ice” (floating pieces! was present on 19 January and
several days before. There was also a report of “slush
ice” at 1800 on the 19th.
Lake water temperatures of 32° F were measured
several feet below the surface at Dunn crib on the
19th. This does not indicate either the presence or
co
o
o
from Dunn crib, a city water intake facility in the
lake off Chicago’s south shore, indicate that “pancake
a
ary to the end of February, 1966, and that reports
WIND DIRECTION, degrees
Lake Michigan off Chicago from the middle of Janu-
g 8 g
150
60
=
a
ie) 4
absence of ice. However, the absence of a long period
a
wm
of extremely cold weather, and westerly winds on sev-
eral days preceding the 19th add to the evidence
above that the lake surface was essentially liquid and
32° F,
5
0°
!0
g
a
a
= 08
on the 19th. Temporary winds shifts occurred at some
stations, but not all.
A better way to evaluate these events on an hour
to hour basis is to examine the meso-scale maps. Figures 110 and 111 show winds, SOs, and temperatures
in the Chicago area for 8 sclected hours on 19 January. The 0600, 0900, and 1200 maps show a westerly
flow, at low speeds, over the Chicago area. At 1500,
convergence over the city was very clear, with north-
east winds at the three TAM stations along the lake
shore and westerly or northwesterly winds inland. The
ec
ke
Wwig o4
=z
3
o2
w
o
uO
0.0
°
2
4
6
8
oO
(12
4
16
WW
27 DECEMBER 1966, CST
2
22
°
Fig. 117—Winds and SO. at TAM-1 and 7, 27 December
1966.
|
240
moe pm
180
+ | -
|
|
I
ce)
o
o
>
°
to
Qo
°o
SO. CONCENTRATION, ppm
WIND SPEED, kt
(sé
o
WIND SPEED, kt
8
wn
WIND DIRECTION, degrees
pn
ow
a
oO
360
= O06
WIND DIRECTION, degrees
colder than the lake. Figures 107-109 showdetails of
SO. and wind behavior at individual TAMstations
$02 CONCENTRATION, ppm
=
°
Therefore, the observed easterly winds are clearly
not the usual kind of lake breeze because the land was
90
2
4
6
8
Io
12
i4
16
i@
27 DECEMBER i966, CST
2
22
Qo
Fic. 118—Winds and S802 at TAM-5, 6, and 8, 27 December
1966.
circulation was still strong over the south end of the
0.8
city at 1700 and the convergence line had retreated
06
0.4
2
0.0
0
z
o
2
4
6
8B
1 t2
4 lb
27 DECEMBER I966, CST
8
20 22
O
Fig. 116—Winds and SO. at TAM-3 and 4, 27 December
1966.
east of TAM-5 and -6 once more and disappeared in
the north end of the city. The circulation continued
to weaken during the next hour; the 1900 map shows
northeasterly winds only at TAM-4 and Meigs Field
(CGX). By 2100 winds were northwesterly over the
whole area once again.
The city wind pattern is clear; it shows that winds
converged over the center of the city for several hours,