Our first shot of fall-like weather came with a trough axis just a few days ago. Guidance at that time suggested this trough would detach from the polar jet stream, and it certainly did so. Dynamics have now led to a deepening upper-level low (ULL) pressure system which has now moved in from the Great Lakes region and is settling over the Ohio Valley. It will be persistent and stick around for the next several days, and will be dictating our weather conditions as a result.
Take a look at 500 hPa winds and vorticity below, its clear to see the ULL spinning over the Ohio Valley and how its become cut-off from the jet stream well to the north now. (Clickable images courtesy of CoD Meteorology website):
NAM 500 hPa Absolute Vorticity and Heights valid for 12 Z Thursday
NAM 500 hPa Wind Speed and Heights valid for 12 Z Thursday
The forcing provided by the vorticity in this ULL will help to trigger scattered showers during the afternoon and evening hours over the next few days with the help of daytime lower-boundary layer destabilization and steep lapse rates up through the mid-levels.
Expect fog in the morning in some low-lying areas before giving way to clear skies in the mornings. Once heating takes place be prepared to bust out the umbrella if necessary!
For Thursday: we should see temperatures topping out in the upper 60’s and near 70 in some places. Afternoon scattered showers are a likely bet. Lows into upper 40’s and near 50 in some areas.
For Friday/Weekend: Gradual warming into the mid and upper 70’s closer to the weekend as the ULL eventually starts to weaken a bit and retreat to the north. Guidance suggests it will be into next week before any warmer weather may start to creep back into our area. Scattered afternoon showers still remain possible.
Seen below is the GFS suggesting the weaker ULL eventually meandering off to the NE:
GFS 500 hPa Wind Speeds and Heights for 12 Z Sunday.
Other relative weather news includes Tropical Storm Matthew which has recently formed east of the Lesser Antilles. This particular storm seems more organized and is forecast by the National Hurricane Center (NHC) to become a Hurricane by Friday afternoon.
Current Atlantic tropical weather situation & water vapor imagery. (Courtesy NHC)
Forecasts from the NHC have Matthew making a rather sharp turn to the north and possibly affecting the Jamaica & Cuba regions by the start of the next work week. This system will continue to be monitored and tracked with satellite and aircraft reconnaissance in the coming days.
Current forecast cone for Tropical Storm Matthew from the NHC.
Overall, more active weather has arrived for us here in the Bowling Green area and for the entire state of Kentucky as well. Cool temperatures were bound to happen eventually!
A Friday post will address the changing weather scenario for us here as we expect warming conditions to eventually move back into our picture, as well as bring updates to the tropical activity (Matthew).