8:30AM Thursday 2/23/12
Don’t let this chilly morning fool you.
It’s going to warm up this afternoon as a storm system heads in our direction from the west. A warm front over Kentucky now will sharpen and head northward through the day… nearing the Ohio River this afternoon and perhaps just northward after that. A strong gradient, or change, in temperature is expected across the viewing area today, with highs in the upper 50s and low 60s north to near 70 in the south.
A strong area of low pressure will ride this front up the OH River Valley this evening, with strongly falling surface pressures out ahead of it. It’s the zone that sees the most prolific pressure falls that has the greatest risk of severe thunderstorm development this afternoon.
Typically a frontal system will provide the best lift for severe storms. However today’s case is a little different. First, the cold frontal wind shift is not very sharp: usually frontal winds shift from south to west or southwest to northwest… today’s wind shift is from more of a southwest to west-southwest direction. This does not promote strong lift along the frontal boundary like ordinary cases. BUT what we do have is a fairly healthy surface low heading up the Ohio River this evening… potentially passing right over our So. Indiana communities. It’s along this track and immediately southward by 75 miles or so where I see the best potential for severe weather.
The Storm Prediction Center tends to agree:
VERY STRONG SURFACE PRESSURE FALLS ARE FORECAST JUSTAHEAD OF THE SYNOPTIC LOW ALONG THE WARM FRONT...WHICH MAY LOCALLY AUGMENT VERTICAL SHEAR EVEN MORE.DISCRETE SUPERCELLS WILL BE POSSIBLE...CAPABLE OF HAIL...DAMAGING WINDS...AND TORNADOES.
Is this a slam dunk forecast? No… why would a forecast ever be simple in the Ohio Valley? 🙂
There are several mitigating factors in today’s severe threat. I already mentioned one… the front is not a sharp wind shift… owing to the best threat in a localized area along the track of the low. Another is the lack of moisture in the atmosphere today. However if storms can overcome this and moisten the column, more instability may be realized and a strong downburst wind potential may result.
So here’s a recap:
Best potential for severe weather locations: Along and north of the Parkways, including Louisville and those locations in Southern Indiana which warm to at least the 60s today have a potential for strong winds, hail, and tornadoes. Areas of our northern viewing area which stay in the 50s for highs (northern tier, possibly) would see a heightened hail threat with any storm but a lower tornado risk. Meanwhile, storms will be more isolated south of the parkways, away from the best available lift.
Timing: After 4PM through the mid-evening hours.
At this point I expect a pretty solid opportunity for a tornado watch to be issued with the potential for multiple severe weather warnings, some tornado warnings can’t be ruled out.
IF a couple of stronger storms can get going and tap some warm, moist air at the surface and the wind shear present, we would be talking about a localized heightened potential for tornadoes. See the SPC map above for the best potential for this to occur. We’ll fine tune this part of the forecast through the day as I mentioned — it’s not a guarantee this will occur.
Also, if less moisture is present than the models currently suggest, this event may not occur at all – which is ALWAYS a possibility this time of the year.
Okay, we’ll update you as we get more information.