Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Apr 04 2023 12:56:35 ACUS01 KWNS 041256 SWODY1 SPC AC 041254 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Tue Apr 04 2023 Valid 041300Z - 051200Z ....THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF EASTERN IOWA...NORTHWESTERN ILLINOIS...EXTREME SOUTHWESTERN WISCONSIN...NORTHEASTERN AND SOUTHERN MISSOURI...ARKANSAS...AND EXTREME EASTERN OKLAHOMA... ....SUMMARY... Tornadoes, severe thunderstorm gusts and large hail are possible today and tonight from the Upper Great Lakes to central Texas. Potential for unusually strong tornadoes is focused today over parts of the mid/upper Mississippi Valley, and tonight over parts of the Ozarks to the Arklatex region. ....Synopsis... The dominant upper-tropospheric feature for this forecast will be a synoptic-scale trough and broad swath of associated cyclonic flow over the western CONUS. Moisture-channel imagery indicates that a cyclone aloft is forming across the Uinta Mountains/Flaming Gorge region of UT/WY, along the trough extending southwestward over the lower Colorado River Valley and northern/central Baja. The 500-mb low should migrate/redevelop northeastward to the Black Hills by 00Z, with trough across eastern CO, northern/western NM, and northwestern MX. BY 12Z, the low should reach eastern ND, with trough across central NE, western KS, and central/southwestern NM. The associated surface low was analyzed at 11Z between SLN-GBD, with another low over southeastern CO, and a quasistationary front connecting them. A warm front extended eastward from the KS low over central MO, southern IL and west-central KY. A dryline was drawn from the same low south-southwestward over western OK, northwest/west-central TX, and northern Coahuila. The KS low should shift northeastward to west-central IA by 00Z, with cold front across extreme southeastern NE to central KS. From there, two branches of the cold front will become apparent: an arctic boundary arching across western KS to central CO, and a Pacific front across the TX Panhandle to far west TX. The dryline should mix eastward during the day and reach northwestern MO, eastern KS, east-central OK, north-central TX, to the Rio Grande Valley between DRT-LRD. The warm front should extend from the low across eastern IA, northern parts of IL/IN, and western/central OH. Overnight, the Pacific front will overtake (by then) the quasistationary to slowly retreating dryline from north-south, such that by 12Z, the combined boundary will extend from a low over northwestern WI across eastern IA, southwestern MO, northwestern AR, and across northeast through south-central TX to near LRD. The warm front, at that time, should extend across central WI, southern Lower MI, and northern OH. A vast area of at least marginal severe potential is evident from the Upper Great Lakes north of the warm front -- where hail from elevated thunderstorms will be the main concern -- to portions of central/east TX tonight as convection grows near the cold front and poses mainly a wind/hail threat. Two relative concentrations of particularly intense and destructive tornado potential are apparent, but still with enough uncertainties attached to preclude unconditional categorical upgrade(s) at this outlook cycle. ....Mid/upper Mississippi Valley region, Upper Great Lakes... Morning convection north of the warm front will rooted in a favorably unstable, elevated inflow layer amid favorable deep shear, and will pose an isolated large-hail threat. Episodes of additional thunderstorms (also offering severe hail) are possible through this evening in this regime. The main concern, however, will be this afternoon into evening east and southeast of the surface low, from the warm front southward 100-200 nm into the warm sector, in and near the "moderate" area. At least isolated supercells will be possible, with potential for strong to violent tornadoes, very large hail, and locally severe gusts. A "middle ground" or consensus scenario suggests that, once thicker low-cloud cover erodes/advects past the area this afternoon, a few supercells form in and cross a warm sector characterized by large hodographs, strong deep shear, and climatologically rare buoyancy, then cross a very favorable warm-frontal zone. MLCAPE of 2500-3500 J/kg is possible beneath 7.5-8 deg c/km midlevel lapse rates and surface dewpoints at least in the mid 60s F. Isallobaric forcing and related backed flow in the warm sector, within a couple degrees of the latitude of the low, should yield enlarged low-level hodographs, with effective SRH of 300-500 J/kg, exceeding 600 J/kg along the warm front, and 60-70 kt effective-shear magnitudes. Optimal values of both CAPE and shear may be somewhat higher if the most aggressive progs verify, and should be very strong along the warm front. The main uncertainty involves warm-sector storm coverage and maturation time before crossing too deep into the warm-frontal zone to remain surface-based. A big influence on this potential will be the extent and magnitude of moisture deficit related to vertical mixing. Models are following their usual biases in this regard -- but to somewhat of an extreme -- with (for example) WRF-based progs like the NAM, SREF members and some HREF members being more cool and moist under an EML, but ultimately developing greater density of storms farther south (with more maturation room) in the warm sector as heating erodes MLCINH. Meanwhile RAP-based progs (including HRRR) develop less activity, with a deep, well-mixed boundary layer more suited toward wind potential evident in their forecast soundings. If the EML remains strong through the afternoon, the deep-mixing scenario is low-probability, but lift in the warm sector also may be restricted. A corridor of frontal convection also should develop from late afternoon into tonight from central IA to eastern KS, moving eastward. This activity may include early-stage supercells with all severe hazards possible, but evolving to wind-dominant QLCS mode with a few tornadoes also possible. Upstream RAOBs at 00Z last night, and 850-mb moisture analysis, revealed a channel of dry air and shallowness of the moist boundary layer from the Texas Coast north-northeastward into MO -- upstream from today's threat area. However, that channel was narrow, perhaps sampled best by the LCH RAOB among those available at this writing at 12Z, and may be constricted further and shunted eastward enough to not be a major impediment to convection, amid the synoptic mass response to the approaching trough. Still, this uncertainty keeps the range of reasonable development scenarios too large to do much with the outlook as it stands, given a very favorable overall meso-alpha-scale setup as discussed above. ....Ozarks to Arklatex and central TX... Isolated warm-sector or dryline thunderstorms may develop before dark, which could become supercells with all severe hazards possible if they can be sustained into an increasingly moist boundary layer with eastward extent. However, the greater severe threat should develop this evening into tonight, as deep-layer lift and the LLJ each increase, along with hodograph size and low-level moisture. The combination of those factors will expand the CAPE/shear parameter space to favor long-lived supercells with a threat for significant (EF2+ tornadoes) at night, along with damaging hail and isolated severe gusts. Surviving diurnal and/or more newly developed evening convection could encounter 2500-3500 J/kg MLCAPE, LLJ-enlarged hodographs with effective SRH 300-500 J/kg, and 1/2-km SRH nearly that large. Coverage of prefrontal/pre-dryline convection also is uncertain over this area because of the strong EML sampled upstream this morning by DRT and FWD RAOBs. Still, associated MLCINH should hold steady or perhaps even diminish for a few hours this evening as boundary-layer theta-e increases (with upper 60s F surface dewpoints likely). As the front/dryline combination impinges on the region overnight, thunderstorm coverage should increase along the associated corridor of maximized lift, with all severe hazards possible. ...Edwards/Smith.. 04/04/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .