ZCZC SPCSWOMCD ALL ACUS11 KWNS 141202 SPC MCD 141202 WIZ000-ILZ000-IAZ000-MNZ000-141430- Mesoscale Discussion 1279 NWS Storm Prediction Center Norman OK 0702 AM CDT Wed Jul 14 2021 Areas affected...northern Iowa...southern Minnesota...southwest Wisconsin...and far northwest Illinois Concerning...Severe potential...Watch possible Valid 141202Z - 141430Z Probability of Watch Issuance...60 percent SUMMARY...Ongoing showers and thunderstorms will begin to pose a sporadic and episodic threat for marginally severe hail and gusty thunderstorm winds this morning. As further destabilization occurs later this morning, a more robust severe potential should materialize. A watch may be needed at some point later this morning across portions of the area. DISCUSSION...Widespread showers and thunderstorms associated with a weak cyclonic perturbation in the mid-level flow continue to move east across the central Plains this morning. The strongest convection is organizing on the leading edge of the precipitation shield, where a seasonably strong 850-mb jet has focused the strongest low-level theta-e advection this morning. Furthermore, despite being near the daily minimum in instability, most-unstable CAPE in excess of 2000 J/kg persists this morning across northwest Iowa ahead of this organizing convection thanks in part to the combination of sustained low-level theta-e advection and 700-500 mb lapse rates between 7 and 8 C/km. This instability is more than sufficient to sustain the ongoing convection through the morning hours, especially given the background large-scale ascent associated with the mid-level cyclonic perturbation. Small hail and gusty winds are possible with the present convection. Thunderstorm intensity should slowly increase through the morning as diurnal heating commences, slowly eroding the residual nocturnal boundary layer, and convection organizes into a mesoscale convective system (MCS). This erosion of the nocturnal boundary layer should allow for elevated convection to transition to surface-based or near-surface-based convection through the morning, increasing the potential for strong thunderstorm downdrafts to reach the surface. Two potential limiting factors for a more robust and widespread severe threat will be the lack of a widespread, higher-end CAPE reservoir downstream of the ongoing convection and modest deep-layer shear. With time, deep-layer shear should increase across the region, aiding the organization of convection into an MCS. Until then, severe potential should be more sporadic, primarily being driven by storm-scale processes. Later, despite differences in intensity and location, high-resolution numerical guidance depicts development of a belt of enhanced low-level flow as the MCS organization increases. Development of this feature would act to enhance corridors of severe wind potential. It may become necessary for a watch to be needed at some point this morning across portions of the highlighted area. However, uncertainties associated with how and when ongoing and developing convection transitions from elevated to surface based or near-surface based are too large to pinpoint when and where a watch would be needed. As such, conditions will continue to be monitored through the morning. ..Marsh/Hart.. 07/14/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...GRB...MKX...DVN...ARX...MPX...DMX...FSD...OAX... LAT...LON 43459587 43779531 44649193 44839042 44238938 43238926 42318967 41889115 41759368 41769548 42699608 43459587 NNNN