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September 2012 Observations and Discussions


NEG NAO

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My concerns at this point would be the lack of juxtaposition of kinematics and instability, as well as the slightly slow timing of the best forcing on most of the models. The GFS has the vigorous shortwave energy over Central PA at 00z Sunday, though, which could probably be good enough for storms in the area right around the early evening hours.

http://www.meteo.psu.edu/~gadomski/AVN_6z/f66.gif

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60kts of 0-6km bulk shear on the SPC SREF over parts of Eastern PA, Southeast NY and into Western NJ.

Worth noting that the SPC SREF also seems to be hinting at a marine layer near the coast with a sharp dropoff in surface based and mixed layer cape values. But even still, the wind fields are impressive when coupled with the 2000 joules of MLCAPE the mean is indicating over parts of NJ and NY.

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Not only that but the updated forecast put out at 1:30 still was calling for mostly sunny and upper 80s

Upton has had quite a few days in the past month where they significantly underestimated cloudcover, even on the morning of (such as today). With the number of hung-up fronts around the area lately, seems like a consistently tough forecast. Spoiled a couple of beach days, though...

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There was a point-and-click forecast this afternoon I've never seen before: Sunny with a chance of sprinkles. It even had a completely sunny icon with the subheading "Chance Sprinkles" below it. Would think a chance of sprinkles at least warrants Partly Cloudy...

Not only that but the updated forecast put out at 1:30 still was calling for mostly sunny and upper 80s

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so far this year NYC has 46 days with a minimum of 70 or higher...6th most on record...The record is 61...

61 in 1906

60 in 2005

54 in 2010

54 in 1908

52 in 1980

46 in 2012

46 in 1876

46 in 1959

It hasn't been a very hot summer but it has and still is a humid one...

I find it surprising that there were so many high minimums in 1876, 1906 and 1908 (and especially with 1906 setting the record), when the effect of UHI would have to have been significantly less of a factor than today, and the avg. temps. during the summer months of those years were not higher than normal by today's standards (perhaps even slightly lower).

Year June July Aug

1876 70.7 76.4 72.5

1906 71.5 74.8 75.3

1908 71.6 76.8 72.5

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Albany at 21z...

Looks interesting for strong/possibly severe storms up here in Albany... the line also looks to move in here around the late noon/evening hours before coming into NYC not long afterwards. I've moved to Albany but still prefer tracking the weather in the NYC area, in addition to probably coming back to NE NJ sometimes.

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The NAM is now more phased and dynamic, but also slower with the frontal passage.

I noticed earlier that the 15z SREF came in a good bit slower as well with the best 0-6km bulk shear a good 50-100 miles farther west valid 00z Sunday. With the 18z GFS showing a slower trend as well..the timing could become a concern or at least something to pay close attention to here over the next few model cycles.

f51.gif

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The NAM is now more phased and dynamic, but also slower with the frontal passage.

I noticed earlier that the 15z SREF came in a good bit slower as well with the best 0-6km bulk shear a good 50-100 miles farther west valid 00z Sunday. With the 18z GFS showing a slower trend as well..the timing could become a concern or at least something to pay close attention to here over the next few model cycles.

f51.gif

There's more of a tilt to the cold front over the region, the line moves through Albany and NYC almost at the same time with this run. Bulk shear ahead of the line is also stronger with this run. The 2 previous NAM runs appear to be outliers with the timing and intensity of the low pressure, this run looks closer to the 12z ECM although I wouldn't be surprised if this run overdid the intensity of the low pressure a bit. Timing is a bit of a concern with this run, with the ECM still showing a slower outcome and the GFS trending slower, although IMO it doesn't look like it would end up much slower than currently modeled.

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This setup for Saturday night looks pretty potent! Surface winds ahead of any squall line per 00Z NAM will be cranking. I see at least 35 kt atop a mixed layer from the sfc to 925 mb beginning about 18Z Sunday, and 50-55 kt at 925 mb east of NYC Sunday evening. Might be overdone but only by about 10%. We'd need a wind advisory even without any storms which would transfer that momentum even more efficiently to the surface. And any LEWPS in that modeled squall line would have to be closely watched for spinups, with the bulk of the related shear concentrated in the lowest 1 km. That would be even more concerning if a weak sfc wave were to develop along the front as some earlier 12Z GFS ensemble members were weakly hinting.

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This setup for Saturday night looks pretty potent! Surface winds ahead of any squall line per 00Z NAM will be cranking. I see at least 35 kt atop a mixed layer from the sfc to 925 mb beginning about 18Z Sunday, and 50-55 kt at 925 mb east of NYC Sunday evening. Might be overdone but only by about 10%. We'd need a wind advisory even without any storms which would transfer that momentum even more efficiently to the surface. And any LEWPS in that modeled squall line would have to be closely watched for spinups, with the bulk of the related shear concentrated in the lowest 1 km. That would be even more concerning if a weak sfc wave were to develop along the front as some earlier 12Z GFS ensemble members were weakly hinting.

In agreement with all of this. Interesting to see such wild timing differences on the GFS between its off hour 18z run and the new 00z run. The newest run is back to bringing the front through just after 00z with a vigorous shortwave over Central Canada.

As far as the setup...its definitely potent as you mentioned. Just a quick glance at the guidance this evening got my attention. The NAM has 0-1km helicity values of 200 m2/s2 just ahead of the front at 00z Sunday and the SPC SREF mean has 0-6km bulk shear of 40 kts over Western NJ just along the front...with 60 kt values back farther to the west.

Surface based instability could be interesting...the NAM had some higher instability parameters yesterday and perusing through some of the cloud data..appears to want to keep some debris in the area beginning as early as 09z Sunday. Still, in such a dynamic environment...the mean of near 1000 joules of MLCAPE on the SPC SREF would suffice (assuming it's not out to lunch). We'll see how it all develops...but I think we'll likely see convection develop in mid-afternoon across Central PA once that vigirous shortwave really rounds the base of the trough and starts kicking the best forcing east. At that point it will be interesting to see how quickly the complex advances east and if it can organize itself..along with, as you mentioned, the potential for spinups given the very favorable low level shear.

NAM_221_2012090700_F48_HLCY_1000_M_ABOVE_GROUND_0_M_ABOVE_GROUND.png

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