06/07/05: FCST: Central / Northern Plains

[nickgrillo]

I'm waiting for today's initation, and just got done looking at the long-range GFS. This upcoming week looks very active, so I guess I'll start with the first good day, lol...

Let's begin with TUEs potential, especially in NE. NAM has a 996MB low centered in NW KS, with dew points expected to be >65F across Central/Eastern NE. The instability will be decent, with >4500J/KG CAPE. Although there is not much upper level support, there is plenty of time for this to change. Definitely some potential on TUE...

 

[bill mudd]

yea I was kinda wondering about Tuesday, and a possible starting point of Denver, making my way east through KS or NB....I know I saw an advisory in SPC that said severe from the 4th through 10th for a very large swath of the northern plains..
any thoughts on this?

 

[Justin Turcotte]

This thread needs expending for all the plains. While NE will have some exceptional instability it will also have a rather stout H70 cap overheads 00z NAM had 12/13 degrees at that level. Further north in the Dakotas there will be the potential for extreme instability with CAPE exceeding 4000 J/kg and LI approaching -10. Both NAM and GFS advertise a theta-e/warm frontal boundary in place across the Dakotas and into MN. Diffluent flow aloft along with some turning with height when combined with the instability suggests supercells are possible or even likely. The SWODY3 currently offers "slight" across this area and I would eventually expect a "moderate" if model continuity continues. The models have been very consistent suggesting a potential target in northeast portion of SD but much too early to pinpoint chase hot spot for Day3.

 

[Ben Prusia]

The models have progged a very interesting setup during the day on Tuesday in the Northern Plains. The 0Z NAM along with the 0Z GFS are forecasting the development of strong surface low pressure systems just off the High Plains. The NAM and the GFS are still differing on the position of the low pressure systems, but the NAM is forecasting a low pressure of 993mb to be situated in SW Nebraska at 0Z Wednesday. The GFS model is forecasting a low that isn't as strong, the 997mb low pressure system to be centered in W Kansas at 0Z Wednesday. However, the models agree on what could be a major storm system that is aimed to strike the Northern Plains on Tuesday. Looking at the areas of highest Theta-E Advection, northeastern Nebraska and southeastern South Dakota are in both of the models sights for highest chances of severe weather. Both models are forecasting a very moist atmosphere in both eastern parts of South Dakota and Nebraska with dewpoints running into the lower to mid 70's. Extreme instability is expected in the area, with SBCAPE values running higher than 4500 J/Kg via the 0Z NAM in southeastern South Dakota. Though storm relative helicity will be higher to the north, anywhere in this area can expect to see supercellular storms develop. However, a capping inversion (via the NAM model) will be in place for most of the day in South Dakota/Nebraska as 850mb temperatures are forecasted to be near 23-25 degrees celsius and 700mb temperatures are forecasted to be around 10-12 degrees celsius, but the GFS model is forecasting a weaker cap. This appears to be a make or break day for the northern Plains States, but is absolutely something worth watching.

Edit: 12Z NAM is showing a deepening low pressure, now progged at 990mb centered around the borders of Colorado/Nebraska/Kansas. NAM is still forecasting a very strong capping inversion over Nebraska which might hinder the chances of initiation across the state, even maybe hindering chances in SD along and south of I-90. Some turning in the winds is also noticed in SD, with surface winds to the South, 850mb to the S or to the E, depending on location, and 500mb to the SW. So far, I would consider EC/NC/NE South Dakota as a potential target.

Graphic for this forecast at "My Chase Forecasts" link below.

 

[Bill Schintler]

Chase target for June 7

Chase target:
20 mi south of Aberdeen, SD.

Timing:
Storms will be ongoing to the north and east of an Aberdeen to Watertown line throughout the day, while explosive new convection will form along an outflow boundary just to the south of the target area around 3 PM CDT.

Storm type and intensity:
Supercell storms producing a full spectrum of severe weather, including very large hail and tornadoes. Additionally, very heavy rain will be likely tomorrow night as storms train over the same areas that receive heavy rainfall tonight.

Discussion:
A series of S/WV’s embedded in the upper trough flow centered in the NWRN CONUS will eject out ahead of the main vort which will be lifting through WY by 00z tomorrow. At the surface, an outflow boundary will serve as the key focus for tomorrow’s weather. There is some uncertainty as to the exact location of this boundary, and NAM guidance is used here as the GFS was too far to the S. MCS development is already underway in NE/SD/ND, and by mid-day tomorrow, these storms will be exiting the NERN corner of SD, laying down an outflow boundary that will be situated along a Mobridge/Redfield/Brookings line by mid-afternoon. NAM and GFS analysis suggests extensive low cloud cover N of US-212 based on H85 RH and UVV fields, however extensive warming of the BL along and S of I-90 throughout the day along with thermal advection into the target area will tend to break clouds up by early afternoon. LCL levels should be in the 1000m AGL range in the target area with the broken cloud cover and outflow-cooled air immediately to the north of the boundary.

Prodigious amounts of moisture and instability will be available for tomorrow’s convection. 00Z KABR sounding showed a nearly 150mb deep moist layer along with a surface dewpoint of 59F. Elsewhere in ERN SD, 00Z dewpoints were in the 60F to 65F range, and the 00Z NAM has initialized well to moisture both at the surface and H85 levels. Given advertised widespread heavy rainfalls tonight, it is possible that evapotranspiration tomorrow may result in even higher dewpoints. Guidance suggests MLCAPEs in excess of 4000J/kg by late afternoon, in addition to deep-layer shear to 60kts with the approach of an 80kt H50 jet max, and 0-3km SRH’s to 300m^2/s^2, supporting a potentially major severe WX outbreak.

- bill

 

[Jason Hetzel]

im cracking up because i knew since yesterday there were going to be very few tornadoes today and i also said it was going to go linear as for i looked at SOUNDINGS and wind models and saw too much undirectional speed shear hence linear activity. also checked with spc on that and both the SPC and the models confirm very few tornadoes today and more linear. pay attention to SPC and not just ALL models... SPC is there for a reason...

 

[Jim Bishop]

Originally posted by Jason Hetzel
im cracking up because i knew since yesterday there were going to be very few tornadoes today and i also said it was going to go linear as for i looked at SOUNDINGS and wind models and saw too much undirectional speed shear hence linear activity. also checked with spc on that and both the SPC and the models confirm very few tornadoes today and more linear. pay attention to SPC and not just ALL models... SPC is there for a reason...

You can laugh all you want but myself, chasers and the SPC (since you clearly look at their forecasts) are all forecasting supercells and a few tornadoes over South Dakota today.

If you did, in fact, look at the model forecasts, you'd find the shear to be more than adequate for supercells. 500mb SSW 40 knots and 850mb SE 25 knots. How is that linear?

Asside from the strong cap, today is a really good setup for supercells with potential for a few tornadoes.

With regard to the cap, I'm worried the 700mb temps will be too warm. LBF sounding shows near 12C. But since winds will be more backed near the surface low (not advecting the 12C temps), storms should fire there. I'm worried because NAM underestimated the 700mb temps on June 4, which kept the outbreak from occurring.

 

[Mikey Gribble]

SPC said...
"SUPERCELLS WITH A FEW TORNADOES AND VERY LARGE HAIL WILL BE
POSSIBLE"

Did you read that part Jason?
You seem pretty confident about there being no tornadoes today considering the fact that it isn't even noon yet. I think some people might end up needing a shoe horn to get their foot out of their mouth by 10o'clock tonight.(hope its not me)

Conditions are not ideal for tornadoes today, but they weren't yesterday either and look what happened. IMO conditions are more favorable today than they were yesterday. I would like to see better directional shear in the lower levels, and as mentioned by several other people, LCL's are not very low. Regardless, I think the amount of deep layer shear, good CAPE, and backed surface winds will be sufficient for a few tornadoes later on this evening. I have a pretty good idea of where my target is going to be for today. Good luck to everyone out chasing.

 

[Tony Laubach]

Hey guys,

Try and keep this civilized... everyone's entitled to their own forecast, regardless of whether or not others may think its good... lets try and keep the attacks out of this...

Thanks,
Tony

 

[Colin Davis]

Originally posted by Jason Hetzel
im cracking up because i knew since yesterday there were going to be very few tornadoes today and i also said it was going to go linear as for i looked at SOUNDINGS and wind models and saw too much undirectional speed shear hence linear activity. also checked with spc on that and both the SPC and the models confirm very few tornadoes today and more linear. pay attention to SPC and not just ALL models... SPC is there for a reason...

Speed shear is not at a loss today, and the same goes for deep layer. Basically, it's 11:00am.

Not saying you're wrong, by any means. Just saying, don't give up on it just yet.

Watch that 850/500mb crossover, if you're into SPC's mesoscale analysis. Look for OFBs to improve directional shear.

The possibilities are endless.

 

[Jason Hetzel]

i never said totally there will not be no tornadoes. any initial discrete storms will certainly be able to produce tornaodes but if you really put it all together by early evening things are expected to quickly go linear. and im not trying to attack anybody so dont worry. im just saying it doesnt seem to be too good of a setup although everything is in place cause some of the crucial components such as the cap are not so great. im just going with a good feeling that its going to start initially as tornadic supercell storms but then quickly converge into a line. none the less you are all right though as for it is way too early to for sure tell but im just thinking its going to go linear and it wont take too long after the first storms start. and yes tornadoes are possible as for its a classic triple-point setup and yes i know what those are and what they can do but it just looks to go linear soon after. im just going to watch and wait and see what happens now. i also need a sounding for that area to see if things may have changed since i last saw the model data and last sounding from early this morning.