SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0240 PM CDT Mon Jun 14 2021 Valid 142000Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS PARTS OF THE CENTRAL APPALACHIANS INTO NORTHERN MID ATLANTIC COAST REGION... ...SUMMARY... Scattered damaging wind gusts appear most likely across parts of the central Appalachians and Mid-Atlantic regions through tonight. ...20Z Outlook Update... Some adjustments have been made to categorical and probabilistic lines to account for latest trends in model output, destabilization and progression of synoptic features. Across the Appalachians/northern Mid Atlantic Coast region, moderate to strong boundary-layer destabilization is largely confined to the coastal plain, near/east of lee surface troughing, with modest destabilization also ongoing across parts of the Allegheny Plateau. Across the valleys to the east of the Allegheny Front, downslope drying has resulted in a corridor of weak to negligible instability, which may inhibit ongoing convection, at least until its remnants reach the coastal plain this evening. There is still some signal in model output of renewed thunderstorm development across parts of northeastern West Virginia by this evening, in response to forcing for ascent downstream of the next perturbation digging southeast of the Great Lakes region (and contributing to more substantive larger-scale trough amplification). This activity may intensify while spreading across northern Virginia and central Maryland, toward coastal areas later this evening, posing a risk for severe wind and hail. ..Kerr.. 06/14/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Jun 14 2021/ ...Central Appalachians and Mid-Atlantic... A leading shortwave trough will gradually shift east from southern ON into NY, while an upstream trough amplifies from the Upper Great Lakes towards the central Appalachians through tonight. A belt of strong mid-level westerlies in excess of 50 kts at 500-mb should be sustained from OH to the DE Valley vicinity through this afternoon, before shifting south in advance of the upstream trough. Multiple rounds of scattered thunderstorms are expected through tonight. The first round will focus along the surface cold front across far eastern OH, western PA, and northern WV as modest buoyancy (MLCAPE of 600-1200 J/kg) develops where greater insolation is underway. A nearly straight-line and elongating hodograph with effective bulk shear increasing to near 50 kt should support a few splitting supercells embedded within an organized eastward-moving cluster. Weak mid-level lapse rates and greater boundary-layer moisture should be limiting factors to a more robust severe threat, but scattered damaging winds and isolated large hail appear possible. Convection will likely be sustained through this evening into tonight owing to the amplification of the trailing shortwave trough along with the presence of richer boundary-layer moisture across the Chesapeake region to NJ. A continued threat for damaging winds, along with a tornado will likely be maximized in these areas between 00-06Z until convection shifts offshore. ...Central High Plains... A mid-level anticyclone will remain anchored near the Four Corners with small height rises to its north through this evening across the central/northern High Plains. Forcing for ascent will be weak, but terrain circulations and an upslope low-level flow component should support isolated, high-based thunderstorm development amid a deeply mixed thermodynamic profile to the east of the higher terrain from northeast CO to eastern WY. Isolated storms may also form along a quasi-stationary front across western to central NE. Pockets of MLCAPE from 2000-2500 J/kg and effective bulk shear of 35-45 kt with mid-upper westerlies atop low-level southeasterly flow supports a conditional severe wind/hail threat. ...Southwest TX... A southwest-moving MCV should progress towards the Trans-Pecos through this evening. On the southern and eastern fringes of ongoing convection, strong surface heating/mixing will result in moderate buoyancy and inverted-v profiles. New storm development during the afternoon near the MCV could pose a threat for isolated strong/damaging downbursts. ...Eastern OR/WA to MT... A shortwave impulse embedded within the broad upper trough off the West Coast should eject inland into OR/WA tonight. A large swath of strong but meridional mid-level flow should further strengthen in association with this wave. While buoyancy will likely remain weak, the highly elongated hodographs yield a conditional threat of a supercell this evening across northeast OR/eastern WA. More likely, elevated convection is anticipated overnight where residual steep mid-level lapse rates may support isolated severe hail and gusty winds with convection that develops in this region through the ID Panhandle. Farther east, isolated high-based convection should develop off the higher terrain of the northern Rockies despite the presence of the nearby ridge axis. Flow aloft will be weak, but the very deeply mixed thermodynamic profiles warrant a risk for isolated severe winds. Read more LIVE: spc.noaa.gov
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