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3/17-3/18 Storm Threat Discussion


Zelocita Weather

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These posts irk me so much. The NAM is a perfectly good model if you know how to read it.

 

People that just want to automatically dismiss it haven't been following weather for very long.

not at 18 z 60 plus hrs out, anybody will tell u that. its been horrible in the long range

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At the surface, this run actually trended a bit south, especially with the heavier amounts in the Mid-Atlantic. DC went from 0.60" to 0.45," and the 0.25" line went from Long Branch at 12z down the shore to LBI at 18z. Interesting that there were better trends at H5, but that's just how the GFS can be sometimes. We'll have to see what happens at 00z. 

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the qpf totals look nearly identical on the GFS from last run to this run, maybe even a tad LESS than 12z. This was not a step forward. Nothing is really looking "up" at this point whatsoever. I know H5 is different, but considering the terrible solutions almost all of the other models have, and the nam seems to be gradually shifting south converging with the others....I don't see a reason to get excited yet, as nothing has trended for the better. Not over yet, no, but definitely nothing positive

Sent from my iPhone

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the qpf totals look nearly identical on the GFS from last run to this run, maybe even a tad LESS than 12z. This was not a step forward. Nothing is really looking "up" at this point whatsoever. I know H5 is different, but considering the terrible solutions almost all of the other models have, and the nam seems to be gradually shifting south converging with the others....I don't see a reason to get excited yet, as nothing has trended for the better. Not over yet, no, but definitely nothing positive

Sent from my iPhone

 

Maybe at the surface... H5 improved.  The GFS now has a different solution. I guess we'll see at 00z.

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the qpf totals look nearly identical on the GFS from last run to this run, maybe even a tad LESS than 12z. This was not a step forward. Nothing is really looking "up" at this point whatsoever. I know H5 is different, but considering the terrible solutions almost all of the other models have, and the nam seems to be gradually shifting south converging with the others....I don't see a reason to get excited yet, as nothing has trended for the better. Not over yet, no, but definitely nothing positive

Sent from my iPhone

i agree that the GFS is still a miss for NY, but it is a very different evolution, and worth noting.    

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I've seen this in recent Upton discos and would like anyone who knows what this means to perhaps lay out an explanation. Sensitivity Signal.

 

THE 00Z/14 SENSITIVITY ANALYSIS IS STILL INDICATING A
LARGE DEGREE OF SPREAD IN MSLP TO THE N OF EACH OF THE MEAN
TRACKS...IMPLYING THAT THE TRACK WOULD BE FURTHER N. THE SENSITIVITY
SIGNAL FIRST APPEARS ON LAND AT 00Z/15 AND APPEARS TO BE ASSOCIATED
WITH THE SHORTWAVE IN THE PAC NW. WILL BE ABLE TO GAIN SOME BETTER
INSIGHT AFTER TONIGHT`S 00Z AND EVEN MORE AFTER TOMORROWS 12Z RUNS
NOW THAT THIS SHORTWAVE CAN BE SAMPLED MUCH BETTER BY UPPER AIR
OBSERVATIONS.

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I really, really hate to even post this because it was obviously a very anomalous storm, but anyone else see the similarities here to the NAM?

 

021700.png

look at how much further north the UL is in eastern canada and the confluence is also farther north....

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This reminds me somewhat of the 3/3 storm, except I notice nobody on-air tv met is putting a snow map up yet. Smart choice. But this storm is different. The polar vortex would really have to work to expand this far southward and give us a miss. This is going to be one of those storms, we'll either get 6 inches or we'll get nothing at all. The rest of the 18z runs which come out soon are not as important as tonight's oz runs IMO. Sure, the trend is southward, but having all the models coming into a consensus at this far out in the game is baffling me a little. I'd say the best chance of seeing snow is from I-78 southward with the jackpot being somewhere between DC and Philly, probably closer to DC if this southward trend continues. If I were N+W of I-287 I wouldn't get my hopes up. But anything can happen. But the March trend has been to miss us more than hit us. Sure, the January and February trend has been to hit us, but we're in a different pattern during those months. One of these wait and see situations...

 

Nice post - especially the comment on the PV, which Upton called out as being a fair amount weaker than the 3/3 event - and welcome. I was actually quite surprised the NWS-Philly put out a map at 4 pm today, about 54-60 hours before the event (showing a general 4-6" for most of the I-95 corridor and S/E of there) which is similar to what they did before the 3/3 "event." I would've thought they might be more gun shy given the debacle that forecast turned out to be (for them and everyone, really) and given that my recollection is they usually wait until 36-42 hours before the event to issue snow maps.

The map is linked, since I don't seem to have the ability to insert a pic in this post (all the buttons are greyed out for some reason).

http://www.erh.noaa.gov/er/phi/WinterDSS.shtml

Also, when you say "north and west of 287" are you referring to Edison? Somerville? Morristown? White Plains? Sorry, just busting chops a bit - I started a thread on the annoyance of that term, since 287 is not a point, per se, and that term is very unclear (even though most think of it as N/W of the intersection of 287/80, according to Craig Allen).

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I've seen this in recent Upton discos and would like anyone who knows what this means to perhaps lay out an explanation. Sensitivity Signal.

 

THE 00Z/14 SENSITIVITY ANALYSIS IS STILL INDICATING A

LARGE DEGREE OF SPREAD IN MSLP TO THE N OF EACH OF THE MEAN

TRACKS...IMPLYING THAT THE TRACK WOULD BE FURTHER N. THE SENSITIVITY

SIGNAL FIRST APPEARS ON LAND AT 00Z/15 AND APPEARS TO BE ASSOCIATED

WITH THE SHORTWAVE IN THE PAC NW. WILL BE ABLE TO GAIN SOME BETTER

INSIGHT AFTER TONIGHT`S 00Z AND EVEN MORE AFTER TOMORROWS 12Z RUNS

NOW THAT THIS SHORTWAVE CAN BE SAMPLED MUCH BETTER BY UPPER AIR

OBSERVATIONS.

 

A sensitivity analysis is typically done with numerical models to gauge the importance of varying the key initial condition dataset variables and the impact of those variations on the model outcome. That's essentially what the ensembles look at. If one averages all the ensemble runs up, one gets the mean of the ensemble, but the range of each variable in time and space (temp, pressure, precip, etc.) seen in the ensemble runs is an indication of how sensitive the model output is to those input perturbations.

So, I'll take a shot at explaining what the NWS comments mean. From what I gather, the statement above is saying that the predicted eventual surface low pressure in the ensembles is highly "sensitive" to the placement of the northern jet branch shortwave and much of that variability is reflected in ensemble members whose SLP is north of the SLP of the mean (think that means more members are north of the mean than south, starting with the time in the model run where the northern shortwave reaches the Pac NW coast), indicating that perhaps the track will really end up being north of where the mean shows it to be now. Would be interested in how close I got...

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A sensitivity analysis is typically done with numerical models to gauge the importance of varying the key initial condition dataset variables and the impact of those variations on the model outcome. That's essentially what the ensembles look at. If one averages all the ensemble runs up, one gets the mean of the ensemble, but the range of each variable in time and space (temp, pressure, precip, etc.) seen in the ensemble runs is an indication of how sensitive the model output is to those input perturbations.

So, I'll take a shot at explaining what the NWS comments mean. From what I gather, the statement above is saying that the predicted eventual surface low pressure in the ensembles is highly "sensitive" to the placement of the northern jet branch shortwave and much of that variability is reflected in ensemble members whose SLP is north of the SLP of the mean (think that means more members are north of the mean than south, starting with the time in the model run where the northern shortwave reaches the Pac NW coast), indicating that perhaps the track will really end up being north of where the mean shows it to be now. Would be interested in how close I got...

Wow, thanks. So it might be sort of a super analysis of the ensembles, that's my take away. That explains the forecaster discussion from the Upton office and the grid forecast at this point. I'd love some input from Upton on this...

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FINAL CALL :

12" or greater : 2% chance

10" or greater : 5% chance

8" or greater : 10% chance

6" or greater : 15% chance

4" or greater : 23% chance

2" or greater : 35% chance

Under 2" : 10% chance

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Just say 2-4, 4-6, etc... The way you've written it here accounts for only 45% of the pdf.

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