5/7/04 FCST: IA & other

A belt of strong midlevel westerlies is forecast to overspread parts of the upper midwest Friday as disturbances ride a zonal flow atop the ridge dominating the central plains. Iowa and Missouri should see impressive deep layer shear as a modest low level jet advects substantial moisture into the area, and surface winds back along a stationary front. Forecast CAPE values over 2500 j/kg are forecast along and south of the frontal zone, and 0-1km shear values suggest supercells with tornadoes are possible.
 
Are you going to be venturing out Amos, or is it too close to finals week?

Do you think they are going to push the slight risk further south for Friday?

Tim
 
Originally posted by Tim Stoecklein
Are you going to be venturing out Amos, or is it too close to finals week?Do you think they are going to push the slight risk further south for Friday?

I wrapped up school last week--finished early so I could be ready--and have been climbing the walls ever since, LOL. So, yeah, I'm all over this. It's the beginning of my chase vacation anyway; I'm out for the long haul. Packing right now, in fact.

As for the slight, I assume you're asking because of how this morning's ETA shunted the front more south. I think that for the Day 2, they'll continue to follow the guidance and orient the risk area relative to the boundary. I'm torn between hoping it stays more southerly, which could mean a better chase day Saturday in more favorable terrain, or keeping it north and out of the Missouri thicket so Friday isn't some nightmarish May 6, 2003 repeat for me.

But since beggars can't be choosers, I'll take what's offered. :wink:
 
I'm liking an area from 50 miles west of Blair NE to 50 miles east of Blair NE(or use Omaha). Or n-s to wherever that boundary sets up. It looks half decent at this time. Could use some better/stronger upper winds above 500mb but will take what we got. I've been looking at some old soundings for some memorable events and they were no stronger then what we have for Friday, given that sfc boundary isn't in nw MO and stays more north.
 
I wouldn't mind that boundary shifting back to the north a bit further, unless I somehow end up in the middle of Illinois. That is not likely at this point though.

Your best bet might be a trip to east it's looking like Mike. Who knows at this point. The mets here in Michigan are being very cautious about their forecasts for Friday and Saturday since they can't decide where the boundary is going to set up. I still vote for a bit further to the north :wink:

Tim
 
Cool! Despite the cold temperatures(58 N suburbs/lakefront to around 70 S of I-80), it looks like the 25% bulls-eye will be accross northern IL/IN. Could have severe storms up to three days in a row, as Saturday could go MOD just west of me! :shock:
 
Friday promises to be interesting in central Indiana since I will be setting a new land-speed record in taking my Aviation Meteorology (aka BeechJet class aka BJ class) final at 3:20. Right now, the plan is to leave directly from the aerodrome to points nearby for what may be the last Indiana chase for some of our posse. The problem is, north of the front, surface-based and mixed-layer CAPEs are piss-poor, as one would expect. However, behind the front, the CIN values are crazy. The best break looks to be southeast of IND at 0Z, with not much before that. CAPE values are much better there, but the helicity drops off significantly. Right now its a choice between the low CAPE or the low helicity. If this forecast persists, then I'll end up taking my time on my final.


Ben
 
A quick glance of the 18Z ETA shows good promise on Friday night as Mike mentioned: Healthy CAPE, Helicities, backed flow along the front and weakening CIHN values. All this seems to point in a general direction between Norfolk and Sioux City. The caveat, weak upper flow. 30knots at 500 doesn't get me too excited. Also, the best lift seemed to be pushing further to the East before 0Z. Interesting what the 0Z ETA wheel of fortune shall bring.
 
Weak Winds Aloft

Tomorrow would look like a potentially great tornado day if the upper level winds were stronger. Most of eastern and northeastern Nebraska into western Iowa will have 500mb winds between 25 and 35 knots. That wouldn't be a problem if the 300mb and 250mb winds were 45-50 knots. Instead, it looks like they're going to be lacking, around 30-40 knots, and that's being optimistic. There's going to be a lot of short-lived mesos tomorrow, and a lot of outflow dominant storms. If there are any tornadoes tomorrow, I would think they would be very brief. I can't chase anyways...family is in town for graduation.

Jim Bishop
http://stormgasm.com
 
Tornado: (In the case Severe Thunderstorms Develop)
Violent Tornados Possible (F4 - F5, or any below).

Just curious, what makes you think violent tornadoes are possible today?

Scott Currens
 
Don't ask - or check the LENGTHY thread on the weather forum about his 'method' of 'predicting' the weather.
 
This is the wrong place to discuss the merits of Kevin Martin's formula. Let's keep this thread focused on today's chances for severe storms. I have asked Buddy to provide meteorological support for any additional forecasts he makes, and I would ask everybody else to stand down as well. Thanks.
 
For the DVN area

The latest ETA 0z charts are showing 250MB winds around 50kts, 850MB winds around 25kts, cape isnt showing anything on the latest plot, Surface Temps in the upper 50's, and dewpoints in the lower 60's, Relative humidity in the 70's, CIN 0...
 
today's forecast

Dense cloud cover and cool outflow is limiting heating across all of Iowa and parts of eastern Nebraska. Strong high pressure north of the stationary front maintains steady northeast to east-northeast surface flow down to the Kansas-Nebraska border and throughout the southern tier of Iowa. Dewpoints in the lower to mid 60's are pooling along the boundary in extreme northern Kansas and working into southern Nebraska. At 15Z, a single station in southern Nebraska reported southerly winds.

Aloft, dry air around 850 mb domintated soundings from Kansas along with a substantial capping inversion. Omaha's sounding appears contaminated (any other opinions on this?) and DVN was apparently undergoing a thunderstorm when they launched. This hot, dry air above the surface will move into the target region and reinforce the already strong inversion.

In the midlevels, I analyzed a small disturbance currently over eastern CO and might have spotted the same on the vapor loop. This is weak if it's actually there, or it's possible I've analyzed the Rocky Mountains--LOL. If somebody with more upper air analysis experience for this area could weigh in, I'd appreciate it. However, I believe the 14Z RUC has picked up this disturbance and moves it into central Nebraska by 0Z, maybe too late to help. The good news upstairs is that Omaha's 500 mb temp is -14C, cooler than forecast by the models.

It would appear that strong convergence along the front should have some chance to break the cap. The next question is, if the storms fire very close to or on the boundary, how long before they become elevated hailers on the stable side? Quickly I would guess. The best chance for surface based convection would seem to be somewhat south of or well off the boundary (if we had another lifting mechanism for instance). The good news here is that the RUC depicts the intersection of a weak surface trough with the boundary around Omaha at 0Z. This creates a convergence area and a small 'warm sector' in which increasing flux convergence could challenge the cap. Whether the front will ever make Omaha is a different question. I have my doubts. As for the appearance of a weak surface trough sufficient to assist in convergence, who knows?

Winds aloft are forecast to remain weak over central Nebraska, suggesting HPs if we're lucky or multicell clusters with hail if we're not. An increasing low level jet this evening should support any storms that appear, and helicity values along the front remain formidable, so tornadoes can't be ruled out if surface-based storms form.

Overall a highly conditional setup. My instinct is to stay in Des Moines for a few hours to see things develop rather than burning pricey gasoline touring the thick overcast along I-80. If I had to pick a target right now, I'd say 50 miles either side of a line from Wilber, Nebraska to Red Oak, Iowa.
 
Re: today's forecast

Originally posted by Amos Magliocco

In the midlevels, I analyzed a small disturbance currently over eastern CO and might have spotted the same on the vapor loop. This is weak if it's actually there, or it's possible I've analyzed the Rocky Mountains--LOL. If somebody with more upper air analysis experience for this area could weigh in, I'd appreciate it. .

Cool. This will definitely help out if the RUC's advertised surface trough appears. Now to get all these features perfectly timed like a Troy Aikman to Michael Irvin post pattern--LOL.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1105 AM CDT FRI MAY 7 2004

ON THE UPPER AIR ANALYSIS...A WEAK SHORT WAVE WAS NOTED ACROSS THE CENTRAL ROCKY MOUNTAINS WITH STILL MODEST MID LEVEL TEMPERATURES ACROSS THE CENTRAL PLAINS. OVERALL...FEEL THAT PRECIPITATION CHANCES WILL BE SMALL UNTIL LATER THIS AFTERNOON...WITH DEVELOPMENT EXPECTED NEAR THE FRONTAL BOUNDARY AS ATMOSPHERE BECOMES INCREASINGLY UNSTABLE AND MID LEVEL CAP WEAKENS SLIGHTLY.
 
http://www.rap.ucar.edu/weather/model/disp...&hours=hr06hr09

Interesting to note how fast the model moves that High to our east hopefully allowing that boundary to lift north quicker then it currently is.

http://www.rap.ucar.edu/weather/surface/sfc_ict.gif

I haven't been up looking too long but was up early and it appears these current winds have veered more to the east now? Judging by the last setup in IA similar to this(night time sups riding the wf in nc IA) the front is about 1-2 counties further south at the same time. Winds seem to want to do the same thing.

Also it appears to me the boundary wants to be move e-w then wnw-ese which would have to help with the 500 flow. Then again something laching onto a boundary curving se would have to help our SR vent winds?
 
SWODY1 1630Z UPPER MS VALLEY...
WARM SECTOR S OF FRONTAL ZONE EXPECTED TO REMAIN CAPPED THRU MUCH OF AFTERNOON. WITH FRONT SHIFTING N ACROSS ERN NEB/IA WITH STRENGTHENING LOW LEVEL JET THIS EVENING...ELEVATED INSTABILITY WILL BE SPREADING NEWD INTO SRN MN/WI TONIGHT. MODELS SOUNDINGS SUGGEST MUCAPES COULD INCREASE TO 1500-2000 J/KG IN THE WARM ADVECTION REGIME MODELS IN AGREEMENT THAT AN ELEVATED SEVERE THREAT IS LIKELY ACROSS SRN MN/NRN WI TONIGHT...

Ouch! In other words, "get a life, you nerds! Don't you know a mega-cap when you see it? Learn to read a sounding!"

LOL!!! :?

Feeling dressed down in Des Moines,

Amos
 
Hahaha, don't you just hate to read stuff like that Amos? This stationary front is playing heck with forecasters and the models alike. I still hold some hope for you guys before the afternoon is over though, but looking at last night's midnight firing time to break the cap, good luck!!

Tim
 
Perhaps this front won't make it far enough north(under better midlevel winds). Though an interesting report west of Lincoln now wonder if that reading is correct for the wind speed/direction.

LOOKS AS THOUGH UPPER WAVE PRODUCING THIS CONVECTION
WILL LIFT NORTHEAST OF AREA BY MID AFTERNOON AND FRONT SHOULD BEGIN TO PUSH RAPIDLY NORTH AT THAT POINT.

From Hastings FD. Hmmm. Maybe that reading west of Lincoln was correct. So it lifts rapidly north and our convergence lessens? We need a mesolow to form around GRI or east. Could happen, it did last similar setup.
 
I think I'm talking to myself on this one now, but oh well, here goes. I say if anything sfc based is going to happen it will be just west of Columbus Nebraka at 5:37. It will then track east and produce it's brief tornado somewhere near Tekamah NE, BUT I will be down in Blair trying to cross the river to intercept it on the other side and miss it.
 
Ya made me bust a gut, Mike. Good thinking on the Columbus call. That shortwave looks to have passed into SW NE and should cause the front to lift up to or North of I-80 a bit later. I'm sitting here in Omaha trying to be patient. Maybe you should just sit on the Iowa side on this one?
 
I would hang right around Neb City-Red Oak, IA. WF has been hanging there and some of the CU along the boundary to the SW has been thinking about popping - hopefully the midlevel instability won't inhibit something close to the surface and you can get something besides hail, though that would be cool too - RUC still predicting precip right in that pocket SW of Neb City along the boundary - here's your OAX sounding:

<img src=http://img47.photobucket.com/albums/v143/mikeperegrine/oax_sounding.gif>
 
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