SPC AC 071245 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0745 AM CDT Tue Apr 07 2020 Valid 071300Z - 081200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO TONIGHT FROM THE SOUTHERN GREAT LAKES AND OHIO VALLEY TO THE MID-ATLANTIC... ...SUMMARY... Severe thunderstorms are possible this afternoon through tonight across southern portions of the Great Lakes region into the Ohio Valley and Mid Atlantic. The strongest storms will pose a threat for very large hail, damaging wind gusts, and a couple of tornadoes. ...Southern Great Lakes/OH Valley this evening into tonight... A weak surface cyclone in south central MN this morning will continue east-southeastward to southern WI this afternoon and southwestern Lower MI this evening. This cyclone is associated with an embedded mid-upper speed max now moving from the Dakotas to MN, in advance of a northern stream shortwave trough. A plume of steep midlevel lapse rates will continue to spread eastward in this flow regime from the MS Valley to the OH Valley, while modest low-level moistening occurs beneath the cap accompanying the elevated mixed layer. The steep lapse rates, some increase in low-level moisture, and substantial deep-layer vertical shear will result in a favorable environment for severe storms across parts of the southern Great Lakes and OH Valley late today into tonight. In the wake of morning convection across IN/OH, destabilization is expected through the afternoon across northern IN/southern Lower MI into northwestern OH. The boundary layer will likely remain capped until late afternoon/evening near the surface low, when thunderstorm development is expected in the vicinity of southwestern Lower MI. Storm initiation is also possible as far west as northern IL, though weakening forcing for ascent and the relatively warm elevated mixed layer suggest the chances decrease with westward extent. Storms that form by this evening will do so in an environment favoring supercells, with MLCAPE near 1500 J/kg and effective bulk shear in excess of 45 kt. Very large hail will be possible given midlevel lapse rates greater than 8 C/km and a semi-discrete initial storm mode. Some upscale growth into line segments will become more probable overnight with an attendant threat for damaging winds. A couple of tornadoes will also be possible where there is sufficient low-level moisture and somewhat greater low-level shear/hodograph curvature close to the warm front across southern Lower MI late this evening. The area around southern Lower MI will be monitored closely today for a potential upgrade to higher hail/wind probabilities. ...Mid-Atlantic this afternoon into tonight... Morning convection across OH will continue to develop southeastward across WV today in a warm advection regime on the northeast edge of the steeper midlevel lapse rates. This convection will reach western and northern VA this afternoon, in concert with daytime heating and resultant steepening of low-level lapse rates. Some vertical mixing of moisture will keep boundary-layer dewpoints modest (in the 50s), but warm afternoon temperatures will promote MLCAPE near 500 J/kg with inverted-v profiles in the low levels. These thermodynamic profiles, in conjunction with effective bulk shear near 40 kt will favor organized clusters capable of producing damaging gusts and isolated large hail. A separate round of thunderstorms is expected late tonight from PA into the Mid-Atlantic with the surface cyclone and embedded mid-upper speed max. Though these storms will likely be elevated, sufficient buoyancy is expected for at least some threat for large hail, and perhaps a few strong/damaging gusts that could reach the surface. ...Lower MS Valley today... Clusters of elevated thunderstorms are developing this morning in the vicinity of southern AR, in a zone of low-level warm advection on the edge of the richer returning low-level moisture across east TX. Storms on the southern flank of the morning convection may pose a threat for isolated large hail and damaging gusts as the low levels destabilize, in an environment with sufficient deep-layer vertical shear for organized storm clusters and perhaps a supercell. ..Thompson/Gleason.. 04/07/2020 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z CURRENT UTC TIME: 1348Z (9:48PM), RELOAD THIS PAGE TO UPDATE THE TIME
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0749 PM CDT Tue Apr 07 2020
Valid 080100Z - 081200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN LOWER MICHIGAN...NORTHEAST INDIANA AND NORTH-CENTRAL OHIO...
...SUMMARY... Severe thunderstorms are possible this evening through tonight across southern portions of the Great Lakes region into the Ohio Valley and Mid Atlantic. The strongest storms will pose a threat for very large hail, damaging wind gusts, and a couple of tornadoes.
...Upper Mississippi Valley/Great Lakes/Ohio Valley/Mid-Atlantic... The latest water vapor imagery shows a plume of mid-level moisture extending from the Mid Missouri Valley eastward into the southern Great Lakes region. Thunderstorms are ongoing within this plume along the leading edge of a band of large-scale ascent. The storms are also located just ahead of a cold front located from eastern Iowa extending into far southwestern Lower Michigan where a 1001 mb low is present. Moderate instability is analyzed ahead of the front across much of the mid Mississippi and Ohio Valleys where MLCAPE is estimated to be in the 1000 to 2000 J/kg range. In addition to the instability, a 60 to 70 kt mid-level jet is analyzed by the RAP over the western Great Lakes. This feature is helping to create strong deep-layer shear profiles across much of the region. This is evident on the WSR-88D VWP at Chicago which has 0-6 km shear near 55 kt with strong speed-shear in the mid-levels.
Further south, the 00Z sounding at Lincoln, Illinois shows 50 kt of 0-6 km shear with a 700-500 mb lapse rate of 7.7 C/km. This is sampling an elevated mixed layer which the RAP shows from eastern Iowa extending eastward into northern Indiana and northwest Ohio. Supercells that develop along this corridor will be capable of producing large hail, with some hailstones
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Wed Apr 08 2020
Valid 082000Z - 091200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO TONIGHT FROM THE MIDDLE MISSISSIPPI VALLEY INTO THE OHIO/TENNESSEE VALLEY...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING ACROSS PARTS OF CENTRAL AND SOUTH CENTRAL TX...
...SUMMARY... Scattered to numerous severe thunderstorms capable of producing large hail and damaging winds, some significant, are expected from mid/late afternoon across the middle Mississippi Valley eastward into the Ohio and Tennessee Valleys through late tonight.
...Mid MS/TN/OH Valleys... Only minor changes to the outlook over this area, including trimming up the northwestern extent based on the position of the cold front and also slightly extending 15% wind/5% tornado probabilities across southern IN.
19Z surface analysis placed a low near the southern IA/IL border, with a cold front extending southeastward through northeast KS. Strong heating has contributed to deep boundary-layer mixing ahead of the front across much of northern MO and northern/central IL (sampled well by the 18Z ILX sounding). Dewpoints are currently in the upper 40s/low 50s across this region.
Strong forcing for ascent both along the front and ahead of the approaching shortwave trough are still expected to increasing thunderstorm coverage over the next few hours. An initially cellular mode will quickly transition to a more linear mode with one or more bowing segments then progresses southeastward. Strong wind gusts remain the primary severe threat with large to very large hail also anticipated. A brief embedded/QLCS tornado or two is also possible once the bowing line segment(s) mature and reach the better low-level moisture farther southeast over southern IL, south