03.06.10

First Chase of the Year?

Posted in Severe Weather Forecast at 1:00 pm by Rebekah

Spring thunderstorms are coming back to the Plains!  The first real chase setup looks like it will be on Monday (at least for the Southern Plains; yesterday there was a marginal chase setup in Nebraska/northern Kansas) .  It doesn’t look great, but early season storm setups rarely do.

Models are finally showing some consensus on this one; a strong upper-level low/trough is forecast over west Texas by 00Z on the 9th (i.e., 6pm on Monday).  Models show a surface low underneath the upper-level low, centered over southeast Colorado/southwest Kansas/west Oklahoma Panhandle/north Texas Panhandle.  Surface winds around the cyclone will draw warm, semi-moist air from the Gulf of Mexico up into west Oklahoma.  The 60F isotherm is forecast to be in either through southwest or central Oklahoma.  It appears that there will be a dryline just ahead of the cold front in the east Texas Panhandle.  Surface dewpoints may be in the 50s in southwest and possibly south central Oklahoma, with the 60F isodrosotherm in central Texas.  Low CAPE values (a measure of instability–desired for much rising motion) of about 500 to 1000 J/kg may be realized in west Oklahoma and north central Texas.  Helicity values (a measure of wind shear) are forecast to be more than decent for rotating storms; between 200 and 350 from 0-1 km in central Oklahoma/north central Texas (as well as a small portion of southwest Oklahoma), and 300 to 650 from 0-3 km in the same region.

Remember how I said the other day there are four primary conditions that severe storm forecasters look for?  Monday’s setup has plenty of lift and shear, but moisture and instability are the greatest limiting factors.  I am concerned that there may be too much cloud cover over Oklahoma and north Texas for enough heating to occur.  I am also concerned that there may not be enough low-level moisture for good storms with low bases.  At present, it looks as if there will be so much forcing that storms will break out, but they will quickly form a squall line.

However, I do think there may be some isolated storms perhaps behind the major line, along the dryline, or tail-end charlies  (storms at the bottom of a line) that might have a chance of producing something interesting.  Even within the line there may be some marginally severe hail.

I am keeping a close eye on this setup and am starting to consider taking a little drive southward on Monday…not so much for the sake of a good chase, but to test out my new equipment and see how coordinated I can be with my new setup on a marginal day.  I figure it’s better to test new equipment on a marginal/bad day than on an excellent day and then have everything go wrong.  🙂  For now, I like the area between Wichita Falls, Gainesville, and Graham, Texas, as well as central Texas (though I wouldn’t want to go that far south unless it looked spectacular)…but that could change with the next few model runs…

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