall, with MUCAPE generally under 250 J/kg occasionally reaching into layers of -20 C or colder temps suitable for lightning generation. This activity will be associated with elevated convective plumes in the conveyor wrapping around the northwestern/western quadrant of the deepening low/middle-level cyclone, and contributing localized convective enhancement to snowfall. For more on the winter-weather threat, refer to WPC heavy-snow guidance, forthcoming SPC mesoscale discussion(s), and local winter-weather watches and warnings. ..Edwards.. 03/07/2018 Read more



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