I’ve
seen several very recent discussions about why NWS Albany didn't issue or were
late to issue a tornado warning on Wednesday's storms. It always seems many are eager to go into a
National Weather Service-bashfest.
First
of all how does the warning process develop?
It
starts with the Storm Prediction Center (SPC) located in Norman, Okla. The SPC
is the one who determines when a tornado
watch will be issued, and where and which
counties will be included. The
SPC will communicate with the local NWS field offices involved in the watch
area. After this, the tornado watch is issued.
Once the watch has been issued, it’s up to the
local field office to expand it or cancel it all together, if they think the
watch is unnecessary. If there is a need for a severe thunderstorm to be
warned, that is up to the local National Weather Service. It is also up to the
local field office to issue a tornado warning if the conditions in the storm in
question warrant it.
There
are many reasons why tornadoes can go unwarned. Here are the major reasons.
1) I've
been inside the Storm Prediction Center, National Severe Storms Laboratory, and
a few local NWS field offices. Everyone in these places works hard and has long
hours...this is especially true for the local NWS operational forecasters. They
are often understaffed and their shifts are long,. For over a week the
Northeast has had a lot of severe weather; when it is like this, the
forecasters can work 80 hour weeks or
longer. .So it's not uncommon that forecasters can become significantly
fatigued on their shifts. This can lead to human mistakes and errors. that lead
to missing things including a potential tornado.
2) In 2013 the NWS intruded changes in an effort
to reduce false alarms. The changes
included both technological and how personal react. The radar algorithms work
differently to allow for minute by minute input of observations. The goal of lessening
false alarms means that forecasters wait until higher confidence exists before
issuing warnings in order to decrease the chance they could be wrong. Many times NWS forecasters now
wait until a tornado has begun before issuing a warning more often than
prior to this new policy, As radar technology get better and better, more low key, generally weaker tornadoes are
seen than ever before. These newly visible low-end tornado signatures on
radar initiate low levels of confidence for forecasters trying to pick out
which signatures features on radar are tornadoes, and which are not. These
minor tornado possibilities often do not get warned due to lower confidence.
3)
. Sometimes, the radar simply cannot
see them. The Earth's curvature causes radar beams to slope
upward after they travel a lengthy distance. This may cause the radar beam
to cut through the top of a storm. As a result it is often too high to discern
if the storm is rotating.
4) Most of y'all know that traditional tornadoes develop from a
rotating thunderstorm (also known as a mesocyclone) When a thunderstorm has a
deep persistent rotating updraft they are called a supercell thunderstorm. Most
of the time a traditional tornado will drop out of a wall cloud under the
parent thunderstorm and lower to the ground. Once it touches the ground it is
called a tornado. Sometimes, tornadoes
develop from the ground up. This type of tornado is called a landspout.
5) A landspout requires a
towering cumulus cloud to be present over a boundary of converging winds near
the ground. This is typically found along a cold front or a gust front. The
converging winds from different
directions collide with each other; this results in a small area of spin.
sometimes this spinning vortex of air will reach the base of the cloud, once
that occurs a landspout tornado is born. Landspouts are typically weaker and
shorter lived than their traditional cousins.
Landspout tornadoes typically last only a few minutes; since a doppler
Radar scan normally takes 4-6 minutes; the landspout could have formed and
dissipated before the scan was completed.
Because radar can’t see rotation at ground level, many times a landspout
can go undetected. When dealing with landspouts a tornado warning is often
instituted late if at all.
6) Then there are QLCS tornadoes. When thunderstorms become
organized, they are called a Mesoscale Convective System (MCS) A QLCS (Quasi Linear
Convective System) is a type of MCS, where the complex of thunderstorms form a
squall line. They typically form along a cold front. The armchair meteorologist
reading this, know the squall line contains heavy rain, strong gusty winds,
frequent lightning, and hail. Sometimes
brief little spin ups can occur along the leading edge of the squall line, . These spin ups are called QLCS tornadoes. This
type of tornado is often short lived and
weaker than traditional tornadoes, but not always. While they can form and dissipate quickly and be
hard to detect, they aren't landspout tornadoes. This is because they form differently. For a QLCS, as the cold front advances, it
lifts warm air out ahead of it. which in turn forms the rain line, as the squall
line develops the rain cools the warm air causing it to sink. This creates what
is called a cool pool. The cool pool produces strong winds. These winds cause
the squall line to bow out. The cold and
dense winds from the bowing line forces warm air to rise (loft); this process
empties the space behind the bow, allowing a small area of low pressure to
form. This area of low pressure draws in drier air above the squall line. This process continues as everything develops
and accelerates. This results in a tilted updraft to form over the top of the
cold pool. As this escalates a rear
inflow jet forms. As the process rapidly
intensifies, vertical stretching of the updraft, which can lead to tornado
formation. Sometimes tornadoes can form
within a subtle weak echo region on the forward flank of the bow containing
high precipitation supercell characteristics. There can also be so called bookend
circulations at the tips of the bow echo that can also lead to Tornado
occurrence. QLCS tornadoes are most
likely to form when the bow is intensifying. QLCS tornadoes are difficult to detect and
often can go unwarned.
7) Technical difficulties. Radar outages, communication outages,
power surges/outages, and thunderstorms near or over the radar site, and
terrain issues can cause problems.
There are other reasons a tornado can go unwarned....But this is
why all warnings should be taken seriously. Far too many take severe
thunderstorm warnings lightly. I've seen
this attitude lead to injury and death. All severe thunderstorms are capable of
producing a tornado in the right environment. So never let your guard down, when a severe
thunderstorm is approaching.
