Issued: 7pm on Saturday, September 18th 2021
Technical Forecast Discussion
Short Term (Saturday 9-18-2021 through Monday 9-20-2021)
Period starts off with a strengthening ridge over Plains region on Saturday with a surface boundary stuck just north of our area. 500H ridge progresses eastward into Great Lakes and Ohio Valley region by Sunday, as this happens, the surface boundary will lift northward from our area. Given that surface high pressure is expected to dominate central Appalachians region, expect hot and humid conditions to remain in place for this weekend under plenty of sunshine in the region. 500H ridge will continue to intensify as it shifts eastward and is expected to center over Mid-Atlantic states by Monday with surface high shifting out into northeastern U.S. by then. Behind the ridge, our area will be under southerly flow with strong moisture return from Gulf of Mexico lifting into Ohio, and this will lead to increasing chances of rain showers and isolated thunderstorms for us. It is also important to note that a trough is expected to develop and settle into High Plains region and parts of northern Mid-West with surface low developing and lifting into Manitoba. Temperatures during this period will be in order of 9°F-14°F above normal with actual highs in upper 80’s, low 80’s on Monday, for high’s with lows in low to mid 60’s.
Long Term (Tuesday 9-21-2021 through Friday 9-24-2021)
Trough over High Plains region will shift into central Plains and western Ohio Valley region and weaken temporarily by Tuesday while our area still remains under the influence of a 500H ridge departing into eastern Quebec regions by this point. Our region will still have a risk of isolated showers as surface flow is still out of south with moisture from Gulf of Mexico continuing to stream into our area. Temperatures will start to cool off much closer to normal levels for highs at least under continued humid conditions in place. As the trough starts to move eastward into most of Ohio Valley region by Wednesday, it is expected to intensify quickly with most models now show a surface cyclogeneses as result of this from late Tuesday night through early Thursday time frame. Given that there is plenty of gulf moisture out ahead of the trough and plenty upward forcing, we will likely see moderate to heavy rainfall at times from this storm which will total up in order of 0.75″ to 1.50″ with isolated 2.00″ mark. If this threat materializes, minor flooding could a risk given our soils are still saturated. The general path of surface low pressure seems to be from central parts of Kentucky by Tuesday night into central sections of Ohio by Wednesday with low pressure lifting into southern Ontario by Thursday. This surface low will also drag a fairly potent surface cold front through our area and bring in true fall weather preview with high pressure settling into our area by late Thursday into Friday. 500H trough is expected to weaken down and lift north into Ontario with height levels rising again by late Friday. Looking at expected surface temperatures, temperatures remain in upper 70’s for high on Tuesday with values cooling into mid 60’s to lower 70’s for highs between Wednesday through Friday with low temperatures dropping all the way into upper 40’s for Thursday through Saturday morning with only exception being Wednesday morning with lows in lower 60’s. Average temperature departures will be about 4°F-9°F below normal during the long term with biggest negative departures coming during daytime hours while nighttime lows would be closer to average values.
