02/20/05 FCST OH, lower TN Valleys

[Mike Johnston]

SPC posted 5% severe probability, w/ mention of possible supercell development, this Sunday in Ohio and Lower TN valleys. Looks like some interesting mid and upper level dynamics, but surface heating the question this early in season.

http://www.spc.noaa.gov/products/outlook/d...k.html#topimage

 

[Nick Parker]

Thanks for bringing this to my attetion. Been so busy with school, i've lost track of keeping up with the models. But you'd never guess anything with the way WFO-PAH is putting it:

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A SMALL CHANCE OF THUNDERSTORMS ACROSS THE QUAD STATE
SUNDAY. NO SEVERE WEATHER IS EXPECTED AT THIS TIME.

 

[George Tincher]

It's nice to see something on the map, but I doubt there's really anything besides a good soaking rain and perhaps a clap or two of thunder to come from this system.

Still, I'll keep an eye on it, as there's nothing else to do anyway. But it appears any hope for supercells is totally dependent on getting some sfc heating going. This was how things shaped up over Arkansas on Sunday and we saw how that turned out. Just a little blowoff from the TX convection held the AR environment in check and no storms developed.

So again, I'll watch. But I'm not going to be holding my breath on this one.

-George

 

[Mike Johnston]

Reply to George

Yes, the experience of the last similar setup and climatology will likely prove out your prognonsis, George.

For the time period in between the Day 3 convection outlook and the current day outlook, I like to simply compare the actual surface observations with those forecast for areas to the south and west of the forecast severe area - especially when the forecast seems heavily conditioned on uncertain outlook for lower level convective factors. This forecast seems uncertain about quality of the upcoming return flow from the Gulf, so I compared actual vs. forecast surface temps and dewpoints today in Tulsa, Lufkin, Poplar Bluff, and Tupelo. Interestingly, although all locations had higher than forecast high temps, actual dewpoints were lower than forecast, perhaps owing to blocking by the surface high located at the mouth of the Mississippi. So...it is kind of hard to picture this day 3 severe setup in the mind's eye at the moment, but the atmosphere sometimes starts to change more quickly the closer we get to March!

 

[George Tincher]

Two of the local newscasts tonight mentioned the possibility of a wintry mix of precip on Sunday. That doesn't sound too good for severe weather probabilities. Hehe.

Sigh.....hopefully March will get here quickly and bring with it some warmer temps.

 

[Stan Olson]

Originally posted by Nick Parker
Thanks for bringing this to my attetion. Been so busy with school, i've lost track of keeping up with the models. But you'd never guess anything with the way WFO-PAH is putting it:

Ah ha, check out the updated HWO.

DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

SCATTERED THUNDERSTORMS ARE EXPECTED ACROSS THE REGION...LATE TONIGHT...SUNDAY AND INTO THE FIRST PART OF SUNDAY NIGHT.
ISOLATED STRONG TO SEVERE THUNDERSTORMS MAY DEVELOP ALONG A WARM FRONT LATE TONIGHT...AS IT LIFTS NORTHEAST ACROSS THE REGION.
A FEW OF THE STORMS COULD PRODUCE MARGINALLY SEVERE HAIL.

ISOLATED STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS THE REGION SUNDAY AFTERNOON AND EVENING...AND ESPECIALLY ACROSS SOUTHERN ILLINOIS AND SOUTHWEST INDIANA. THE STORMS ARE EXPECTED TO FIRE ALONG AND AHEAD OF AN APPROACHING COLD FRONT. THE MAIN HAZARDS WILL BE DAMAGING WIND AND HAIL.

SPOTTER ACTIVATION MAY BE REQUIRED SUNDAY.

How much did you pay them to change that? Looks interesting, just depends on how much heating and clearing occurs.

-Stan

 

[Robert Dewey]

I'm not really seeing that good of a risk for tomorrow. The only area I could imagine something popping up would be extreme southern IL.

The best wind fields across the area in question come in around 18Z, while SFC instability is zero, with temperatures barely making the 50's. Then, the warm front pops northward a bit, with temps reaching the low to mid 60's by 00Z, but by that time, the best wind fields are moving off to the east, but that still leaves some decent shear in the area. Instability is rather weak as well, barely hitting 1500J/KG between 18-00Z - Looking at the latest VIS satellite and NEXRAD data, it looks like that area will probably be socked in by cloud cover.

So, it would be a tough call until tomorrow morning, when you can get a look at the satellite data, radar, and SFC obs, in addition to the short range RUC forecast to see how the wind field, boundary, and any potential instability might pan out.

 

[Scott Olson]

I was wondering this morning why this area had not yet been placed in a slight risk category. Most of the stronger parameters from the ensemble is based on the ETA which puts a pretty nice bullseye on the poplar bluff, MO to southern IL. Even the GFS seems to support some severe development in this area, while the MM5 & RUC pretty much support little to no thunderstorm development. I think before all is said and done the slight risk will probably extend back into Texas. In the target area heating is going to be very mariginal. Although shear is good which can make all the difference. I'll wait for the 0z run to see if their is more agreement.

 

[Mike Johnston]

Day 2 SPC Outlook

Today's original Day 2 outlook did have the Arklatex in the slight risk category, then was revised to move back up to the lower OH valley. Note for Day 2 and 3 forecasts, the probabilistic forecast breakpoints go from 5% to 15%, with no 10% in between. If you read the text of the original, and then the revised, almost looks like both areas are "on the bubble." Current observations and RUC model still make this setup hard to envision, though.

 

[Amos Magliocco]

This setup reminds me a little of the 4-20 scenario from last year, though I do NOT think what happened then will happen tomorrow, and I think the difference between February and April is huge, and I'm not forecsating a tornado outbreak. At all. Not even a little one. (okay maybe one tiny little funnel--lol)

Seriously, what reminds me of 4-20 is the quick airmass recovery on a strong LLJ and the saturated boundary layer afterwards. MLCAPE here is unexpectedly high perhaps because very little mixing will occur, and I'm struck by how similar the values are to the SBCAPE. Can someone remind me where the parcel comes from in the SB calculation? Like 4-20, perhaps SBCAPE in this case is the more accurate measure. 4-20 also had low LCLs, and tomorrow's is progged at 737m at Salem, IL.

One key difference, however, was that, according to Jon Davies, 4-20 had a majority of CAPE below 500mb where it was co-located with the best directional shear in the vertical. Eyeballing the 12z NAM forecast soundings for Salem, Illinois (KSLO) at 33h and 36h, it looks as though tomorrow's CAPE is evenly distributed, a 'tall and skinny' profile. Bad news for this setup, in my opinion. Almost as bad as the FREEZING COLD temps in the 'target area' at the moment. LOL!! Not very convective. Bring your scarf.

But, with MLCAPE forecast ~1000 j/kg and 0-1k SRH of 393 m2/s2, I think the mention of possible tornadoes is justified in the SWODY2.

 

[Andy Wehrle]

Surprised there have been no comments on this so far today. Mesoanalysis maps are showing increasing instability moving toward Arkansas and Missouri with -4 LI into southwestern Missouri and dewpoints in the 60-64 range in western Arkansas. 1630Z outlook upped probs from 15-15-2 H/W/T to 25-15-2.

 

[John Farley]

I'm standing by for a local chase in SW IL. Latest satellite (20:32Z) seems to be showing some TCU from NW of STL down toward Lake of the Ozarks. SPC is considering watch issuance within the next hour. Since initiation is likely to occur so close to my location, I'm just going to watch and wait to see what happens in the next hour or so, hoping for a chase somewhere just east of the Mississippi River in SW IL. There may be better action later farther to the southwest, over S. MO or AR, but much of that may occur after dark. Good luck to all who head out - can't argue with a chance to chase in February!

 

[Jayson Prentice]

It looks like the best chance for seeing a tornado or two will be in the MO/AR border area. But as you said, that may occur around the 00z and 03z timeframe. I think you might have to pass that IL border if you really want to see some action, the severe thunderstorm watch will probably not include many IL counties. Good luck to all who attempt to head out...