A couple of thunderstorms are possible Wednesday afternoon and evening across parts of the Sacramento Valley and adjacent northern Sierra Nevada.
SPC AC 201702 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1202 PM CDT Tue Mar 20 2018 Valid 211200Z - 221200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... A couple of thunderstorms are possible Wednesday afternoon and evening across parts of the Sacramento Valley and adjacent northern Sierra Nevada. ...Discussion... As a still evolving mid-level perturbation accelerates northeast of the southern Mid Atlantic coast Wednesday through Wednesday night, significant surface cyclogenesis is expected to proceed, generally east/southeast of the Mid Atlantic and southern New England coast. In its wake, models indicate that large-scale ridging will continue to build across the Intermountain West into the Plains, as a prominent mid-level low within a northern branch of split mid-latitude westerlies digs off the British Columbia and Pacific Northwest coast. To the southeast of this latter feature, the remnants of a closed low and upper troughing (within the southern branch of the mid-latitude westerlies and the subtropical westerlies) are forecast to accelerate toward the California coast. While the most significant remaining impulse is not expected to reach coastal areas prior to 12Z Thursday, a number of smaller scale perturbations are expected to progress inland within relatively strong southwesterly mid/upper flow. In response to these developments, generally dry and/or stable conditions likely will prevail across much of the nation, with little risk for thunderstorms. However, one exception may be across parts of the Sacramento Valley into adjacent portions of the northern Sierra Nevada, where some thunderstorm activity appears possible Wednesday afternoon and evening. ...Northern California... Preceding the approaching upper troughing, a plume of seasonably moist air emanating from the subtropical Pacific appears likely to spread inland across coastal areas. Models generally indicate that precipitable water around or in excess of 1 inch will advect northward into/through the Sacramento Valley Wednesday afternoon, where/when a residually cool mid-level environment may remain supportive of weak surface-based or near surface-based destabilization. Aided by an area of forcing for ascent associated with at least one mid/upper perturbation, a couple of thunderstorms appear possible during the late afternoon and evening. In the presence of strong vertical shear, vigorous convection capable of small hail and perhaps an isolated/brief, weak tornado may not be out of the question. The tornado risk will probably largely hinge on the extent of any insolation occurring across the Sacramento Valley. At this time, this threat still appears negligible. ..Kerr.. 03/20/2018 CLICK TO GET WUUS02 PTSDY2 PRODUCT NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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