8/18/04 FCST: Midwest/Great Lakes

SPC mentioned upgrading to a MDT if better instability can develop... The latest ETA brings in a somewhat-favorable scenerio for the Great Lakes. I am really up for a chase, so we'll see....

Discuss:
 
Nick, i read this before looking at the new day two and nearly jumped out of my chair. Thats the best news i've heard in a while.

Time to go read spc day two.


ok, read the dis. sounds like a squall/derecho type event. Not supercells but hey when there has been cool cloudy weather for the last week and a half i'll take what i can get. I remember this morning APX. said 65 knot shear near the bridge and 45knot near sag. bay. Could be interesting.
 
LOL... I started a thread on this topic the same time you did - I deleted it though... Here is my original post -

Looks like a decent threat for severe thunderstorms tomorrow afternoon through tomorrow evening/night. Very intense low pressure system will move eastward - North of Lake Superior during the day (988MB), with a very strong front swinging through the region. Latest ETA suggests that moisture should pool along and ahead of this front, as it becomes somewhat semi-stationary. Forecast soundings from lower MI look VERY impressive as far as speed shear is concerned, with 50knts making down to 9K-10K FT... Combined with a little directional shear in the 0-3KM layer puts helicity to near 200M2/S2. Low level and bulk shear paremeters would suggest that supercells would be a very real threat, but given the fact that the upward motion is situated in a linear fashion and SFC convergence (which is also very intense) is strongly linear, storms should form into a single line (But as usual, nothing can be ruled out). ETA suggests storms will roll through southern MI between 21Z WED and 03-06Z THU from west to east (generally), with instability still at or near 1500J/KG through the night time hours, which would likely sustain a line of thunderstorms.

This event looks like it has the potential to be a hybrid derecho event (widespread wind event, containing properties of both serial and progressive events - Such as May 31 1998), given the length/strength of the forcing along the front, very intense wind fields (especially for August!), strong height falls, very strong dry air intrusion between 500-300MB... Only real thing missing is monster CAPE values.

We shall see

Robert
 
AHH, Why is it everytime severe weather events could happen the site i use for the eta and ruc goes down?! :x :x :( :cry:

anyone have a site i can look at to check out the eta's convective perameters for tomorrow?
 
After taking a second look at the model data, I would have to say I do see some decent tornado potential over a small area - Extreme southwestern MI into northwestern IN. Plan view shows 0-3KM helicities over 350m2/s2 in that region, combined with CAPES of 2000J/KG and some decent forcing coming through around 00Z. That would probably be the beginning of any squall line or derecho activity (initiation), which is when any supercellular activity is most likely to occur.
 
Latest 18Z ETA is looking kind of interesting... The weak 500mb wave (evident on the 500mb vorticity fields), is a tad bit stronger, which rides just ahead of the cold front between 21Z and 03Z across lower MI. There is a slight chance that this wave could enhance low level directional shear if a SFC reflection (at least a very weak one) were to develop in response to any mesoscale features caused by the wave.

Unmodified sounding from near LAN (42.66;-83.30) indicates 3000J/KG of CAPE available by 21Z WED right before the wave crashes through (Td's are higher this go around). Wind fields will be quite strong, ETA still shows 0-3km helicity of 150-200M2/S2 across southern lower MI, but the speed shear is more impressive than the directional shear. By 03Z, LLJ kicks in with 40knts right off the deck at 2.5K FT. Forcing still looks to be strongly linear, so I expect a pretty significant line of storms to develop.

ETA also appears to be slightly faster with the front on the 18Z run compared to the 12Z run, which would be good for areas east of LAN, when the previous run had the front just clearing the region by 06Z VS. 03Z with the new run...
 
I believe !!

Wishful thinking perhaps but I have not chased since the feedback of 2 weeks ago. So I will take what I can get. I will await the 6Z 1 day before picking a target.

I see an intense squall line that will be hard to chase. Perhaps tornadoes in broken segments, and bows. I just recently read this..
http://www.erh.noaa.gov/gsp/localdat/Nov11...02_Severe_2.pdf
and the
INCREASINGLY STRONG TROPOSPHERIC FLOW
in the SPC day 2 caught my eye.
Real life study of an active squall line will at least be educational.

Squall lines = broad target range = need for recent radar data so I may try not to stray to far from a good WI-FI spot.

I fear that the Lake will have a dampening effect. Is Lake Michigan a storm killer year round or just in the spring ?

Probably take a lazy target area in NW Indiana. Diminishes Lake effect and keeps driving to a minimum.
 
maybe someone wants to start a thread for the lower great lakes/ohio valley for friday? Look at what the northern ind. discussion had to say.
ETA CAPES
WERE EVEN HIGHER FRIDAY AFTERNOON THAN WEDNESDAY EVENING...WITH
VALUES IS SOME SPOTS ABOVE 3700 J/KG. ETA/GFS 0-3 KM STORM RELATIVE
HELICITY OVER 250 M2/S2 SOUTH AND SE OF FWA...SO SEVERE STORMS
CERTAINLY POSSIBLE. GFS NEAR MARION HAS AN IMPRESSIVE SRH OF OVER
800 M2/S2 FRIDAY AFTERNOON! :shock: :shock:
 
Originally posted by tom hanlon
I fear that the Lake will have a dampening effect. Is Lake Michigan a storm killer year round or just in the spring ?

Probably take a lazy target area in NW Indiana. Diminishes Lake effect and keeps driving to a minimum.

Its not nearly as much of a killer now that the water has warmed into the 60s. What hurts storms in the spring is that 40 degree water temp compared to a 80 degree air temp. If there is a derecho type of event, the waters of lk mich will do little to the storms as they cross since they should be moving at a good rate.

What pops into my mind is the derecho of may 31st 98. Went over the water at 70mph, the water had no effect on it at all. If anything, the wind near the shore of lk mich would have been higher since the water offers much less friction then the land and its trees, buidings, etc .
 
Originally posted by Jeremy Lemanski
maybe someone wants to start a thread for the lower great lakes/ohio valley for friday? Look at what the northern ind. discussion had to say.
ETA CAPES
WERE EVEN HIGHER FRIDAY AFTERNOON THAN WEDNESDAY EVENING...WITH
VALUES IS SOME SPOTS ABOVE 3700 J/KG. ETA/GFS 0-3 KM STORM RELATIVE
HELICITY OVER 250 M2/S2 SOUTH AND SE OF FWA...SO SEVERE STORMS
CERTAINLY POSSIBLE. GFS NEAR MARION HAS AN IMPRESSIVE SRH OF OVER
800 M2/S2 FRIDAY AFTERNOON! :shock: :shock:

I would wait 'til at least THU before posting a thread on that event. I looked at the 18Z ETA and see no hint of 800M2/S2 - more like 150M2/S2, with CAPEs around 3000J/KG. Setup tomorrow actually looks better to me... Anyway, the reason I would wait for a thread is because the exact location will be highly dependant on where the frontal boundary sets up, which will likely change from model run to model run (i.e. the 18Z ETA has the best setup over OH now, VS. IN)...
 
ETA 00Z still seems on track. The 500mb vort that was evident on the 18Z ETA is now gone, and the front appears to have slowed down by a couple of hours, putting the timing close to what he 12Z ETA had. Lapse rates also appear a bit lower this go around - from 6.7C/KM (850-500) to 6.2C/KM.

CAPE does climb to near 3000J/KG tomorrow afternoon, but there is no real significant trigger around, so I don't see a real big thunderstorm threat (unless some outflow boundaries from todays storms linger around). Main show should be late tomorrow evening across western lower, extending hrough the early night across the east. ETA drops CAPE of significantly between 21Z and 00Z, but this is due to how the ETA handles SFC moisture (it pretty much scours things out around and after 00Z). Adjusting for this change in moisture (averaging the 21Z and 00Z dewpoints), I still come out with CAPE values around 1800J/KG through 03Z across many locations, before the front comes through. Forcing along the front is also very strong - as evident by the 700-500mb vertical velocity field, and the SFC wind/moisture convergence. Dry air intrusion is also very intense - with <30% slamming into the region... Given that... I am Still expecting a line of severe thunderstorms, as helicities are now lower than the previous ETA runs - 150m2/s2 to 200m2/s2...

As for a derecho event... I think it's still possible given the intensity of the of the 500mb height falls (i.e. rapid intensification), good wind fields, and very strong forcing. I believe 1800J/KG would be enough to sustain a serious line of storms through the night time hours WED into THU... Not really sure how to calculate speed of the storms if they were to form into a derecho type event, but it does seem that it could outrun the cold front and perhaps arrive a bit sooner than expected across central/eastern lower MI...
 
Havn't seen any big changes in the 12Z ETA...

Still expecting a decent line of storms to roll through pretty much all of lower MI this evening/thru the night time hours. Not sure why SPC has most of lower MI in only a 15%, since this does appear to be a good setup for a line of storms with damaging winds. Past few model runs have been showing CAPE values of 1250-1800J/KG between 03-06Z across various locations in southern lower MI (slight inversion is evident, but that diminishes as good convergence/column saturates), coupled with good wind fields (shear is pretty much line-normal to the expected squall line), 700-300mb dry punch, and very strong convergence/forcing along the front.
 
Looks like things are falling apart somewhat. Indianapolis and/or N Indiana NWS AFD or HWO mentioned feedback as a possible issue.

I am going to make it a casual chase day and park myself in W OH or E IN and see what satellite and radar show me.

Not expecting much but you gotta try.

Some models showed a high SWEAT index in S IN today. So I am hesitant to head to far N. Especially with SPC downgrading the northern risk.

I 70 at the IN/OH line or perhaps a hundred miles N of there. Depends on how things build today.

Late summer is spent chasing mathematical anomolies.. so it goes.
Tom
 
Originally posted by tom hanlon
Looks like things are falling apart somewhat. Indianapolis and/or N Indiana NWS AFD or HWO mentioned feedback as a possible issue.

I believe they were talking about the GFS model for FRI when it comes to convective feedback. The SFC low today is real, and can be seen on the SFC analysis (the strength can be seen by the OBS in MN - temps in the 50's and winds gusting to 40knts!)...

I still think there is a good chance for severe storms, but they will be very late this evening or tonight. So really, not much to chase...
 
DTX Downplaying the threat a ton in there afternoon dis.

SO ANY CONVECTION THAT FIRES THIS
AFTERNOON AHEAD OF THE COLD FRONT SHOULD REMAIN BELOW SEVERE LIMITS

Something that really bugs me is when they issue the afternoon dis. at 1.40pm when storms could fire. Why not wait til around 3 or 4 like you usually would and see whats happening before making any bold statements.?
 
THE STRENGTH OF THE FRONT (NORTHWEST WINDS
GUSTING IN EXCESS OF 40KTS AND TEMPS DROPPING INTO THE 50S ACROSS
MN) COMBINED WITH INCREASING INSTABILITY SHOULD SET THE STAGE FOR A
SQUALL LINE LOCATED ALONG THE FRONT. THIS FRONT IS FORECAST BY ALL
THE MODELS TO SWEEP THROUGH THE AREA THIS EVENING. EXPECT STORMS TO
APPROACH NORTHWEST PORTIONS OF THE FORECAST AREA (LUDINGTON) BETWEEN
7 AND 8 PM...SWEEPING SOUTH ACROSS THE AREA THROUGH 2 OR 3 AM IN THE
MORNING.

GIVEN THE LLJ OF 30-35 KTS AND A MID LEVEL JET NEAR 70 KTS...
STRONG DAMAGING WINDS ARE THE MAIN THREAT. DECENT SHEAR IS PROGD IN
THE 0-1KM LAYER WITH HELICITY VALUES IN EXCESS OF 100.
THEREFORE..LEFT THE MENTION OF A TORNADO IN THE HWO...BUT FEEL THE
MAIN THREAT BY FAR WILL BE WINDS.

GRRs discussion at 1:15pm doesn't look bad. DTX definately downplaying though...
 
Right now there are currently CAPE values in the 2000 - 2800 (I hope I read it right) range here in SE Nebraska, but it appears that there's a fairly strong cap in place. They are talking thunderstorms possible later tonight and tomorrow.

Le sigh.
 
Tornado Warning for Menominee County in Michigan. Any confirmation of a tornado on the ground or was this just pick up on radar?
 
You were correct about the feedback
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
225 AM EST WED AUG 18 2004

.DISCUSSION...

FOCUS REMAINS ON PRECIP CHCS THROUGH SAT.

MODEL GUIDANCE REMAINS IN DECENT AGREEMENT WITH HANDLING OF MAJOR
FEATURES THROUGH THE PERIOD. ONLY ISSUE CONTINUES TO BE THE GFS
CONVECTIVE FEEDBACK AND ASSOCIATED ERRONEOUS DEEPENING OF SFC LOW
COME FRI-SAT.

I read that through rather quickly on my way out the door. Just the word Feedback as I skimmed the discussion.
 
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