SPC Nov 12, 2017 1730 UTC Day 2 Convective Outlook

By Newsroom America Feeds at 12 Nov 12:22

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1117 AM CST Sun Nov 12 2017 Valid 131200Z - 141200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS MONDAY ACROSS COASTAL AREAS OF WASHINGTON AND NORTHERN OREGON... ...SUMMARY... Thunderstorms may impact parts of coastal Washington and Oregon on Monday, with some accompanied by the risk for locally damaging wind gusts and a tornado. ...Discussion... Models indicate that one initial vigorous short wave trough and embedded closed low will progress inland of the Pacific Northwest coast during this period, as another digs across the northeast Pacific, to the west of the British Columbia coast. The lead impulse is forecast to weaken considerably after advancing inland, but it appears likely to contribute to suppression of upper ridging across much of the Great Basin/northern Intermountain West into northern Rockies, as the strongest remnant portion accelerates into/through southern Alberta and Saskatchewan by late Monday night. Elsewhere, a subtropical high may remain prominent across the Baja of California, northern Mexico and adjacent portions of the southwestern U.S., but models do indicate the continued development of broadly cyclonic mid/upper flow across much of the Southeast, including the Florida Peninsula. This is expected in the wake of one mid-latitude short wave trough progressing across/northeast of the Mid Atlantic and southern New England coast, and may be accompanied by the northeastward acceleration of an upper impulse out of the Caribbean vicinity, across Cuba and the Bahamas by late Monday night. ...Pacific Northwest... Before weakening occurs with the inland progression of the lead impulse, models indicate that a 90-100+ kt 500 mb jet may nose into the Oregon coast during the day Monday, with 50-70+ kt flow at 850 mb, to the south/southeast of an associated deep, occluding surface cyclone migrating into the Vancouver Island/northwestern Washington vicinity. At the same time, at least near coastal areas, there appears a window of opportunity for strong wind fields and shear to coincide with weak boundary layer destabilization, supported by insolation beneath the lower/mid-level dry slot, and steepening lapse rates beneath the inland progressing mid-level cold pool. This regime may become conducive to low-topped thunderstorm development, including discrete cellular activity, which may be accompanied by some potential for at least brief/weak tornadoes in the presence of large-clockwise curved low-level hodographs. Otherwise, stronger convection will probably enhance the risk for locally damaging surface gusts (associated with downward momentum transfer), before wind fields/shear and instability wane Monday evening. ...Florida... In association with the evolving upper pattern, a cold front appears likely to advance southward through much of the Peninsula and Keys Monday afternoon through Monday night. This will mostly be accompanied by low-level cooling and drying as near surface winds shift from easterly to northerly. However, weak to modest boundary layer destabilization near/ahead of the front appears possible, and may become sufficient for isolated to widely scattered thunderstorm activity, mainly near Atlantic coastal areas. ..Kerr.. 11/12/2017 Read more



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