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Early April Winter Pattern Likely


CoastalWx

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my qpf maps are look a bit corrupted...but i think it was like 15 mm for you. It cuts the primary so far north that there is a strong snow band up near ART at 12z Saturday.

Thanks...yeah it had the band getting into CNE too on that run.

Either way, tough to get excited for anything more than light slop until the Euro can start showing a more intense band and dynamics.

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Congrats Mitch

5z1htc.jpg

Nice band of 800-600 mb theta-e frontogenesis is the culprit. Here's a GrADS plot I came up with. I decided to write my own scripts after the FSU meso band site went down. I am writing for negative EPV. I think I've got it, but I'm not totally convinced of the results being accurate yet. Needs more testing. I'll post the EPV plot FWIW. Just take it with some grain of salt. As this is a weak event, I don't think there would be a deep layer of negative EPV and RH > 80%. In in a nor'easter, you'd expect the layer to be much deeper.

post-48-0-58092000-1333077058.gif

post-48-0-87248400-1333077076.gif

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Nice band of 800-600 mb theta-e frontogenesis is the culprit. Here's a GrADS plot I came up with. I decided to write my own scripts after the FSU meso band site went down. I am writing for negative EPV. I think I've got it, but I'm not totally convinced of the results being accurate yet. Needs more testing. I'll post the EPV plot FWIW. Just take it with some grain of salt. As this is a weak event, I don't think there would be a deep layer of negative EPV and RH > 80%. In in a nor'easter, you'd expect the layer to be much deeper.

Great maps Mitch...the FSU site going down is one of the most frustrating things because I loved looking at that site. The EPV stuff is great too...they didn't have that on the FSU site.

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ORH on the NAM. Sweet. LOL, just a quick 9" in 5 hours.

120331/0900Z 33 13006KT 32.3F SNOW 13:1| 0.2|| 0.00|| 0.00|| 0.013 13:1| 0.2|| 0.00|| 0.00|| 0.01 100| 0| 0

120331/1000Z 34 09004KT 31.7F SNOW 14:1| 1.4|| 0.00|| 0.00|| 0.104 14:1| 1.6|| 0.00|| 0.00|| 0.12 100| 0| 0

120331/1100Z 35 08006KT 31.4F SNOW 16:1| 2.5|| 0.00|| 0.00|| 0.159 15:1| 4.1|| 0.00|| 0.00|| 0.28 100| 0| 0

120331/1200Z 36 07007KT 31.2F SNOW 18:1| 2.3|| 0.00|| 0.00|| 0.126 16:1| 6.4|| 0.00|| 0.00|| 0.40 100| 0| 0

----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---

120331/1300Z 37 06004KT 31.2F SNOW 16:1| 2.1|| 0.00|| 0.00|| 0.129 16:1| 8.5|| 0.00|| 0.00|| 0.53 100| 0| 0

120331/1400Z 38 05005KT 31.5F SNOW 9:1| 0.9|| 0.00|| 0.00|| 0.099 15:1| 9.4|| 0.00|| 0.00|| 0.63 100| 0| 0

120331/1500Z 39 05007KT 32.8F RASN 0:1| 0.0|| 0.00|| 0.00|| 0.031 15:1| 9.4|| 0.00|| 0.00|| 0.66 86| 0| 14

120331/1600Z 40 05008KT 35.0F RASN 0:1| 0.0|| 0.00|| 0.00|| 0.007 15:1| 9.4|| 0.00|| 0.00|| 0.67 65| 0| 35

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I've noticed this before... The NAM does this with these -NAO shuns ... It tends to "sinusoidally" impact, wane then come back from ~60 to ~48 to ~18 hour leads. We saw those 60-72 hour runs go nuts, then then these 60 hours runs back to nil, now the 48ers are coming half way back. I've seen it do this enough to wonder if there is a predictive validity out there that can be honed by considering the differential ...decay if you will. The next run might come back yet more, but then the 18 hour lead looms and backs off...maybe by 1/3 or even 1/2 type thing.

Just something to consider, but I'm right about this observation overall.

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I've also got a CSI script that uses the same expression as on the FSU site when it was working. Again, not totally convinced of its accuracy yet. The plot looks very much like the EPV one as CSI is generally present where EPV is negative. You can also have CI where EPV is negative too, which is why I overlaid CAPE. Oh...sorry about the acronyms: CSI is Conditional Symmetric Instability, EPV is Equivalent Potential Vorticity, CI is Conditional Instability, and I think we all know what CAPE is. I won't go through the whole explanation now, but basically we can use EPV, CSI, and frontogenesis to diagnose areas where a death band may occur.

post-48-0-15268600-1333077804.gif

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I've also got a CSI script that uses the same expression as on the FSU site when it was working. Again, not totally convinced of its accuracy yet. The plot looks very much like the EPV one as CSI is generally present where EPV is negative. You can also have CI where EPV is negative too, which is why I overlaid CAPE. Oh...sorry about the acronyms: CSI is Conditional Symmetric Instability, EPV is Equivalent Potential Vorticity, CI is Conditional Instability, and I think we all know what CAPE is. I won't go through the whole explanation now, but basically we can use EPV, CSI, and frontogenesis to diagnose areas where a death band may occur.

The CSI/ML fronto on the NAM suggests the death band would be from NY State into SW MA and along the MA/CT border for a bit until going ESE into RI.

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Great maps Mitch...the FSU site going down is one of the most frustrating things because I loved looking at that site. The EPV stuff is great too...they didn't have that on the FSU site.

Although I can't be certain of it, I think the scripts may have been stopped because there may have been an error in the CSI depth plots. I became suspicious when I wasn't able to replicate the map for the 10/29 storm after getting an old NAM grid off of NOMADS. After much fiddling with my GrADS scripts, I was able to replicate it, but only after discovering that the FSU script wasn't doing what it was supposed to as it was plotting the depth of the layer of 95% or greater RH. It was not plotting the depth of the symmetrically unstable RH layer > 95%. The frontogenesis plots were fine as I was able to reproduce those.

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