Tornado Threat Case Powerpoint

Hurricane Warning
Hurricane Warning Seasonal Forecast
The 2008 North Atlantic Hurricane Season is rapidly approaching now, with less than 3 months until the season starts on June 1st. This means it is time for the second annual Hurricane Warning Hurricane Season Forecast. Last year’s forecast was fairly successful, with a call for above average activity with 11-14 named storms, 6-9 hurricanes, and 3-5 major hurricanes. There were 15 named storms storms in actuality, with only 14 fully tropical storms, 6 hurricanes, and 2 major hurricanes.

El-Niño Southern Oscillation (ENSO)

The first factor that will be considered for the 2008 hurricane season forecast is ENSO. ENSO is a large scale oscillation of ocean temperatures in the Pacific between warm and cold that has effects on the weather across the globe. In recent months, a strong La Niña has formed, which is the cold half of the ENSO cycle. The strong La Niña can be seen on the chart below; it is the area of cold water anomalies stretching from South America to the western equatorial Pacific.

A La Niña usually results in lower wind shear across the North Atlantic, providing an environment more favorable for tropical cyclone formation and propagation. The question then arises, will the La Niña continue through the hurricane season? My forecast is for the La Niña to continue into the hurricane season since it is very strong at this point but, it should start to weaken towards ENSO neutral (a relative lack of ocean temperature anomalies) towards the latter part of the season. The models that are used to predict ENSO (below) are in agreement with this assessment, although it should be noted they are subject to large errors.

Sahelian Rainfall Anomalies

The Sahel of Africa is considered a birth place of tropical cyclones. Every year, dozens of tropical waves depart Africa for the Atlantic from this region, sometimes becoming monstrous Cape Verde hurricanes. This has spawned research into the rainfall patterns of the region, in order to determine if they have any effect on tropical cyclone formation in the Atlantic. Sahelian rainfall has been below average during the last year over the southern Sahel, with the northern Sahel experiencing near normal to even above normal rainfall. In the figure below, I have put a black circle around the coastal region of the Sahel because that is the part of it which I believe is the most relevant to tropical cyclone formation. My theory is as follows. Drier than normal conditions over the coastal Sahel cause easterly waves to become drier and hotter just before they enter the Atlantic. This results in a greater temperature difference between the wave and the water, which can then help the wave become more significant and perhaps provide the extra nudge that will result in it becoming a tropical cyclone down the road. Of course, a dry Sahel is a double edged sword, and it will likely contribute to Saharan Air Layer (SAL) outbreaks. However, since the northern Sahel is near normal to wetter than normal, the more sandy part, maybe that will inhibit SAL outbreaks at the same time. It is up in the air, as always, on how much of an affect the SAL will have on tropical cyclones in the Atlantic this year. This is because the SAL likely depends on other factors than rainfall in the Sahel, such as the strength and position of the Azores high.

Normals and Adjustments Based On Current Factors

There are normally 10 named tropical cyclones in the Atlantic, 6 hurricanes, and 2.5 major hurricanes (according to the National Hurricane Center). The first adjustment for this season that I will make is +2 named storms since in recent years we have been finding tropical cyclones that we wouldn’t have normally found in the past, due to their size and sometimes remoteness. The next adjustment will be another +2 named storms due to drier than normal Sahel conditions. I will finally add another +3 for La Niña. Normal ratios will then be used to determine the amount of hurricanes and major hurricanes.

The Forecast

Named Tropical Cyclones: 16-18
Hurricanes: 8-10
Major Hurricanes: 3-4

Essentially I’m calling for a well above average season, probably more active than last year.

Tornadotony.com
Day 1 Convective Outlook
Valid from 6 AM CST Monday, March 3rd, 2008, to 6 AM CST Tuesday, March 4th, 2008
Issued at 11:00 PM CST Sunday, March 2nd, 2008

…There is a High Risk of severe weather in Much of Louisiana, West-Central Mississippi, and Souteastern Arkansas…for the threat of an outbreak of large, violent, long-tracked tornadoes…

…There is a Moderate Risk of severe weather surrounding the High Risk, including Extreme Eastern Texas, Western and Southern Louisiana, Southern Missississippi, Western Alabama, and the Western Florida Panhandle…

…There is a Slight Risk of severe weather surrounding the Moderate and High Risks, and extending northward to the Lower Ohio River Valley…

***A MAJOR SEVERE WEATHER OUTBREAK IS LIKELY OVER THE LOWER MISSISSIPPI VALLEY TOMORROW, WITH STRONG TO VIOLENT TORNADOES, LARGE HAIL, AND DAMAGING STRAIGHT-LINE WINDS LIKELY***

***LOCATIONS IN THE HIGH RISK INCLUDE: ALEXANDRIA LA, MONROE LA, NATCHEZ MS, BATON ROUGE LA, VICKSBURG MS, JACKSON MS, MCCOMB MS***

Synopsis
Strong positively tilted trough currently amplifying across the Great Plains. Sfc cyclogenesis will occur along the Gulf Coast in advance of the trough. Strong cold front will slow down slightly as cyclone lifts northeastward, dividing cold air to the west and north and warm, moist air advected in to the south and east. Warm moist air will be advected in by a 60 kt LLJ overnight and over the day tomorrow. Strong shear at all levels, along with deep boundary layer moisture and moderate instability, will create an environment condusive for strong, long lived tornadic supercells tomorrow across the MDT and HIGH risk areas.

Lower Mississippi into the Southeast
Thunderstorms, some possibly severe, should be ongoing at the beginning of the period in Eastern Texas. Further east, significant low level moisture advection and cold mid level temps will help with destabilization, contributing to SBCAPEs invof 500-1500 J/kg in the MDT/HIGH risk areas. Any insolation will further increase destabilization, with values possibly reaching 2000J/kg in the warm sector. The storms should move eastward and break up into more discrete storms in Louisiana as dynamic forcing shifts northward into AR. The strong LLJ will contribute to curved, long hodographs, supportive of strong to violent tornadoes with the supercells that move into the area. Further south and east, additional supercells could develop in the weakly capped free warm sector, and the hodographs support significant long track tornadoes with these as well. 0-1km SRH of 250-500m**2s**-2 and deep-layer shear of 70kt will likely be achieved across the High Risk region, which, with weak linear forcing, should lend to conditions favorable for long-tracked supercells capable of producing violent families of tornadoes over long distances.

Activity should slowly recongeal into a squall line further east in central Mississippi as base of longwave trough induces strong height falls over the cold front. Though instability may wane a bit with loss of daytime heating, continued strong low level shear will continue the threat of strong tornadoes overnight. In addition, minimal inhibition across Alabama will lead to the possibility of additional pre-frontal convection. Any storms that form ahead of the squall line will likely produce strong-violent tornadoes. However, uncertainty in exact eastward progression of front and of coverage of overnight prefrontal activity precludes and eastward extention of the high risk at this time.

Further north, linear forcing will promote a squall line that will push eastward across Tennessee. Given strong kinematic fields, damaging winds are possible with this line, even with minimal instability. An isolated tornado or hail event also cannot be ruled out.

This is a very dangerous situation. Please keep apprised of the latest severe weather developments in your area.

THIS IS NOT AN OFFICIAL FORECAST. Please consult the Storm Prediction Center or your local National Weather Service office for official critical and life-saving information.

Jim and Tony

Day 1 Severe Weather Outlook
06Z 02 Mar 2008

There is a MDT risk of severe thunderstorms for SW OK and N CTRL TX.

Surrounding the MDT risk area, there is a SLGT risk of severe thunderstorms for MUCH OF OK, EXTR ERN TX PANHANDLE, and much of N CTRL TX.

SYNOPSIS: Water vapor imagery and upper air analysis indicate a lead shortwave invof NM/AZ/MX border, being kicked out by an amplifying longwave trough over the Intermountain West. The LLJ is expected to veer and strengthen tonight. Deep moisture profiles already exist in much of the risk area with a strongly capped mixed layer above the moist layer, due to a strong 700mb dry punch. Moisture will continue to advect northward as the longwave trough amplifies and moves eastward. In advance of the trough axis, lee surface cyclogenesis will occur in western TX during the day tomorrow. The combination of deep moisture and strong dynamics will set up a chance for a localized severe weather event in portions of OK and TX tomorrow.

OK & TX: In response to the deepening sfc low, a dryline will sharpen across western TX tomorrow, and then mix eastward across the day. Meanwhile, to the north, a cold front will move southward, reaching possibly a CHI-STL-FWD line by the end of the forecast period. An elevated mix layer will keep things well capped and preclude significant morning convection from clouding up the warm sector. The strongest LLJ forcing should remain well to the north and east of the slight risk area. Destabilization should occur through the day; modified forecast soundings indicate SBCAPE’s around 1000-1500 J/kg with cold 500mb temps allowing for steep mid level lapse rates. As this occurs, increased dynamic forcing from the longwave to the west, an erosion of the cap, and convergence along the dryline bulge invof the Red River, will allow for storms to form in the early evening hours. Elongated, curved hodographs will allow for the potential of tornadoes with discrete supercells. As time goes on, the surging cold front will overtake the dry line, resulting in a forced squall line by the end of the period. Forecast hodographs still indicate some tornadic potential with embedded supercells or any storms that manage to form ahead of the line.

Some uncertainties still exist. Believe the GFS has a better handle on the cap strength and the initial shortwave trough, based on obs. A stronger initial shortwave could move by in the morning and leave subsidence in its wake, and the cap could fail to break in the early evening until the squall line is forced by the surging cold front. Should this scenario occur, the tornadic risk would be drastically reduced. Any drastic reducing of insolation will strengthen the cap. Attm, a 15% nonhatched tornado risk seems to be the best way to go.

FURTHER NORTHEAST: Forecast soundings indicate some CAPE all the way up to Chicago. Convergence along the cold front could spark some strong thunderstorms. These thunderstorms should remain linear and have slow eastward progression due to the orientation of the shear vector, especially in MO and southern IL. The strongest updrafts will have the potential to produce some marginally large hail and some gusty winds.

DISCLAIMER: NOT AN OFFICIAL FCST… FOR THAT STUFF GO TO SPC.

FORECASTER: Jim

Tornadotony.com
Day 2 Severe Weather Outlook
Valid from 6 AM CST Monday, March 3rd, 2008, to 6 AM CST Tuesday, March 4th, 2008
Issued: Saturday, March 1st, 2008, at 11:00 PM CST

There is a Moderate Risk of severe thunderstorms for far southeastern Texas, much of Louisiana, southeastern Arkansas, most of Mississippi, and western Alabama.

There is a Slight Risk of severe thunderstorms surrounding the Moderate Risk and extending northward in southwestern Tennessee.

Mid-South/Lower Mississippi Valley
The stage will be set for a potentially violent severe weather outbreak from Monday morning through Tuesday morning.

Intense convection, in the form of a squall line and possible embedded supercells, will be ongoing at the start of the period from western Arkansas by 12z Monday. Further south and southwestward, the atmosphere will be capped prior to frontal approach. As the front approaches, it is anticipated that convection will develop along it. Given that forcing will not be terribly strong, a mixed mode of embedded supercells and bows are possible, with damaging winds and tornadoes. Although it looks most likely that this will be in western or central Louisiana at this time, I have opted to pull the moderate risk into southwestern Texas as the models trend slower with the system.

The greatest threat to life and property will be ahead of the squall line in the free warm sector Monday afternoon and night. Minimal capping and inhibition will be in place here. SBCAPE of 1500-2000J/kg or more are likely up to about Jackson, Mississippi, with 500-1500J/kg SBCAPE possibly extending as far northwestward as Pine Bluff, Arkansas. These moderate-strong instability values will be in place in an environment with extreme wind shear through all levels of the atmosphere. Conservative estimates indicate 0-1km SRH values of 200-400m**2s**-2 with 0-6km shear of up to 70kt in the Moderate Risk region. The region will also be in the right-front quadrant of the jet disturbance, which will lend to lesser VV, lesser forcing, and greater tendencies for cells to remain discrete. An outbreak of intense supercellular thunderstorms is anticipated ahead of the squall line, with very large hail up to softball-size, winds up to 80 MPH, and strong to potentially violent tornadoes all possible.

As the activity continues overnight, the squall line is expected to accelerate eastward. As instability diminishes toward morning, the line should overtake discrete convection and progress to just east of the Alabama-Georgia border by 6 AM Tuesday. A few tornadoes and damaging winds will still be possible with the line.

THIS IS NOT AN OFFICIAL FORECAST. Please consult the Storm Prediction Center or your local National Weather Service office for official critical and life-saving information.