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Miscellaneous
Thu, 25 Feb 2010
Winter Weather Update- Thu 10:30 PM
No change with latest NAM data. 0.42 inches water to fall as snow before 1 PM Fri. High winds and below freezing temps. Snow showers linger into the afternoon and evening. The drive in the morning will be a challenge.
posted: Feb 25 2010 at 10:39 pm
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Winter Weather Update- Thurs 7 PM
Just a quick update:
No surprise that there hasn't been the sort of accumulations that were talked about at this time yesterday. Solar Insolation and warmer temps kept snow from accumulating. The news is saying "the real storm is just starting". True in terms of the cold and wind. GFS and NAM data have about 0.40 inches water falling as snow tonight into Friday morning, then tapering to snow showers during the afternoon. Likely accumulations will be 4-7 inches, although there is still uncertainty with the QPF value of 0.40 inches.
The big issue will be the high winds and ice. Power outages are likely. I'll update later this evening, about 9:40 PM
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posted: Feb 25 2010 at 6:57 pm
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Winter Weather Update- Thurs 7 AM
I'm beginning to think that the NAM model (with lesser snow amounts) and a lull in snow activity in the afternoon (as the main low stacks up in northern NJ) is going to be the better of the two models. The experimental High Resolution Rapid Refresh model supports this lull in snowfall during the afternoon.
In addition to the uncertainties of maximum precipitation, it appears that the thermal profiles of this storm may keep warmer temps at the surface. So while it will fall as snow, accumulations on roadways will be less than grassy surfaces. Still not able to give a final accumulation prediction; it will depend on whether you're measuring things on the driveway or the grass. But I'm leaning towards 4-7 inches and less on roads by Friday morning. Still a guess.
The biggest predictable problem with this storm will be the winds affecting trees with some heavy snow on branches. Winds pick up tonight. Trees may come down. Ice will be a problem early Friday morning.
So for today, heavy snow this morning, but driving will be doable. Snow tapers this afternoon, then picks up again this evening. The amount of snow this evening is still uncertain. It will be a difficult commute Friday morning.
Here's the issues with this storm which prevent a clear-cut forecast:
1. Model disparity- GFS and NAM are different.
2. Temperatures are going to be close to or above freezing. While the precip will fall as snow, it will be wet snow or may mix with sleet and rain. Trying to predict accumulations will be a guess at best.
3. "Insolation" (Solar infrared transmitted through the clouds) becomes an issue at this time of year. The sun is higher in the horizon and there's more thermal effects during the day on roads. This means that accumulations on grassy areas are often much larger than dark asphalt that absorbs heat. Road conditions during daylight hours are often better than expected.
4. The storm involves an upper closed low and a blocked jet flow. The models have significant trouble with locating areas of maximum precipitation with closed lows.
With these points in mind, here's what's expected to happen:
Deep low pressure system is expected to develop over NYC/ Northern NJ on Thursday. The low will be developing as a result of interaction between an upper low and a surface low. This system to undergo "explosive cyclogenesis" and retrograde (move from east to west) as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature. With closed lows, the distribution of precipitation is extremely difficult to pinpoint. It appears that the thermal profile of this storm (too warm at surface) will also be an issue.
This storm has more "known unknowns" and "unknown unknowns" than any recent storm. Expect interesting (and unpleasant) weather, high winds later. Bad commuting conditions Friday morning.
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posted: Feb 25 2010 at 7:09 am
[/weather/feb10] permanent link
Disclaimer: I am not a meteorologist and provide this information as a hobby and for entertainment (mostly my own :-) . While attempts are made to predict the weather as best as I can, use at your own risk! I am NOT responsible for any direct or indirect consequential injury/damages due to your use of these forecasts. Always check the NWS Official Forecast for your final plans.
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