• UTC: 2018-09-20 17:04

tornado/severe thunderstorm watches

  • SPC Sep 20, 2018 1630 UTC Day 1 Convective Outlook
    on September 20, 2018 at 4:16 pm

    SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1109 AM CDT Thu Sep 20 2018 Valid 201630Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM NORTHERN IOWA TO SOUTHERN MINNESOTA AND WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms over parts of the Upper Midwest this afternoon and evening should produce damaging wind gusts, tornadoes and sporadic large hail. ...Upper Midwest... Only minor changes have been made to the ongoing forecast today. Morning visible satellite imagery and surface analysis show the primary warm front extending across central IA. This boundary will develop/move northward through the day and into parts of MN/WI by this evening. Intense low-level shear profiles will develop along and north of the boundary, resulting in significant conditional potential for supercells and associated tornadoes. However, 12z CAM solutions show very limited discrete convective development in this region prior to the approach of a severe squall line this evening. Nevertheless, will maintain the ongoing tornado risk probabilities due to conditional concerns, and due to potential for QLCS-associated tornado threat this evening. By late afternoon, an intense squall line will develop along the cold front sweeping into eastern NE, western IA and southwest MN. Strong wind fields, ample instability, and significant large-scale forcing all support the risk of rather widespread damaging winds with the storms. The activity should spread quickly eastward across the ENH risk area through mid-evening. Damaging wind gusts are the main threat, but hail and a few tornadoes will also be possible - especially near the synoptic low track over southeast MN and western WI. ..Hart/Coniglio.. 09/20/2018 Read mor […]

  • SPC - No watches are valid as of Thu Sep 20 16:17:02 UTC 2018
    on September 20, 2018 at 4:16 pm

    No watches are valid as of Thu Sep 20 16:17:02 UTC 2018. […]

  • SPC - No MDs are in effect as of Thu Sep 20 16:17:02 UTC 2018
    on September 20, 2018 at 4:16 pm

    No Mesoscale Discussions are in effect as of Thu Sep 20 16:17:02 UTC 2018. […]

  • SPC Day 2 Fire Weather Outlook
    on September 20, 2018 at 4:01 pm

    SPC Day 2 Fire Weather Outlook Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1059 AM CDT Thu Sep 20 2018 Valid 211200Z - 221200Z ...NO CRITICAL AREAS... Fire weather concerns are expected to be minimal on Friday. See discussion below for details. ..Leitman.. 09/20/2018 .PREV DISCUSSION... /ISSUED 0142 AM CDT Thu Sep 20 2018/ ...Synopsis... Longwave ridging aloft will dominate much of the western CONUS on D2/Friday. The strongest mid-level flow will be shunted north of areas with critically dry fuels. At the surface, some troughing is expected in the northern Rockies as the next shortwave trough moves towards the Pacific Northwest. A preponderance of guidance shows only weak troughing which will limit surface wind speeds to below critical thresholds. ...Please see www.spc.noaa.gov/fire for graphic product... Read mor […]

  • SPC Day 1 Fire Weather Outlook
    on September 20, 2018 at 3:18 pm

    SPC Day 1 Fire Weather Outlook Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1017 AM CDT Thu Sep 20 2018 Valid 201700Z - 211200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHERN CA... ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN WY... Overall the ongoing forecast is on track. The only change was to join the two elevated areas across the Great Basin as breezy and dry conditions are expected across much of southeast ID into northeast UT. For more details, see discussion below. ..Leitman.. 09/20/2018 .PREV DISCUSSION... /ISSUED 0119 AM CDT Thu Sep 20 2018/ ...Synopsis... An upper-level trough will pass over the northern/central Rockies today. A well-timed mid-level jet will overspread southern Wyoming and adjacent areas during peak afternoon heating. At the surface, a deepening cyclone in the Central Plains will progress to the northeast with its attendant cold front pushing through the northern Great Basin into the central Rockies. Farther west, high pressure off the northern California coast, in conjunction with surface troughing within the Sacramento Valley, will lead to strong northerly flow through the Valley and adjacent terrain-favored locations. ...Sacramento Valley... Strong northerly flow will reach 15-20+ mph, particularly in areas where flow is channeled by the terrain. The strongest surface winds will occur earlier in the day with the pressure gradient diminishing by late afternoon. Though RH recovery overnight will likely abate fire weather concerns early on, high resolution guidance is in agreement that RH values will fall to 5-15% for long enough duration to warrant a critical designation. Just outside the terrain-favored regions, at least elevated fire weather conditions can be expected. ...Southern Wyoming and vicinity... While temperatures behind the cold front will be cooler, the dry, continental air mass behind it will still foster critical fire weather conditions during the afternoon. The strong, post-frontal pressure gradient with the deepening cyclone to the east will be supplemented by modest mixing of the mid-level jet to the surface and lead to 20-25 mph surface winds. Elsewhere, surrounding the critical region, elevated conditions can be expected with similarly low afternoon RH and lighter surface winds of 15-20 mph. ...Portions of eastern Utah... An elevated fire weather area has been introduced into parts of eastern Utah where latest guidance shows a strong surface pressure gradient causing surface winds behind the cold front to increase to 15-20 mph. Afternoon RH values are expected to fall to 5-20%. Locally critical conditions may also develop within favored terrain areas where flow will be channeled and enhanced. ...Snake River Valley... Strong surface pressure gradient behind the cold front will drive 15-20 mph winds through the Valley. Afternoon RH values falling to 5-20% will lead to elevated fire weather conditions. ...Please see www.spc.noaa.gov/fire for graphic product... Read mor […]

  • SPC Sep 20, 2018 1300 UTC Day 1 Convective Outlook
    on September 20, 2018 at 12:59 pm

    SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Thu Sep 20 2018 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM NORTHERN IOWA TO SOUTHERN MINNESOTA AND WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms over parts of the Upper Midwest this afternoon and evening should produce damaging wind gusts, tornadoes and sporadic large hail. ...Synopsis... In mid/upper levels, a broad area of ridging is forecast to move eastward across the southeastern U.S., while a progressive northern-stream fetch prevails from the Pacific Northwest across the Great Lakes to New England. Embedded in this flow fetch will be the most influential upper-air feature for this forecast: a well- defined synoptic-scale trough now apparent in moisture-channel imagery from the northern Rockies across northern UT to the Four Corners region. This trough is forecast to move eastward by 00Z to the western Dakotas, eastern CO and eastern/southern NM. By 12Z the trough should reach northern MN and central NE, lagging back over eastern NM with increasingly positive tilt overall as the northern portions accelerates eastward. At the surface, 11Z analysis showed a frontal-wave low between MCK-LBF, with cold front across northeastern KS and east-central CO. A warm front extended from the low across south-central NE to near OMA, the east-southeastward over southern IA and north-central IL. As the mid/upper trough approaches, the low is forecast to deepen and move northeastward to southeastern MN near MSP by 00Z, then cross eastern Lake Superior overnight. The trailing cold front should reach western IA, southeastern NE and southeastern CO by 00Z, then by 12Z, southern WI, northern MO, south-central KS, and northeastern NM. By 12Z the cold front should reach OH, the lower Ohio Valley, southern OK, and the Permian Basin region. The warm front should move northeastward across the upper Mississippi Valley today ahead of the low, with some modulation by outflow from prior convection to its poleward side. ...WI to central Plains... Scattered thunderstorms are expected north of the warm front throughout the period, offering predominantly a large-hail hazard. Additional thunderstorms should develop this afternoon along the cold front as it impinges on a diabatically destabilizing warm sector, in a buoyancy/shear parameter space favorable for severe. Deep shear and low-level SRH will increase northward in proximity to the low, with low-level moisture and boundary-layer lapse rates also becoming favorable. Frontal lift, deep shear and midlevel lapse rates each are expected to diminish gradually with southwestward extent ahead of the cold front, though at least isolated severe hail/gusts may occur from frontal convection as far southwest as the central High Plains. With the dominant cold-frontal storm mode becoming linear rather quickly, the supercell/tornado potential appears most concentrated from the surface low across the warm frontal zone, as long as effective-inflow parcels are surface-based. The mesoscale environment near the warm front, across southeastern MN and western WI, conditionally will be quite favorable for severe, including a substantial tornado risk with any sustained/discrete supercell that can form. The main question involves coverage, which is related to strength of local lift and how many such storms can occur as a result. Forecast soundings east and northeast of the low show sufficient low-level airmass recovery to support MLCAPE 2000-2500 J/kg (locally approaching 3000 J/kg), amidst effective-shear magnitudes of 45-55 kt, with effective SRH 400-600 J/kg along the warm front and 250-450 J/kg in the proximal warm sector. The frontal squall line should offer mainly a wind threat, with isolated large hail, and a QLCS-embedded small tornado or two possible in the northern parts of the line where it encounters high-SRH inflow-layer air. The squall line should weaken this evening into early overnight hours as it encounters a nocturnally stabilizing boundary layer. ...Lower MI... Convection now over southern Lake Michigan and the IL/WI border region is expected to proceed eastward across much of central Lower MI today. The southern fringes of this complex, and/or additional thunderstorms developing along its outflow-reinforced baroclinic zone, should encounter favorably most and diurnally destabilizing boundary layer with surface-based effective-inflow parcels, as the frontal zone retreats northward. Heating and high theta-e in the adjoining warm-sector boundary layer will offset modest lapse rates in mid/upper levels enough to yield 1500-2000 J/kg MLCAPE, amidst 45-50-kt effective shear magnitude. Relatively maximized low-level shear in the baroclinic zone will support at least marginal multi- hazard severe potential in any sustained convection that can remain surface based. Meanwhile, isolated large hail will be possible with elevated convection north of the front. ..Edwards/Peters.. 09/20/2018 Read mor […]

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