4/24/09 FCST: MN/IA/WI

[Jeremy Den Hartog]

4/24/09 FCST: MN/IA/NE

Hello,
As this is my first 'FCST' posting here, hopefully I do things correctly. I'm currently looking at my first chase of the year (hopefully). Right now, there are several days over this weekend that seem somewhat promising. Initially I am targeting Friday for a southern Minnesota, northern Iowa chase - since it's right in my backyard I can't miss it. The current GFS run is forecasting dewpoints in the upper 50s or low 60s. There also appears to be a fair amount of shear in the area and the instability looks decent. However, by no means am I as talented as many of you here with forecasting. What does everyone else think about the potential of this setup?

 

[Derrick Herndon]

Well this is the only day during the upcoming "event" I will be able to chase. I would be able to chase the East NE area. One thing I am noting about this region is that the boundary appears to be aligned with the mid-level flow. So it is possible that if storms initiate near the Grand Island area they could interact with the boundary and parallel it as the move NE. Perhaps this will increase the tornado threat. Also the storm motions are favorable. Still too far out for these details but that is what I see attm.

 

[Ryan Wichman]

I have been keeping an eye on this set up since Saturday (I did not want to be the first one to post on the possibility and jinx it!). The first thing that caught my eye when looking ahead to the Friday/Sat time frame was the strong low level jet. The most impressive moisture return into Midwest so far this year. The one thing that seems to be lacking is a lot of upper level support at this point. This far out I don't want to name anymore details, but the possibility of a weekend chance other than the southern plains sounds awesome!

 

[Skip Talbot]

Hey Jeremy, thanks for starting this thread, as I too was looking at this day for a possible chase op.

I think there are a few potential targets here. Starting with the one you bring to light, there is a mainly stationary front forecast to extend from northern WI, through MN, IA, and NE. It seems that the GFS and WRF tend to agree somewhere in the vicinity of 1000 J/Kg will be present along with adequate speed shear. My main concern with playing this target, however, is the storm mode. The midlevel winds are paralleling this front, and when storms do go up on the front, they may train and choke each other. There could be a window of opportunity at initiation for supercells though.

Both models place a triple point where this front and the dryline intersect, somwhere near the central KS/NE border. This is the area I'd consider most chaseable for this setup. Instability is again forecast to be in the vicinity of 1000 J/Kg per the GFS and WRF. Surface winds back more here for better directional shear, and if anything goes up south of the triple point, it will be able to tap enhanced directional shear as it approaches the more east-west orientated boundary.

Further south in KS and OK along the dryline should also be onsidered. The WRF is plotting higher instability at about 2000 J/Kg. However, the cap is forecast to be considerably stronger here. We might be looking at a cap bust or a nocturnal event in this area. The low level jet is strongest in this area, however, and as it ramps up after dark storms could really take off.

So given the capping issues, I'd play near the triple point where low level directional shear should also be enhanced. I don't expect an outbreak from this event, due to the modest instability and the rather light speed shear as the trough hasn't quite arrived yet. It could be a good day before the day event, but Saturday is another story.

 

[Michael O'Keeffe]

The NAM continues to show a potentially good chase day over S NE into N KS. Good moisture, 2000+ j/kg CAPE, and sufficient shear should be enough to get a a few isolated supercells near the triple point region in SC Neb. It could possibly be a cap bust, but the NAM is consistently breaking out a nice isolated blob of precip near I80 close to Grand Island. If a storm can latch onto the boundary a threat for tornadoes could become the case. As of right now if the moisture does verify I think it could be a pretty good day before the day chase.

 

[Ryan Wichman]

Previous remark I had posted here was for the 23rd not the 24th, disregard my comments

 

[jshields]

mods can we add nebraska to the title if needed? i've been watching friday for a while now and the models have been pretty consistent on a decent setup for friday. temps are forecast to be in the mid 80's with dews above 60 leading to about 2000 CAPE over most of eastern neb/western iowa. the cap looks to be pretty stout, but there is a fairly narrow ribbon right along the cold front where the cinh is eroded by late aft/early evening. the shear isn't overly impressive either with the stronger wind fields further north but it looks like there will be a fairly good LLJ that kicks in late in the evening. the new day2 outlook has a 30% hatched area centered over eastern ne/western iowa. even with the low 60's dewpoints the temp/dewpt spread might be too great to get any large number of 'naders, but it looks like very large hail and damaging winds will be likely. if i can get out of work i will definitely head out maybe somwhere just west of lincoln. maybe i'll get lucky and the LLJ will help me with a tornado

 

[Larry J. Kosch]

Need To Add WI to the List

mods can we add nebraska to the title if needed?

I've already asked the guy that initiated the thread. For some reason he cannot change the main heading. He did change the sub-heading (at the start of the thread) to include NE.

Looks like SPC has streched out the SLIGHT RISK area to include WI. So we need to have that sub-head expanded to include Wisconsin. Thanks LJK.

 

[Jeremy Den Hartog]

I agree, Wisconsin should be added to the heading as well (but I can't 'edit' it anymore so a mod will have to). It appears that west central Wisconsin is my new target for tomorrow. They are expecting a weaker cap so storms will initiate sooner there which may lead to a window for super cells and maybe a tornado to develop...the only big problem is it may be kind of hard to see. If my memory serves me right, that part of Wisconsin is hilly and has a lot of trees...hopefully not

 

[Michael Stanga]

WRF showed a small bubble precip breaking out on the I-90 corridor I thought I saw, take that for what its worth.

going to watch this one more closely..no target as of yet but but I am thinking a northern Iowa target (if for no other reason than pure optimism that I wont find myself near omaha tomorrow and how long of a drive that would be to get there and back) im writing off wisconsin as of now...might relook at it later however

 

[Jeremy Den Hartog]

WRF showed a small bubble precip breaking out on the I-90 corridor I thought I saw, take that for what its worth.

going to watch this one more closely..no target as of yet but but I am thinking a northern Iowa target (if for no other reason than pure optimism that I wont find myself near omaha tomorrow and how long of a drive that would be to get there and back) im writing off wisconsin as of now...might relook at it later however

Thanks for the heads up about the WRF. Of course at this point, nothing is 'set in stone' for where I'm going. I am leaning towards Wisconsin due to the day 2 convective outlooks from the NWS painting a 30% chance of severe weather for northwest and west central Wisconsin. This is also the case in eastern Nebraska and western Iowa. However, in Nebraska/Iowa the cap is supposedly stronger (unless I'm reading things incorrectly). That being said, there is the possibility for supercells and tornadoes in both areas - in particular towards the initiation of storm development. Later on, wind and hail will be the primary threat though...

In either case I guess I'm in a favorable location (Mankato) where I'm basically in between one or the other - I just have to decide which to go after

 

[Jared Farrer]

the models have really been all over the place. I am liking the the most recent run as far as better shear pretty much everywhere. It really puts it at being possible for IA and eastern NE. Except it down plays CAPE again. But theirs still plenty to work with.

 

[Josh Richardson]

Well as some have already mentioned North Central IA is becoming a favorable target and I have already written off heading west for this setup. I dont see quite the potential some are talking about on here as I believe things wont have the chance to stay supercellular long, WRF at least breaks the cap first up in the NC IA/Southern MN area before sun down and maybe we can get a brief window of opportunity in there. Exact target will come in the morning but I almost guarantee it will be somewhere up here near Mason City.

 

[Bill Schintler]

Chase Target for Friday, April 24

Chase target:
20 miles west of Mason City, IA.

Timing and storm mode:
Storms, initially supercellular, will initiate between 4 and 5 PM CDT. Storms will rapidly develop to the south and west, as the complex evolves into a line with embedded supercells. Storm bases will be relatively high, with the primary severe threat being hail and wind.

Synopsis:
The WRN CONUS trough will slowly move S and E over the next 36 hours, as a number of compact disturbances translate E within this flow. Further S, a shortwave and associated area of convection over IA and IL will shift E; this will be followed by shortwave ridging. A weak upstream trough over CO and NM will be our next weather maker as it shifts E and merges with the stronger NRN stream. This pattern will result in a continued differential advection of an EML from the SWRN states and increased Gulf moisture from the S. At the SFC, a SW/NE oriented CF will slide slowly SE into NWRN IA during the day Friday. Meanwhile, the primary SFC low develop over ERN CO/NWRN KS. A secondary compact low should develop further E along the front in NCNTRL IA after 21Z as a mid-level shortwave becomes increasingly defined along the SRN fringe of the strongest H3 flow.

Discussion:
Moisture availability is a concern, with the latest NAM on track with LLVL moisture verification at 00Z – after a recent trend of overestimating moisture. Upstream soundings (AMA, MAF, EPZ, and ABQ) indicate very steep lapse rates through 500mb; while a slot of modest but deep moisture was noted as far N as TOP. This differential advection of moisture and steep lapse rates should contribute towards a moderately unstable environment by late afternoon Friday.

Capping will remain strong until late in the day owing to the EML, until lift increases from the W as a narrow axis of strong UVM tracks W to E along the IA/MN border, resulting in a compact frontal wave and localized SFC convergence. Aiding in weakening CIN will be a surge of SFC moisture into CNTRL IA late in the period. Surface-based storms should initiate between Mason City and Algona along a narrow thermal ridge, with Upscale development into WRN IA by early evening. LLVL directional shear will be strong along and immediately N of the front, despite relatively weak LLVL flow, with the region located along the NRN fringe of a moderate SWRLY LLJ. Storms will evolve into a MCS during the evening across CNTRL IA as a LLJ increases to 50 kts and noses into the region. MLCAPE’s should increase to 1500J/kg by 00Z, 04/25/09, as nearly dry-adiabatic lapse rates overspreads IA from the SW above an inversion located around 750 mb.

PS: I'll be available for nowcasting during the afternoon on - PM me.

- Bill
9:40 PM CDT, 04/23/09

 

[Andrew Revering]

I wouldn't chase Wisconsin!! That's my advice for what its worth. If you live in Mankato, go south! Not *just* because of the terrain, but I think overall the target looks a lot better in Iowa.

I really like the area from about Mason City to Fort Dodge to Atlantic, IA. Pending consulting my chase partners, I think Fort Dodge, IA is going to be a great starting point.

I am concerned that between all the models I've seen, there is great inconsistency between the models regarding if there is going to be initiation, if any initiation that does take place is going to be before dark, and of those models that do show initiation, it's either along I-90 in southern MN or in north-central Iowa. So I kind of fear the Albert Lea, MN bust scenario where we all sit there and look at each other and go home again.