Below is a more thorough explanation about what our Outlook means. Each term that is used and its definition will is listed below each heading.
A violently rotating column of air capable of producing widespread wind damage. Tornado strengths vary from weak to catastrophic. The Enhanced Fujita Scale can be found below: (Information provided by Wikipedia)
|Scale||Wind Speed||Damage Description||Damage Image|
|EF-0||65-85 MPH||Minor or no damage.
Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over. Confirmed tornadoes with no reported damage (i.e., those that remain in open fields) are always rated EF0.
|EF-1||86-110 MPH||Moderate damage.
Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken.
|EF-2||111-135 MPH||Considerable damage.
Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
|EF-3||136-165 MPH||Severe damage.
Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations are badly damaged.
|EF-4||166-200 MPH||Extreme damage.
Well-constructed and whole frame houses completely leveled; cars and other large objects thrown and small missiles generated.
|EF-5||> 200 MPH||Total destruction of buildings.
Strong-framed, well-built houses leveled off foundations are swept away; steel-reinforced concrete structures are critically damaged; tall buildings collapse or have severe structural deformations; some cars, trucks and train cars can be thrown approximately 1 mile (1.6 kilometres).
The specific time we expect the potential hazard to occur. The timing will get more specific as confidence increases and as we get closer to an event. Something such as MON. AM or FRI PM will be used. If it is expected into the overnight hours then FRI PM-SAT AM will be used.
This is basically how certain or uncertain we are about the hazard to occur. We will use the following values for confidence: VERY LOW, LOW, MEDIUM, HIGH, and VERY HIGH. Confidence generally becomes more certain as we get closer to an event and as model data gets more consistent. It is important to note that forecasting can be very challenging and sometimes even hours before an event there can be low confidence in a hazard occurring.
Where, and how much the potential hazard is expected to occur. The following values are used: ISOLATED, SCATTERED, NUMEROUS, and WIDESPREAD. These terms can be a little confusing, so here is a general breakdown of what they mean:
Isolated means the hazard may appear now and then in some areas, but not everywhere. It will also be brief and short-lived. For example, a damaging wind event may occur in northwest Alabama then again in southern-middle Tennessee. This is a good example of an isolated severe thunderstorm. A pop-up tornado may occur in one place and then another.
Scattered means it will happen in quite a few places but again not everywhere. Another example: Large hail and damaging winds occurred in Decatur and Athens, but not in Huntsville. 2 severe thunderstorms were scattered, and did not last very long. One or two tornadoes may touch down but given the severe weather parameters they should not last very long and should not be significant.
Numerous means quite a few areas have the potential to see the hazard. Some of the hazards may be long-lasting, depending on the hazard. For a tornado, it may be a little bit stronger and last a little longer, and there may be quite a few severe thunderstorms.
Widespread means everyone has a pretty high chance of seeing the hazard, and the hazard may be long-lasting and significant.