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SPC Jun 20, 2024 0600 UTC Day 1 Convective Outlook

1 year 3 months ago

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Thu Jun 20 2024 Valid 201200Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHEAST AND OVER THE CENTRAL HIGH PLAINS... ...SUMMARY... Storms may produce scattered damaging gusts over parts of the Northeast on Thursday. Scattered severe storms are also expected over parts of the central High Plains. ...Northeast... Upper anticyclone currently centered over the middle Atlantic will gradually build west across the CONUS during the day1 period. As this occurs, some flattening of the height field is expected over southern QC into New England. Modest 500mb flow will extend along the international border, but much weaker mid-level winds will be noted over the lower Great Lakes into southern New England. This stronger flow over Canada will encourage a surface cold front to advance south into northern ME, arcing west along the international border into southern lower MI by 18z, with subsequent southeast movement expected across the Northeast into the early evening. This boundary will serve as the focus for convection later today as surface temperatures quickly soar through the 80s into the lower 90s. Additionally, while deep-layer shear will not be particularly strong along the northern fringe of the upper High, PW values are seasonally moist with 1.5-2 inches expected south of the frontal zone. Damaging winds are the primary risk with convection today. ...Central High Plains... Weak 12hr mid-level height rises are forecast across much of the interior western US through early evening as an upper trough repositions itself from WA/OR into CA. This will ensure a corridor of modest southwesterly flow at mid-levels from the Four Corners region into the central High Plains. Within this flow a few weak disturbances may track across the central Rockies into the Plains. Each of these features could encourage robust convection. Latest guidance suggests a weak lee cyclone will evolve over northeast CO by late afternoon in response to one of these features. LLJ is also forecast to respond across western KS into SD. As a result, an easterly boundary-layer component will be noted across the NE Panhandle into eastern WY. NAM forecast sounding for CYS at 22z exhibits negligible inhibition but MLCAPE on the order of 2000 J/kg with 35kt surface-6km bulk shear. HREF guidance strongly suggests convection will evolve over the higher terrain of south-central WY/CO fairly early, then propagate downstream, growing upscale into a possible MCS within the warm-advection zone. Convection should advance into the central Plains after sunset aided by strengthening LLJ. Initial storm mode should be supercellular and large hail is expected. Severe wind gusts could materialize along the leading edge of the MCS if it matures as expected. ..Darrow/Thornton.. 06/20/2024 Read more