Thursday, January 14, 2010
Spring Storms Possible Next Week
After a couple of weeks of cold weather across East Texas, changes in the upper air pattern could lead to some strong storms, including severe weather, by mid week. A negatively tilted trough will be swinging through the southern plains helping to bring in Gulf moisture and warmer air across East Texas by Wednesday afternoon. Dewpoint temperatures will reach the lower to middle 60s across most of East Texas making Wednesday fairly muggy (see below).
Temperatures Wednesday night into Thursday morning will remain in the lower to middle 60s as well, much above normal (see below). This will allow for thunderstorm activity to continue well into the night. Right now it look as though high temperatures will top of Wednesday afternoon in the middle to upper 60s but, if this system is as strong as advertised I would not be surprised to see a few 70s across East Texas, especially south of I-20.
The warm moist air at the surface combined with colder temperatures aloft will provide plenty of instability for thunderstorm development. The surface based Lifted Index will be between -4 and -8 Wednesday afternoon and evening, more than enough to support severe thunderstorm growth (see below).
The amount for CAPE (convective available potential energy) is forecast to be very high as well for this time of the year. Many times in the cold season we see severe weather events in a low instability high shear environment, like our tornado outbreak last month. CAPE values were running between 500 and 1000 that day and you can see we could have values between 1000 and 2000 this upcoming Wednesday (see below).
The next ingredient needed for supercell development is wind shear. 0-6km shear really needs to be greater than 30 knots to provide the best environment for supercell development and by looking at the image below, most of East Texas has 0-6km wind shear 30 and 50 knots. This is not as much as was advertised for the 12/23/09 event (0-6 km shear between 50 and 70knots) but is enough to produce supercells, especially with CAPE values at or above 1500 J/kg.
The forecast sounding and hodograph paint a potentially dangerous situation Wednesday afternoon and evening. Looking at the sounding we can evaluate the severe weather potential (see below). We see positive CAPE with the yellow line, parcel temperature, well to the right of the environmental temperature, red line. Nearly half of this CAPE is between the -10°C and -30°C isotherm, or the hail growth region. With positive CAPE and wind shear, large hail would definitely be a threat. We can also see the winds in the positive CAPE region as high as 70 knots. The forward flank downdrafts of any storm that develops could tap this wind and bring it to the surface. So high winds would be a threat as well.
Finally for the tornado threat. The hodograph shows a large clockwise turning of the winds with height. Below is an image of the 0-1km hodograph. This layer of the atmosphere is where the air is ingested into the storm. So there would be plenty of vorticity available in the lower levels for low level mesocyclone development which could lead to isolated tornadoes.
Overall it does appear over the next week to ten days the weather pattern will be more like spring than we would find in January. Any time we see warm moist air from the Gulf surge northward we have to be on the watch for severe weather. The event forecast for Wednesday is many days out and we will probably see some overall changes in the forecast between now and then. I do want to stress to long range models have been performing fairly well 6 to 7 day s out as of late. Again, the event on 12/23/09 was forecast well in advanced. If the current forecast trend continues, we could see another significant severe weather event.