Dryline Speed

[Jared Orr]

(mods, feel free to move this to beginner thread if necessary)

Hi all, I was wondering what the best way is to determain dryline progression speed? I'm assuming that where the dryline is during a certain time in the day can determain this speed since all drylines originate from the same general longitude.

For instance, on the 15Z maps, where is the average dryline roughly located during it's eastward progression? Furthermore, where would a swift dryline or slow dryline be located?

I live in Kansas City, Mo, so I haven't done a whole lot of dryline research until this last year, since most drylines either retreat or become overtaken by a cold front before reaching KC. *sigh*

Gracias!

~Jared

 

[Chris Nuttall]

Drylines don't start at the same longitude all the time. It varies. Dryline position and propagation is directly related to the moisture and wind fields.

The dryline sets up wherever there is a sharp moisture gradient. A key to look for in determining the position of the dryline are dewpoint and wind fields. Generally, there will be high dewpoints and S to SE winds east of the dryline, and low dewpoints and SW winds behind it.

As far as propagation goes, there are a lot of factors that come into it. Some of them include depth, quality, and gradient strength of the moisture, strength and direction of the surface wind field ahead and behind the dryline, and the influence of the upper-level fields (jet max, incoming vort max).

I've seen drylines develop well east of I-35, and I've seen them develop near the TX/NM state line west of Amarillo only a few days apart. It just varies with each event.

Climatologically in the Southern Plains, the dryline tends to initially develop very near the Caprock Escarpment. A lot of this is related to depth of moisture and how it relates to terrain sloping upward towards the west. However, the last two years have been very dry for the Texas Panhandle. With a lack of evapotranspiration and low-level moisture, the dryline has been developing near the TX/OK state line and even farther east.

But, this could happen anywhere. For example, if a lot of rain has fallen east of I-35 in the early spring but west of I-35 is the Dust Bowl Part II, then the dryline will probably establish itself along I-35. Every storm system and every situation is different. Basically, what I'm getting at, is that there is no hard-and-fast longitude that the dryline always develops along.

 

[Jared Orr]

Thanks Chris for your thorough response! I was not aware that drylines started in a variety of longitudes. I thought they virtually all originated near the CO/KS border or TX/NM border longitudes. I always love learning new stuff on this forum.

Here's another question... I've heard that drylines are many times associated with LP supercells. If the supercells on the dryline are recieving plenty of moisture to the south-east, why does this happen? Does the dry inflow from the west evaporate some of the precip?

 

[Scott Weberpal]

Thanks Chris for your thorough response! I was not aware that drylines started in a variety of longitudes. I thought they virtually all originated near the CO/KS border or TX/NM border longitudes. I always love learning new stuff on this forum.

Here's another question... I've heard that drylines are many times associated with LP supercells. If the supercells on the dryline are recieving plenty of moisture to the south-east, why does this happen? Does the dry inflow from the west evaporate some of the precip?

You may have that slightly backward. LP supercells are probably more likely to develop along a dryline but aren't exclusively associated. If the storm is receiving plenty of deep, moist inflow the storm likely won't be LP even if it develops along the dryline. If you get an LP along the dryline, it's likely because moisture ahead of the dryline is shallow and/or not sufficient to creat a large flux of moisture into the storm. It is often difficult to get very deep moisture onto the higher terrain where the dryline often is, thus the higher likelihood for LP mode.

I'm not a dryline expert and one of the West Texas guys may be able to provide better insight, but hopefully I provided enough of a basic overview.

 

[Jared Orr]

Thanks Scott. That makes a lot of sense.

Alright, well I'm out of questions...

I rediscovered a great read as well for dryline forecasting...

http://www.stormtrack.org/library/forecast/dryline.htm

Good stuff. anyway.. cheers!