Administrators NorthGeorgiaWX Posted July 16 Administrators Posted July 16 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Tue Jul 16 2024 Valid 161300Z - 171200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL/NORTHERN NEW YORK AND SOUTHERN VERMONT... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ELSEWHERE OVER MUCH OF THE NORTHEAST...AS WELL AS PARTS OF: CENTRAL PLAINS...SOUTH-CENTRAL HIGH PLAINS...OZARKS...AND LOWER MISSOURI/OHIO VALLEY REGIONS... ...SUMMARY... Strong to severe thunderstorms are possible from the central Plains to the Northeast. Greatest severe-thunderstorm threats within that are over parts of the central Plains and upper Ohio Valley to parts of the northern Mid-Atlantic and western New England. ...Synopsis... The mid/upper-level pattern will feature an amplifying large-scale ridge over much of western North America, though the anchoring high over the Four Corners is expected to weaken somewhat in terms of absolute height value. Downstream, a belt of mostly cyclonic flow will extend from the northern Plains and Upper Midwest across the Great Lakes, Ohio Valley and Northeast. A synoptic-scale trough -- accompanying a cyclone now over northwestern ON -- is forecast to move southeastward, reaching north-central ON north of Lake Superior and northern MN by 00Z. By 12Z tomorrow, the trough (with intermittently closed 500-mb low) should extend from James Bay across Upper MI to southeastern MN/northwestern IA. Farther downstream, an MCV was apparent in composited radar imagery, moving into southwestern ON from southeastern Lower MI. This feature, and the accompanying shortwave trough/vorticity lobe, are expected to progress to the western NY/western Lake Ontario region by 18Z, then east-northeastward over northern NY and northern New England through the rest of the period. Another MCV appears over west-central KS from an ongoing cluster of convection and precip extending over the lower Missouri Valley region, though its intensity and track still are rather uncertain. At the surface, the 11Z chart showed a cold front from near the neck of ON southwestward across southern WI to northeastern KS, parts of the OK Panhandle, and northeastern NM. The front was diffused in several places by outflow from recent or ongoing convective processes. By 00Z, the front should reach southwestern QC, northwestern OH, southern IL, southern MO, and northern OK, becoming quasistationary over the northern TX Panhandle and northeastern NM. The front should move into the St. Lawrence Valley and Lower Great Lakes by 12Z. Aided by convective outflow, the western part of the front should continue southward across much of OK and parts of northwest TX tonight, while decelerating in most other areas. ...Northeast... Scattered thunderstorms are expected to develop as soon as the late morning hours into midday across western NY, while earlier activity over southern ON also moves toward the same region. Convection should move generally eastward across the outlook area through the afternoon, evolving upscale into a forward-propagating complex aided by strengthening of the midlevel winds ahead of the MCV. The main threat will be a swath of damaging, at least sporadically severe gusts. A more conditional risk exists southward into the northern VA/Chesapeake Bay/northern Delmarva region, where coverage may be more isolated to widely scattered, but also with damaging wind common in any sustained thunderstorms. The mesoalpha-scale environment will be characterized by stronger deep-layer forcing and mass response (to the approaching MCV) in northern areas, and greater low-level theta-e and diurnal-heating- driven destabilization to the south. Lower-elevation surface dewpoints should range from the mid 60s F in the north to low/mid 70s in the southeastern areas, with peak/preconvective MLCAPE increasing to the 1000-1500 J/kg range -- locally near 2000 J/kg in southeastern areas. Well-mixed subcloud layers will help to promote continued downward momentum transfer from the region of enhanced midlevel flow. Given enough cold-pool aggregation/organization, a rear-inflow jet may develop to aid further in organizing the complex. Meanwhile, to the south, the wind threat should be more spotty, with a mix of discrete and clustered multicell convection involved. ...Central/Southern Plains... Isolated to scattered thunderstorms are expected to develop this afternoon mainly north of the synoptic front -- and potentially in two main areas: 1. Central/northern NE near a surface trough, with residual moisture and diurnal heating providing favorable instability amidst northwest flow and favorable deep shear. Weak large-scale scent, preceding a subtle northwest-flow shortwave trough, should help to maintain favorably steep lapse rates and minimal inhibition for afternoon convective initiation. Although low-level winds should remain weak, deep shear will be strong enough to support a blend of multicell and supercell modes, with severe gusts and hail each possible, before activity weakens late this evening. 2. An initial upslope-flow regime over southeastern CO, spreading into parts of western southwestern KS and the OK/TX Panhandles with time this evening. The associated easterly component of near- surface winds will enable favorable storm-relative winds in the inflow layer, convergence along convectively generated boundaries, and moist advection into the region. A hot, deeply mixed subcloud layer should foster severe-gust potential as activity moves/builds eastward to near the KS/OK border through this evening. ...Lower Missouri/Ohio Valleys... Ongoing clusters of strong-severe thunderstorms will continue to pose a threat for damaging gusts and occasional large hail as they move eastward across parts of northeastern KS and northern MO this morning. See SPC Severe Thunderstorm Watches 544 and 545, and related mesoscale discussions, for near-term details. Some of this regime may extend into northern parts of the modifying outflow air this afternoon as part of the next process discussed below. Farther south and east, the threat has increased for scattered to numerous thunderstorms to form this afternoon, offering a relatively dense concentration of potential for severe gusts and occasional large hail. Activity should be focused along and near a combination of an outflow boundary from previous MCS activity (stalling, then retreating northward over the lower Ohio Valley to eastern MO) and the frontal zone (northern Ozarks region). By mid/late afternoon, strong heating and rich low-level moisture (surface dewpoints commonly in the low-mid 70s F) will combine to minimize MLCINH, in and near the eastern part of a field of relatively steep midlevel lapse rates covering much of the Great Plains. MLCAPE from 2500- 3500 J/kg should be common. Even with such high dewpoints, heating will be strong enough to foster well-mixed subcloud layers in support of severe-gust potential. Also favoring the wind threat will be potential for aggregation of smaller-scale clusters into cold pools with forward propagation and forced ascent. ..Edwards/Broyles.. 07/16/2024 Read more View the full article Quote
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