Abstract
An Alberta clipper moved over western New York state on 11-12 January 2004, producing snowfall amounts of up to 27 cm in portions of the region during a roughly 12-h period. In addition, lightning and thunder were reported. Such systems, known primarily for their fast motion and relatively dry nature, are not generally associated with significant snowfalls. A postmortem analysis of this event, following an ingredients-based methodology, revealed that as the weak low approached the lower Great Lakes, it came under the influence of coupled 300-hPa jets that produced enhanced divergence and significant upward vertical motion over western New York, resulting in the enhanced convective snowfall over the region for a limited time. Instability and possible enhancement via the Great Lakes are also investigated, which show that while there was at least modest instability over the region during the time of heavy snowfall, lake enhancement was unlikely.
Highlights
The prediction of wintertime precipitation can be challenging, and the consequences of even correct forecasts can be significant
In mid-January 2004 up to 27 cm (11 in) of snow fell across western New York state, accompanied by thunder and lightning, as an Alberta clipper moved over the region
Local forecasters were skeptical of this figure, believing it to be overestimated, as revealed in this excerpt from the Warning Forecast Office (WFO) Buffalo area forecast discussion (AFD) issued at 2006 UTC 11 January 2004: A clipper crosses Lake Ontario late tonight and should bring a general 2 to 4 inches as it passes by
Summary
The prediction of wintertime precipitation can be challenging, and the consequences of even correct forecasts can be significant. In mid-January 2004 up to 27 cm (11 in) of snow fell across western New York state, accompanied by thunder and lightning, as an Alberta clipper moved over the region. Such systems are not generally known for producing such intense precipitation, as noted by Bluestein [1] and Thomas and Martin [2], and the vigorous nature of this particular system surprised even seasoned local forecasters who are well acquainted with prolific snowfalls. Enhanced snowfall amounts are possible via an influx of Great Lakes moisture (Harms [13]; Cinzani and Changnon Jr. [15]; Silberberg [16]; Angel and Isard [17]) or through the effect of intense upper-level forcing in the presence of reduced static stability (Silberberg [16]; Gallus Jr. and Bresch [18])
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