Issued: 3am on Saturday, June 5th 2021
Technical Forecast Discussion
Short Term (Sunday 6-6-2021 through Tuesday 6-8-2021)
NDTA to our north will continue to build ridging into the forecast area. While there will be positive VORT (mainly from weak curvature effects) across the Ohio Valley on Sunday, it will not be enough to drastically lower heights across the forecast area. This will keep the region quite warm through the entire short term–expect highs to reach in the middle and upper 80s (with perhaps a 90 or two here or there. Modest low level south-southwesterly flow will be a great aid in transporting gulf moisture into the forecast area through much of the short term as well. This will allow heat indices to reach well into the 90s through the entire short term as well. With weak PDVA resulting from a decaying cutoff upper level low (decaying due to NDTA within the system’s center), numerous disorganized diurnal convective cells will initiate across the state through the entire short term. Convective temperatures should be reached by late morning each day, allowing for initiation quite early. While instability indices appear favorable (with CAPE values between 1100-2000 j/kg) throughout the entire Sunday-Monday-Tuesday period, a chaotic, weakly sheared kinematic environment will prevent any cell from becoming organized, becoming long lasting, and reaching severe limits. As the boundary layer decouples in the evening/nighttime hours, expect this convective activity to quickly die out. Lows will run quite warm–in the upper 60s and lower 70s. With dew points remaining in the middle 60s, radiation fog will be likely, especially in the river valleys.
Long Term (Wednesday 6-9-2021 through Saturday 6-12-2021)
Strong NDTA will continue to build ridging across much of the central and eastern CONUS for the beginning of the ling term, keeping the region warm and humid. More widespread PDVA from the decaying upper low will overspread the forecast area, allowing for more widespread convective activity throughout the day Wednesday. Just as the cells expected in the short term, disorganized, short-lived single cells and multi cells are to be expected in with a very unfavorable kinematic environment for convective organization. PDVA will continue into Thursday and Friday, keeping clouds and convection around through this time as well. Meanwhile, out on the Pacific coast, PVA from both shear and curvature effects will propagate a highly amped trough ashore by the early hours of the day Wednesday. Because of the high amplitude nature of this trough, it will not initially have a fast wave speed. However, an advection lobe associated with a shortwave embedded within the longwave will round the base of this, enhancing the wave speed quite a bit. Strong PDTA in this region will greatly assist in this as well. Aforementioned PDTA and NDTA downstream of this feature will quickly work to tilt this feature negatively by the time it reaches the Rockies on Thursday morning. However, the eroding feature over the Ohio Valley will hinder this from completely occluding. Phasing between this feature and the decaying feature will work to occur on Friday, as lee cyclogenesis is expected to occur over eastern Idaho/western Montana Wednesday night into Thursday due to 1.) stretching of aloft VORT as it slopes down the mountains, 2.) stretching of SFC VORT generated along a downstream temp gradient, and 3.) net mass loss of air within the left exit of this feature, increasing isallobaric wind, temperature advection, and further enhancing aloft features. PDTA from this cyclone will be the main culprit of the phasing of these features over the northern central lowlands Friday night into Saturday. This will allow flattening of the ridge over our region, allowing temperatures to cool into the lower 80s Friday and Saturday. Broad SFC low pressure is expected Friday and Saturday as the phasing of these features occurs, with more scattered convective activity continuing.