SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0156 PM CST Mon Jan 25 2021 Valid 252000Z - 261200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING ACROSS PARTS OF NORTHEASTERN MISSISSIPPI AND NORTHWESTERN ALABAMA INTO MIDDLE TENNESSEE... ...SUMMARY... A few severe thunderstorms are possible this evening within a corridor across northeastern Mississippi and northwestern Alabama into middle Tennessee. This includes a risk for potentially damaging wind gusts and perhaps a couple of tornadoes. ...20Z Outlook Update... Adjustments to the categorical and probabilistic outlook lines were made to account for the progression of synoptic and sub-synoptic features, and latest trends concerning ongoing destabilization. ...Mid South vicinity... Low-level moisture return is ongoing on southerly return flow across the lower Mississippi into Tennessee Valleys. This appears to be contributing to modest boundary-layer destabilization (including CAPE up to 500-1000 J/kg), which is expected to continue developing northeastward as an initial short wave impulse, which has emerged from the Southwest, progresses east-northeast of the central Great Plains late this afternoon and evening. As the associated frontal wave migrates into the lower Ohio Valley, there appears a window of opportunity for vigorous convective development focused along/just ahead of the trailing surface trough across Tennessee into Mississippi. This may coincide with a 40-50 kt southerly 850 mb jet axis, along which enlarged low-level hodographs may become support of supercells structures accompanied by the risk for damaging wind gusts and/or a couple of tornadoes. With the influence of the mid/upper forcing on the warm sector expected to be glancing/short-lived, it appears this risk will be maximized this evening, but at least some severe weather potential may linger as remnant convection spreads eastward/southeastward overnight. ...Arizona... A corridor of modest boundary-layer destabilization is ongoing across the international border into southern Arizona, ahead of the vigorous short wave impulse now turning inland of the southern California coast. Coincident with strengthen of west-southwesterly flow to 30-40+ kt in the 850-700 mb layer, the environment may become conducive for isolated thunderstorm development with the potential to produce strong surface gusts approaching or briefly exceeding severe limits. ..Kerr.. 01/25/2021 .PREV DISCUSSION... /ISSUED 1025 AM CST Mon Jan 25 2021/ ...TN Valley today... A progressive shortwave trough continues to move across the central Plains today, with an associated 100kt+ mid level jet extending from north TX into MO. The primary surface low for this system is over northwest AR, with a warm front extending eastward along the KY/TN border. Strong low-level wind fields are present across the warm sector, with sufficient CAPE to pose a marginal risk of a few fast-moving storms capable of gusty winds. However, model guidance continues to suggest that slight veering in the low-level winds will weaken convergence/forcing and limit coverage of deep convection. ...MS/AL/TN this evening and tonight... After dark, a few thunderstorms are expected to form over parts of MS/Al and middle TN along/ahead of the advancing cold front. Low-level and deep-layer vertical shear profiles in this area will be favorable for storm organization/rotation, and will maintain the marginal probabilities for isolated tornadoes or damaging wind gusts. The primary forecast concern in this region will be storm coverage, and poor thermodynamics in the lowest 3-4 km suggest that updrafts may struggle to intensify. This area will continue to be evaluated in later outlooks.
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