5/20/09 FCST:NE/SD

[Sam Hall]

Yes, agreed, for tomorrow any storms that do develop will be high based due to the moisture/temperature situation. It's not a great dryline at all, for a good dryline I'd want no moisture almost to the W (maybe 20s/30s) and 60s or so to the immediate E LOL! A dryline is similar to a cold front in that it lifts the air ahead of it aiding the growth of thunderstorms and I feel it will be interesting that an additional cold front will be moving perpendicular (sort of) to the slight dryline tomorrow... but as Jason says above (just noticed your post, Jason, hence my edit here lol) I, too, would look towards the more experienced here for confirmation and info... and also observe what actually happens tomorrow!

But, wind profiles are much nicer, so could support rotation in storms that develop. Today the cap was just ridiculous and any radar echoes that developed near the mountains in MT died off as they passed the hills, presumably again due to the lack of moisture and forcing to keep the cumuli growing.

700 mb temps a bit better tomorrow, ETA progging 10 C or so, still with good surface temps and winds we have a better chance of something popping through, and a CIN hole in central/western areas of NE. So, North Platte and around - maybe towards Scottsbluff is my current feeling for a target tomorrow. We are currently in Valentine, NE.

I am still learning after 5 years of chasing too Neil, so even though when stuff doesn't happen, I am very interested to learn the reasons and improve my forecasting targets for the subsequent chase-years Currently, I am interested in thinking about what will happen when the cold front intersects the slight dryline. Maybe the 'dryline' is not defined enough to do anything, but I wondered whether it may cause some instability with moisture converging from the cooler air behind the front and slightly moist, hot air infront...

Anyway on to tomorrow!!!

 

[Sam Hall]

PS, Jason, are you referring to a dryline bulge? Or is that something else? PM me if you don't want to reply here as it's not generally speaking about the forecast tomorrow

 

[Bill Schintler]

Chase Target for Wednesday, May 20

Chase target:
Hyannis, NE (east-central panhandle).

Timing and storm mode:
Convection should initiate between 4 and 5 PM CDT, with high-based multicell storms the dominant mode. A few rotating storms will also be possible, especially within the few hours following initiation when a few photogenic storms will be likely. Storm motion will be towards the east at 20 mph. Unfortunately, this is in the Sand Hills area where both the road network and visibility are poor.

Synopsis:
The Hudson Bay upper low will finally shift east towards the Canadian Maritimes while the trough over the northwestern CONUS deamplifies and overspreads the Upper Midwest and northern Plains. Low pressure currently over western SD will track northeastward towards Lake Superior. By Wednesday afternoon, a second low will organize along the CF in northeastern CO.

Discussion:
This is somewhat of an unusual setup in that storms will develop behind the CF where SFC moisture will increase in an upslope regime. This setup brings to mind that of May 28. 2006; where dewpoints were highest N and W of the front where supercell storms formed. Moisture will increase along and behind a slow moving CF, with dewpoints increasing to nearly 60F by 00Z, 05/21. Little temperature gradient exists across this frontal boundary, with the cool air remaining well to the N over WRN ND.

Broken CI will overspread the NE panhandle after 3 PM, signaling the approach of a weak ULVL wave S of the strongest flow. Storms should initiate by late afternoon as convective temperatures between 86 and 88 F are breached and convergence increases along the SFC boundary. T/Td spreads AOB 40F will result in high cloud bases and enhanced potential for microburst winds. Deep-layer shear, AOA 30 kts along the southern periphery of the stronger H5 flow, will fall off rapidly S of I-80. By early evening, LLVL directional shear will increase with the area on the southern nose of a 30kt LLJ.

- bill

11:10 PM CDT, 05/19/09

 

[John Wetter]

Looking at the data so far tonight, I'm still thinking it could be a decent day. Obviously no tornadoes, but in the area around Valentine and to the SW look pretty good. I think just enough of a S/W to make things go and then live off of the upslope. Obviously we're kind of pulling at straws here.

The other area I keep looking back at is West-central MN toward Watertown, SD... Another spot to watch.

Preliminarily, I'm thinking Valentine, NE.

 

[Jason Persoff]

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.

 

[Jason Persoff]

PS, Jason, are you referring to a dryline bulge? Or is that something else? PM me if you don't want to reply here as it's not generally speaking about the forecast tomorrow

Actually, up until this am's obs, this was most certainly part of the equation for today . But now...it's not even a bulge: it's all dry.

But yes, the dryline bulge and the dry punch are similar vernacular for the same phenomenon.

 

[Mark Blue]

Our 2009 chasecation has officially begun as of today! We left Denver this morning and are currently traveling I-76 towards the NE panhandle. We are initially targeting Gordon, NE where we will setup shop and watch conditions as they develop. From the data I've looked at it appears the best 'ingredients' are along the NE / SD border. Things should spark off around 22Z this afternoon with the arrival of the cold front. I was happy that the SPC upgraded this set up to a Slight Risk this morning. The best upper level energy is further north of the chase area, but it appears the best EHI and lifting is stacking up around the border or right where we're headed. Hopefully the dewpoints will nudge up from their current mid 40s to low 50s levels as time goes on today. I may refine our target later and will post any updates as they develop.

 

[Larry J. Kosch]

Severe Weather Potential for Western NE

I am especially thrilled to see this particular NAM model shot. (See below)

(The 700 mb chart shows the forecasted vertical velocities (colors), heights (bold white lines), temperature in Celsius (thin red lines) and wind vectors.)

If I'm reading the charts right, it looks like we will have vertical velocity in the plus 10-12 range in Western NE.

I agree with the other storm chasers that this is a primary dryline setup. There will be a strong wind flow going SW-NE across most of NE. And the dew point setup isn't all that great either.

But if the dryline starts backing up, the upslope lifting will come into play. And we could have severe weather, in spite of the marginal conditions.

If it fires up, good luck, Vortex2!! Same goes out to the other storm chasers in Nebraska today!!

 

[Jason Persoff]

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'm 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.

 

[Matthew Crowther]

I think the target today is somewhere near Chadron- here is the 12Z WRF depiction of precip at 00Z:




Te 15Z RUC suggests that initiation may actually begin a bit later and in extreme eastern WY. I think that a couple of nice supercells are likely.

 

[Larry J. Kosch]

Radar Image from Julesburg

I see on the radar from Julesburg KS at 2:50 PM CDST the following image. (See below)

A group of storms is crossing the NE/WY border. There is also a clear boundary outlined in the middle of NE. I wonder if that is a boundary indication? Dryline perhaps??

EDIT: Sorry I need to correct myself. That boundary line I asked about is the current position of the cold front pushing thru NE. (See second photo). SPC is having a mesoscale discussion about a possible SWW to be posted later this afternoon.

 

[Jason Persoff]

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.