Tornadoes in California a Rarity? Not so!
If you were to ask the average Californian whether tornadoes were a common event in California, you’d likely receive an odd stare before a definite answer of “no.” However, this answer is completely incorrect, as tornadoes are much more a common phenomenon than many would think, with about six to seven being reported each year. Although California tornadoes are not quite to the scale and intensity that much of those in the midwest are recorded to be, they are still tornadoes nonetheless and pose just as much a danger, capable of uprooting trees, ripping off roof tiles, and knocking down power lines.
So, how often do tornadoes in California occur, and when? California receives the majority of its severe thunderstorms and tornado warned or watched storms throughout March and April. As the springtime seasons begin, temperatures begin to warm, though the wintertime low pressure systems that bring California’s rain have not quite subsided. These conditions create a favorable environment for convective storms from which severe weather such as lightning, hail, heavy rain, and even tornadoes may form. The vast majority of these tornadoes form throughout the California valley, with the exception of the Los Angeles area along the coast.
For the tornadoes that do form within the California valley, a significant amount of these occur in the northern Sacramento valley area in Butte County, California. From 1970-2014, Butte county had a recorded total of 16 tornadoes, though this number is outdated as Butte county has since experienced a few more tornadoes in the past few years. None of these tornadoes have ever exceeded an EF2 rating, but have nonetheless produced significant damage with one producing millions of dollars in damage to crops throughout the area.
Tornadoes throughout California, although few, are nothing new nor rare. Weak and short-lived, they often do not cause much damage, but nonetheless can still pose a great danger to those living within the affected areas.
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© 2018 Weather Forecaster Alexis Clouser
How does Weather Impact Spring Migration? (Credit: BirdCast, TropicalTidbits, codmeteorology, RadarScope)
Photo Credit: Pixcove
Discussion: Many of us understand that radars are used to monitor hydro-meteorological phenomena, whether that be rain, snow, hail, and anywhere in between. However, radars do not just focus on capturing weather. Anything that flies into the range of the radar beam can appear as reflectivity. Migratory birds are one non-meteorological feature that are commonly seen on radar.
A small group of birds on radar can show up as what appears to be small rain showers whereas large migratory groups are visualized as a larger mass of light to potentially moderate rain. There are other radar parameters that can be used to decipher actual rain showers from birds such as correlation coefficient (a measure of how uniform the object being observed is) where typical numbers at or below 0.8 are common for birds with rain closer to 1.
Here is an example of birds on radar migrating from Cuba to Key West, FL. The returns on the radar are close to 5-10 dBZ perhaps around a few lower teens in a few spots. This relates to a light to perhaps nearing a low-end moderate migration. The radar reflectivity correlation to the size classification of a migration is according to Gauthreaux et al. (1999) and stated on birdcast.info/research/review/.
As mentioned before, typical correlation coefficient values around 0.8 and below relate to objects other than rain. As seen above the cc values are near 0.8-0.9 and lower in some areas signifying a migration of birds from Cuba to Key West, Florida.
There are different weather factors that can trigger a bird migration. The major assisting factor is the wind direction and speed. Birds favor a tailwind regardless of the time of the year. During the spring migration, when birds are traveling north across the United States, a southerly flow is preferable. The forecast from the website birdcast.info shown above (this website has other information including a live map) the night of April 9th into the 10th features a sizeable migration from Texas on northward into the Mississippi Valley. The GFS MSLP forecast image for 06Z April 10th (below), during the nighttime hours, shows a strong low pressure across the central High Plains. Notice the similarities between the forecast medium migration region and where the pressure gradient (tight, packed close together lines running southwest to northeast) aka relatively strong southerly winds reside (Texas, Oklahoma, into the Mississippi Valley). This tailwind will trigger a low and in portions a medium migration according to the forecast.
Precipitation can act as a limiting factor. This is where uncertainty develops when forecasting migration. On the previous Birdcast image, the precipitation is outlined over the forecast. The site mentions where precipitation and favorable migration conditions coexist, variability and significant unknowns are present in the forecast.
Above, a “flying eagle” supercell typically known as a V-Notch. The shape looks like an eagle with the wings pointed upwards. Image courtesy of @tornadotrackers via radarscope. Radar imagery valid June 19, 2018.
On a loosely related note, there is a type of supercell that looks like a bird on radar. The image above shows a strong supercell thunderstorm with a configuration on radar that is typically known as a V-Notch or “Flying Eagle”. This is typically present with the strongest and tallest updrafts. Radar has great application to not only detecting powerful and dangerous supercells like the one shown above but other important features such as bird migratory patterns.
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©2019 Meteorologist Joe DeLizio
DISCUSSION: As far as low-pressure systems go, there is little to no doubt that the 2 April 2019 Nor’easter will go down in history as one of the more impressive coastal storms of all-time. Despite the fact the worst of the impacts remained just offshore, this storm system still most certainly “strutted its stuff.” More specifically, as the developing storm system underwent a period of rapid intensification, there were successive rounds of impressively intense convection which consequently developed both just offshore and along the immediate coastal regions of North Carolina. Even with the storm being as intense as it was becoming during the evening hours of 2 April, there was still somewhat of a “gift” to the immediate coastal regions based on the fact that the majority of the system’s core circulation remained just offshore.
Thus, as a result of the bulk of the most intense part of the rapidly intensifying low-pressure system remaining just offshore from coastal North Carolina, the strongest winds, largest waves, and the heaviest rainfall also remained offshore for much of the night. However, even with the worst of the nor’easter remaining just offshore, there was still very substantial and impressive convection offshore during the evening and late evening hours as shown above (courtesy of imagery provided by Mark Nissenbaum). As the convection continued to intensify with time (as shown above), you can also see how the deepest convection also gradually experienced a “curling effect” in a cyclonic fashion in accordance with the corresponding wrap-up of this extra-tropical cyclone.
This became even more impressive with time since as the storm intensified and wrapped up (or deepened in other words) with time, the core part of the system’s circulation took on an appearance that what somewhat resembled a supercell thunderstorm at certain points. To be clear, supercell thunderstorms are more typically Spring and Summer-time convective storm types which form most often across the U.S. Plains states. This just goes to show that even a large low-pressure system such as a nor’easter can take on appearances akin to much smaller mesoscale atmospheric phenomena if the atmospheric dynamics are truly profound and come together just right.
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© 2019 Meteorologist Jordan Rabinowitz