SPC Mar 8, 2018 0700 UTC Day 2 Convective Outlook

By Newsroom America Feeds at 8 Mar 2018

SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1130 PM CST Wed Mar 07 2018 Valid 091200Z - 101200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY NIGHT ACROSS MIDDLE AND UPPER TEXAS COASTAL AREAS... ...SUMMARY... Strong thunderstorms may impact portions of middle and upper Texas coastal areas Friday night, accompanied by at least some risk for severe hail. ...Discussion... A blocking upper ridge is expected to remain prominent, centered in the vicinity of Newfoundland and Labrador through this period. However, models continue to indicate that a broad/deep closed low, initially centered near the Hudson/Champlain Valleys, will elongate eastward toward the Canadian Maritimes. This is forecast in response to the progression of a significant impulse pivoting around its southern through eastern periphery, which appears likely to support renewed cyclogenesis across the Atlantic into the Canadian Maritimes. As this occurs, it appears that broadly confluent cyclonic mid-level flow east of the Mississippi Valley into the western Atlantic will lose some amplitude Friday through Friday night. Upstream, within belts of westerlies emanating from the mid-latitude and subtropical Pacific, models continue to indicate that several short wave perturbations will progress through and to the east of the axis of larger-scale ridging across the West. However, spread among the model guidance increases by the end of the period as these features progress east of the Rockies into the High Plains. Perhaps in advance of the southernmost of the mid-latitude impulses, a modest surface cyclone may develop and migrate southeastward out of the south central High Plains toward the Red River Valley. In response to the mid/upper developments, including the southeastward progression of a low-amplitude subtropical perturbation across parts of the Rio Grande Valley toward the western Gulf of Mexico, guidance indicates that a substantive return flow of moisture may commence on southerly low-level flow. By late Friday night, it still appears that mid/upper 60s F surface dew points will advect into mid/upper Texas coastal areas, with lower 60s through much of central Texas and mid 50s+ north of the Red River into eastern Oklahoma. This is forecast to coincide with considerable steepening of lower/mid tropospheric lapse rates southward and eastward across the southern Plains in response to differential thermal advection. ...Texas coastal areas into northwest Gulf of Mexico... Despite the inland moisture return and potential weak to moderate boundary layer instability (or near boundary layer based instability, with CAPE of 500-1000+ J/kg) across parts of southern through eastern Texas, weak low-level forcing and considerable mid-level inhibition probably will tend to inhibit convection. However, in response to the east/southeastward progression of the subtropical impulse, at least some model output continues to indicate the initiation of widely scattered thunderstorms is possible near mid/upper coastal areas Friday evening. If this occurs, the environment (aided by favorable convective layer shear) appears supportive of strong to severe storms, perhaps an isolated supercell, with large hail the primary severe hazard. Thereafter, an increase in thunderstorm coverage is expected primarily over the northwestern Gulf of Mexico, in the presence of weak warm advection and weaker inhibition. ...Ozark Plateau... A modest southwesterly low-level jet may be maintained across the Red River Valley into the Ozark Plateau through Friday night, providing the source for elevated moisture return which may support widely scattered thunderstorms prior to 12Z Saturday. Models appear increasingly suggestive that stronger mid-level inhibition may suppress thunderstorm development through this period across parts of central/eastern Oklahoma, where CAPE might be more supportive of a marginal severe hail threat. Low thunderstorm probabilities are being maintained across eastern Oklahoma due to uncertainties, but severe probabilities still appear less than 5 percent at the present time. ..Kerr.. 03/08/2018 Read more



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