Patches of high & mid clouds splotch the sky with warm, nice sunshine. The deeper 850 mb moisture for fair weather cumulus remains Indy metro & southward & that is where they have formed today, rather than farther north into our area. This is close to where the 60-degree dew point line is generally located.
Tonight, with patchy high/mid clouds pulling away, patchy dense fog is possible. Lows will run 51-56.
Sunday & Monday look great with lots of sun & highs back to 81-84 with lows in the 50s. It will cool just a hair Tuesday with highs at 77-81.
Wednesday & Thursday will return back to 81-84 with lows by Wednesday & Thursday nights in the 60s.
Data continues to show a gusty, windy system with several waves of showers & t’storms Thursday to Friday & perhaps Saturday.
There is a question as to whether the front will pass Friday at some point or as late as Saturday. This will become much more apparent in the coming days. With the models wobbling back & forth, I would prefer to let the dust settle before settling on an exact day of frontal passage.
Regardless, it appears scattered showers & t’storms are possible by late Thursday as cold front & first surface low approaches. These may increase in coverage Thursday night, before a break ensues. Strong south-southwest winds of 20-30 mph will likely be steady through the afternoon-night.
Although it appears that Hurricane Rachel remnants will not make a right turn toward the U.S. per National Hurricane Center forecasts & long-range data, there is a lot of deep tropical moisture that will likely be pushed northward. So, I still think locally-heavy rainfall is good wording.
As for Friday or Saturday, several things can be discerned:
1) It is likely that a strong upper jet streak (core of very strong winds way up in the troposphere) will swing in from the southwest & cause second surface low to deepen rapidly over northeastern Illinois.
2) Dynamics are forecast to be strong & shear impressive with fall system that will deepen from 1002 mb to about 992 mb in 10 hours in its track from Missouri to Michigan.
3) It is likely that severe weather event will unfold with this deepening from Oklahoma to southeastern Iowa, Missouri & western Illinois to Arkansas.
4) Here, issue is instability. Today, CAPE forecasts are not impressive here at 200-500 J/kg. Forecasts have been more impressive in previous days. This said, it is too unclear how surface instability will evolve to put much forecast on severe outlook for our area. We will just have to monitor. My confidence is much higher in severe threat west & southwest of our area, than here.
5) Timing is an issue. Prior, data suggested Wednesday-Thursday rainfall time frame, which slowed to Thursday-Saturday. Recently, there has been that Thursday-Friday trend. This also said, I can tell you that I can pinpoint the rainfall potential down to Thursday late-Thursday night & again Friday. Whether the actual front & best lift come through Friday morning, Friday afternoon or Saturday morning is in question………………heck it may end up being Saturday afternoon. It is too hard to say this far out.
To combat this issue, I took a medium road with frontal passage & best lift coming through in the Friday to Saturday morning time frame. This will remain the wording until early week when I can get a better handle on it. We may even see temperatures drop from the 60s Saturday morning to 50s in the afternoon.
6) I still like the mention of locally-heavy rainfall (1-2″) even in the Friday-Saturday time frame, given the lift & tropical moisture.
On thing is for sure, it will cool off rather quickly & dramatically from 80s for highs to 60s, then 50s behind this system. A couple to perhaps three nights may see lows in the 30s in the viewing area. Frost is possible.
The good news it that trends point to this rather ordinary early-October cool wave being brief. 60s & 70s may return again thereafter with drier weather.