11/15/05 FCST: Midwest

[rdale]

Not too often we look at a Day2 moderate in Mid-November! I'm just concerned about a lack of insolation and little (if any) surface-based potential. Not that I wouldn't like to see a widespread event, but I just don't know that significant severe is going to be that widespread given the amount of clouds that should be in place.

Still a very dynamic system, so winds will be a factor one way or another, but I wonder if the snow side of this event will end up gaining more press?

- Rob

(Clarifying that this is in reference to the Great Lakes area - not down south ;> )

 

[Robert Dewey]

All I have to say about this system is WOW. The height falls are nearly 60M in 6 hours, and that's at 850MB (per 06Z NAM)!. Overall severe weather threat looks decent, probably occuring all the way up the length of the cold front in some form or another (strong line with embedded supercells further south, standard line of convection further north). This event has me thinking on the order of October 24, 2001 - only slightly further south.

I'll probably repost a bit later after looking at the 12Z models in-depth.

 

[nickgrillo]

Isolated damaging tornadoes and destructive winds should become a major threat tomorrow afternoon across the OH/MS vallies and up into the Great Lakes. Fast-moving supercells will likely develop shortly after 18z within zone of large-scale forcing ahead of amplifying upper trough and associated +60kt SW LLJ from central IL (along cold front) and southward. My current thinking is that another focused area of significant tornadoes could be on the MI/OH border near warm frontal zone by 21z. Given the magnitude of large-scale forcing -- current thinking is that instability will be sufficiant enough to sustain deep moist convection in this extreme-sheared environment. The strong low-level shear (300-500m2/s2 0-3km SRH) coupled with MLCAPEs >500j/kg across IN/OH (and much stronger to the south) should be sufficiant enough to sustain supercells with tornadoes (some could be strong along warm front) and destructive winds with any bowing structures.

 

[Ronnie Bradley]

I'm looking at the ETA models over at cod.edu and it looks like the low by 12Z Tuesday will be in the south central Kansas area. The winds indicated look something fierce at the 850mb level. By 18Z, the low moves toward the Kansas City area.
The 700 mb level looks similar. Once you see the 500mb level, there is a core of winds over NW Arkansas, NE Oklahoma and S.Central Missouri blowing at 80 - 90 kts from the WSW / SW. 250mb wind levels look similar.
Be advised: if one were to chase storms in these areas, they will be fast movers.
After the low tracks ENE, then NE, the action will shift east.
Its looking like eastern Missouri, Illinois, most of Tennessee, northern Mississippi and Alabama had better watch this one close!

Right now, KLZK's VWP is looking busy with SE surface winds around 15 kts and stronger SW winds (35 kts and up) above 4,000 ft.

 

[Justin Turcotte]

General consensus at the office is to side with the Canadian GEM though NAM and GFS are similar with most features. Liking extreme eastern IL and IN for sig severe and tornado threat. Upper level winds will be screaming over this area on Tues leading to SRH values bewteen 400 and 700 for IND at 21z. The GEM backs the winds more than the NAM or GFS. Band of heavy rain will be ahead of the warm front lifting north through IN. There could be a lot of low level grunge in the wake of the front which would hinder insolation/instability. The magnitude of shear should in part make up for the lack of instability. I won't totally rule out a spinning storm in vicinity of triple point dryslot interesection in northern IL or extreme southern WI depending on your favorite model prog. Further south along and east of the Mississippi River Valley instability will be stronger given better moisture and less cloud. Quite possibly a squall line from MI to the Gulf coast. Maybe a tor or two in the Ohio/Tennessee Valleys during the evening before the line moves into more stable air.

 

[Bill Tabor]

Very interesting day and I can't totally make up my mind as to whether the moderate is too much or if it should be a high risk - LOL! The most obvious thing I notice is that dynamics are obviously very strong although expected cape and li's are forecast NAM / GFS as being pretty low in northern half of outlook area. That said, this is also where the neutral to neg tilt 500mb and upper jets are screaming over and that should make up a lot of the difference. In some respects (as I remember) some of the northern area might be similar to what we saw Sat for IA with high wind dynamics and low instability. On the southern end we don't have the dynamics (as much) but we have better dewpoints and instability. If the current NAM solution is true I might be interested even in the tornado / severe potential of eastern OK very early on 12z because of nearby short wave influence and trough. Possibly even as far south as DFW. The warm front should be a focus for the large dynamics in low instability environment, but the southern trough and associated cold front may also focus some decent severe possibilities as it moves eastward throughout the day.

This is a very large event encompassing many states as I see it including extreme ne Tx, eastern OK, AR, southern and south eastern MO, northern LA, northern MS, northwest AL, western TN, southern IL, southern IN, KT, and possibly parts of OH.

At the moment I have a hard time narrowing it down, but generally I agree that a widespread severe event is possible in these locals. Hail, and high wind is obvious, but scattered tornadoes are possible. Perhaps small outbreaks of tornadoes in certain locations where upper dynamics, instability, and boundaries can interact are possible as well. These will be fast moving storms and I imagine most northern storms will not be very tall. I expect most torns (if not all) to be F3 and lower and somewhat long tracked simply because of the speed of the storm.

I think SPC and NWS along with emergency crews will have their hands full with this one. Perhaps I will try and hone in on specific areas later as time allows.

 

[Glen Romine]

Tomorrow will be an interesting day weatherwise - the extent to which it will be significant in terms of severe weather though seems very conditional. We haven't probably seen a storm intensification in the Midwest like what is forecast to occur tomorrow since 1998.

As for the svr threat - the obvious question is what magnitude of instability will be in place. Mid-level trajectories from behind the system are from the northern plains - which isn't going be very helpful for mid-level lapse rates. In fact - intense cold air advection around 700 mb in height overrunning the surface front by mid afternoon will aid in steep low-level lapse rates, with 0-3 km CAPE approaching 200 J/Kg in the NAM model, but subsidence associated with this cold air advection is also leading to horrible mid-level lapse rates. Could be a very narrow axis of favorable conditions. Otherwise - very questionable instability for sustaining supercells in the midwest region even with favorable dynamics. Will need to see some mesoscale heating to provide pockets of enhanced instability not currently captured in the model forecasts I've looked at. Getting a storm out off of the cold front could be tough - but could ride out ahead on the nose of the 700 mb CFA as it presses ahead of the surface front during the early afternoon. Since this is in my neighborhood - I'll be watching to see how things evolve of course - but likely looking at a storm intercept mode than a chase with the forecast mid-level flow strength.

Glen

 

[Gabe Garfield]

I agree with Glen that instability is most likely going to be the main issue. If strong instability can develop, I would expect that an outbreak of tornadoes would occur. This system is heavily favored from a climatological perspective, and the mean positions of synoptic features are eerily similar to big outbreaks of the past (e.g., 11/10/02, 10/24/01, and *gasp* 4/3/74).

However, insolation may be hard to achieve tomorrow. The '74 outbreak had the advantage of very dry air aloft which helped to ensure that convective coverage would be relatively limited in spite of the massive forcing for convection. Tomorrow, that will not be the case. All of the mechanisms for rising motion (warm air advection, DPVA, etc) will be in high gear tomorrow so there will likely be a convective mess (with little insolation occurring except on the mesoscale, as Glen also noted).

Be that as it may, there are two things I really like about tomorrow. First, the weak cap. Though this will likely limit the severity of tomorrow's severe weather episode, this will also aid in allowing the formation of isolated cells ahead of convective lines. Second, I believe the ETA is probably underforecasting CAPE due to convective feedback. If pockets of CAPE >2000 j/kg can develop (as SPC suggests), I would expect that a few strong tornadoes will be possible. It is impossible to forecast tornado intensity, though this setup would favor the full range of F-scale ratings.

We shall see...

Gabe

 

[Jeff Snyder]

Copied from a duplicate thread:

Looking over recent models, and figures, it looks like there could very well be a severe weather threat/outbreak, across portions of SE US, I know however there is already a topic for the midwest, but given different atmospherical situations, there needs to be one for the SE.

As you know, there is already, a moderate risk for portions of TN, and southern/northern states. It looks like a low pressure system will move through the Missouri, by tuesday evening. Thunderstorms will fire up along this line, and cause a threat for damaging winds, hail, and possible isolated tornadoes, wind fields are very strong, and show a chance of powerful winds. These storms will have a lot of precipitation embedded in the front of the line, on an easterly course, through TN, VA, and parts of NC.

For Me: Supercells may develop in the Middle-Tennessee vicinity, given the wind fields, could give sufficent shear for supercell development. What the supercells all revolve around is the amount of daytime heating, my regions gets, and from looking at the Theta-E, we may see some very high, even extreme temperatures, for this time of the year, so supercell look very iminent, as to tornadoes and hail. I am really up for a chase tommorow, but it looks like initiation will be later in the night, which will just allow me to get some lightning shots, but I'm up for anything. I think first of all, I will head out to Nashville, TN, and wait for whatever comes, then I will either go north into parts of KY, or just gor further west.....

 

[Brandon Clement]

I agree Gabe 100%.

I am really liking the area just to the Southwest of Memphis. The current forecast has the temps at 72/68 but just a little sunshine and it would be be optimal. The weak cap will allow storms to form out in front of the line and this time of the year has historically been good to this area. The dynamics are not anything like they are farther north, but IMO this area will have the best mix of shear/cape needed to produce a tornado or two. The terrain in this area is also pretty good, only problem is crossing the Ms. It would be nice if this comes in just a tad farther SE so I could get a chase in the Ms delta because the motion tomorrow is going to make it very challenging. Right now I am shooting for Forest City Ar so I can stay ahead of the front and will have two options to cross the Ms river.

HWO for SE Arkansas is positive:

IN EASTERN AND SOUTHEASTERN ARKANSAS FROM MIDDAY TUESDAY UNTIL THE LINE OF THUNDERSTORMS ARRIVES TUESDAY AFTERNOON...THE POTENTIAL EXISTS FOR ISOLATED THUNDERSTORMS TO DEVELOP. ANY OF THESE THUNDERSTORMS COULD PRODUCE SIGNIFICANT TORNADOES ALONG WITH DAMAGING WIND AND MAYBE LARGE HAIL.

 

[Robert Dewey]

I'm thinking more along the lines of a derecho setup for tomorrow evening / night, with the potential for widespread and destructive winds from MI southward. The entire checklist for a strongly-forced cold season derecho is filled, and the very strong forcing and barcoclinicity would suggest a linear configuration along the cold front...

A cross section created perpendicular to the SFC pressure and cold front (starting point in northern IL, ending point NY, intersecting my location near Detroit) shows some interesting features. First off, I see winds as high as 70KNTS in the first couple thousand feet, and 90KNTS at 700MB - All with very little inversion! Second, there appears to be a "burst" of dry air descending from the upper levels of the atmosphere, which quickly overtakes areas just along and behind the front with RH values as low as 10% at 700MB... That would definitely enhance downdraft potential.

Given that, I don't think it will take much (if any) instability along the front to generate a strongly forced line of convection. NAM does generate 250-300J/KG of 0-3KM CAPE with SFC Td's of 60F just ahead of the front, so there is at least SOME instability available... But again, I think the biggest kicker will the amount of forcing and low level wind fields.

 

[Andrew Khan]

A Derecho does look possible, since these storms will be coming up along a line. Supercells are looking more and more iminent for east TN, as well as SE KY, and SW VA. I will definetly be chasing tommorow.

 

[Nick Parker]

Ok, going to be bit of a newbie here, but any idea's on what time this event will reach the Mississippi River? Been sitting here for the past hour running NAM, GFS, and RUC and can't seem to make my mind up?

Looks to be one heck of a day! (Sitting here listening to it rumble outside right now) Hopefully we can get the clouds to break tomorrow and get some decent instability. Confidence is looking high for the southern portion of my area for right now. Wind fields in the northern part however, are looking poor.

With NWS PAH calling this a "signifigant outbreak", hopefully will get a few people perked up around here.

Good hunting out there!

(Sorry if this post doesn't agree with the TOS. Im just very curious.)

 

[Justin Bailey]

Memphis, TN HWO-ALSO...THERE
IS THE POSSIBILITY OF SUPERCELLS DEVELOPING IN ADVANCE OF THE MAIN
LINE OF THUNDERSTORMS. THE MAIN THREAT WITH THESE SUPERCELLS WOULD
BE TORNADOES.

Nashville, TN HWO-SEVERE WEATHER INCLUDING WIND DAMAGE...HAIL AND TORNADOES COULD
OCCUR AT ANY TIME TUESDAY...BUT THE MAIN FOCUS WILL BE A SQUALL LINE
LATE TUESDAY AFTERNOON AND EVENING. WIDESPREAD WIND DAMAGE SHOULD BE
EXPECTED WITH THIS SQUALL LINE...AND PREPARATIONS SHOULD BE MADE FOR
WIDESPREAD POWER OUTAGES.

Special Weather Statement, Morristown, TN NWS office-THE AMOUNT OF INSTABILITY (WHICH WILL ULTIMATELY DETERMINE THE
STRENGTH OF THE THUNDERSTORMS) REMAINS IN QUESTION AT THIS TIME...AND
WILL DEPEND ON HOW MUCH WARMING OCCURS ON TUESDAY ACROSS THE AREA.
RIGHT NOW...IT APPEARS POSSIBLE THAT RECORD HIGH TEMPERATURES COULD
OCCUR ACROSS THE AREA...WHICH COULD RESULT IN A SIGNIFICANT SEVERE
WEATHER OUTBREAK ACROSS THE TENNESSEE RIVER VALLEY TUESDAY NIGHT.

Pretty intense wording. Looks like the TN Valley could be in for it. Good luck to all who decide to chase one of the fast moving supercells or the possible derecho.

 

[Andrew Khan]

Special Weather Statement, Morristown, TN NWS office-THE AMOUNT OF INSTABILITY (WHICH WILL ULTIMATELY DETERMINE THE
STRENGTH OF THE THUNDERSTORMS) REMAINS IN QUESTION AT THIS TIME...AND
WILL DEPEND ON HOW MUCH WARMING OCCURS ON TUESDAY ACROSS THE AREA.
RIGHT NOW...IT APPEARS POSSIBLE THAT RECORD HIGH TEMPERATURES COULD
OCCUR ACROSS THE AREA...WHICH COULD RESULT IN A SIGNIFICANT SEVERE
WEATHER OUTBREAK ACROSS THE TENNESSEE RIVER VALLEY TUESDAY NIGHT.

Pretty intense wording. Looks like the TN Valley could be in for it. Good luck to all who decide to chase one of the fast moving supercells or the possible derecho.

I am almost very sure, there will be enough instability to the east of the Cumberland Plateau to support supercell development, as well as the fairly harsh wind shear, and favorable wind profiles. Theta-E, is howing that it will be extremely hot tommorow, along with SFC temps. For East TN, this could even be our record heating in November ever, which makes it more ominoius, as to whether or not something will occur. The supercells could possibly move so fast even at 60 kts along with a low level jet, that they might be hard to chase unless you got in front of them, prior to there arrival.