FIGURE 3

Observed 2100 GMT 28 January 1977 surface pressure field, corrected to sea level, to the nearest millibar. Pressure range extends from 982 mb at the macrolow (L) to 1020 mb over the western Ohio Valley. Dashed lines are isallobars (millibars) computed by taking the difference between the pressure fields at 1800 GMT and 1500 GMT. Ithaca, New York is denoted by *.