Tuesday, March 22, 2011

March 22 Forecast Discussion

Low pressure will be moving east into the Ohio Valley with a warm front and trailing cold front. The cold front will definitely be the maker of the severe storms expected tomorrow over the Ohio Valley. The warm front will be dragging warm and humid air into that area from the Florida section of the US.
Additionally, with a defined warm front area, storms will be likely across the cutoff of the warm front on the East Great Lakes.
Cold air will be dragged down from Canada following the cold front and storms. The cold air will try to wrap around the low pressure but will run into the stronger force of the warm air. I would not be surprised to see some storms develop in those areas as well.
High pressure in the Rockies will keep that area high and dry, however low pressure off the Northwest coast will keep some areas wet and cloudy, a common climate for that area.
Intense blizzard across the Upper Midwest will move off and go into the Eastern Great Lakes.

March 22 Current Thinking

This Current Thinking is due to the severe weather occurring out west.

These storms HAVE already produced MULTIPLE tornadoes.
However, these storms are weakening.

Wind shear is holding these storms together, thus also keeping an isolated tornado chance in play for likely much of the night.
Should current thinking continue, hail chances would reign as the main threat as this storm complex goes into the Midwest more.
A squall line has developed, and it is moderately strong at this time.
It is unknown if this is the peak strength or if it will increase.
We will see as it goes on.

POTENTIALLY DANGEROUS SITUATION MARCH 22

This is a PDS bulletin.

PARAMETERS INDICATING EXTREMELY SEVERE WEATHER ARE RISING TO HIGH LEVELS.
BELOW IS THE CRAVEN/BROOKS SIGNIFICANT SEVERE WEATHER PARAMETER. VALUES ABOVE 20 (20,000) ARE CONSIDERED CORRECT CONDITIONS FOR SIGNIFICANT SEVERE WEATHER.
VALUES AT 90,000 ARE CONSIDERED EXTREMELY DANGEROUS.
NEXT, WE WILL SEE THE SIGNIFICANT TORNADO PARAMETERS. VALUES GREATER THAN 1 ARE FAVORABLE FOR SIGNIFICANT TORNADOES WITHIN THE HOUR.
WE SEE THE VALUES AT 3, INDICATING A DANGEROUS SITUATION.
FINALLY, WE WILL SEE LAPSE RATES. VALUES UP TO 9.5 ARE ABSOLUTELY UNSTABLE IN THE ATMOSPHERE.
IF YOU ARE IN ANY OF THESE DANGEROUS AREAS IN THESE IMAGES, PREPARE AT ANY TIME TO TAKE IMMEDIATE COVER.

March 22 Heavy Snow Potential Special Bulletin

This is a special bulletin about a potentially heavy snow period for about 3 hours in North Wisconsin.
Below is an image from the University of Illinois Ensembles.
This is maximum reflectivity, meaning that is the most that would show up on radar. Notice how intense that is in Wisconsin. That could pose some extremely serious problems.
However, we must also know what the predicted AVERAGE is supposed to be.
Below is the average of that same member of what the average is supposed to be.
Even so in the average above, it is still a dangerous situation.
Please be careful out there tonight, as Duluth is supposed to receive over 1 foot of snow in a blizzard.

March 22 Severe Weather Overview- Happening Now

This is an overview of the severe weather due to happen over the course of today.
We will start with how unstable the atmosphere will be, since that plays a big role in severe storms.

BEST LIFTED INDEX
The Best Lifted Index was very surprising this morning. Values of this sort are usually found around in Mexico. Below is the latest image of right now from the RUC.
First off, notice the value of -12 out in Iowa. That is an extremely delicate situation. Should severe storms enter that area with the value of -12, I would definitely expect very large hail and strong tornadoes. Luckily, that will not happen. It may happen this evening, but not right now.
Let's fast forward 12 hours to when the severe weather is projected to actually happen.
First off, we do see a weak definition of a squall line. However, the SPC actually cut off the tail end of the outlook, leading me to less and less believe the idea of a squall line throughout the Plains and south central US. It looks more like a small squall line as well as clusters of disorganized storms.
Anyhow, it appears values of -6 and -4 will be in the severe area.  Main concern will still be in Iowa, where maximum values appear to be -8. Overall, this is definitely a situation to watch for Iowa.

LAPSE RATES
Another indicator of instability is lapse rates. Remember, values at 9.5 are 'absolutely unstable'. Below is the RUC image form right now at the time of publishing.
Lapse rates are temperature drops with height. We see an extremely unstable situation in Nebraska at this time, with values from 8.5 to 9 degrees.
Next, let's fast forward 12 hours to the severe weather time frame.
These values aren't very impressive where the storms are forecast to occur. However, still back in Iowa and Nebraska, the lapse rates will remain very high and unstable.

FORECAST RADAR REFLECTIVITY
This is basically what the radar is forecast to look like in the near future. Let's take a look 10 or 12 hours in the future using the RUC to see what the storms will look like.
That line extending south was actually a weak squall line in hour 10. However in this image, hour 12, we see the storms only beginning to affect the area. This RUC method has been right in some situations while wrong in others. However, this looks like a good bet, but I would add in areas of yellow if I could to this image. Below is an animation of a WRF run from Wright Weather.
This animation is an overall good tool to use as a predicted radar lookout 48 hours in the future.

STORM PREDICTION CENTER'S OUTLOOK
So these are the SPC's outlooks for today's severe weather. The images, in order, are the overall risk, hail risk, tornado risk, and damaging wind risk.



It appears to be no coincidence that the tornado risk and damaging wind risks are in the same areas, as atmospheric turbulence can create damaging surface winds as well as violent tornadoes. The Hail risk is also most concentrated in the wind/tornado threat, leading me to believe any storms that develop in that area will have strong lifting, meaning it will be able to throw water droplets high enough into the air to freeze into hail. That hail risk also extends into Illinois and the Southern Great Lakes. It appears that, although that lifting mechanism will weaken as the complex moves off, that lift will remain able to generate small hail.
This has been an overview of a Happening Now situation. These are issued when a weather event is due to happen today.