Philly Winter Weather Update- Mon 9 PM
Tonight's NAM just available shows temps too warm for accumulating snow. Well, that clarified quicker than expected.
posted: Nov 26 2012 at 9:15 pm
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Philly Winter Weather Update- Mon 8 PM
The NAM model continues to forecast over a half inch of water falling in our area, starting before daybreak. Last night's models had temperatures supporting snow. Today's models are slightly warmer making it unclear what form of precipitation will fall.
The GFS model has been some drier with less precipitation and milder temps.
It still looks like a mix of wet snow and sleet mixed with rain will fall. It's unclear how much if any will accumulate. It is possible that the only accumulation will be on grassy surfaces. A low confidence scenario but one where we still could get a surprise heavier accumulation.
posted: Nov 26 2012 at 8:53 pm
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Philly Winter Weather Update- Sun 11 PM
The latest NAM model has 4-6 inches of snow falling Tuesday morning into afternoon. Stay tuned for updates.
posted: Nov 25 2012 at 11:16 pm
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Philly Weekend Weather Weather - Fri Afternoon
A strong cold front moves through Friday evening, as an upper air sharp trough moves through on Saturday. Cold air will move in tonight and Saturday, as the upper cyclonic flow takes hold and the pressure gradient will result in windy conditions. Considerable low level cloudiness associated with the upper trough will be with us for much of Saturday.
The upper trough relaxes on Sunday as mild air aloft quickly returns, giving some mid-level cloudiness in the morning and more sunshine in the afternoon. Surface temps remain colder than average.
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Sat 11/24: Considerable cloudiness, windy and colder. More sunshine likely in the later afternoon. High 45.
Sun 11/25: Mid-level cloudiness in the morning, more sunshine in the afternoon. High 44.
posted: Nov 23 2012 at 3:31 pm
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2012-2013 Winter Philadelphia Climate Outlook
It's getting late in the fall season and I usually try to put forth my Winter Climate Forecast by this time of the year. This year, I'm finding the prediction for this coming winter less clear-cut. My general expectation was that we would have a colder than normal earlier winter season through December, followed by a milder than average January and February. My temperature forecast is guided by the current peak of the solar cycle and its associated increase in total solar irradiation. Superimposed on the solar cycle increase are the clear signals of global warming, so my above normal temperature forecast seems like a slam dunk. (But nothing in climate prediction is really a slam-dunk.)
While a warmer than average temp forecast might appear to mean less snow, it really doesn't take much cold air to have snow. The current pattern (High pressure blocking in the Atlantic) favors some very stormy weather - yes, that means snow - for the winter here, although there is a good chance that the pattern might change by the end of December, since this pattern has been with us for much of the Fall and they tend to change after several months.
So in summary, I expect milder on average temperatures, but more than average precipitation (likely more snow/ice instead of more rain), based on the current pattern. I have lower confidence in this winter prediction compared to recent past years.
posted: Nov 22 2012 at 9:14 am
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Philly Weekend Weather Update - Sat AM
Milder temperatures are moving in, but much of the warmer air will be moving aloft over the cold air at the surface, causing some midlevel cloudiness in a pseudo-warm front type situation. The MOS guidance keeps broken to overcast skies with us today (Saturday), and to a lesser extent on Sunday. This sort of stratification often occurs in November. With the high pressure in place, the layer of clouds at its periphery often results in the the high being referred to as a "dirty high" pressure system.
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Sat 11/10: Considerable cloudiness, some breaks of sun possible. High 56.
Sun 11/11: Considerable cloudiness, some breaks of sun more likely. High 65.
posted: Nov 10 2012 at 9:49 am
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Philadelphia Winter Weather - Wed 12PM
The latest NAM model cranks out over 1 inch of precipitation as snow for Philadelphia. IF the NAM is correct, and if surface temps get as low as forecast, there's the potential for as much as 6-10 inches. Difficult to tell how much melting will occur on streets vs grassy surfaces or when temps will fall to freezing, but a significant snowfall of 6-10 inches is possible, not likely. More likely is considerable melting and about 2-5 inches.
Meanwhile, the GFS has backed off precipitation considerably, to only 0.3 inches water resulting in only an inch or two accumulation. With such large model differences, the confidence in this forecast is below average. Interesting differences-- will watch and we'll find out! :-)
posted: Nov 07 2012 at 12:17 pm
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Philadelphia Winter Weather - Tues 11PM
The latest GFS model just in has a rather cold flow interacting with the nor'easter expected to move up the coast. The GFS cranks out over 0.6 inches water with temperatures of the atmosphere able to support snow falling. (Tonight's NAM has things a bit warmer).
If the GFS is correct, much of the precipitation, especially north and west of the city will fall as snow. Whether or not it is able to accumulate is less clear, since it will be falling during the day when surface temps are close or slightly above freezing. Nonetheless, at least 3 inches of snow is likely with possibly 5 or more a possibility. Stay tuned.
posted: Nov 06 2012 at 11:19 pm
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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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