After an exceptionally mild November with, for the first time on record, not even a snowflake seen at the official Buffalo NY observation site, the first three weeks of December proved even milder relative to normal. In fact, every day from 21 November through 23 December had above normal temperatures, with only 1.1" of snow during the period.
However, a pattern change was being signaled by the medium range NWP models during the final few days before the Christmas holiday, with upper-level blocking developing over Greenland and the subsequent development of an upper-level low pressure area over the northern Great Lakes. By the evening of 23 December, the evolution to the new upper air pattern was well-underway, which can be seen by clicking on the "Display Graphic" button below, which shows the 500, 700, and 850-hPa surfaces and mean sea level pressure/1000-500 hPa thickness analyses for 00 UTC 24 December 2001.
Eta-12 analysis, 00Z 24 Dec 2001 at 500, 700, 850-hPa, SLP and 1000-500
hPa thickness.
Because of the exceptionally warm late fall temperatures, lake surface temperatures (LSTs) on all the Great Lakes were much warmer than normal. The graphic below shows the LSTs used by the Eta-12 model at each Lake Erie grid point, in 0.1°C, for the duration of the forecast we will be analyzing for this case. Note that much of Lake Erie's LST is in excess of 7°C, with the eastern downwind portion nearest Buffalo at 8°C or slightly higher!
The pre-storm situation here is in sharp contrast to December 2000, when Buffalo NY was in the middle of the 7th coldest December on record, and the lake had already begun to freeze. On average, the LST at Buffalo during the latter half of December decreases by 1°C, from about 3°C on 15 December to 2°C by the end of the month. The LSTs at the eastern end of Lake Erie are thus 5°C or so above seasonal normals, and are more typical for mid-November, rather than late December.
