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[Ed Lizard]

Thought I'd copy a post here for higher visibility...

Question on ensemble means. If one takes the means of, say, 50 lower resolution to begin with models, since the troughs and ridges would not be in the same position on each perturbation, wouldn't the ensemble means tend to 'broaden' troughs and ridges and even if the strenth of the features was similar each perturbation, wouldn't the different positions produce what appears to be weaker troughs and ridges?

[isohume]

Thought I'd copy a post here for higher visibility...

Question on ensemble means. If one takes the means of, say, 50 lower resolution to begin with models, since the troughs and ridges would not be in the same position on each perturbation, wouldn't the ensemble means tend to 'broaden' troughs and ridges and even if the strenth of the features was similar each perturbation, wouldn't the different positions produce what appears to be weaker troughs and ridges?

In general yes...you see this often with the SREF and the GEFS mean heights, mslp, etc. It's the nature of ensemble output....however I've seen cases where the soln spread is very low leading to more dynamical looking patterns. Which of course, doesnt always mean the model has the correct idea either. It still needs to be weighted.

I like to use the ens spread magnitude or stdv as a means to see what set of solns the ensembles converge on moreso than the others and how this compares with the various op models and their dprog/dt solns. I generally give the ensemble mean more weight in the mid range periods tho.

[The Great Zo]

Question on ensemble means. If one takes the means of, say, 50 lower resolution to begin with models, since the troughs and ridges would not be in the same position on each perturbation, wouldn't the ensemble means tend to 'broaden' troughs and ridges and even if the strenth of the features was similar each perturbation, wouldn't the different positions produce what appears to be weaker troughs and ridges?

In general yes...you see this often with the SREF and the GEFS mean heights, mslp, etc.

There was a good example of this with one of the recent tropical cyclones -- though I can't remember which one. The GFS and the individual ensemble members had a well-defined tropical cyclone (showing up well on the 500 MB heights). The tracks were a bit different, though. This caused the ensemble mean to eventually show a weak and broad area of lower heights, rather than the tight signature of a tropical cyclone. It wasn't that the ensemble members weren't showing a tropical cyclone -- it's that the average of the different tracks smoothed it into indiscernibility.

[Amped]

There was a good example of this with one of the recent tropical cyclones -- though I can't remember which one. The GFS and the individual ensemble members had a well-defined tropical cyclone (showing up well on the 500 MB heights). The tracks were a bit different, though. This caused the ensemble mean to eventually show a weak and broad area of lower heights, rather than the tight signature of a tropical cyclone. It wasn't that the ensemble members weren't showing a tropical cyclone -- it's that the average of the different tracks smoothed it into indiscernibility.

Is it possible that the ensemble mean is actually a physically impossible solution?

[icebreaker5221]

Is it possible that the ensemble mean is actually a physically impossible solution?

It could be. If half the ensemble members recurve a TC east of a shortwave and half the members miss the shortwave to the west, the ensemble mean could take the TC right through the trough, which is generally an impossible solution (not counting weird trough-merger scenarios).

Or even in a more general sense, the mean of a collection of balanced (geostrophic, hydrostatic, etc.) members will not necessarily be in balance, making it an unrealistic solution.

[Amped]

It could be. If half the ensemble members recurve a TC east of a shortwave and half the members miss the shortwave to the west, the ensemble mean could take the TC right through the trough, which is generally an impossible solution (not counting weird trough-merger scenarios).

Or even in a more general sense, the mean of a collection of balanced (geostrophic, hydrostatic, etc.) members will not necessarily be in balance, making it an unrealistic solution.

Thanks, I was thinking it might split a storm into 2, which I have never seen a TC do.

[Analog96]

Thanks, I was thinking it might split a storm into 2, which I have never seen a TC do.

It won't split the storm into two. It would smooth it out so much that you get such a "smoothed" solution you would see a very "weak" hurricane move into a very "weak" trough.

[okie333]

It won't split the storm into two. It would smooth it out so much that you get such a "smoothed" solution you would see a very "weak" hurricane move into a very "weak" trough.

Actually in extreme cases (10 members show cat-5 hurr moving W, 10 members show it moving E) you would see it split in two... but in most cases it would be smoothed because true 180 splits are extremely rare, especially for storms of that strength.

[Alpha5]

For all the mets out there....

I'm curious as to how, if at all, the ENSO affects H5 patterns over North America. How does the ENSO, being at the tropics affect our weather up in the mid latitudes. I understand that the Polar Jet is more active during a Nina and the STJ is stronger during a nino, but why does that happen?

Thanks in advance

[isohume]

For all the mets out there....

I'm curious as to how, if at all, the ENSO affects H5 patterns over North America. How does the ENSO, being at the tropics affect our weather up in the mid latitudes. I understand that the Polar Jet is more active during a Nina and the STJ is stronger during a nino, but why does that happen?

Thanks in advance

ENSO theory like all other teleconnection theories should be viewed within a wider spectrum. There are always many different teleconnections, forcings, global blockings, etc, working in concert on the atmosphere at any given time.

Anyway...to address your specific question...the going theory suggests ENSO displaces the upper level heights and therefore the upper level jet locations due to increased or decreased convective activity along the tropics...and it depends what phase ENSO is in as to where these enhanced and prolonged areas of convection occur.

In a ENSO positive phase....the Pacific Jet is aligned in a more zonal config leading to enhanced and increased storm activity along the west coast...and higher cool season heights across the ern conus. In an ENSO negative phase the Pacific Jet is more variable and usually displaced more northerly...leading to a variable but mostly an east coast trof config allowing colder and wetter conds across the ern conus and over the Pacific NW. These are very general guidelines and like I said earlier...all other factors must be considered when assessing any potential ENSO impacts.

[Alpha5]

ENSO theory like all other teleconnection theories should be viewed within a wider spectrum. There are always many different teleconnections, forcings, global blockings, etc, working in concert on the atmosphere at any given time.

Anyway...to address your specific question...the going theory suggests ENSO displaces the upper level heights and therefore the upper level jet locations due to increased or decreased convective activity along the tropics...and it depends what phase ENSO is in as to where these enhanced and prolonged areas of convection occur.

In a ENSO positive phase....the Pacific Jet is aligned in a more zonal config leading to enhanced and increased storm activity along the west coast...and higher cool season heights across the ern conus. In an ENSO negative phase the Pacific Jet is more variable and usually displaced more northerly...leading to a variable but mostly an east coast trof config allowing colder and wetter conds across the ern conus and over the Pacific NW. These are very general guidelines and like I said earlier...all other factors must be considered when assessing any potential ENSO impacts.

I understand, thanks for the help.

I was just looking for how the ENSO contributed to the overall teleconnection community.

[Ed Lizard]

Any usefulness at all in the ESRL reforecast GFS ensembles? Only ask because a couple days in a row would seem to suggest Gulf activity based on precip.

[isohume]

I understand, thanks for the help.

I was just looking for how the ENSO contributed to the overall teleconnection community.

Oh cool...I wasn't trying to downplay your question. However, I have seen folks take ENSO theory rather literally or give it too much weight wrt general seasonal forecasting.

[hckyplayer8]

How can you get negative returns of reflectivity on a radar scan?

From memory, I haven't seen it too often.

[AtticaFanatica]

How can you get negative returns of reflectivity on a radar scan?

From memory, I haven't seen it too often.

What you see on radar displays are radar reflectivity in units of dBZ, which results from taking 10 times the log of radar reflectivity factor (Z) in different units, so if Z is between 0 and 1, you'll get a negative number b/c of the log.

[metalicwx366]

What is a basic summary of all the things you Pro mets/ Meteorologist needed to learn to become a Pro met/ Meteorologist?

Also, how can it snow with temperatures well above 32 degrees?

[am19psu]

What is a basic summary of all the things you Pro mets/ Meteorologist needed to learn to become a Pro met/ Meteorologist?

Also, how can it snow with temperatures well above 32 degrees?

Upper level math and physics. You need to get through Differential Equations, Fluid Dynamics, and Thermodynamics before you can really start learning how the atmosphere works.

If it is below freezing in the atmosphere except right at the surface, snowflakes can hit the ground before melting.

[Thunder Road]

Is there a correlation between a hurricane's speed and the amount of surge produced?

I know a larger size creates a bigger surge. But, for instance, if Irene had been moving twice as fast, its winds would have been stronger (probably) but would the surge have been less?

[am19psu]

Is there a correlation between a hurricane's speed and the amount of surge produced?

I know a larger size creates a bigger surge. But, for instance, if Irene had been moving twice as fast, its winds would have been stronger (probably) but would the surge have been less?

Yes, there is a resonance frequency with forward motion. I forget what the exact number is, but I think it is somewhere around 10 m/s (20 kts). There was an Environment Canada guy working on that relationship.

EDIT: Here is a recent paper from Rego and Li (2009)

EDIT2: The guy I was thinking of was Pete Bowyer. You can find his paper on trapped fetch waves (which essentially produce the same result) on Google Scholar.

[Ed Lizard]

Anybody want to do a primer on the stratosphere/QBO? I see HM discuss it a lot, but it would appear one needs a pre-existing knowledge to follow. Some things, the common teleconnections and indices, Wiki or other internet sources have good right-ups. write ups.

Not so the QBO. How does the stratosphere affect the troposphere, and what are the basic mechanics behind an apparant stratosphere/Sun spot link?

[Thunder Road]

Yes, there is a resonance frequency with forward motion. I forget what the exact number is, but I think it is somewhere around 10 m/s (20 kts). There was an Environment Canada guy working on that relationship.

EDIT: Here is a recent paper from Rego and Li (2009)

EDIT2: The guy I was thinking of was Pete Bowyer. You can find his paper on trapped fetch waves (which essentially produce the same result) on Google Scholar.

Thanks. I'm doing a presentation at my HS tomorrow on how Irene could have been worse (i.e. faster forward speed and no ERCs), and then the absolute worst-case scenario, just for s&g's. Basically a landfall on Cape Henlopen at a 45-degree angle with the coast or thereabouts.

[Chambana]

Question,might be a stupid one at that but it's something ive always wondered and have yet to figure it out. Why do significant storms, severe weather outbreaks, blizzards, hurricanes etc..seem to happen overnight? I've never figured it out... For example... The groundhogs day blizzard really ramped up over night, as did a severe weather outbreak here earlier In April. Just seems like you can never catch a raging blizzard in the afternoon, or a tornado at 10 in the morning.

[Hoosier]

Question,might be a stupid one at that but it's something ive always wondered and have yet to figure it out. Why do significant storms, severe weather outbreaks, blizzards, hurricanes etc..seem to happen overnight? I've never figured it out... For example... The groundhogs day blizzard really ramped up over night, as did a severe weather outbreak here earlier In April. Just seems like you can never catch a raging blizzard in the afternoon, or a tornado at 10 in the morning.

I'm not a met but a lot of this is just coincidence. There are probably many significant daytime events that you just aren't remembering. As far as severe weather, there can be a nocturnal strengthening of a low level jet which can sustain strong/severe thunderstorms well after dark. 10 AM isn't the best time for tornadoes because it is before peak heating and there is usually less instability to work with, but tornadoes can occur at any time of day. I'm sure a met could add a lot more.

[PottercountyWXobserver]

A question for anyone to really answer. I was wondering what would be a couple of meteorological books I could purchase that goes extremely in depth. I already own basic intro books, I'm looking for advanced information. Really any books you mets think were good books in college that helped you learn past the basics would be great.

[isohume]

A question for anyone to really answer. I was wondering what would be a couple of meteorological books I could purchase that goes extremely in depth. I already own basic intro books, I'm looking for advanced information. Really any books you mets think were good books in college that helped you learn past the basics would be great.

The books met students use in college are pretty math and physics intensive. But if you have a good grasp of calculus and calc-based physics, a couple good books to help understand atmospheric dynamics and thermodynamics, etc are Holton's Introduction to Dynamic Meteorology and Fundamentals of Atmospheric Physics by Salby.

[schlontz]

The books met students use in college are pretty math and physics intensive. But if you have a good grasp of calculus and calc-based physics, a couple good books to help understand atmospheric dynamics and thermodynamics, etc are Holton's Introduction to Dynamic Meteorology and Fundamentals of Atmospheric Physics by Salby.

Mesoscale Meteorology in Midlatitudes by Markowski is another really good book that actually does cover a lot of the basics.

[isohume]

Mesoscale Meteorology in Midlatitudes by Markowski is another really good book that actually does cover a lot of the basics.

True...but PottercountyWXobserver wanted info on books beyond the basics.

[LocoAko]

A question for anyone to really answer. I was wondering what would be a couple of meteorological books I could purchase that goes extremely in depth. I already own basic intro books, I'm looking for advanced information. Really any books you mets think were good books in college that helped you learn past the basics would be great.

If you know vector calculus and differential equations, Martin's "Mid-Latitude Atmospheric Dynamics" is a good alternative to Holton IMO. Also, despite having it and never actually reading it ( ), "Weather Analysis" by Dusan Djuric seems to be fairly advanced but lacking long and tedious derivations. For Thermodynamics, we used Grant Petty's "Atmospheric Thermodynamics" - I think that it covered everything needed and in an approachable way.

[PottercountyWXobserver]

Thanks guys, much appreciated! I have some calculus background so I think I can comprehend the intro to dynamics. I'v heard bad things about the Hulton book lol not necessarily knowledge wise but a rigorous and tedious read.

[BadgerWXman]

Martin's "Mid-Latitude Atmospheric Dynamics," Grant Petty's "Atmospheric Thermodynamics"

Both of them were professors of mine at UW, and they were both exceptionally good teachers.

Both of them play in the same cover band called "The Sundogs" (Martin in front and GP on the right):

Cool dudes.