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SPC Jul 2, 2024 2000 UTC Day 1 Convective Outlook

1 year ago

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0252 PM CDT Tue Jul 02 2024 Valid 022000Z - 031200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN IOWA...NORTHERN MISSOURI...NORTHEAST KANSAS...AND FAR SOUTHEAST NEBRASKA... ...SUMMARY... Scattered to numerous damaging thunderstorm winds, a few tornadoes, and occasional large hail appear most likely this afternoon and early evening over parts of southern/central Iowa, northern Missouri, and northeastern Kansas. ...20z Update... The Marginal (level 1 of 5) risk has been removed from much of NE/SD/WY in the post-frontal airmass. This area is well behind a moist axis oriented across central KS into IA, and dewpoints have generally fallen into the 40s and 50s F with only weak instability noted. Ongoing convection across western NE earlier produced gusts to around 35 kt. While some gusty wind potential will be possible with any storms across the area, overall cover and severe potential appears low. Some modest trimming of the Marginal (level 1 of 5) risk has also been done from eastern NE into northern IA and southeast MN where ongoing clouds and precipitation has largely modified the airmass such that instability is low and severe potential should remain south of this area. Otherwise, refer to the previous outlook below for more forecast details, and MCD 1511 for short term severe information across IA/MO. ..Leitman.. 07/02/2024 .PREV DISCUSSION... /ISSUED 1128 AM CDT Tue Jul 02 2024/ ...Iowa/Missouri into Northeast Kansas and Vicinity... Elevated thunderstorms with a marginal/isolated hail threat are ongoing late this morning across eastern NE and southern IA in a low-level warm advection regime. This activity is also being aided by modest large-scale ascent associated with a subtle mid-level vorticity maximum moving eastward over the central Plains. The primary upper cyclone and related surface low will remain over central Canada today, with a cold front extending southward over the northern Plains/Upper Midwest and continuing southwestward into the central Plains. An effective warm front extends northeastward from a secondary surface low in north-central KS across northern MO into southern IA. This boundary will likely serve as a focus for severe thunderstorms this afternoon and evening as it attempts to lift further northward into IA. The 12Z sounding from TOP showed a very moist boundary layer, with precipitable water values through the column greater than 2 inches and somewhat steepened mid-level lapse rates. Robust daytime heating of this airmass along/south of the front will likely aid the development of moderate to strong instability by mid afternoon, even though mid-level temperature remain somewhat warm. A belt of stronger (40-55 kt) southwesterly mid-level flow associated with the subtle central Plains shortwave trough will likely overspread the frontal zone across IA and northern MO in the same time frame. With sufficient veering/strengthening of the wind field with height through mid-levels, around 35-50 kt of deep-layer shear is expected to promote organized convection, including the potential for both supercells and a bowing cluster. Thunderstorms should intensify by early to mid afternoon near the front across southeast NE/northeast KS into southern/central IA and perhaps northern MO. If this initial development can remain at least semi-discrete for a few hours, then sufficient low-level shear near the warm front would support a threat for a few tornadoes. Isolated severe hail may also occur with any sustained supercell. Otherwise, upscale growth into an MCS by mid to late afternoon appears likely given the mainly linear/frontal forcing and mid-level flow aligned mostly parallel to the surface front. Scattered to numerous damaging winds generally ranging 60-70 mph should become the primary severe hazard by late afternoon and early evening across IA and northern MO, but embedded QLCS circulations will also be possible. Convection should tend to weaken later this evening as it approaches the MS River and encounters a less unstable airmass. ...Southern/Central Plains... Additional convection should develop along the front with southwestward extent into KS and the southern/central High Plains. Given a well-mixed boundary layer and steepened low-level lapse rates with daytime heating, isolated to scattered severe/damaging winds should be the main threat with this activity. Modest low-level upslope flow in the post-frontal regime may encourage the development of isolated supercells across parts of southeast CO and vicinity. Occasional large hail and severe wind gusts may occur with any intense convection that can persist, but confidence in a small bowing cluster developing from this activity this evening remains low. Other occasionally strong to severe convection may develop southeastward from eastern WY into western NE this afternoon and evening. Weaker instability across this region should keep the overall severe threat rather isolated. Read more