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First guess thru final call D.C. area


Ian

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I like this given the seasonal trend, not sure why the usually stoic ellinwood is going higher.

Good upper-level dynamics via an entering vort max and divergence via the left-exit jet region. These will create better lift and enhance the QPF over our area (to an extent).

Couple things I am worried about. NOGAPS not being considered at this time...CMC also has had issues handling this system. I do think the op GFS is too suppressed. Mesoscale models are pumping in a stronger ridge both ahead of the western trough and the southern wave. For the former, the magnitude of DPVA will be enhanced as a result--hence the inverted trough extending from the northern plains and through the OV later in the forecast period. DC should see a good threat for accumulating snow under such scenario. A coastal, imo, would likely not be good. First the angle of the upper trough would not be ideal. The storm would likely be compact and it would be mostly a coastal VA threat. Second, the low level circulation would be dominated under such scenario, and the inverted trough in the low levels would be dominated by the coastal threat and DC/BA could get shafted. Something along the 06Z GFS is actually pretty decent, and considering I think it is too suppressed, perhaps 2-5" and a slight raise in pops to 45% with a 45% brush to DC/BA if a coastal gets going. A good threat this winter, nothing blockbuster, but better than nothing for sure.

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Couple things I am worried about. NOGAPS not being considered at this time...CMC also has had issues handling this system. I do think the op GFS is too suppressed. Mesoscale models are pumping in a stronger ridge both ahead of the western trough and the southern wave. For the former, the magnitude of DPVA will be enhanced as a result--hence the inverted trough extending from the northern plains and through the OV later in the forecast period. DC should see a good threat for accumulating snow under such scenario. A coastal, imo, would likely not be good. First the angle of the upper trough would not be ideal. The storm would likely be compact and it would be mostly a coastal VA threat. Second, the low level circulation would be dominated under such scenario, and the inverted trough in the low levels would be dominated by the coastal threat and DC/BA could get shafted. Something along the 06Z GFS is actually pretty decent, and considering I think it is too suppressed, perhaps 2-5" and a slight raise in pops to 45% with a 45% brush to DC/BA if a coastal gets going. A good threat this winter, nothing blockbuster, but better than nothing for sure.

For the CMC, big red flag comes in the way it handles the southern wave. Discussed a lot in previous posts, but the CMC handles low amplitude waves/phases/"kick-outs" poorly as it does the breakdown of longwave troughs into low amplitude waves--a general bias of the model. CMC consistently tries to weaken the southern wave then "kick it" out NE as a warm front--effectively inducing dynamic height rises in the height field and greatly increasing the magnitude of DPVA as a result. This is why the steroidal runs are developing on the CMC. That kind of amplification so early is unlikely mainly owing to the early southern wave and the way it influences the the low level moisture field and the advection patterns. Also the CMC has been awful with any consistency--a look back a couple days ago to its 12Z run is a good example as it tried to over-amplify the western trough early and send the main storm through IA and the Great Lakes. This is mostly why the CMC is being tossed at this moment in time. That said, DC folks should be happy to see a viable threat--and the threat doesn't rely on a massive coastal.

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I'm sticking with 4-6" with a greater than 50% probablity.

i've always been in the 2-4/3-6 camp thus far if it works out but it's hard to go greater than 50% probability at this range.. maybe by tomorrow.

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Have we learned nothing from the Xmas forecasting debacle about calling for snow amounts so far out in time during such a chaotic pattern?

:yikes:

50% chance of getting something

50% chance of getting nothing

This is a much better threat for actually getting snow though. The Christmas debacle hinged upon a very sensitive coastal bomb. Here you have a legitimate shot of snow without needing the stars to align and a monster coastal to get snow. In fact, a coastal, if it developed fast enough, would likely hurt your chances as it would dominate the inland low level circulation.

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This is a much better threat for actually getting snow though. The Christmas debacle hinged upon a very sensitive coastal bomb. Here you have a legitimate shot of snow without needing the stars to align and a monster coastal to get snow. In fact, a coastal, if it developed fast enough, would likely hurt your chances as it would dominate the inland low level circulation.

Man I wish you were around last year for us

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This is a much better threat for actually getting snow though. The Christmas debacle hinged upon a very sensitive coastal bomb. Here you have a legitimate shot of snow without needing the stars to align and a monster coastal to get snow. In fact, a coastal, if it developed fast enough, would likely hurt your chances as it would dominate the inland low level circulation.

Looks like the Delmarva Peninsula may be in the sweet spot for this one.

:popcorn:

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50% OTS or near miss with <1"

25% 1-4"

25% 4"+

NWS now up to 50% off 30%. My confidence continues to increase. I believe snow is now more likely than not. I will make a second guess tonight.

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