SPC Forecast Products Storm Prediction Center

  • SPC Feb 21, 2019 0830 UTC Day 3 Severe Thunderstorm Outlook
    on February 21, 2019 at 8:23 am

    SPC 0830Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0222 AM CST Thu Feb 21 2019 Valid 231200Z - 241200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SATURDAY THROUGH SATURDAY EVENING ACROSS PARTS OF CENTRAL/EASTERN ARKANSAS...THE MISSOURI BOOTHEEL...WESTERN/CENTRAL KENTUCKY...WESTERN/MIDDLE TENNESSEE...NORTHERN MISSISSIPPI AND NORTHWESTERN ALABAMA... ...SUMMARY... An organized cluster of severe thunderstorms may evolve Saturday in a corridor across the Ozark Plateau through the lower Ohio Valley, with additional severe storms possible across the lower Mississippi into Tennessee Valleys. Considerable wind damage may accompany these storms along with the risk for tornadoes, some of which could be strong. ...Discussion... In phase with the subtropical westerlies, a vigorous short wave impulse of mid-latitude Pacific origins is forecast to accelerate northeast of the southern Plains through the Great Lakes region during this period. Strong cyclogenesis may already be underway by 12Z Saturday near the Texas/Oklahoma Panhandle vicinity, and models continue to indicate that the rapid evolution of a broad and deep cyclone will proceed northeastward into the Great Lakes region by the end of the period. This likely will include the intensification of a cyclonic mid-level jet, including speeds in excess of 100 kt at 500 mb, across the southern Plains Red River Valley, through the middle Mississippi and Ohio Valleys. Across the evolving warm sector, models indicate that south/southwesterly winds will strengthen to 50-70+ kt through the 850-700 mb layer. Although the warm frontal zone probably will surge north of the Ohio River, and into/through the lower Great Lakes region by late Saturday evening, an initial position roughly along the Ohio River west-southwestward into the Ozark Plateau may provide the main focus for severe thunderstorm potential. Early period convection, associated with weak elevated destabilization above the front, may inhibit, or at least slow, boundary-layer destabilization to the north, while leaving a remnant surface boundary. In association with the onset of stronger surface pressure falls, surface dew points are expected to increase through the lower/mid 60s along and south of this boundary. Coupled with strengthening large-scale ascent, this is expected to contribute at least weak boundary-layer destabilization supportive of an evolving organized mesoscale convective system. CAPE on the order of 500+ J/kg appears possible. Given the strength of the environmental wind fields (and shear) within the convective layer, the convective system may be accompanied by considerable potential for strong and damaging wind gusts. It appears that this may initiate over parts of central and eastern Arkansas by midday, before progressing east-northeastward through the lower Ohio Valley by Saturday evening. A few tornadoes, some strong, are also possible, particularly with discrete supercells which may form near/just ahead of mainly the southern flank of the evolving system. More discrete storms, including supercells, may eventually develop as far south as the lower Mississippi Valley through portions of the southern Appalachians by late Saturday night. ..Kerr.. 02/21/2019 Read mor […]

  • SPC - No watches are valid as of Thu Feb 21 08:24:01 UTC 2019
    on February 21, 2019 at 8:23 am

    No watches are valid as of Thu Feb 21 08:24:01 UTC 2019. […]

  • SPC - No MDs are in effect as of Thu Feb 21 08:24:01 UTC 2019
    on February 21, 2019 at 8:23 am

    No Mesoscale Discussions are in effect as of Thu Feb 21 08:24:01 UTC 2019. […]

  • SPC Feb 21, 2019 0700 UTC Day 2 Convective Outlook
    on February 21, 2019 at 5:42 am

    SPC 0700Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1141 PM CST Wed Feb 20 2019 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON THROUGH FRIDAY NIGHT ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY INTO THE SOUTHERN PLAINS... ...SUMMARY... Strong thunderstorms may impact portions of the lower Mississippi Valley Friday afternoon, into portions of the southern Plains by late Friday night, accompanied by at least some risk for severe weather. ...Discussion... While amplified large-scale ridging, within the mid-latitude and subtropical westerlies, prevails across much of the eastern U.S., to the north of persistent prominent subtropical ridging centered near the Bahamas, models suggest that mid/upper flow will undergo transition across the eastern Pacific. It appears that a blocking mid/upper ridge will become increasingly prominent near or just southwest of the Gulf of Alaska. Downstream of this feature, one short wave impulse is forecast to turn inland of the Pacific Northwest coast and weaken, while another more vigorous perturbation digs to the west of the British Columbia coast. In response to the upstream developments, a vigorous short wave trough (and embedded mid-level closed low), initially near the southwestern U.S. international border area at 12Z Friday, likely will remain progressive. Models suggest that it will come increasingly in-phase with the subtropical stream and take on an increasing negative tilt while accelerating across New Mexico and southwest Texas, into the southern High Plains. It still appears that associated forcing for ascent will provide support for a rapidly developing cyclone by 12Z Saturday across the Texas Panhandle vicinity. Preceding the cyclogenesis, considerable thunderstorm activity may be ongoing early Friday in association with weak elevated destabilization above a warm frontal zone, in a corridor from the Ark-La-Tex vicinity through the Tennessee Valley. This front may remain one focus for continuing convection through much of the period, while gradually advancing northward into and through the Ozark Plateau and lower Ohio Valley. As cyclogenesis commences, additional thunderstorm development is likely across parts of the southern Plains Friday night. ...Lower Mississippi Valley... Models indicate that modest boundary-layer destabilization will take place in a corridor south of the initial warm frontal convection, roughly across parts of central Louisiana through portions of western and central Mississippi by late Friday afternoon. Aided by daytime heating, CAPE on the order of 500-1000 J/kg may develop, in the presence of strong shear beneath 40-50 kt mid-level flow (around 500 mb). Although forcing to support the initiation of surface-based storms remains unclear, the environment may become conducive to the initiation of a few discrete storms capable of producing at least marginally severe hail and wind. ...Southern Plains... Guidance generally suggests that any appreciable severe weather potential probably will await the onset of strengthening large-scale forcing for ascent associated with the developing cyclone. This may not begin to interact with increasing Gulf moisture return until late Friday night/early Saturday (23/09-12Z time frame) across parts of northeast Texas into southeastern Oklahoma and adjacent portions of Arkansas and Louisiana. But the evolution of thermodynamic profiles characterized by increasing convective instability and CAPE on the order of 500-1000 J/kg, even if based above a residual near-surface stable layer, may still become conducive to storms at least capable of producing severe hail and wind by daybreak Saturday. ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind: 5% - Marginal Hail: 5% - Marginal ..Kerr.. 02/21/2019 Read mor […]

  • SPC Feb 21, 2019 0600 UTC Day 1 Convective Outlook
    on February 21, 2019 at 5:22 am

    SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1118 PM CST Wed Feb 20 2019 Valid 211200Z - 221200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Scattered thunderstorms are possible across the Southeast and southern Mid-Atlantic States today but the risk of severe thunderstorms appears negligible. ...Synopsis... Upper pattern is expected to amplify today as the low currently centered over the upper Midwest ejects northeastward and the shortwave trough currently off the Pacific Northwest coast digs southward along the West Coast. By 00Z, a deep upper trough will be in place west of the Rockies with an embedded low centered over the southern CA/NV border and a long and broad fetch of southwesterly flow extending from southern AZ. ...East TX...Southeast...Southern Mid-Atlantic... A stalled front will likely extend from the central AL/GA border southwestward to the central LA coast and into the western Gulf of Mexico at the beginning of the period. Strengthening low-level flow and resulting isentropic ascent within this frontal zone will promote elevated thunderstorm development from east TX into northern AL, with thunderstorms likely ongoing early this morning and continuing through the evening. Limited instability should temper updraft strength, keeping the severe probability low, despite favorable shear. Additional thunderstorm development is possible farther east (i.e. across southern AL and central/southern GA) amidst modest moisture advection and low-level confluence. Expectation is for most of these storms to be elevated, although reduction of surface-based convective inhibition by moisture advection may allow for isolated surface-based updrafts. Storm interaction with the stalled front may also allow for brief updraft augmentation. Even so, this region is displaced east of the stronger mid- and low-level winds, limiting vertical shear and the potential for updraft rotation/organization. ..Mosier/Bentley.. 02/21/2019 Read mor […]