5/7/04 FCST: IA & other

[Amos Magliocco]

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.

 

[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?

Tim

 

[Amos Magliocco]

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:

 

[Mike Hollingshead]

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.

 

[Tim Stoecklein]

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

 

[David Draun]

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:

 

[Ben Cotton]

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

 

[Mike Hollingshead]

http://www.wxcaster.com/modelskewt.php3?mo...STATIONID=72557

Not to shabby. That is for Sioux City IA Friday evening. Could use some stronger winds aloft and lower lcls but we'll take it. Always nice when it says 100% on sup potential.

http://www.wxcaster.com/modelskewt.php3?mo...STATIONID=72557

That is the meso-eta same time and location. Sweet looking hodo. Lcls and CINH MUCH better on the meso-eta. 1200 m down to 882 m.

 

[Tim Jones]

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.

 

[Jim Bishop]

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

 

[Scott Currens]

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

 

[rdale]

Don't ask - or check the LENGTHY thread on the weather forum about his 'method' of 'predicting' the weather.

 

[Amos Magliocco]

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.

 

[Buddy Sallee]

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...

 

[Amos Magliocco]

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.