07/04/05 FCST: GREAT LAKES

[Robert Dewey]

Latest 00Z NAM has caught my eye around 66-72HRs. Nothing spectacular as far as supercell potential goes, but squall line development looks possible. Many people have outdoor plans on the 4th of July, and what better way to celebrate than to have natures fireworks? Anyway, this is what we got:

Nice northwest flow event appears to be shaping up. Higher SFC temps and low level moisture advect into the region overnight SUN, with Td's rising up towards 70F. This combined with temps in the mid to possibly upper 80's (depending on any cloud cover, how high Td's actually get) could raise MLCAPE up to around 2500J/KG or higher. In the mid levels (500mb), a jet max of 50knts develops as the shortwave gets pinched between the upper level low to the north, and the upper level high to the south. Wind speeds between 850-500mb average out to around 30-40knts, which is sufficient for linear development. A pretty extensive dry slot also punches into the region at 700mb, which would enhance downdraft potential. To set things off, we have a weak cold front sliding through the region, and with little to no CAP (700mb temps drop like a rock between 18Z and 00Z, for 8C to 6C - which is already low), things should fire relatively easily.

NAM seems to output some precipitation across the entire state mid afternoon on, and given how well it verified with the previous event, I would be more inclined to believe what it shows in the future runs. SFC theta-e isn't all that great, but if we manage to get some better low level moisture pooling, or higher SFC temps, that could be increase a bit.

The GFS is fairly similar, though a bit stronger with the shortwave and further south with the main shortwave. Not sure, but it looks like some convective feedback develops around 60HRS near IA/IL (evident on the 500mb vort fields). Anyway, GFS offers much more in the way of directional shear...

Still plenty of time, so us Michiganders can discuss things...

 

[Robert Dewey]

Okay, 18Z stuff rolling in, and we will see what I can come up with. Any other Michiganders that feel like posting a forecast, go right ahead :wink:

The 18Z NAM has slowed down a bit, which is good - We don't want things to blow through too early. The 18Z GFS has backed away from it's convective feedback problems that plagued the 00Z through 12Z runs, though it does show some development of a wave. The 18Z NAM now shows this wave, though, but I am starting to think that this may be some sort of MVC (Mesoscale Vorticity Center) that the models are trying to pick up on.

Overall, instability still present, though I am a slight bit concerned about moisture return. Latest NAM is only forecasting MLCAPE of ~1500J/KG (per the COD site), though SBCAPE makes it to nearly 3000J/KG... Would like to see Td's a bit higher. Overall, the setup still looks favorable for the development of an MCS. Deep layer shear appears to support the growth of supercells, but the lack of significant directional shear should preclude the development of anything more than an isolated tornado.

 

[Aric Cylkowski]

I think the NAM is still having issues on the 6z run this morning.

The GFS 00z says that by afternoon, we should be seeing temperatures into the lupper 80s. However, using the rap.ucar stuff, I can't get a guage on specific lifted indicies or CAPE. The jet stream may be with us, albeit weakly.

Without further information, this forecast is down to temperature, dewpoint and jet stream. With those three components, I'm expecting thunderstorms on Monday but I cannot gauge their severity. I'm going to wait until the RUC becomes active to make a final call.

 

[nickgrillo]

I don't really know what to say about the prospects for severe weather for MI. Infact, there really isn't any, lol, well that's not totally true. For todays setup... Winds in the whole state aren't that good, especially on the 0Z NAM, but they should be good enough to support a bit of organized severe weather. Looking at the 00Z NAM, it's giving way to nearly 2500J/KG of CAPE, but pretty much no low-level shear is available. A few isolated storms could go up in the northern half of MI ahead of the CF by 22Z, with more of a widespread line forming along the CF by late-afternoon. NAM shows a couple SFC troughs around the system... This could also be a focal point for convection initation.

The main threats from any storm that can become severe will of course be damaging winds, along with some large hail. I think todays line won't be too fierce, but, at least maybe we'll see some lightning behind fireworks.

Man... I have GEMPAK now, and I still can't use it. I'd sure would like to view data through it and make a nice outlook map... :? :roll:

 

[Robert Dewey]

I don't really know what to say about the prospects for severe weather for MI. Infact, there really isn't any, lol, well that's not totally true. For todays setup... Winds in the whole state aren't that good, especially on the 0Z NAM, but they should be good enough to support a bit of organized severe weather. Looking at the 00Z NAM, it's giving way to nearly 2500J/KG of CAPE, but pretty much no low-level shear is available. A few isolated storms could go up in the northern half of MI ahead of the CF by 22Z, with more of a widespread line forming along the CF by late-afternoon. NAM shows a couple SFC troughs around the system... This could also be a focal point for convection initation.

The main threats from any storm that can become severe will of course be damaging winds, along with some large hail. I think todays line won't be too fierce, but, at least maybe we'll see some lightning behind fireworks.

Man... I have GEMPAK now, and I still can't use it. I'd sure would like to view data through it and make a nice outlook map... :? :roll:

Actually, the wind field looks pretty good. We have 20-30knts at 850mb, 30-35knts at 700mb, and upwards of 40-45knts at 500mb. The only issue I see is potential instability. If we can hit big numbers, then the unidirectional speed shear will be more than enough. In fact, by 15-18Z, the RUC shows nearly 25knts of shear between 0-3km - pretty impressive low level shear. Modifying a RUC 15Z sounding for a parcel of 88F/67F yeilds nearly 3500J/KG of surface based CAPE, which would obviously be good. The NAM shows the front hanging up around central lower MI by 00Z, and the WRF shows good convective development along it. Currently, Td's are nearing 70F in OH, decreasing rather significantly in IN/IL, then cranking back up into the low 70's across IA (vegetation likely aiding). So, it would seem pretty reasonable that Td's could climb up to around 68F with a southerly flow, and with sufficient heating, things could get unstable. Mid level lapse rates are quite steep as well at over 7C/km.

EDIT: 06Z RUC just came in, and I don't like what it's showing. It has a Td minimum spreading from IL to MI between 09Z and 18Z. It also shows quite a bit of moisture at 500mb hanging around, which could be mid level cirrus. Instability is the key to this event. Without it, we probably won't see more than a few showers.

The main question is, what happens to the MCV? Does it develop into a wave on the front, and if so - how deep? Obviously the deeper the wave is, the slower the front will move. The MCV could also locally enhance shear quite a bit. The GFS brings this through between 00Z and 06Z, while the NAM is much further south. If we are able to build up good instability tomorrow, and convection along the front holds off (AND the GFS verifies), supercells would be a good bet with the MCV around 00Z in SW lower MI, to 06Z in SE lower MI. That's alot of "if's" and "and's", especially since the GFS is probably overdone with the wave...

Complex issues aside, the overall threat for severe weather seems decent. Main mode of convection will likely be linear given the strength of low level shear.