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Moving Through December - Changing Patterns and Changing Diapers


ChrisM

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We the GEFS as we stated were always suspect with that. Looks much closer to euro ensemble.

Also I didn't think that follow up wave was going to work out like the euro had. The euro does that stuff sometimes.

We all mentioned that the gradient would be overhead and may not be epic. We can't stress that enough. It's dangerous to assume that we go into a pattern that has produced before and assume it will happen again. It's very difficult predict how snowfall will break out. It's not the best pattern but it isn't a disaster either. We'll have some opportunities with this change coming up. Maybe it's more NNE but who's to say right now.

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The 06z GEFS actually looked pretty encouraging for the Tue wave. Ensemble mean suggested good support for light-mod precipitation, indeed 6/12 ens members on the raleigh wx site showed a wave impacting the area on Tue with a 7th developing a coastal low with the next shortwave on Wed. Most were on the warm side but a few were fairly significant. The 12z GEFS has backed off on this potential, but with a few headfakes from the Euro, Canadian, and GEFS, it cannot be completely ignored. There are several shortwaves swinging down the upstream side of the developing trof next week, so model error is likely.

I'm also mildly intrigued by the Wed possibility. The longwave trof axis if finally in a good position by this timeframe. The structure remains positive tilted and the shortwave timing and interaction is poor. But if the models miss a robust s/w in the flow and/or the timing is improved, the Tue - Thurs timeframe could potentially produce a coastal low that affects at least SE areas.

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12z GEFS members just rolling in. A few appear to switch rain to snow for higher elevations of SNE on Tue. I can't view the full suite yet, but considering the less impressive mean QPF, there doesn't appear to be the more robust coastal low centers that a few of the 06z members showed. I still think the entire midweek period has a low chance for a surprise snow. 300mb is supportive, but the baroclinic zone is suppressed too far southeast. If we were dealing the year 2000 model programming, I would have more confidence in a surprise bust.

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Favorable height anomoly charts at day 10-15 are a dime a dozen. The error is so large as to render them almost useless as harbingers of snow. Sure they have some utility in forecasting temperature and precipitation anomolies, but even if a favorable regime arrives as predicted (questionable), there is no way to predict rain, snow, or dry.

Day 10 temperature progs are scarcely better than climo, esp near the Atlantic at our latitude. If you look that far out for snow it will always feel two weeks away and/or you will miss the mid-range threats that pop up without long range warning. It is just not an effective way to make a synoptic forecast. Sure it is fashionable, but that doesn't make it useful. I want to see a threat on the mid-range guidance (at least 300mb and 500mb), not the long range anomoly charts to get excited. Otherwise the rug will get pulled out from under. Just look at the 10 day ensemble spaghetti plots. They are like children's crayon drawings. 10 days of error progatation is enough to create a spread in the 558dm height contour from Maine to the tropics.

i specifically posted 6-10 day ensemble anomaly charts also just so someone wouldn't post "well it's always beyond day 10!)

It doesn't matter, you obviously know more than I do about this.

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i specifically posted 6-10 day ensemble anomaly charts also just so someone wouldn't post "well it's always beyond day 10!)

It doesn't matter, you obviously know more than I do about this.

It's not personal. I have nothing against you or your knowledge. And since we don't know each other I'm guessing you don't know too much about my knowledge either, apart from what I write.

6-10 day anomaly charts are obviously a lot more useful than longer range charts. I believe that's clearly the timeframe where most wintry threats become apparent. My problem is with long range forecasting and the infamous "pattern changes." I think uneducated guys like Bastardi started it and perpetrated to the masses disinformation.

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