Moderate Risk: 3/28/17

The Storm Prediction Center (SPC) has issued a Moderate Risk today for northern Texas and southwestern Oklahoma.

Associated with the Moderate Risk is a 10% tornado threat ring along the US-287 corridor and south to I-20.

The SPC is basing this threat on the deep trough that is passing through New Mexico and into Texas today.  Combining this with the developing mid-latitude cyclone moving out of the Permian Basin and moisture moving in from the southeast, it is shaping up like a typical spring Great Plains severe weather event.  Unlike the scenario a few days ago, there seems to be ample moisture moving into central Texas from the Gulf of Mexico today.  Given the shear from the approaching trough, the strong southeasterly breeze at 850 mb providing the necessary moisture return, and the approaching dryline and cold front associated with the mid-latitude cyclone, supercells are expected to develop in the warm sector.

Synoptically speaking, the 300 mb NAM chart (from Unisys) shows a shortwave trough pushing through New Mexico.  A weak jetstreak is ejecting into the threat area by 00 Z.

The 500 mb NAM chart shows some strong Positive Vorticity Advection (PVA) moving out of New Mexico by 00 Z.  However, there is not nearly as much in the threat area.  The 18 Z chart shows this as well, but is not included in this post.

The 700 mb NAM chart shows rapidly-rising air all over the Texas Panhandle by 18 Z.  This indicates strong convection.

The 850 mb NAM chart shows the northern advancement of the warm front into southern and central Oklahoma by 00 Z. Warm Air Advection (WAA) is present throughout the threat area as winds blow across the thermal gradient from warm to cold.  Warm (and likely moist) air is streaming in rapidly from the south and southeast.

The 12Z upper air sounding from Fort Worth, TX, shows no Convective Available Potential Energy (CAPE) or Convective Inhibition (CINH) at this time.  It also shows a tiny thermal inversion, and the 0-3 km average lapse rate is only 4.5 C/km.  However, once you punch through the variations in the boundary layer, there is some skinny CAPE available all the way up to 200 mb.

The hodograph from Fort Worth, TX, shows that shear is adequate. The deep-layer shear was 25 kts, and the low-level shear was 39 kts. The deep-layer shear was marginally enough to support rotating storms, and the low-level shear was enough to support tornadoes, though both of these figures will increase as the trough approaches

The 12Z upper air sounding from Lake Charles, LA, gives a better representation of the approaching air mass.  The surface dewpoint was 70 F, and there was already 1592 J/kg of CAPE in this area.  The shear and lapse rates were low in this area this morning, limiting the severe potential here, but this air mass is moving northwest into our Moderate Risk area. shows a sharp, bulging dryline through the western and central part of Texas by 21 Z.  This sharpened dryline will be the initiation point for some storms to form. Given that the winds blow almost parallel to the dryline, storms may become linear quickly along this boundary. also shows the CAPE reaching 2000 J/kg in northern Texas by 21 Z.  One CAPE peak is just north of the dryline bulge.  Given this peak, and the fact that the winds blow perpendicular to the warm front in this region, storms may remain discrete along the warm front for while longer than along the cold front/dryline.

Currently, the surface observations (from the SPC Mesoscale Analysis Map) show strong winds from the south and southeast.  Dewpoints have already reached the mid to upper 60’s in central Texas, and the dryline currently runs through the western Texas Panhandle, and through western Texas towards Big Bend.

The Supercell Parameter is expected to increase to 16 near Dallas, but above 8 throughout most of the Moderate Risk area over the next six hours.  The supercell threat is greatest in the warm sector, behind the warm front, but ahead of the cold front/dryline.

The visible satellite imagery shows some convective-looking clouds forming near the dryline, and lots of cloud streets pointing to their moisture source – the Gulf of Mexico and eastern Texas.

The enhanced infrared satellite imagery shows that most of the clouds are thin at this time.

The water vapor satellite imagery shows the dryline and cold front combination approaching the Texas border from the west.  The upper-level center of circulation is in southwestern New Mexico, and the mid-latitude cyclone is northeast of this.   The moisture streaming in from the Gulf of Mexico is below 700 mb, which is to be expected, and does not show up on this image.

Overall, I expect there will be storms today. I think this system looks more promising than Sunday’s, based on the ample moisture and depth of this trough.  It looks like everything we had on Sunday, plus more.

If I were chasing today, I would probably target somewhere closer to the warm front.  I would pick somewhere near Paducah, Crowell, Guthrie area, and see what develops.

Thank you for reading my forecast.

The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from College of Dupage – SATRAD


About highplainschasing

This blog is about my tales in storm chasing. My name is Seth Price and I am an instrumentation instructor at New Mexico Tech. My amateur radio call sign is N3MRA.
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