The above radar loop shows a thunderstorm that produced one-half-inch diameter hail and an EF-2 tornado in Manzanita, Oregon, on Friday...leading to several reports of structural damage to houses and buildings and prompting a state of emergency.
Before I go any further, I will quickly elaborate on Tornadoes versus Funnel Clouds versus Waterspouts.
Funnel Clouds: Tornadoes that do not touch the ground.
Waterspouts: Tornadoes over water. If the waterspout continues on land, it becomes a tornado.
Tornadoes: Originate as Funnel Clouds, and sometimes as Water Spouts.
I'll break the Manzanita Tornado down below
A thunderstorm capable of producing a waterspout is observed on Portland Weather Radar offshore of Tillamook County at 10AM Pacific Time. A distinct "Hook Echo" is seen this storm, indicating a strong updraft region (on the left), generally near where a tornado would form. On the right, velocity imagery shows intense rotation within the storm (red & green next to each other), and has place a tornadic vortex signature to indicate this storm as capable of producing a tornado.
The severe thunderstorm begins to make landfall, dropping hail the size of pennies. The "hook echo" is well-established, and the storm takes the shape of a supercell thunderstorm. Supercell Thunderstorms are known to be the most violent, and can contain significant rotation capable of producing tornadoes. In this case, velocity imagery shows this rotation very clearly.
The supercell thunderstorm looses a bit of shape, likely because of the impact it has made with the land surface and local terrain. Nonetheless, the strongest rotation is seen within this storm at this time just offshore of the Town of Manzanita, with "gate to gate" (opposing) shear values of roughly 140 knots, indicating enough rotation for an EF-2 Tornado.
Radar 3-D imagery at the time the Manzanita Tornado was reported. Unlike severe thunderstorms and tornadoes through the Central & Eastern United States, which can grow to over 60,000 feet tall and can destroy several towns in a matter of minutes, thunderstorms, waterspouts and tornadoes in the Pacific Northwest don't appear quite as ominous, but can still be very dangerous. Shown in this image is the "core" of the thunderstorm, generally where the largest hail and rain drops can be found.
The key to this storm that struck Manzanita on the 14th of October was the strong wind shear found within. This is evident by a quick sandwich slice of this storm as it made landfall, showing a diagonal stack with height of the red & pink reflectivity values (known as dBZ). When wind shear allows these storms to diagonally align, this allows for strong updrafts & downdrafts within, enabling large hail, strong wind gusts, and even tornadoes.
Meteorologist Dan Schreiber
Smalltown Weather is a Weather Ready Nation Ambassador
Dan Schreiber is a freelance meteorologist with experience