Saturday, October 31, 2009

Wednesday, October 21, 2009

Heavy Rain/Storms Possible Tonight

The above image shows the forecast rainfall for the next 48 hours. With plenty of lift and moisture in place, heavy rain appears likely overnight tonight into tomorrow morning. Because of this, most areas north of I-20 in East Texas are under a flash flood watch.

Another concern, although it is very small, is that there is a chance of mini supercells across the region tonight into tomorrow morning. A mini supper cells have mini characteristics of a classic supercell but on a much smaller scale. A few of the storms tonight have been showing signs of low level rotation indicating a mini mesocyclone, hence, a mini supercell.

Below are a few images of the forecast across East Texas at 7AM tomorrow. The 1st image is of the lifted index. Any value below 0 shows there is buoyant surface are that could lead to surface based convection. LIs around East Texas are in the -2 range tomorrow morning.

The second image shows the amount of SBCAPE, or energy available for thunderstorm updrafts. The values are very low, less than 500 in most areas. However, most of this CAPE if found in the lowest layer of the atmosphere which will be encountering lots of spin. This will help lead to a few storms having low level mesocyclones. The image below the SBCAPE shows the amount of CAPE between 0-3km. This low level CAPE is enough to help in tornadogenesis.

The next image shows the amount of 0-1km SRH in the atmosphere. This value is approaching 200 over much of East Texas. Again, this value would allow for tornadoes to develop.

The chances of a tornado developing tonight is less than 2% this evening and overnight but, we will have to watch the storms closely.

Monday, October 19, 2009

An El Nino Winter Ahead

So what does that mean for East Texas? If you look at the average weather for an El Nino year you will see we usually see wetter and cooler conditions. This is due to the storm track being placed across the Gulf Coast States keeping cloud cover and precipitation in the area. Will the cooler and wetter conditions combine to see more winter precipitation across East Texas? With the storm track farther to the south, the chances of winter weather would seem to be greater. I will give a more detailed look at what i expect this winter in the up coming days. Below are images showing what we normally expect in an El Nino winter.

Tuesday, October 13, 2009

Wild Cold Weather Across The Country

Photo credit: L.M. Baker with the MHA Times, New Town, North Dakota.

Over much of the Northeast and Midwest, temperatures this summer were cooler than normal. Many areas setting record lows for the coolest summer months on record. This cool weather seems to be setting the stage for what could be a fairly cold winter across much of the United States. Cold temperatures have already been seen across much of the northern states so far this October and record snowfalls amounts have fallen across the Plains. One of the most interesting features I read about with this current outbreak of cold weather was the development of a waterspout over a lake in North Dakota during snow showers. We normally think of waterspouts be a tropical phenomenon but they can occur anytime there is an area of low level instability. The following is a report from the National Weather Service in Bismarck, ND:

A waterspout formed over Lake Sakakawea, near New Town, around 10 AM CDT Friday morning, October 9, 2009. The National Weather Service received several reports of a waterspout and other funnel clouds over Lake Sakakawea Friday morning. L.M. Baker, a reporter with MHA Times of New Town, took pictures of the spout and forwarded them to local broadcast media and the National Weather Service. In the pictures it is evident that the spout is over the lake, is in contact with the water surface, and that water is being lifted into the air. The spout was visible for several minutes and dissipated before reaching land. Other funnel clouds were reported over the lake. It was reported that they did not touch the water surface.

A waterspout is, in simple terms, a tornado over the water. Waterspouts are not common in North Dakota, and this one did not form from a thunderstorm.

Several factors contributed to the formation of this waterspout. Low pressure over the state was already producing upward motion and large scale circulation in the atmosphere. Cumulus clouds, associated with a cold front passing through the area, were producing snow showers. The combination of very cold air, in the upper 20s, and relatively mild water, near 60 degrees, caused significant instability in the lower several thousand feet of the atmosphere over the lake. This instability enhanced the instability associated with the low pressure and snow showers and changed atmospheric conditions over the lake. Strong surface winds interacting with the terrain around the lake may have formed a small vortex (rotating air) that translated onto the lake. This vortex may have been stretched vertically by the updraft (rising air) of the snow showers, leading to the waterspout forming. The spout dissipated quickly as it neared land as conditions from the land surface up through the atmosphere over it were more uniform than those over the lake.

This is a good example of the land – water – atmosphere interactions that drive our weather.

The following is snowfall from Nebraska this past weekend:

Snowfall Location County
17.0 8 WNW North Platte Lincoln
16.0 6 NNE North Platte Lincoln
15.0 North Platte - Third and Maple Street Lincoln
15.0 North Platte Lincoln
15.0 Paxton 6 W Keith
15.0 Sutherland 1 N Lincoln
14.0 Mason City Custer
14.0 5 E Westerville Custer
14.0 12 W Callaway Custer
13.0 3 E North Platte Lincoln
12.0 15 NNE North Platte Lincoln
11.8 North Platte - Southwest side of town Lincoln
11.0 Ogallala Keith
10.0 20 S Arnold Custer
10.0 Lewellen Garden
10.0 10 NE Lemoyne Keith
9.6 9 WSW Wallace Perkins
9.0 7 NW Madrid Perkins
8.0 Arthur Arthur
7.0 10 NE Oshkosh Garden
6.2 Grant 3 S Perkins
6.0 Tryon McPherson
6.0 Stapleton Logan
6.0 Grant Perkins
0.5 Mullen Hooker

Crazy winter weather for so early in the season.

Friday, October 9, 2009

Cass County Storm

Numerous reports of wind damage, including a report of 20 homes damaged west of Linden, were reported across East Texas this morning. Above is an image of velocity data taken from the storm as it moved through Cass County. Along the gust front three areas of rotation are seen including a strong TVS (tornado vortex signature). This was the only indication of rotation across East Texas through the entire event. Below is a radar loop of the storm as it moved across the county. If you look closely you will notice an inflow notch were the strong TVS is located in the velocity data above. We will see what hit Cass county after the weather service completes a survey.

Thursday, October 8, 2009

Heavy Rain, High Winds, and Isolated Tornadoes Possible!

A strong cold front will be moving into East Texas Early Friday morning and along and ahead of this front, there is a chance of severe storms, including isolated tornadoes. The image above is of a forecast radar image for 7AM tomorrow morning. Instead of seeing a straight line of storms we see more of a wavy pattern. This is called a line echo wave pattern and in many cases this type of storm system will produce very gusty winds and isolated tornadoes. Many East Texas tornadoes occur in patterns such as the one moving through East Texas tomorrow morning.

In addition to a slight risk of severe weather, heavy rain will be a concern. The amount of moisture available for thunderstorms is unusually high for this time of the year thanks to a strong southerly flow off the Gulf this afternoon. As the cold front moves into East Texas, it will force this warm moist air up and over the front producing widespread heavy rain behind the main line of storms. Some places, mainly north of I-20, could see 2 to 4 inches of rain tomorrow. The image below shows the storm total precipitation that is forecast. Notice the heavy rain forecast across the northwest counties of East Texas, where flooding was a problem in September. We also see a bulls eye of heavy rain across our southeastern counties however, we have not seen as much rain here over the past 30 days so flooding is not as great of a concern.

Now most of the dynamic energy needed for severe weather will move north of our area but there are a few features that jump out at me that could lead to gusty winds and isolated tornadoes. The image below is from a short range high resolution forecast model which shows the amount of instability available as the line of storms enters East Texas tomorrow. Most of East Texas is colored in pink which indicates surface based lifted index values less than -6°C. This is more than enough instability for intense thunderstorm updrafts.

The next image shows there will be lots of moisture available as the dark blue colors indicates dew point temperatures in the low 70. You will also see a couple of small low pressure areas, or mesoscale lows, indicting areas of backed winds leading to low level rotation. With the amount of moisture available, cloud bases will be very low increasing the threat of isolated tornadoes.

There will also be moderate amounts of energy to help with thunderstorm development. The image below shows the amount of surface based CAPE. A large area of East Texas has CAPE values over 2000 J/kg out ahead of the storms, providing additional energy for thunderstorm updraft. What is not shown is much of that energy is confined to the lowest levels of the atmosphere, where there is more spin available. This could help in developing low level mesocyclones which could produce an isolated tornado.

In the final image, the amount of 0-1km storm relative helicity, or the amount of low level spin in the atmosphere, is shown. Most of East Texas is at or above 160 which is enough when you combine the amount of CAPE to produce an isolated tornado. You can also see areas of enhanced 0-1km helicity near the mesoscale low pressure areas. This could really enhance the possibility of isolated tornadoes as the line moves through.

So as this line of storms moves through tomorrow morning, we could see some wind damage and isolated tornadoes. Overall I believe the main threat will be flooding rains but we will be monitoring the situation very closely.

Tuesday, October 6, 2009

Today's Severe Weather Threat

A strong cold front will move into East Texas this afternoon and evening bringing with it the possibility of strong to severe thunderstorms. Right now the main threat of severe weather appears to be strong gusty winds and hail up to the size of pennies. This morning, a layer of warm air just above the surface is putting a lid on thunderstorm development until immediately behind the front. This trend will continue until temperatures this afternoon reach the middle to upper 80s across East Texas. Once these temperatures are reached we will see air lifted ahead of the cold front increasing thunderstorm development. Winds throughout the atmosphere ahead of the cold front are out of the southwest limiting the amount of turning of the winds with height, a big factor needed in tornado development. However, with any additional daytime heating this afternoon, enough instability could form to compensate for the lack of vertical wind shear so we can’t rule out an isolated tornado, especially over the northeaster parts of East Texas.

In addition to severe weather, parts of East Texas today with come close to having dangerous heat index values. Tremendous amounts of Gulf moisture are in place across East Texas and as temperatures approach 90 degrees, especially across our southwestern counties, heat index values will range between 100 and 105 degrees this afternoon. Across most of East Texas heat index values will reach the middle to upper 90s, something we have not experienced in a while across East Texas. Please use caution later this afternoon with any strenuous outdoor activities.

Friday, October 2, 2009

Thursday's Storms

Well, as forecast a line of strong storms developed out ahead of a fast moving cold front Thursday evening. The severity of the storms was not quite as strong as I thought they would be but none the less, most of East Texas was given a spectacular lightning display with heavy rain and gusty winds. Yours truly drove all over East Texas with my chase partner Paul Lachowsky looking for places to take lightning photos. Unfortunately from all the angles we approached the storms, the lightning was hidden from us by very heavy rain and small hail. We got hundreds of illuminated sky capes but very little in the way of actual lightning bolts. A few of our viewers had better luck just staying at home. Tim Ogrodnik was again lucky in capturing a few lightning shoots and was kind enough to send them my way. The shoot of the actual bolts is from him, I need to take lessons.

For the most part the severe weather remained west of our viewing area last night however, there were many large trees blown down and power outages reported across western Upshur County. As for hail, I can vouch for pea size hail in a few locations as the loud ting of hail hitting Paul’s truck greeted us in a few locations.

A couple of interesting photos I took last night included a look at the back edge of the storms with clear skies immediately behind the line. I love seeing the back edge of a thunderstorm with stars all around.

The second photo was a tree that was struck by lightning last night in front of Bullard High School. The tree was still smoldering as you can see the orange glow of the trunk and the rest of the tree smoldering on the ground to the left. Wish I could have seen the bolt hit.

Thursday, October 1, 2009

Today's Severe Weather Threat

We have been discussing the possibility of severe weather today since the beginning of the week and it looks as though everything will come together to produce a widespread, gusty wind event. A strong cold front to our northwest will move into East Texas along the I-30 corridor this evening and sweep through all of East Texas by Friday Morning. The main threat with this line of storms will be gusty winds however, temperature decrease a good deal in the mid levels of the atmosphere so I can’t rule out large hail with this line of storms, especially along and north of I-20. All of East Texas has been outline for a slight risk for severe weather with the greatest chance across North East Texas. Right now it appears the line of storms should form along the I-30 corridor around 7PM, enter the I-20 corridor around 10PM, and the Lufkin Nacogdoches area around 1AM. By Sunrise tomorrow the front should be through all of East Texas and drier cooler air will move in.

We could also see a few isolated storms develop this afternoon out ahead of the squall line. If temperatures can reach the middle to upper 80s we will see enough surface based instability for robust thunderstorm updraft development. Enough wind shear will be present this afternoon for any storm to take on supercellular characteristics. A south southwesterly flow at the surface will minimize the tornado threat but we could see large hail and high winds with these storms as well. So until the front moves through your neighborhood, severe weather is a possibility.