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18Z Discussion


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wow...:axe:

you kidding me?

people need to relax

again people that live in ground zero for this need to understand small changes in the track do not affect them much, but a 30 mile shift can greatly affect those on the back edge of heavy precip where the last 2 shifts of the GFS took them from 10" to 2". A small shift is a bigger deal to some based on location. I can understand their anxiety.

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Based upon....what? The fact it's not as wet as it once was? The RUC , in general, is rather bad with its QPF amounts and placement. While the NAM is more useful within 36 hours, it's still not the model of choice most days. Winter recon impacts on the guidance should be more fully digested by the 00z runs. Wait and see. There's a reason why HPC stopped using 18z guidance in their day shift qpf package. =)

DR

I'd go with the nam/ruc/mm5 now. The Gfs usefulness is now gone

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again people that live in ground zero for this need to understand small changes in the track do not affect them much, but a 30 mile shift can greatly affect those on the back edge of heavy precip where the last 2 shifts of the GFS took them from 10" to 2". A small shift is a bigger deal to some based on location. I can understand their anxiety.

models usually have some trouble with the backedge though... more often than not it seems places near the edge do better than the qpf maps show. this is pehaps somewhat atypical of a storm but i wouldnt be flipping out yet.

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again people that live in ground zero for this need to understand small changes in the track do not affect them much, but a 30 mile shift can greatly affect those on the back edge of heavy precip where the last 2 shifts of the GFS took them from 10" to 2". A small shift is a bigger deal to some based on location. I can understand their anxiety.

You know as well as I do none of the models are really very good with predicting the back edge of precip. They were too far SE with the heaviest bands in every storm last winter. People worrying about each 10 mile drift left or right on the QPF plots are sort of insane.

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models usually have some trouble with the backedge though... more often than not it seems places near the edge do better than the qpf maps show. this is pehaps somewhat atypical of a storm but i wouldnt be flipping out yet.

I am 99% sure a heavy band will set up west of DCA and they will do fine. The models always fringe them and then they get a mega-band and catch up.

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You know as well as I do none of the models are really very good with predicting the back edge of precip. They were too far SE with the heaviest bands in every storm last winter. People worrying about each 10 mile drift left or right on the QPF plots are sort of insane.

I agree 100 percent with what you and Randy just said, but at the same time we all know its natural to be nervous when your sitting on the edge and a fickle 20 mile shift means 8" or 1". If I had to bet based on actual current conditions I would say the models are shifting a little too far east right now while the low goes through its formative stages and will correct west again tonight some. But if I was going to be in Leesburg or Reston or Westminster I sure would be nervous waiting on the h5 to cut off and see how much the flow can back in.

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I am 99% sure a heavy band will set up west of DCA and they will do fine. The models always fringe them and then they get a mega-band and catch up.

Often a band sets up rather far to the W or NW of these systems somewhere unexpectedly, sometimes it can even screw the areas further SE because it produces sinking motion over them...but this would be more typical to set up further northward up the coast in places like NW CT, interior SE NY, or NE PA.

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Often a band sets up rather far to the W or NW of these systems somewhere unexpectedly, sometimes it can even screw the areas further SE because it produces sinking motion over them...but this would be more typical to set up further northward up the coast in places like NW CT, interior SE NY, or NE PA.

I am sure I was only dreaming it each time it has happened down here in a coastal.

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I'd go with the nam/ruc/mm5 now. The Gfs usefulness is now gone

Based upon....what? The fact it's not as wet as it once was? The RUC , in general, is rather bad with its QPF amounts and placement. While the NAM is more useful within 36 hours, it's still not the model of choice most days. Winter recon impacts on the guidance should be more fully digested by the 00z runs. Wait and see. There's a reason why HPC stopped using 18z guidance in their day shift qpf package. =)

DR

Hee Hee

THEGREATDR says don't count any chickens until later this evening.

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I've been watching these runs for 10 years. I knew the nam would end up wetter and more NW than the Gfs before the day ended

The NAM is notorious for having overdone QPF in the short term before these events on the 18 and sometimes 6 runs as I said earlier...often the 06Z runs tend to have a west bias too...I agree to an extent about the GFS....it seems to always cut amounts, sometimes severely within 6-18 hours before the event starts....I expect on the 00Z or 06Z runs its going to show greatly reduced QPF further on up the coast, reaching into NYC/PHL/NJ and eventually SNE...it often winds up over correcting itself to an extent as it usually is overdone 24+ hours out, but it seems to knock things down too much....I've seen it go from dropping 1.00 liquid 24 hours out to 0.50 or 0.60 6-12 out.

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Yep, makes jason's call look good, better than 6-8 or some of the higher amounts. I thought we might see it edge back wwrd. So much for my thoughts.

Anecdotally, the model trends seem to favor a slight bias to lower precip. amounts

and/or more generous amounts but not much further west than western shores of the Bay.

Simply put, take the most generous model(s) and trim by 30% except for NE New Jersey

to Harrison, NY and NE toward Boston.

3 to 6 with the higher amounts east, seems safe.

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