Tuesday, May 19, 2009

Chase Forecast for Wednesday, May 20, 2009

///UPDATE 5.20.09 @ 2030
Wow...and that's that. Pea size hail and some rain. That was all. No good structure except a small rear-flank hail core. Cells just never got their stuff together. Thus far, the tally for me this year is: zero TOR watches, zero SVR watches, zero TOR warnings, and zero SVR warnings. No severe weather at all. Next prospects for anything don't appear likely until the weekend, and even more realistically next week. I'm just flabbergasted.

///UPDATE 5.20.09 @ 1417
SPC issues an MCD for this area and storms pushing out of WY are now taking on a better radar appearance. Any move to the north is now on hold.

///UPDATE 5.20.09 @ 1400
Early afternoon ambivalence...

The LCLs appear much better (about 500ft lower) in SD in the area and CIN appears to be wearing off in that area. Satellite suggests that the convergent field in that area is isolated, but looks pretty clumped like a cluster, and that worries me a bit.

I'm not thrilled with the stuff pushing off of the SE WY area either. The LCLs are very high there and they have a pretty linear appearance to them. The best Td in the region looks to be Chadron which is reporting 73/50. N and S of there Tds are very low (in the 30s).

So I'm going to go to Hemingford, NE, at the moment. This seems to offer the lowest tradeoffs, but still with some hopes.

And I was way wrong earlier about the winds not backing. They definitely are rotating to the SSE just S of I-80. Also, a mesolow has evolved on mesoanalysis right at the junction between SD/WY/NE PH. That settles the need to push north from Bridgeport, NE, where I'm writing this.

///UPDATE 5.20.09 @ 1130
Geeez...I'm in Ogallala now, planning on zipping up US26 toward Bridgeport, NE. In fact, I laughed when I saw that the new Spotternet location (which is pretty slick) locates me at the moment "1 mile south of L and L trailer park". I was unaware that that was a new geographic destination.

The winds here are almost out of the west, and the current mesoanalysis shows that Tds have just plummeted across the NE PH. 3hr Td change is highest over the Badlands NP. All indications thus far show that most convergence will be on the back end of the cold front where WNW winds will abut the westerly winds here.

I am increasingly inclined toward Alliance, but will reassess in Bridgeport. Still posting in FCST thread because we're still hours away from any nowcasting. A bit disheartening seeing the day playing out even drier than I'd expected.

///UPDATE 5.20.09 @ 0800
Chase day...

Today feels a lot like watching a waiter who's stacked the cups too high, and they're just slightly askew, beginning to tilt over. Will he make it or won't he? And that is how the vertical look at the atmosphere this am appears: out of synch, delicate, almost too fragile for something good to happen.

My surface analysis reflects this. The best CAPE is well south of the best upper level support. Worse, the air is forecast to dry out at all levels substantially as the T/Td depressions intensify.

I can only hope at this point that the upper level impulse will somehow combine with the other meager ingredients to give up some okay cells over beautiful chase terrain. I'm going to remain in N Platte for now, though expect I'll be heading north toward Valentine, NE, as the day progresses.

///UPDATE 5.19.09 @ 2000
12z NAM continues to focus a dry punch along the Sand Hills (along the NE/SD borders) Thurs 00z. I'm inclined to believe the progs given the amazing southerly winds blowing across I-80 today transporting the thin moisture up to this area. Upper level support, naturally, is much further north, but a shortwave should rotate through by tomorrow afternoon/evening. I'm hoping the winds to respond a little more than they're progged at the surface. If we can get any backing with the upslope, tomorrow actually could be a diamond in the rough. I'm counting on it; even a single photogenic storm would be rapturous.

So I've pulled into North Platte and look forward to pulling out pen & paper in the morning. Tomorrow, the chase is on.
So, I've decided to stay in leisurely mode, and won't be attempting MT or SD today (5/19) as I'm in Lincoln, NE, and that's way too much of a stretch. So my focus will be on tomorrow. Initially I was going to continue my drive straight to Denver, but today will be a leisurely roll toward the NE/CO border for tomorrow's potential convection.

Current target is North Platte, NE.

At the surface, the cold front will meander SE-ward and will be in a NE/SW orientation from CO up to E SD. A dry punch appears pretty well demarcated in W KS with Td's in advance of the intrusion a mere 45-50 (though that's more than enough in the CO/WY/NE area). Sfc winds will be a touch problematic as they'll be out of the SSW, and risk running more or less parallel to the front. But, if the forecast low in NE CO can tighten up a bit, we may see some backing winds in response. T/Td spreads are on the order of 30-40 deg if the highs verify, meaning very high based storms. These still can be photographic treats, and may offer good, highly visible lightning shots. And in this regime, that's a lot.

CAPE will be in ample supply...if we were in FL. But in the Plains it will be CIN vs. CAPE in a duel of the air parcels. Assuming we hit the Tc, we should see CIN erode sufficiently and hopefully capped enough to allow only a few cells to poke up (instead of MC clusters). The 700mb temps are summer-warm (at or above 10 deg).

As a disturbance pushes across the region, there is hope of a teeny jet streak at 250mb (W around 50 kt) with a stretch-of-the-imagination entry region at 500mb (W winds only around 20-30 kt there). 800mb winds are out of the SE.

So, using my IF-casting model. If the cap can be overcome by the front and daytime heating, if the parcels can keep it together enough to become organized, if the sfc winds back more, etc., than iffy conditions will spell some beautiful single cell high-based storms. If we're luckier, they'll situate the selves over some good looking shrubbery (sufficient to make the Knights Who Say Ni proud), and we'll get photographic storms.

In this pattern, it's really all I could hope for. It's enough for me to be heading to N Platte today.

Again, you can follow my progress by looking at the car-shaped icon in the map below.


Allenspark Lodge said...

Duuude... this is, like, english... right?

Jason Persoff, MD (the StormDoctor) said...

Engrish, actually ;). You guys should get some gorgeous weather up at the B&B!

Allenspark Lodge said...

Fifty five degrees, gentle breeze, bright sun... living large in the Rockies!