prepared by Tim Vasquez
Want to try your hand at forecasting for a historically important
storm event? Presented here are various surface charts that
cover events that occurred in the 1970s, 1980s, and 1990s.
You'll have the opportunity to scrutinize each chart in detail,
and won't know what the date or event is until you're ready.
A text narrative is presented for each map, which will provide
hints. Experienced chasers should NOT read these narratives
until after you pick your target area, as it will influence your thinking.
AREA: Sorry, these are all Southern Plains maps. I may post
some Northern Plains or Midwest maps in a future installment.
PRESSURE: All pressures are plotted as altimeter settings. This
measure of pressure is the same as that reported on NOAA
Weather Radio and on TV, and is depicted on this map as
units, tenths, and hundredths of an inch of mercury.
Therefore "993" is 29.93, and "005" is 30.05. You will plot
isobars every 0.05 inches. Altimeter settings were used by
severe weather forecasters on
a widespread basis back in the 1980s due to the lack of
sea-level pressures at about 30% of weather stations.
Why? The widespread overnight station closures in the pre-ASOS era
made 12-hour temperature changes unavailable,
which in turn made r-factors for SLP computations unavailable
(and in some cases r-factors were not developed for various
stations). SLP values are much more common nowadays, however
the use of 12-hour temperature data in order to dampen out
the effects of heating actually masks some mesoscale disturbances.
Therefore it's not at all a bad thing to continue analyzing
PRINTING: Test out these graphics on your printer before
you print a lot of them. Some browsers have an annoying
tendency to split large graphics across multiple pages.
If this happens, copy the graphic to the clipboard with
a right-click of the mouse, and paste it in your favorite
graphics program. Use it to print the map.
DOING GOOD ANALYSIS: Some tips to do a better job
analyzing the maps:
Spend less time in high pressure areas, where contrasts
will flatten out, and more time in low pressure, where
contrasts and baroclinicity will intensify.
Start by lightly sketching out where the boundaries
(fronts, drylines, wind shift lines, and outflow boundaries)
appear to be.
Isobars should always kink into frontal boundaries. There are
clear meteorological reasons why this is so. The kinking is
not necessary with drylines and other features.
The primary characteristic of a front is
temperature contrasts. The front must be on the south
edge of the contrast zone. If anything, you should walk
away with a firm understanding of frontal placement!
The primary characteristic of
a dryline is dewpoint temperature. The dryline
must be on the moist edge of the contrast zone.
If it is unclear where to place a dryline in a broad zone,
do not place it any further east of the zone in which
convection could be supported; but do not place it west
in an area too dry to support convection. Obviously
this is a judgement call sometimes!
Never ignore a data point. Your isobars should accept each
point of data unless there is good reason. What looks
strange may amplify as you draw into an important feature,
and can make you think more about what is happening there.
If you are convinced it is faulty data, circle the parameter.
Certain stations contain systematic errors. For example,
Guadalupe Pass TX (GDP); Junction TX (JCT); Marfa TX (MRF);
and sometimes Lufkin TX (LFK) all transmit pressures that
don't fit well on the map. These can be ignored for
the time being. Encountering them on this map
If you are trying to do an exceptionally high-quality
analysis job, place a piece of Kleenex underneath your drawing
hand. This will prevent pencil lines from smudging and will
keep skin oils from degrading the paper.
Chase Case A
Chase Case B
Chase Case C
Chase Case D
Chase Case E
Chase Case F
Chase Case G
Chase Case H
Chase Case I
Chase Case J
Chase Case K
Chase Case L
FAST DRYLINE MOVEMENT:
Shallow moisture (rapid vertical mixing)
Strong westerly component in troposphere (moisture advection suppressed)
Time of maximum heating (enhanced vertical mixing)
SLOW DRYLINE MOVEMENT:
Deep moisture (slow vertical mixing)
Weak westerly component in troposphere (moisture advection supported)
Time of minimum heating (suppressed vertical mixing)
FAST WARM FRONTAL MOVEMENT:
Shallow or mildly cold air, or highly sloped frontal surface