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,