Download Severe Weather Forecasting

Severe Weather
Forecasting
Meteorology 1010 Professor Dastrup
This assignment required us to find, include, and analyze a
severe thunderstorm pattern,
Lynsie Brown
8/1/2011
The watch that I found was posted 745 PM CDT on Wed July 27, 2011. I was excited to
come across this one because I had been watching for a few days and had not seen anything
significant. When it posted a Tornado watch, I knew I needed to jump on it. This watch came
out of Norman, Oklahoma and was posted as Urgent. The following is the SPC watch.
SEL4
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 694
NWS STORM PREDICTION CENTER NORMAN OK
745 PM CDT WED JUL 27 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
EAST CENTRAL IOWA
NORTHERN ILLINOIS
EXTREME NORTHWEST INDIANA
EXTREME SOUTHERN WISCONSIN
LAKE MICHIGAN
EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 745 PM
UNTIL 100 AM CDT.
TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 35 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 40 MILES WEST SOUTHWEST OF
DUBUQUE IOWA TO 30 MILES EAST NORTHEAST OF MEIGS FIELD ILLINOIS.
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU4).
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.
DISCUSSION...CLUSTER OF STORMS...SOME WITH EMBEDDED SUPERCELL
STRUCTURES...WILL CONTINUE TO EXPAND ALONG THE SURFACE WARM FRONT
NEAR THE IL/WI BORDER. STRONG INSTABILITY AND VEERING LOW-LEVEL
SHEAR PROFILES WILL SUPPORT STORM-SCALE ROTATION WITH DEVELOPING
STORMS ON THE BOUNDARY...WITH THE POSSIBILITY OF LARGE HAIL AND A
TORNADO OR TWO IN THE NEXT COUPLE OF HOURS. UPSCALE GROWTH OF THE
CONVECTION WILL RESULT IN STRONGER COLD POOL GENERATION AND AN
ATTENDANT RISK FOR DAMAGING WINDS.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
650. MEAN STORM MOTION VECTOR 28020.
...THOMPSON
Hazard
Likelihood
Tornadoes
Moderate
EF2+ Tornadoes
Low
Severe Wind
Moderate
65 kt+ Wind
Moderate
Severe Hail
Moderate
2"+ Hail
Moderate
Hazard
Likelihood
Tornadoes
Moderate
EF2+ Tornadoes
Low
Severe Wind
Moderate
65 kt+ Wind
Moderate
Severe Hail
Moderate
2"+ Hail
Moderate
Hazard
Likelihood
Tornadoes
Moderate
EF2+ Tornadoes
Low
Severe Wind
Moderate
65 kt+ Wind
Moderate
Severe Hail
Moderate
2"+ Hail
Moderate
Hazard
Likelihood
Tornadoes
Moderate
EF2+ Tornadoes
Low
Severe Wind
Moderate
65 kt+ Wind
Moderate
Severe Hail
Moderate
2"+ Hail
Moderate
We can see from this watch that there were warning for tornados, high winds, and hail.
A tornado is formed when violent wind creates a column of air that rotates (a vortex). The
vortex sucks in the air from the bottom from all different directions and is spiraled up to where it
eventually combines with the stormy air of a much larger thunderstorm created in a
cumulonimbus cloud.
Hail is formed when small ice pellets gather moisture as they are volleyed through
clouds, bouncing around on the down and updrafts. They collect the moisture when they are in
the lower levels, then they are super-cooled as they are forced upward in the updraft and
continue this cycle until they are too heavy to be supported in the cloud. Hail can grow to the
size of softballs in severe enough weather and can pose a great danger to property and life.
The high winds gusts that are noted in this watch are significant at 70 mph, when
considering a hurricane is issued at 74 mph. We also hear mention of embedded “supercells”,
which are massive clouds that produce fantastic storms, as well as tornadoes (although not all
supercells are tornado-producing). Enormous amounts of latent heat are required to fuel a
supercell and must have just the right conditions and need support from an inversion layer to
keep the air full of moisture.
An infrared image such as this shows the amount of heat contained in the clouds. The
level of heat is what reflects the image of the cloud, and as I noted earlier, it takes a great amount
of latent heat to produce a tornado. We can see the brightness of the images coming from the
specified area shows significant activity.
I debated on including this visible image, as it is not very visible due to the time of day,
but you can see the cloud cover in western Kansas and eastern Colorado that are contributing to
this storm.
Above is a Contiguous view of the U.S which shows the cells we see in the following
Doppler image coming out of Dodge City, Kansas.
In analyzing this Doppler image, we can see towards the middle left where there are
small areas of red and green right next to each other, and also in middle, a small area where the
same is occurring. This shows a great chance of rotation occurring which could result in a
tornado. The Doppler works by sending out a signal that reflects the amount of activity
(precipitation, winds, etc.) a storm is producing. Blue is the least amount, then green, moving up
the scale to purple which is very significant. When strong winds are moving in opposite
directions, they mix and create conditions for a tornado, and on Doppler, they show up as the
reds and greens mixing as previously mentioned.
I feel like the huge amount of information I have processed during this course finally
clicked in this section. I, like many people, have a fascination with severe thunderstorms. While
I would never want to experience a tornado, I love learning about them and seeing the massive
storm clouds that are associated with them. My favorite part of the news has always been the
weather, and my husband thinks it is funny, because that is the part of the news he would prefer
to put on mute. I feel like now I have a much better understanding of what ridges, troughs, high
and low pressure, warm and cold fronts are, and what the various “weather patterns” are. While
I still have so much to learn, I feel that I can make sense of the different satellite images are, and
I definitely have a better understanding of how they work. I am hooked on the Storm Prediction
Center website and have added it to my favorites, knowing I will be visiting it very often in the
future.