07/04/2005 TALK: GREAT LAKES

[Robert Dewey]

Since this really isn't a forecast, I'm gonna start a TALK thread...

SPC doesn't even have a SLGT out for the region on MON. This is probably due to the fact that northwest flow events are relatively hard to forecast - you have timing issues, whether or not any previous days convection will interfere, low level moisture return, etc..

Personally though, I would have gone SLGT. Whenever I see instability greater than (MLCAPE) 2000J/KG, and a +50knt jet max around 500mb - it should at least warrant a SLGT risk. I see the IWX went ahead and put a SLGT risk in their local HWO product, which seems reasonable to me. But again, major drawbacks, at least between the 00Z NAM and the 06Z NAM are timing. GFS still has somewhat of a convective look to it, but the development of a wave along the front is completely possible, though probably not to the extent the 06Z GFS shows. That would end up enhancing low level directional shear quite a bit, but could also disrupt moisture flow by firing all of the convection a little too far south for my liking.

 

[Jeremy Lemanski]

the fact that northwest flow events are relatively hard to forecast

That is it, the NW flow events can be crap, with little to no severe weather, or rain for that matter, or they can be huge and catch everyone completely off guard, the event in WI last june 23th, link to event write up: http://www.crh.noaa.gov/mkx/document/tor/062304.php.

NW flow events are always interesting, because usually they have good dynamics with them, and if you get the heating/moisture needed,you have all you need for severe weather.

 

[Alex Lamers]

I'm not really seeing northwest flow evolving. Looks more west-southwesterly to me...nice jet possibly backbuilding in the afternoon/evening due to latent heat release if MCS decides to crank up tomorrow. Jet could turn more westerly on the 4th but not seeing much northwest component. Nevertheless I think there should be some decent complex somewhere. SPC SWODY2 mentions possible upgrade tomorrow across IA/NE/MO. This makes sense and i think the threat would transition down into the Ohio Valley or Mid Mississippi Valley on Day 3. I think we could have convective debris issues across WI and the Lk Michigan region so I'm not too pumped up yet.

...Alex Lamers...

 

[Robert Dewey]

I'm not really seeing northwest flow evolving. Looks more west-southwesterly to me...nice jet possibly backbuilding in the afternoon/evening due to latent heat release if MCS decides to crank up tomorrow. Jet could turn more westerly on the 4th but not seeing much northwest component. Nevertheless I think there should be some decent complex somewhere. SPC SWODY2 mentions possible upgrade tomorrow across IA/NE/MO. This makes sense and i think the threat would transition down into the Ohio Valley or Mid Mississippi Valley on Day 3. I think we could have convective debris issues across WI and the Lk Michigan region so I'm not too pumped up yet.

...Alex Lamers...

Yeah, the NAM has been trending away from NW flow at 500mb. The reason for this is that the shortwave is digging further south with each run (indicating a stronger wave), versus the embedded wave the NAM previously had. While the wave is digging deeper, it seems the NAM is also speeding things up. It also has some garbage out ahead of the front, and hopefully that will be gone before it hits MI. The cold front, according to the latest NAM, is supposed to drape down through central lower MI by 00Z (June 5th) and kind of wash out.

 

[Jeremy Lemanski]

judging from the discussions out of apx/grr, It is again an all or nothing event. Morning convection could again screw the day up completely. Tomorrow and tomorrow night should tell the tale.