July 14, 2014: BIG Cool Down Coming

TODAY'S WEATHER: A few spots across the area, mostly across northern areas of southern IL, had to deal with some severe weather today in association with the secondary and "main" cold front. There was a severe thunderstorm watch posted for areas north of US-50 in IL and IN this afternoon, where a few severe thunderstorm warnings were issued. The Lawrenceville Airport in Lawrence County, IL recorded a 63mph wind gust as the storms blew threw there. Most of the region, though, was spared from the severe weather just dealing with some showers. Temperatures weren't terrible but the humidity was there this afternoon. Highs today ranged from the mid to upper 80s across the Lower Ohio Valley, with a 86F at EVV, an 87F at LOU, and the warm spot of 89F at PAH.

COOL DOWN COMING: Yes, a very nice cool down is coming. It will feel more like September or even early October as an anomalous upper low and trough dig in over the Eastern US. Starting tomorrow morning you'll feel it. It will be in the lower 60s to start tomorrow, with afternoon highs ranging from 72F-76F across the region. Of course dewpoints will be dry probably dipping down to near 50F by tomorrow afternoon. It's going to be a gorgeous day no matter where you head.

18z GFS 500mb level valid 4pm tomorrow - shows the upper low centered on top Lake Huron

Great looking surface map as well with a nice northerly wind w/ surface high pressure to our west as CAA takes place - GFS valid 4p tomorrow

Tomorrow night is going to be a very cool morning, getting pretty close to record territory. Lows will range from 52-56F areawide. The record Wednesday morning at Paducah is 56F set in 1967, record at Evansville is a tough to beat 47F set in 1930, and for the Louisville area it is 55F. We will be close to records in some areas. Wednesday will be about the same as Tuesday - mix of sun and cumulus clouds and perhaps a touch warmer. Highs 75-79F. Just great. Wednesday night cool again, with low temps 54-58F. The low humidity and comfortable will continue AGAIN for Thursday, as general "trougheness" will remain. Highs a touch warmer again, but still very nice 77-81F. Slight chance of rain will exist Friday for areas in KY, but shouldn't be a big deal as the mid level wave instigating the precipiation should steer south enough to be a nuisance. There will be more clouds around during the day Friday due to the increased moisture associated with the mid level shortwave, but the temperatures will once again be comfortable in the mid to upper 70s for highs.

To wrap things up, I wanted to show you a graphic showing how far south this cool air outbreak will stretch. Take a look at this map showing surface temperatures across the southern half of the US. Look at far south the closest 80F contour is. It's well down into Arkansas and Tennessee! And the closest 90F? Way down on the Gulf Coast!

18z GFS valid 4p tomorrow - 2m temperatures. 70s for highs as far south as Tennessee & Arkansas.

Get out and enjoy this cool spell! I think the humidity will become noticeable again by Saturday, but certainly 5 days of low humidity and comfortable temps is welcome as it's a rarity here in mid-July. Thanks for reading!

July 12, 2014: Look at the Severe Risk for Tomorrow

TODAY'S WEATHER: A few showers/storms late this morning and into the early afternoon today gave way to a pretty nice day, albeit humid. The high made it to 85F at EVV this afternoon, after 0.26" of rain was recorded with the convection earlier in the day. The low this morning was a muggy 72F.

SEVERE WEATHER OUTLINE: The real purpose of this post, though, is to outline the severe risk for tomorrow evening. The Storm Prediction Center has placed the entire Lower Ohio Valley under a slight risk for severe thunderstorms tomorrow afternoon and evening:

SPC Convective Outlook for Tomorrow, July 13

The threat is associated with a cold front that will dive across the Great Lakes into the Ohio Valley tomorrow. Forecasting the convection to fire well north of the Ohio River by 4 PM tomorrow, and gradually push southeast across the region heading into the evening hours. Here is the simulated radar reflectivity from the 12z NAM 4KM for tomorrow, valid at 7 PM CDT:

NAM 4KM shows convection south of the Ohio River by 7 PM.

With CAPE values expected to exceed 2,000 J/KG tomorrow afternoon, along with effective bulk shear values above 30kts, the storms should have no problem organizing into bowing line segments. Damaging wind is the main threat with these storms tomorrow, along with a chance of a tornado. The large hail risk is lower than previous events as the freezing level is well above the surface, in the 600mb range. Of course the hail potential is still there, but it will have to fall through a decent layer of above freezing air before reaching the surface.

Another threat for tomorrow is the heavy rainfall. The heavy rain threat is elevated for tomorrow greater than it normally would because of PWAT values approaching if not exceeding 2" just ahead of the boundary (basically, the atmosphere's ability to "ring" out the moisture available through all levels). Precipitable water values over 2" mean that the atmosphere is LOADED with moisture. Flash flooding is a big concern. Here is the projected PWAT values for tomorrow evening coming from the 18z run of the NAM:

Greatest precipitable water values (in excess of 2") across Southern IL into Southwest IN at 7 PM, according to the NAM.

REFRESHING air will be the story heading into midweek. I'll have details on that coming up after this severe weather. Follow @wxSam on Twitter for realtime updates tomorrow.