10/5/09 FCST: OK/KS/TX

[Brandon Lawson]

I believe a lot of that is from Olaf, but I'm not positive.

I was trying to see where our batch of 60-70 degree dewpoints (currently sitting over central Texas) disappear to tomorrow. NAM has a shortwave moving right over Texas and yoinking (good technical term instead of veering) the surface to 850 winds right along with it. So from mid-day tomorrow into Monday morning, we're looking at west winds over Texas and some dry-air advection clearing out what would be a good pool of moisture. Looking at WV imagery, you can see the wave currently over New Mexico making its way eastward.

I'd like to see Olaf make some good eastward progress tonight and tomorrow. Perhaps the incoming wave can push it along a bit and get that upper-level moisture out of Oklahoma. But I guess I'm not expecting too much.

 

[Greg Blumberg]

Dang. The models just really have not been cooperating in providing a good solution for Monday.

I'm with the others on saying that Olaf is the cause of our models providing wild horrible solutions. First of all, I will state that the quality of the upper air obs network in Mexico can be iffy (so I'm told.) My main point is that I do not believe the models are accurately initializing the data about Olaf. Both the 0z NAM and GFS say that as of 0z, the Olaf surface center of circulation is just west of the Baja peninsula. Satellite shows the area of convection to be much further east at 0z, and I cannot find any surface obs out in the Pacific that can accurately identify a center of circulation. Visible satellite shows a pretty well defined area of surface circulation, but I don't completely trust satellite derived winds. Also if satellite derived winds were created around 0z-1z, which is right before the models were run, then it's highly possible that the winds derived are not accurate. Translation: when it's dark, you can't derive accurate surface winds from visible satellite. On top of that we also have to consider the Mexico mountains and how the models handle mountains with these systems. If we cannot tell where this system is exactly, then what is the chance the models can?

I'm at the point of forecasting for Monday that I am throwing out all the models and am starting to do this the old fashioned way. Unless the models start making sense in the next 24-36 hours, this is going to be a chase day where you find out whether or not you're going the day of.

My forecast for how Olaf is affecting the area comes from the concept of competing for air within the plains. We have Olaf south/southwest of us, sucking in the air towards the south/southwest, and we have our system coming in from the west, attempting to pull the same air northward. Whichever system decides to give up first will determine the fate of the warm front for Monday. I will be monitoring Olaf and the position of the front in TX tomorrow and then be making my decision.

 

[Patrick Marsh]

My forecast for how Olaf is affecting the area comes from the concept of competing for air within the plains. We have Olaf south/southwest of us, sucking in the air towards the south/southwest, and we have our system coming in from the west, attempting to pull the same air northward. Whichever system decides to give up first will determine the fate of the warm front for Monday. I will be monitoring Olaf and the position of the front in TX tomorrow and then be making my decision.

It's a lot more complex than simply applying mass conservation to the airmass originating over the central US. The fundamental issue at stake here is/was the constant isentropic upglide and resultant precipitation north of the warm-front, combined with the increase in drier air at low-levels north of the front.

Yesterday and last night, as warm, moist air was being lifted over the warm-front, precipitation north of the warm-front was falling into an increasingly cooler, drier airmass. As such, the temperatures north of the warm-front could not increase. This continual reinforcement of cooler air north of the warm front will acted to retard any northward advancement of the warm-front.

Now, as the best H850 warm air advection, (think south-to-north winds normal to the surface boundary), has shifted east, an ESE-ENE H850 wind pattern has taken shape across Texas. With little to no southerly component to the H850 flow, warm air advection is non-existent across Texas at this level. Thus, the warm front really shouldn't advance northward much, if at all, today.

Until a decent southerly component can return to the H850 winds across Texas (namely, another system begins to eject out into the plains), the warm front will most likely be a stationary front. Once the next system begins to eject into the plains, we'll have the same issues at hand - warm-air-advection leading to isentropic upglide leading to precipitation north of the warm-front which will fall into a cooler, drier surface airmass which will tend to hinder the northward advancement of the warm front.

Based on the progged strength of the system ejecting into the plains, and what I expect the magnitude of the precipitation shield north of the warm-front to be (partly as a result of the moisture associated with Olaf), I would be surprised if the warm-front made it much further north than the I-20 corridor. Thus, limited surface instability in Oklahoma. However, if a decent low-level jet / warm air advection regime can get going, I certainly wouldn't rule out elevated thunderstorms, with large hail being the primary threat.

 

[cdcollura]

Good day all,

Wow ... Even SPC (unlike last week) has picked up on the down-sides of the models, and a measly "See Text" is all I see FCST today over the panhandles area.

As I mentioned earlier, the models so far out grossly have been over-estimating moisture and instability ... So simply relying on them will be like a hot date "falling through" ;-(

Second, NASCAR is in town for many cities in the central USA, so both motel and car-rental rates will be tripled ... Just another caveat to keep in mind.