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CanisLupusArctos · 12-13-2007, 11:54 AM

One more local effect to add to the list: Last winter I began thinking that Lake Winnipesaukee acts as a runway for warmer ocean air when there's a major coastal storm (lots of wind). In the major windy storms of last February and March, I found that the snow was changing to sleet and freezing rain here in Center Harbor, even while places like Gilford and Laconia were still having plain snow. The temperatures on the island were also warming higher than those away from the lake.

This led me to guess that when the storm's wind is very strong from the east, the lake's NW-SE orientation (with mountains on both sides) was helping to funnel maritime air farther inland than it was otherwise reaching.

The effect shut down when the storm moved farther north, giving us more of a NE wind rather than East or SE... and any mix would change back to snow.

Something to consider for this weekend's storm will be evaporative cooling in the dry arctic air now in place, should warm air try to intrude. That happened a couple times last winter when arctic air was in place but warm air was forecast to change the snow to mix. The mix never happened, because the dewpoints in the arctic air were so low that the first couple hours of precip evaporated before hitting the ground, cooling the air the same way your skin gets cold when water (or rubbing alcohol) evaporates off it. Gradually the dewpoint rose to a point where the snow could finally reach the ground, but by the time that happened, the air had cooled 5 or 6 degrees -- just enough to keep the snow from mixing with rain/ice.

12-13-2007, 11:54 AM	#22
CanisLupusArctos Senior Member Join Date: Jan 2007 Location: Center Harbor Posts: 1,049 Thanks: 15 Thanked 472 Times in 107 Posts	Local effects One more local effect to add to the list: Last winter I began thinking that Lake Winnipesaukee acts as a runway for warmer ocean air when there's a major coastal storm (lots of wind). In the major windy storms of last February and March, I found that the snow was changing to sleet and freezing rain here in Center Harbor, even while places like Gilford and Laconia were still having plain snow. The temperatures on the island were also warming higher than those away from the lake. This led me to guess that when the storm's wind is very strong from the east, the lake's NW-SE orientation (with mountains on both sides) was helping to funnel maritime air farther inland than it was otherwise reaching. The effect shut down when the storm moved farther north, giving us more of a NE wind rather than East or SE... and any mix would change back to snow. Something to consider for this weekend's storm will be evaporative cooling in the dry arctic air now in place, should warm air try to intrude. That happened a couple times last winter when arctic air was in place but warm air was forecast to change the snow to mix. The mix never happened, because the dewpoints in the arctic air were so low that the first couple hours of precip evaporated before hitting the ground, cooling the air the same way your skin gets cold when water (or rubbing alcohol) evaporates off it. Gradually the dewpoint rose to a point where the snow could finally reach the ground, but by the time that happened, the air had cooled 5 or 6 degrees -- just enough to keep the snow from mixing with rain/ice.