When should you chase?
Early Season vs. Late Season Storm Chasing
Many people are under the misconception that storm chasing begins and ends
in the month of May when, in fact, this is not the case. It is generally true
that, on average, the severe storm activity shifts northward as summer
approaches. However, the severity does not generally decrease. Many times supercells
and tornadoes intercepted during the late spring and summer can make your
chase year successful, ask any veteran chaser. Consider a few points about
late season chasing:
1) During the early spring, cold fronts sweep through the plains
removing most of the low-level moisture so crucial for severe storm
development. It can take several days for sufficient moisture to return in
the wake of a strong cold front leaving chasers "high and dry"
for the duration. If the "wrong" weather pattern is in place,
one could suffer through several such cold air outbreaks earlier in the
spring. The result would be very little severe weather activity in April
and May. A few years where this occurred were 1983, 1992, 1993 and 1997.
Cold air mass intrusions like these decrease in both frequency AND
intensity as the spring matures resulting in more potential chase days.
Furthermore, in the late spring and early summer (June through July) weak
cold front passages actually create an environment very favorable
for supercell (rotating) storms in the high plains (the higher terrain of
eastern Colorado, Wyoming and western Nebraska) a day or two after the
front moves by. In fact, such a scenario is the reason why so many
tornadic storms occur in this region from June through July and often
through the remainder of the summer months. Email a few storm chasers and
ask them where they like to be in June and July!
2) The ultimate source of the low-level moisture so crucial to severe
storm development and intensity, the Gulf of Mexico, is much warmer in
late spring than earlier in the year. Hence, much more moisture is readily
available for storms in the late spring and this moisture can easily take
up residence in the high plains, northern/central plains and Midwest where
the high-altitude westerly winds are prevalent by spring (these west winds
at high levels of the troposphere are also very important for severe storm
3) Since the prevailing westerly winds (often associated with the jet
stream) at middle and high altitudes tend to weaken during late spring,
storms move more slowly thereby making them much easier to intercept.
During the rare early and middle spring tornado outbreaks, these winds can
exceed 90 mph resulting in storms racing northeastward at 40-60 mph. This
means you may not be able to catch a storm on such a day or, if you
position yourself just right, you might get just one shot as the storm
races by. Moreover, since weather systems are moving from west to east
more slowly in June, often times it is possible to see severe storms in
the same area for several days in a row.
4) Many notable storm chasing events have occurred in June and July
during our 13 years of chasing. Just to name a small fraction of the very
a) June 1 - June 17, 1990: Multiple severe tornado outbreaks over a
vast region of the plains and Midwest.
b) June 15, 1992: We chased a massive storm in northern Kansas for 7
hours. This storm produced over 30 tornadoes during its life time and we
filmed 9 of them.
c) June 7, 1993: Saw a large tornado (1.25 miles wide at the ground)
near Sioux Falls, South Dakota moving north at 55 mph.
d) June 2-9, 1995: The best week of storm chasing ever for me and
many other chasers. All the storms occurred in west Texas and the Texas
panhandle including many F2-F5 tornadoes.
e) July 17, 1996: A splendid supercell that developed near Webster,
South Dakota which produced a very photogenic tornado.
f) June 11, 1997: Large tornadoes in the eastern Texas Panhandle.
g) June 13, 1998: Major localized tornado event in Oklahoma City.
Overshadowed by the once-in-a-lifetime May 3, 1999 outbreak.
h) June 20, 1999: Classic tornado in eastern Montana on Tour 4.
i) July 2001: Numerous significant supercells and tornadoes occur
throughout the plains.
And countless other incredible storms which fill the video tape libraries
of countless storm enthusiasts.
Are there disadvantages to chasing in the late season? Sure! Here is a
table which lists the primary advantages and disadvantages of Early versus
Late season chasing:
Early Season: April 1 through May 31
Late Season: June 1 through July 31
|Jet stream is usually strong leading to more frequent
||Jet Stream may contort itself into a configuration
unfavorable for storms and drive cold fronts into the gulf.
||Jet Stream is weaker so
storms move slower and are easier to catch than their early season
||Jet stream may disappear completely meaning nothing but
uninteresting summer thunderstorms.
|Often time most severe thunderstorms occur within a few
hour drive from Oklahoma City.
||Many storm chasers take their annual vacations in May,
so extreme traffic congestion occurs around storms.
||Can have several days of great storms in the high plains
meaning little travel. Less chasers are out meaning no traffic
Roads are sparse in the high plains. There are
usually several areas which look equally favorable making for
|The Mexican plateau and the higher terrain of New Mexico
are not that hot, so "capping" is frequently less of a
||Sometimes there is too much thunderstorm activity
(inhibits tornado formation) in one area due to a lack of a cap
||Often there is tremendous instability (energy for
storms to grow- related to low-level moisture availability).
||Sometimes the cap is much too strong so you just get a
|"Sloshing dryline" sets up many years in the
Texas Panhandle resulting in classic supercell events.
||Some years, the dryline never makes it out of New Mexico
until June. Active dryline years results in a record number of
chaser's jockeying for position.
||Some of the most prolific Texas Panhandle tornado events
have occurred in June.
||It is easy to miss the transition from southern plains
to northern plains resulting in a "big" busted chase or two
as the activity shifts northward in early to mid June.
1.) The cap is difficult to explain, but briefly, it is
frequently associated with a layer
of relatively warm and dry air formed over the elevated deserts (2-4 km above mean
sea level) of New Mexico, Arizona and northern Mexico during springtime as
the sun heats this region. Because it's so hot at its base, this layer of
air is characterized by convective overturning, which homogenizes - or
mixes the layer - through its depth. Thus, this airmass is often called
the "elevated mixed layer" (or EML). The prevailing southwesterly winds often blow
the EML out over the lower terrain of the Great Plains and
Midwest. This provides an effective barrier to thunderstorm updrafts but
this barrier is sometimes overcome if the low-level moisture, warming and
lifting is great enough. When this happens, big severe storms develop.
2.) The dry line is intimately related to EML. It is the leading edge of
the desertified air mass AT THE GROUND
and is often a key player in severe storm formation in the plains. The dry line exhibits a "diurnal cycle" (night and day) whereby it
moves eastward during the day (due to earthward mixing of high-level
westerly momentum within the EML) and retreats at night. Such a cycle often
repeats itself for days at a time, thus the term "sloshing dryline"
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