SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1234 AM CDT Fri Sep 10 2021 Valid 101200Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY ACROSS PARTS OF CENTRAL AND EASTERN OREGON... ...SUMMARY... Strong thunderstorms could impact parts of central and eastern Oregon this afternoon and evening, posing at least some risk for severe weather. ...Synopsis... The westerlies will remain generally progressive across the northern mid-latitudes of the Pacific and North America through this period, with a number of substantive embedded short wave troughs. One of these is forecast to accelerate out of the Northeast, through the Canadian Maritimes, preceded across the northwestern Atlantic by Hurricane Larry. Models indicate that an upstream perturbation emerging from the Canadian Prairies will dig across Manitoba into northern Ontario by 12Z Saturday, as yet another perturbation migrates into the northern British Columbia coast. Preceding, and to the southeast of, the trailing short wave trough, a weaker impulse within a separate branch of the westerlies is forecast to accelerate inland of the Pacific coast through the northern Rockies by late tonight. This may contribute to some further suppression of a still prominent mid-level high becoming centered over the southern Rockies, but an associated broad plume of warm lower/mid tropospheric air, now overspreading much of the Great Plains, may continue to advect eastward across the Mississippi Valley. Downstream, weak troughiness may linger across parts of the Southeast, but weak mid/upper ridging appears likely to otherwise prevail across much of the southern mid- and subtropical latitudes. In the wake of the short wave trough exiting the Northeast, seasonably high moisture content, including precipitable water of 1.5-2.0+ inches, will remain confined to a plume across the Gulf of Mexico through the Florida Peninsula, generally along and south of a stalling/weakening frontal zone. However, another plume of high moisture content may surge northward through the Gulf of California, in the wake of Hurricane Olaf, as it slowly begins to migrate west of the southern tip of Baja California Sur. ...Great Basin/northern intermountain region/northern Rockies... A broad swath of moderate (30-50 kt) southwesterly flow in the 700-500 mb layer, to the east of the inland advancing short wave trough axis, could contribute to at least some potential for locally strong to severe gusts in scattered thunderstorm development over a broad area of the Intermountain West today. However, there is some continuing signal within the various model output, including convection-allowing guidance, that a corridor of somewhat better severe weather potential could develop this afternoon across parts of central and eastern Oregon (near/north of the Harney Basin into the southern slopes of the Blue Mountains). In the wake of early day cloud cover and precipitation, steepening lapse rates beneath the modest (around -14 C at 500 mb) mid-level cold core of the inland advancing trough may contribute to a corridor of CAPE on the order of 500-1000 J/kg. Coupled with favorable shear near a 40-50 kt jet streak around 500 mb, it appears possible that the environment could become conducive to the evolution of a small eastward propagating, organized cluster of storms, perhaps initiating as an isolated supercell. Aided by melting of small hail and downward momentum transfer, this activity could pose a risk for strong wind gusts before convection weakens this evening. ..Kerr/Bentley.. 09/10/2021 Read more LIVE: spc.noaa.gov
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