Friday, March 18, 2011

Severe Weather Situation #006 Assessment

The Severe Weather Situation for this evening is now cancelled as the storms are no longer severe.
This is the follow-up assessment to this Severe Weather Situation.

Q and A

Why didn't the National Weather Service predict this?
Unless they were carefully tracking all the parameters, pop-up severe storms are extremely difficult to predict, let alone where. However, there were hints that severe weather could break out.
Hint: A cold front was moving in to the area.
Hint: Best Lifted Index reached levels of -8, which is considered fairly to moderate unstable.

I do feel the National Weather Service could have upped the chances of thunderstorms rather than 10-20%, but their forecast is their forecast, and I will not dispute it.

March 18 RUC Best Lifted Index Forecast Discussion

This is an image of the 00z RUC model Best Lifted Index 12 hours out.
Instability will be present across the South Central US tonight into tomorrow morning. Due to this instability, I would not be surprised to see some spotty strong to severe storms along a cold front and low pressure system currently working their way across the US.
With index numbers down to -6, the atmosphere will be stable, but this is morning after all. Tonight's index numbers go as low as -8, which is considered fairly to moderately unstable. In summary, I do expect at least some more storms to develop, likely pop-up storms and not in an organized pattern.
With values in the 10-15 range above 0 up in the Midwest, I certainly don't expect much of anything to occur tonight into tomorrow morning.
That's all for tonight, keep an eye out for more discussions tomorrow.

March 18 Forecast Discussion

This is an image from the 18z GFS 24 hours out.
Fairly weak low pressure over the Northern Rockies will once again bring a warm up to the Rocky Mountain areas. This low pressure will create windy conditions in the Nebraska area. This is not due to a warm air transport area but a small skirmish against warm and mild air masses.
High pressure in Canada will provide a Canadian cold air mass to move south into the Northeast region. Should current projections play out, that low pressure may be able to begin a battle of severe weather over the Plains into the Midwest.
Down in the south, high pressure will dominate the weather as it sits off the coast, providing for a warm and humid tomorrow. This will be assisted by another high pressure to the east of Florida.
When all is set and done, it is possible there could be a severe weather event in the Plains down south to the South Central regions of the US, back up possibly into the Midwest.
Another Forecast Discussion will be issued tomorrow.

Severe Weather Situation #006

Severe thunderstorms are popping up in Central Texas at this time.

At 7:33pm CDT... GOES satellite data and radar confirmed strong to potentially severe thunderstorms were in Central Texas.

These storms have warranted severe thunderstorm warnings at this time.

Threats out of these storms include... Golf Ball size Hail... and damaging winds in excess of 60 mph.

Specific Concerns...
A severe thunderstorm in ECTOR COUNTY in West Texas is showing a combination on velocity radar indicating that weak rotation may be occurring.
People in ECTOR COUNTY and in WEST ODESSA...ODESSA...GOLDSMITH...NORTH COWDEN...GARDENDALE will be affected by this storm.
This storm is also producing cloud to ground lightning.

Weather Explained: Lapse Rates

What are Lapse Rates?
Lapse Rates is what tells the decrease of temperatures the higher you go in the sky. It is also a measure of instability. The more difference there is between levels, the more instability there is.

How can you tell if the atmosphere is unstable?
Values in images less than 5.5-6 degrees in the images are considered very stable, while values near 9.5 degrees is considered incredibly unstable.
Below is a Sample Image from March 18, 2011.
In this image, we definitely see good instability in the Plains into the Midwest.

March 18 Severe Weather Forecast Discussion

This is a forecast discussion concerning a potential severe weather event early next week.
We do have potential for a severe weather event, mainly across the Central Plains west into the Southern Great Lakes.
I'm sure you are wondering what the heck that image above means.
Well, that image is a picture of the 12z GFS Lapse Rates. A Lapse rate is the temperature change with height. The faster the temperature decreases with height, the more unstable the atmosphere is.
In the Central Plains, there does appear to be a good deal of instability as the temperature may be rapidly decreasing with height.
The Weather Centre feels this time is the appropriate time to issue a Severe Weather Event Image (SWEI). The SWEI is below.

The Weather Centre has outlined the Central Plains to southern portions of the US as the greatest potential for a severe weather event. The Southern Great Lakes and Midwest portions are also under a lower potential for a severe weather event. The image below represents the risk level for the Greatest Potential area on Monday.
This has been a forecast discussion from The Weather Centre.

Slight Radiation reaches Sacramento, CA

Traces of radiation have been found by monitors in areas of Sacramento, California. These traces are from the damaged nuclear facilities in Japan.
At this time the traces are far below levels that would harm humans.