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Saturday, November 29

The question is: Will it rain or will it snow?!

Written by: Bob Metcalfe

(Image courtesy of

Sometimes precipitation type can be one of the most difficult aspects of weather to forecast. About a week ago we had a storm that could have gone either way towards rain or snow, and we ended up with a few inches of snow from it (although a good amount of that could be attributed to the lake effect snow that fell AFTER it passed.) Yet again, we have another early season storm that will head up the eastern seaboard and give western and central New York meteorologists a headache when it comes to the forecast.

The image you see above is actual forecast model data that we use here in our weather office to help guide us as to whether it will rain or snow. This data is referred to as "conditional precipitation type." The time frame for these images is for the hours of 7AM-1PM Monday.

The data we are concerned with is the left two panels. The top left is showing that conditions are met (but do not GUARANTEE) that snow could fall at that time for the westernmost side of New York state. But wait, compare that to the conditions for rain below it! I see some overlap there! So this literally translates into the forecast model saying "Well, conditions exist for it to snow, but it could also rain." This is precisely why we can't let computers make the forecasts, and why meteorologists are as important now as they were before the dawn of computers!

As of this writing (9PM Saturday), we strongly believe that we will see more of a rain event, especially during the beginning of the storm late Sunday/early Monday. Our highs have been 40 or above for a few days, and the atmosphere is reasonably warm enough to prevent a pure snow formation at least for a little while. It will not at all be impossible to see flakes mix in, and maybe even a minimal accumulation, but for now we think that rain and quick-melting wet snow will be about the worst of it during the day Monday. Just be alert, this forecast could change a bit as the storm is still in its formation stages.

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