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Weekend Storm Discussion Part II, 2/18-2/19


stormtracker

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Yeah, I mentioned earlier this morning that it was much colder for that one. The real "item" I was focusing on was the blocking in the northeast. If you had 500 maps from 0z Jan 29 and then compared them to the maps at 0z on Jan 30, iirc, you'd see quite a difference in them, again, iirc. That's what I'd think is at least on the table here. Weaken that or speed it up, and I'd think the precip might gain some latitude.

Also, do you have the time stamp for that map? I'll bet it came sometime late day Jan 29, because the 0z maps from the night before gave us virtually no precip, and my morning forecast on that Friday was for a 20% chance of flurries on Saturday that turned into 7 inches of snow.

no.. not sure on time but says midday so probably midday. ;) i think i have some other maps at home saved but that came from cwg. the gyre to the north and confluence with it zipped out with great speed that time. it could happen here too but so far there's not a super signal for that. still time tho.

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Split the difference of all the different QPFs and DC gets maybe 0.3-0.4 snow and it's still far and away the best event of the year.

Too bad I'm going to wisp for the weekend, but yea no one should be complaining if the storm delivers enough snow to cover grass blades fully... which >.2'' of precip can easily do.

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that storm was much colder both during the storm and in the leadup.. not to mention it was almost a month earlier. so there are critical differences.

this was the gfs a day out

gfs_ten_030m_1-29-10.gif

Forecast map for midday Saturday from the Global Forecast System model shows high pressure to the north of D.C. with the storm centered to the south. Credit: NCEP.

How did that one end up? Did it shift north?

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Great points raised.. I think this will come down to just monitoring the models, because this storm looks be really big with lots of moisture.. Definitely will monitoring satellite and radar imagery tomorrow. But back to the Euro, to me its precip shield should be larger. I do think the track will be near the Virginia Capes. Just some thoughts there.

We'll see what happens.

That is what happens when DMC takes over along the front. I wouldn't go jumping off bridges across the north yet though. DMC can wreak havoc on any one deterministic model run.

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Thanks. Could I trouble you to explain a bit more? Are you saying that deep moist convection at the nothern front causes a sharper cut off due to, I guess, 'burn out' issues?

I kind of discussed it to you in post 720 ;)http://www.americanw...ost__p__1381549

But in short, how moist convection develops across the warm sector in positive tilt waves can have large influences in how energy is distributed during cyclone development. Large MCS's that develop along the warm front can displace large amounts of energy away from the cyclone center/upper shortwave/anomaly which can inhibit northward moisture transport as well as change advective processes which also play a role in cyclone development. Negative tilt troughs/waves are not affected nearly as much in a negative manner like this, and in fact, usually are enhanced by the presence of deep, moist convection since it has a tendency to "feed" directly into the upper cyclone which results in rapid intensification/bombing.

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I kind of discussed it to you in post 720 ;)http://www.americanw...ost__p__1381549

But in short, how moist convection develops across the warm sector in positive tilt waves can have large influences in how energy is distributed during cyclone development. Large MCS's that develop along the warm front can displace large amounts of energy away from the cyclone center/upper shortwave/anomaly which can inhibit northward moisture transport as well as change advective processes which also play a role in cyclone development. Negative tilt troughs/waves are not affected nearly as much in a negative manner like this, and in fact, usually are enhanced by the presence of deep, moist convection since it has a tendency to "feed" directly into the upper cyclone which results in rapid intensification/bombing.

In case anyone is reading who wants a primer on these terms, this may help:

http://www.theweathe.../habyhints/127/

or

http://www.usatoday.com/weather/tg/wtrough/wnegtilt.htm

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Here's a snippet from HPC's latest discussions:

"

HOWEVER...MUCH UNCERTAINTY REMAINS...INCLUDING THE

INITIALIZATION/BEHAVIOR/EVOLUTION OF SEVERAL SMALL-SCALE SHORTWAVE

TROUGHS ACROSS THE NORTHERN PORTIONS OF THE CONUS AND SOUTHERN

CANADA...WHICH WILL HAVE A DIRECT BEARING ON THE PRECISE

TRACK/DEPTH OF THE LOW. ADDITIONALLY...MUCH IS UNCLEAR ABOUT THE

ANTICIPATED QPF AND INFLUENCE FROM CONVECTIVE PROCESSES AND

ACCOMPANYING NORTHWARD MOISTURE FLUX FROM THE GULF OF MEXICO. IN

SUMMARY...THE ACCOMPANYING SPLIT-FLOW REGIME APPEARS TO HAVE

LIMITED PREDICTABILITY

...AND AS SUCH...A DETERMINISTIC CONSENSUS THAT MAXIMIZES THE USE

OF HIGHER SPATIAL RESOLUTION WHILE PROVIDING MULTIPLE DYNAMICAL

CORES/MODEL PHYSICS PACKAGES TO INCREASE THE DISPERSION...SEEMS

MOST PRUDENT. THIS APPROACH IS BEST APPROXIMATED BY THE 12Z

GFS...AND IS SUPPORTED BY THE GFS/ECMWF ENSEMBLE MEANS...ALBEIT

WITH LESS DEFINITION. REFER TO THE QPFPFD AND QPFHSD FOR MORE

INFORMATION ON QPF AND WINTER WEATHER PREFERENCES.

CONFIDENCE: ABOVE AVERAGE ON TRACK...BUT BELOW AVERAGE ON TIMING"

http://www.hpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdhmd

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Help a dummy out here. What are they saying?

Here's a snippet from HPC's latest discussions:

"

HOWEVER...MUCH UNCERTAINTY REMAINS...INCLUDING THE

INITIALIZATION/BEHAVIOR/EVOLUTION OF SEVERAL SMALL-SCALE SHORTWAVE

TROUGHS ACROSS THE NORTHERN PORTIONS OF THE CONUS AND SOUTHERN

CANADA...WHICH WILL HAVE A DIRECT BEARING ON THE PRECISE

TRACK/DEPTH OF THE LOW. ADDITIONALLY...MUCH IS UNCLEAR ABOUT THE

ANTICIPATED QPF AND INFLUENCE FROM CONVECTIVE PROCESSES AND

ACCOMPANYING NORTHWARD MOISTURE FLUX FROM THE GULF OF MEXICO. IN

SUMMARY...THE ACCOMPANYING SPLIT-FLOW REGIME APPEARS TO HAVE

LIMITED PREDICTABILITY

...AND AS SUCH...A DETERMINISTIC CONSENSUS THAT MAXIMIZES THE USE

OF HIGHER SPATIAL RESOLUTION WHILE PROVIDING MULTIPLE DYNAMICAL

CORES/MODEL PHYSICS PACKAGES TO INCREASE THE DISPERSION...SEEMS

MOST PRUDENT. THIS APPROACH IS BEST APPROXIMATED BY THE 12Z

GFS...AND IS SUPPORTED BY THE GFS/ECMWF ENSEMBLE MEANS...ALBEIT

WITH LESS DEFINITION. REFER TO THE QPFPFD AND QPFHSD FOR MORE

INFORMATION ON QPF AND WINTER WEATHER PREFERENCES.

CONFIDENCE: ABOVE AVERAGE ON TRACK...BUT BELOW AVERAGE ON TIMING"

http://www.hpc.ncep....php?disc=pmdhmd

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