3/27/08 FCST: TX/OK

[Rich Thompson]

I always wait for the storm system AFTER the one that brought in the polar air for any good amount of moisture. Soundings verify that the moisture depth is very shallow. Even without soundings the OK Mesonet showed nicely how shallow the moisture was this morning. 60 Td's in eastern OK down to 40's in western OK. Topography is quite useful for determining moisture depth when there is no dynamic forcing at the surface. I think next week will be a lot better, however that is a different discussion for a different thread.

Kenny,

One note about moisture return in the wake of these polar intrusions - poor moisture quality (i.e., mixing ratio or Td values) is a better reflection of a recent frontal intrusion, while moisture "depth" is more complicated. Very deep cold intrusions (extending up to, say, 700 mb) will result in deep mixed layers over the warmer ocean. Meanwhile, something akin to a dryline passage will support a very shallow mixing depth due to small ocean-air temperature differences and relatively warm temperatures above the surface. Thus, a stronger front (in terms of vertical depth) can support a deeper returning moist layer. The moisture depth problems across the southern Plains today has more to do with parcel trajectories than the recent frontal intrusions.

The killer with the past few frontal intrusions have been the disruption of the maritime tropical boundary layer all across the Caribbean Sea, and the persistence of nely low-level trajectories across the same area. We'll have to re-create the 70-75 F boundary layer Tds at the time of the seasonal SST minimum.

Rich T.

 

[Kenny Drake]

Kenny,

One note about moisture return in the wake of these polar intrusions - poor moisture quality (i.e., mixing ratio or Td values) is a better reflection of a recent frontal intrusion, while moisture "depth" is more complicated. Very deep cold intrusions (extending up to, say, 700 mb) will result in deep mixed layers over the warmer ocean. Meanwhile, something akin to a dryline passage will support a very shallow mixing depth due to small ocean-air temperature differences and relatively warm temperatures above the surface. Thus, a stronger front (in terms of vertical depth) can support a deeper returning moist layer. The moisture depth problems across the southern Plains today has more to do with parcel trajectories than the recent frontal intrusions.

The killer with the past few frontal intrusions have been the disruption of the maritime tropical boundary layer all across the Caribbean Sea, and the persistence of nely low-level trajectories across the same area. We'll have to re-create the 70-75 F boundary layer Tds at the time of the seasonal SST minimum.

Rich T.

I probably should have clarified my words in that post a little more. I didn't mean to relate shallow moisture depth to previous frontal intrusions. The post was more or less a collection of random thoughts put together. However, it is a good point to make because I have heard moisture depth with regard to prior frontal intrusions related in completely the opposite (and wrong) way before.