Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1144 PM CDT Tue Sep 05 2017 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF SOUTHERN NEW ENGLAND... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MIDDLE ATLANTIC TO SOUTHERN GA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN SIERRA NEVADA... ...SUMMARY... Isolated severe thunderstorms are possible across portions of the Mid-Atlantic States and Southeast, portions of southern New England, and also across portions of the northern Sierra Nevada. ...Eastern US... Mid-level flow is expected to increase on the front side of eastern US trough during the day1 period with 500mb speeds increasing from 70kt to near 90kt by the end of the period along the Mid-Atlantic coast. This evolution will force a synoptic front east of the Appalachians to a position from central MA, southwest across coastal Carolinas into southern GA by 18z. Latest model guidance suggests limited surface heating will be noted ahead of the front but stronger across the Southeast where buoyancy is expected to be somewhat greater than across higher latitudes. Deep southwesterly flow should increase near the frontal zone such that any storms that develop across the warm sector should be sufficiently sheared for potential storm organization. Even so, instability is expected to remain seasonally weak and severe coverage should be isolated in nature. If breaks in cloud cover allow boundary layer to heat more than expected, subsequent increase in instability could warrant higher probs. ...Northern Sierra Nevada... Late evening water vapor imagery depicts a well-defined short-wave trough off the northern CA coast which is forecast to approach near-shore regions by 07/00z. Southeasterly mid-level flow and large-scale forcing for ascent should increase across the northern Sierra Nevada ahead of this feature and a convectively active day is expected in response. Forecast soundings for this region suggest ample instability and steep lapse rates necessary for the production of hail and gusty winds. ..Darrow/Picca.. 09/06/2017Read more
from SPC Forecast Products http://ift.tt/s7Jkvo
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