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Tuesday, August 3, 2021

SPC Aug 3, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Tue Aug 03 2021 Valid 031300Z - 041200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER SOME PARTS OF CENTRAL/EASTERN OREGON AND WASHINGTON... ...SUMMARY... Isolated strong to severe thunderstorm gusts will be possible this afternoon and early evening over over some parts of central/eastern Oregon and Washington. ...Synopsis... The CONUS portion of the large-scale upper-air pattern -- western ridge/eastern trough -- will change little through the period. A 500-mb high will remain near LAS, with ridge northward to the northern Rockies. A compact vorticity lobe and associated shortwave trough are apparent in moisture-channel imagery about 150-155 nm offshore from WA/OR, with an embedded circulation center roughly west of AST. This perturbation should move east-northeastward through the period, crossing the Olympic Peninsula around 00Z, and reaching northeastern WA/southeastern BC around 12Z tomorrow. Meanwhile, a series of shortwaves will traverse a broad cyclonic- flow field covering most of the nation east of the Rockies. At the surface, a wavy, stationary to slow-moving cold front was drawn at 11Z from just off the coast of the Carolinas to southern GA/northwestern FL, westward over southern LA and south-central TX. A weak frontal-wave low is progged to develop today over the southeastern GA area and ripple northeastward, with some deepening possible tonight near coastal northeastern SC and southeastern NC. Farther northwest, a weak surface low initially drawn between DLS-PDT may move slowly north-northeastward along a quasistationary trough extending from central OR to eastern WA. ...Interior Pacific Northwest... Isolated to widely scattered thunderstorms are possible in two main areas: 1. Eastern OR, perhaps extending into the Hells Canyon area before convection dissipates this evening. Strong diurnal heating/mixing will strip away MLCINH and reduce dew points somewhat, while enough moisture still remains in the profile to support high-based thunder potential. MLCAPE may reach the 300-800 J/kg range, with around 30-40 kt peak effective-shear magnitudes. This area appears to have the best-organized threat for strong/locally severe convective gusts. 2. Central/northeastern WA ahead of the shortwave trough, where DCVA preceding the trough will begin to overlap an area of favorable moisture and residual, diurnally driven warmth in the boundary layer. Those factors may provide enough low-level theta-e to support orographically aided thunderstorm formation, along with some potential for development near the surface trough. A strongly mixed boundary layer in the lower elevations will support isolated downburst potential. Convective coverage is more uncertain than farther south, and may be quite isolated, but will refrain from removing this area entirely for now, pending mesoscale trends and additional numerical guidance based on 12Z and later observational input. A relative minimum in convective potential should exist between the two regimes, south of the greater large-scale ascent preceding the shortwave trough, and northwest of the surface low where boundary-layer flow and convergence are weak. ...Southeastern CONUS... Isolated to scattered thunderstorms will be possible in a broad swath from south TX to FL and parts of the Carolinas, both south of the front and where sufficient residual moisture lingers to its north. The greatest convective coverage may be over the northern Gulf, central/northern FL, and the eastern Carolinas to adjoining Atlantic. While an isolated damaging gust from a water-loaded downdraft may occur almost anywhere in these areas, organized severe potential appears minuscule, but for one conditional, late concern. During the last few hours of the period, thunderstorms should increase in coverage and intensity near the central/southern NC coastline (including southern Outer Banks), as low-level lift strengthens near and southeast of the low. At this time, the most favorable CAPE/shear parameter space is expected to remain offshore, but may brush the coast as well. This would be dependent on mesobeta-scale precip processes, specifically whether too much precip does not cover the coastal areas and prevent favorable destabilization. Severe potential appears too conditional for a categorical outlook area, but will be assessed further for potential to develop inland. ..Edwards/Leitman.. 08/03/2021 Read more LIVE: spc.noaa.gov
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