More Newbie Questions:

[Darrin Rasberry]

Greetings all. I thought I would toss a few more "newbie" questions out there and see if I can get them cleared up. There's probably quite a few in here that are some pretty solid boneheaded questions, but that's what this section of the forum is for

1. What is LEWP? I guessed "east west progression" for the last three letters; another chaser guessed (or knew) "linear" as the first letter but we didn't get to talk about the term after that. I'm guessing it applies to parameters that favor a west-to-east linear line of storms, since it was used to predict the high wind line that crossed over here yesterday.

2. Is there more to a stationary front than "a front that doesn't move?" What do they mean for storm motions and development in general? For instance, suppose there is a situation where a cold front descends to a certain point and then stops. What does that mean in relation to other setup parameters?

3. Questions about low pressure systems. True or false:

a) Lows can be anywhere in the atmosphere - 500mb, 700mb, 850mb and surface. Low pressure systems at different levels in the atmosphere in a given storm setup are interconnected.

b) A strong enough low at the surface can mean a low aloft.

c) "Upper low dig, nothing big." (Extra credit: why?)

d) A low pressure system acts as a sort of vacuum cleaner. Suppose the atmosphere was in perfect equilibrium (no winds anywhere) and a low developed and did not move; wind directions would head toward the low like winds hit a vacuum cleaner on the carpet. In other words, if you were north of the center of the low, winds would be coming from the north; if you were south of the low winds would be coming from the south, etc. The winds swirl around a low here on Earth with a counterclockwise component due to the Coriolis effect.

e) Motions of a low pressure system create sharp warm fronts and cold fronts in any level of the atmosphere. A closed-off low lifting with a northerly component would pull up winds and hotter temps from the south (warm front), and higher TDs from the Gulf, with a clear differentiated area of winds forming a boundary caused by the physics of the low's motion. A low moving with an easterly component would create a similar sort of "wind field" south of the low where winds from the north would sharply differentiate with winds from the south, creating a cold front since a greater area of colder temps would result.

f) A barely moving and strong surface/aloft low such as on May 22/23 that involves the correct parameters for storms would form a sort of "inland hurricane" where storms situated to the east of the low would move north, storms situated more northerly would take a westerly component, and storms situated to the west of the low would truck south.

NOTE: I know nothing about lows, so these are sort of pot shots.

4) When faced with a north/south target shot over a large system, what do you look for when deciding on north or south?

5) What conditions do you look for most on your laptop/from a nowcaster on the Current Conditions SPC page (or some other page if you use that instead), and also in the sky with your own eyes, to determine where a storm will pop?

6) What is the distance one storm has to be from another storm to not be "cut off"?

7) What is your favorite atmospheric setup to chase? Warm front setup, cold front setup, dryline/something setup, etc.

Thanks for answering any of these questions that you can. All input is much appreciated.

 

[Chris Bowman]

1. What is LEWP? I guessed "east west progression" for the last three letters; another chaser guessed (or knew) "linear" as the first letter but we didn't get to talk about the term after that. I'm guessing it applies to parameters that favor a west-to-east linear line of storms, since it was used to predict the high wind line that crossed over here yesterday.

A LEWP is a line echo wave pattern. On radar it would look like a smaller bows within the main convective line.

2. Is there more to a stationary front than "a front that doesn't move?" What do they mean for storm motions and development in general? For instance, suppose there is a situation where a cold front descends to a certain point and then stops. What does that mean in relation to other setup parameters?

A stalled out front can act as a trigger for thunderstorm development. Storms that move along or ingest that boundary would have an enhanced tornado threat. As far as other parameters there could moisture pooling along the boundary, some variation of the surface winds which may enhance storm inflow.

3. Questions about low pressure systems. True or false:

a) Lows can be anywhere in the atmosphere - 500mb, 700mb, 850mb and surface. Low pressure systems at different levels in the atmosphere in a given storm setup are interconnected.

True

b) A strong enough low at the surface can mean a low aloft. [

True

c) "Upper low dig, nothing big." (Extra credit: why?)

I haven't heard this expression It would seem that if an upper low is digging there would be stronger jet energy diving down the back side. The digging may make the low come out a little later than previously expected.

d) A low pressure system acts as a sort of vacuum cleaner. Suppose the atmosphere was in perfect equilibrium (no winds anywhere) and a low developed and did not move; wind directions would head toward the low like winds hit a vacuum cleaner on the carpet. In other words, if you were north of the center of the low, winds would be coming from the north; if you were south of the low winds would be coming from the south, etc. The winds swirl around a low here on Earth with a counterclockwise component due to the Coriolis effect.

True. In your example a pressure gradient force would act to move air towards the low. The Coriolis force would deflect that air and in the northern hemisphere would act to move the air in a counter-clockwise manner.

4) When faced with a north/south target shot over a large system, what do you look for when deciding on north or south?

One big thing, and may be what killed discrete storms the other day, is how the shear and upper winds are oriented to the boundary and/or surface winds. Using the other day as an example I would have targeted southeast Nebraska if I had the time off. Winds were more southeasterly there and just looked better for that reason. Since I had to be to work at midnight I was stuck with what looked like a marginal area for discrete storms in southern Kansas. Winds were 170 to 190 and it was hard for the storms to move away from the line once things went up.

5) What conditions do you look for most on your laptop/from a nowcaster on the Current Conditions SPC page (or some other page if you use that instead), and also in the sky with your own eyes, to determine where a storm will pop?

I want to find something that will trigger the instability. Since this is usually a boundary I look for surface convergence in the observation network, radar/satellite data. For forecasting boundaries I have theta-e convergence built into many of my convective procedures.

7) What is your favorite atmospheric setup to chase? Warm front setup, cold front setup, dryline/something setup, etc.

I would just like to not be working just once when a classic setup arrives. I want a well defined dryline with southeast winds pumping low 70's dews into said dryline. Enough shear to get severe storms but not so much they move so fast. Shear oriented perpendicular to the boundary to get more discrete storms.

I didn't answer all your questions because some of them I just didn't know how to without thinking too much. It's approaching 5 am and the brain function is slowing significantly.

 

[Shane Adams]

What is your favorite atmospheric setup to chase? Warm front setup, cold front setup, dryline/something setup, etc.

Days like May 24. I'm a HUGE fan of high instability/low shear days, because you can get intense tornadic storms and they barely move, which lends itself to mistakes like I made that day (getting out too late). The problem with this type scenario is many times you'll have contrast issues because of rain/haze, but IMO it's more than worth it. As long as your road network remains friendly, you can get in close and see what's really happening below the storm, through the haze, because the storms hardly move.

Classic dryline/TP situations are also wonderful, but as I said, I love boundary poppers on high instability days, because storms barely move. And I've also always believed that high instability/low shear storms can do things that "classic" situation storms don't, such as distinct propagation. You just seem to see the craziest stuff on those days where one storm finds a boundary and goes nuts.