The average date for the first frost and freeze in Indianapolis takes place on October 11th and 14th, respectively. Right on cue, the first frost of the season will take place for most central Indiana neighborhoods over the weekend. If you happen to miss out on the frosty conditions this week, reinforcing chilly air will descend on the region early next week.
We forecast (3) of the upcoming (7) nights to fall into the 30s. This is, obviously, a significant change from the extended summer like conditions we’ve been dealing with as of late. One primary driver behind the significantly cooler pattern has to do with the change in the PNA. The shift towards a positive PNA will result in the cooler air remaining in place with more staying power than the fleeting cool shots of a few weeks ago.
A series of cold fronts will sweep through the Ohio Valley over the upcoming couple of weeks and each will likely feature progressively cooler conditions.
With the positive PNA in place, it’s no surprise to see the mean trough setting up shop over the eastern portion of the country.
At the surface, we see the cool pattern taking hold into not only the short-term, but the 10-15 day range, as well.
A cold front will sweep through the region Wednesday evening and will lead to a better chance of more concentrated showers and thunderstorms for our hump day. Precipitable water values (PWATs) will approach 2″ Wednesday afternoon which is almost unheard of by October standards. As a result, a couple of the storms may be accompanied by locally heavy rainfall.
Winds of change will be blowing in earnest Wednesday night and Thursday morning and a legit fall feel will greet us out the door! Most of central Indiana can expect temperatures to be falling into the 40s Thursday morning along with a nice northwest breeze.
Longer term, a new storm system (including remnant moisture from Sergio) is expected to impact our weekend weather. We’ll trend our forecast wetter with reviewing some of the latest data. Sunday appears to be the wettest day.
An even more impressive push of fall air will follow on the heels of Sergio’s remnants early next week, including the potential of frost for more of the Ohio Valley, including central Indiana.
II. TD 14 will strengthen into Tropical Storm Michael later today and eventually a hurricane before making landfall along the Florida panhandle during the middle of the week. The remnant moisture of Michael will then race northeast and impact the flood-ravaged Carolinas during the latter stages of the work week.
III. As Michael’s remnant moisture tracks northeast into the Carolinas, a strong cold front will sweep through the Mid West and Ohio Valley. Better chances of organized showers and thunderstorms will arrive ahead of the front Wednesday. Once the front passes, a dramatic wind shift to the northwest will push a MUCH cooler and drier air mass into the region.
IV. We note the PNA (Pacific North America pattern) is flipping to a positive state and that will drive a more sustained period of colder air during the medium and longer range period- or mid and late October.
The air will grow cold enough to support the potential of frost during the 5-10 day period on at least a couple of nights. Additionally, reinforcing chilly air may ignite the lake effect to our north and northeast during Week 2… “Times, they are a changing!”