Issued: 7pm on Tuesday, September 21st 2021
Technical Forecast Discussion
Short Term (Tuesday 9-21-2021 through Thursday 9-23-2021)
Our short range forecast starting out with a shortwave trough over parts of central Plains states this afternoon and evening with our region being at the far western end of strong 500H ridge, which was over our area this past weekend. Given the expected 500mb configuration and general low level flow, this would suggest a stream of heavy atmospheric moisture moving northward into Ohio Valley region from Gulf of Mexico with rain breaking out ahead of the cold over most of Indiana and western Ohio by Tonight. There will rainfall in our area during daytime hours as well due to WAA, but look for rain chances to reduce during later in the day before chances increase once again by late tonight into early Wednesday morning. As we head into late Wednesday morning into afternoon hours, shortwave over Plains region will have moved eastward into western parts of Ohio Valley, centered near IL/IN boarder, and it is expected to have intensified with overall neutral tilt configuration, this means due north to south orientation of the trough. Trough eventually takes on a negative tilt by Wednesday evening and peak in intensity by early nighttime hours and centered over far northwestern Ohio during that time period. On surface level, this trough will allow formation of a surface low right over portions of central Ohio with cold front expected to extend down right through our area by afternoon hours with line of showers and thunderstorms approaching. SPC does have marginal risk given the high dew points out ahead of the strengthening surface low along with some strong winds aloft may allow for some bowing segments of storm which may have low end tornado and damaging wind threat, but given overall instability and thermodynamics is weak, I am not expecting much in the way of severe weather. Main concern will be moderate to heavy rain at times moving into our area during the passage of front during Wednesday afternoon/evening time frame. Look for rain totals between 0.5″-1.0″ with total of 0.75″-1.50″ expected counting the WAA rainfall, isolated higher amounts possible. This trough will gradually weaken throughout the day on Thursday with chances of rainfall dropping substantially from this point and expect the upper level low to finally lift into southern Ontario by Thursday night. Temperature wise, we are mainly looking at temperatures being in upper 60’s to low 70’s due to cloud cover and this will continue through about Wednesday afternoon before we sharply cool into the 50’s by late Wednesday evening with upper 40’s possible by early Thursday morning. Cloudy, breezy, and damp conditions will likely hold highs in upper 50’s to low 60’s on Thursday afternoon with wind chills down to upper 40’s.
Long Term (Friday 9-24-2021 through Monday 9-27-2021)
As we enter into long term range, expect our overall weather conditions to quite down fair bit compared what is expected over next 48 hours. This period is expected to start out with continued weakening and departure of upper low which allows heights to rise once again with more zonal-ish flow under broad dip in the trough form Rockies into parts of Interior Northeast region. Looking further down to the surface, high pressure is expected to build in right over Tennessee Valley, and will lead to much brighter conditions for us under clear skies. Further to our northwest, another shortwave trough is expected to develop over High Plains region by Friday evening and this will quickly translate southeastward into most of Ohio Valley with main axis lie over UP Michigan area. Surface low is expected to form over central Ontario with cold front extending down into Ohio which clears our area by Saturday evening. Moisture return this time does not look impressive, that being said we could see some isolated rain showers in our area. This shortwave will gradually move eastward into Québec province by Sunday with general trough also expected to move out by late Sunday with upper level heights once again rising. By late Sunday into Monday, the 500H ridge over central sections of the country will continue to intensify and expand eastward during this time frame. Despite the rise in height values, our flow is still out of northwest direction so we will continue to have dry and less humid conditions. Looking at the temperatures during this period in detail, expect morning low temperatures each morning to be in the mid-upper 40’s range with high temperatures holding steady in low-mid 70’s. These temperatures values are very typical of what we expect during late September period.