Is this the correct way of forecasting storms?

[Sam Kennedy]

(I'm not sure if this should go in the beginner or advanced section, so feel free to move it if your a mod )

I've been reading www.theweatherprediction.com and came across the "Thunderstorm Cookbook" http://www.theweatherprediction.com/severe/cookbook/

I decided to try it out with forecast lab, and was wondering if I am doing this right.

First I looked at the 850mb chart to try and identify the low level jet.

I highlighted in red the areas where I think the low level jet is.

Next I looked at the 700mb chart and compared it to the 850mb chart to check for speed and/or directional shear.

I highlighted in red areas with speed and/or directional shear.

After that I looked at the 200mb chart to find the upper level jet.

I highlighted the area where the upper level jet passes over the areas I marked out before.

Lastly I look at the surface chart to find boundaries, and check the overall directional and speed shear.

The red line is where I think the boundary is, because there seems to be a change in wind direction around that area. I also noted that there is a large difference between the surface wind direction and the 700mb wind direction. Also, the dew points aren't particularly high, but on the TWP site it says the low level jet can change them quickly, and also it is coming from the Gulf, so I would expect them to rise through the day.

I foregot the date but a lot of storms seemed to have fired east of the highlighted areas, but it is hard to tell because Forecast Lab doesn't show the data for those areas

So am I doing this right or is there something I'm missing? Anything else I should add to it?

 

[Kevin Crawmer]

I will give you my 2 cents on this....it is just my opinion on the matter.

My strategy is usually like this:

Outside of day 1--I look at larger scale features. The UA Charts are good. I really like getting info off of the skew-Ts and hodographs too. Some of the things mentioned in the "cookbook" are good to get an idea of the magnitude of event that is coming up. As you know, you need 1) moisture, 2) instability, 3) lift, 4) shear (speed and directional). Dews are easy to find, CAPE values are generally easy to find > 1 day out except for days where pockets of sunshine are crucial to elevated CAPE values. Your lift is found by looking at the boundaries like you have done. Look for warm fronts, cold fronts, and drylines this far out (smaller outflow boundaries on the day of the event). As far as shear goes, soundings are a good way to look at it all together as a group. Remember that surface winds need to be slightly backed to be ideal for tornadogenesis (usually out of the SE or SSE). These should rotate clockwise with height.

On the day of the event--Look at your surface charts, satellite imagery, and radar to look for the boundaries of interest. Look at forecast soundings to get accurate measures of all of the parameters. When you get out, LOOK AT THE SKY! Watch things develop. If you can tell that towers are getting sheared off or choked out by the cap then you know to evaluate other areas and see if it could be worth your while making a move somewhere else.

I haven't been at this long, but I usually go with that general format.

 

[Kevin Crawmer]

Also, your "boundary" appears to be a warm front. Look to the west and you will see a little bit of what looks to be a weak dryline (dew points dropping from 5-10 degrees over a relatively short amount of time). I don't know if it would be strong enough to fire convection though...I'm not an expert at dryline chasing. There is also a trailing cold front and the low is well-defined. Draw those in too. Depending on the other parameters the warm-front or triple point area may be a good play. There is definitely good moisture along the warm front. As far as your area of "shear", I would look over the skew-Ts or hodos to evaluate this. Or different UA maps (SFC, 850, 700, etc) and look for the changes in direction and height.

Good luck...keep reading, it will all make more sense soon.

 

[Sam Kennedy]

I do normally look at Skew-T charts, but in Forecast Lab you don't get soundings for that area, but I always look at them when I can. By UA charts do you mean 'Upper Air' Charts?

 

[Kevin Crawmer]

Yes, UA=Upper Air. Sorry. Hope all that helps. Hopefully others will jump in too.

 

[J. Sims]

Okay I want to ask this do you compare the maps and look for areas where the wind is going in opposite directions and different levels?

 

[Kevin Crawmer]

Ideally you want a SE or SSE wind at the surface. You want a clockwise turn with height. You want the surface winds to be a bit robust and you want those to increase with height. Hopefully this coincides with good dewpoints (>55F), adequate CAPE (1000+, preferably 2000+), and look for a forcing mechanism (warm front, cold front, dryline, or outflow boundaries).

 

[Jeff Duda]

In the case you've pictured, Sam, I don't really see a traditional low level jet. The higher wind speeds at 850 mb in this case are more of a function of the closed low there. Usually a low level jet is a mesoscale feature not tied to a synoptic feature, and would be a little larger in size.

Also, low level jets in the southern great plains never come out of the north. That one in the west is not a low level jet.

For the jet you marked at 250 mb, it's probably much more widespread than the area you've highlighted, but you have the right idea of overlapping the best features at various levels to find where the most support is.

 

[Bill Tabor]

That's a good basic start Sam. There can be a lot more to it. It can become very verbose, but it is good to start with the basics to get a general idea and then fine tune.

For a decent severe storm you typically need moisture, instability, shear, a trigger / focus mechanism, and you need actual precipitation / convection. In particular you left out moisture. You have to analyze dewpoints available at the surface and depth of moisture. You will also want to look for surface features such as low pressure areas particularly if coincident with upper lows and shortwaves. Analyzing jets and speed / directional shear can help determine areas of more intense severe weather in particular coincident with areas of higher instability. Finally you need to make sure you can get rain, convection, precipitation. If the cap / inversion is too strong you will have all the ingredients but it will be a pretty blue bird blue sky day. If you can break the cap, then all hell may erupt if you have maximized all your features into one target area.