Following a nice start to the week, our weather gets active again as we head into the weekend with a round of showers expected late tonight and into tomorrow morning.
Fortunately, this first round is expected to be sub-severe and fairly light with most areas picking up less than a quarter inch of rain. Showers look to exit by afternoon behind a cold front that looks to drop temps back to near 70 for a high on Thursday.
While Thursday night and most of the day on Friday appear to be quiet, as a strong low develops over the Southern Plains, a warm front will push into our region bringing a surge of warmth and moisture and the potential for strong storms as we head into Friday night.
While the Storm Prediction Center keeps the "greatest risk" (an enhanced risk in this case) to our west, they have placed much of the Lower Ohio Valley, including our viewing area, under a Slight Risk for severe storms late Friday and Friday night.
A quick analysis of the data shows that the wind profile would be sufficient for strong to severe storms and the warm front is expected to serve as the focus for storm development.
However, instability may be limited for parts of our area with the GFS showing CAPE (convective available potential energy) on the order of 1,000 units or less for most of Southern Indiana. CAPE does ramp up for our Kentucky Counties with perhaps a better chance for seeing a few damaging wind or hail makers into the overnight on Friday night.
Let's time it out with AdvanceTrak...
AT shows most of the storm development late Friday evening and overnight before diminishing by morning.
This seems to be in line with what most of the "synoptic" models are showing (i.e., the GFS/EURO) and could cause issues for the Great Balloon Race Saturday morning.
As far as severe potential is concerned, I think it will be limited to areas along and south of the river with the main threats being hail and wind.
Moving ahead into the day on Saturday, a surge of warmth and low level moisture will make it feel very summer-like. This "juiced" atmosphere with temps well up into the 80's will increase instability for the entire area giving us expected CAPE values on the order of 1,000 - 2,500 units. This would be more than enough to fuel thunderstorms. However, we will be lacking a "trigger" or forcing mechanism to get storms started as the warm front will have lifted north into Central Indiana by Saturday afternoon.
This means that after the morning round of showers/storms, we will be mainly dry through the afternoon hours on Saturday.
That could change Saturday night with model data indicating that scattered showers/storms will develop late as the "low level jet" (wind flow a short distance above the surface) increases helping to aid in the development of "elevated" as opposed to surface based storms.
While a few of these could be strong, a lack of instability during the overnight should mitigate any real severe threat.
Moving ahead into Sunday, the Storm Prediction Center keeps the Slight Risk (15% risk area) to our west/south.
The slow moving storm system to our west approaches and deepens producing strong storms into the Lower and Middle Mississippi River Valley during the day on Sunday.
Ahead of this storm we will see a strong southerly flow and good heating which may help to increase instability.
This could set us up with a west to east moving squall line of storms Sunday evening/Sunday night.
Analyzing the data we see that because of a significant warm layer of air aloft, instability might be mitigated some with the GFS showing around 1,000 units of CAPE for most of our area late day Sunday.
While this is on the lower end of what you would expect for severe storms, it might be enough when combined with a ROBUST wind field that develops in response to the approaching low with the GFS showing 70+ knot winds a short distance above the surface (at 850 mb level).
So what do I think?
I think that heavy storms are likely for much of the area Friday night and a few severe storms will be a possibility especially if they get going into our Southern Counties where instability will be maximized. Overall I think the tornado risk is low with this set up though.
Despite the Storm Prediction Center forecast, there could be a legitimate severe threat Sunday evening if the squall line arrives near peak heating. The later it comes in, the lesser the threat. However, considering the amount of wind energy aloft, it might be able to overcome less than impressive instability. Damaging winds would be the main threat.
The other factor to consider this weekend is just how much rain will we see? While the GFS keeps the heaviest stuff to our west into the Middle Mississippi River Valley, rainfall totals of 2 to 4 inches, if verified, could cause some flooding concerns.
That's a lot of rain! We'll be watching.
WDRB Meteorologist Jeremy Kappell
Email me at firstname.lastname@example.org