Mid Atlantic Met Class Thread

[baroclinic_instability]

I'm not positive on this, but I don't actually think it is the vertical stacking of the lows that causes the "eye" - or it is, but not always. When lows vertically stack it signals the occlusion process happening and the ceasing of much further strengthening. All cyclones eventually vertically stack and occlude, but clearly not all cyclones have "eyes". I think the eye formation process has more to do with the frontal structure and occlusion process of some cyclones vs. others. Shapiro-Keyser style cyclones are much more likely to develop an eye (and are also more likely to develop over water, and hence affect the EC region with snow) due to the progression of the warm front. Anyway, this may be a technicality from what you wrote, so I apologize if I'm simply repeating what you've said.

http://weatherfaqs.org.uk/node/98

In general yes, but this can be deceiving because certain storms can exhibit what seems to be a vertically stacked config but are actualy undergoing rapid cyclogenesis. Instant occlusion storms are an example where the surface cyclone can undergo rapid intensification well after the storm has stacked/occulded at the surface.as the main surface low "bends" westward. Intense marine cyclones like the Shapiro-Keyser model with seclusions.

A great example is vertical stretching of a deep PV anomaly interacting with a moist/warm low level baroclinic zone. This type of cyclogenesis happens often on the lee side of the Rockies as deep PV's can stretch vertically rapidly intensify given the right low level thermal environment.

See the April 14-15th 2011 severe weather outbreak/blizzard.

[dtk]

Coming from a software engineering background, I am curious what programming language most models are developed in? Also, what kind of computers are they using to process all of the algorithms?

Almost exclusively FORTRAN (some C++). The NCEP operational computer as well as those at both the UKMet Office and ECMWF are IBM power clusters (6 for us, and 7 for them, I believe). NCEP is getting a new supercomputer in 2013, but the contract was just recently awarded and the details haven't been made available.

[TL97]

During severe season, what is meant by CAPE?

[Amped]

PVA is usually colocated with sthe strongest height falls. At least from what I estimate on the map. Sometimes there is a stray mesovortex that doesn't lower heights much.

[mappy]

During severe season, what is meant by CAPE?

From wiki, though I am sure a met could explain for you further if needed

http://en.wikipedia.org/wiki/Convective_available_potential_energy

[CoastalWx]

Funny thing about this storm...NAM was by far (if I remember correctly) one fo the best guidance in terms of rapidly bombing that surface low and developing that warm sector moist convection and wrapping it into the deform band. That storm had a trop fold I believe.

I think you are thinking of the Jan 11-12 storm perhaps?

[Eskimo Joe]

During severe season, what is meant by CAPE?

CAPE is an acronym for Convective Available Potential Energy, and is used as a metric when identifying the potential for convection (thunderstorm activity). It must be stressed that CAPE is the end all for determining severe weather risk, but is certainly important. Remember that air must have buoyancy (ability to rise) and then condense to form clouds, rain, hail, etc and CAPE provides a measure of this buoyancy. The higher this buoyancy, the quicker air will rise and begin the formation of thunderstorms. The CAPE value is measured in Joules per kilogram (J/Kg) and, generally, you need a minimum of 1,000j/kg of CAPE to see severe weather (Blanchard, 1998). CAPE can reach values of up to 5,000J/Kg, but that is reserved for rare events, such as large scale severe weather outbreaks. Here in the Mid Atlantic a good day is when CAPE gets to ~2,000J/Kg. There are two other types of CAPE talked about in forecast discussions and severe weather outlooks: MLCAPE (Mixed Layer CAPE) and SBCAPE (Surface-Based CAPE). Unfortunately I am not adept at explaining these two terms, but if you were to Google: SPC + MLCAPE or SPC + SBCAPE there are several good snippets of information. Hope this helps!

Reference:

Blanchard, D. O. (1998). Assessing the Vertical distribution of Convective Available Potential Energy. American Meteorological Society, 13, 870 - 877.:

[das]

I don't have much to add other than repeating how good this thread is, and thank you for the information.

Coming from a software engineering background, I am curious what programming language most models are developed in? Also, what kind of computers are they using to process all of the algorithms?

The computing systems are really a system of systems with Supercomputers doing a lot of the heavy lifting and mainframes and client/server stuff taking a significant amount of local load. Here's a high-level diagram of the overall architecture, with some stuff redacted out:

Here's a slide deck that details most of the infrastructure and its tie in to numerical weather prediction modelling. There are some interesting computing systems links on slide 68.

https://skydrive.liv...B544483E3%21258

The local office stuff is typical of a remote or regional office. Local, high-res models with smaller domains are run at these sites so that 1) the main computing systems are not impeded and 2) it offers the local offices more flexibility in ad-hoc runs for significant or hyper-local forecasting needs. Here's a pic of our local office:

http://www.erh.noaa....r/computers.htm

Here's a draft roadmap for the NextGen exascale computing systems that will likely power all sorts of government-facing numerical and graphical predictive analysis systems, including those in NOAA, going forward. I only have the draft on this workstation. Ping me via PM if you want the latest and I'll dig it up when I can.

https://skydrive.liv...B544483E3%21257

[WxUSAF]

Speaking of CAPE and following up about the skew-T discussion, the amount of CAPE can be directly calculated from the skew-T by adding up the area between the parcel trajectory (along a moist adiabat) and the environmental temperature profile. So, if there's a lot of room between the two, you can know the CAPE is high before looking at the calculated parameters directly.

The "opposite" of CAPE is CIN (convective inhibition) and is also measured in J/kg. CIN occurs when the parcel trajectory will lead it to be colder than the environmental temperature. If the parcel is colder, it's not buoyant in the free atmosphere and needs to be forced to a height in the atmosphere where it is bouyant before it can freely begin to rise. When people speak of a "cap", there means the atmospheric profile has a certain amount of CIN to overcome.

[mappy]

Speaking of CAPE and following up about the skew-T discussion, the amount of CAPE can be directly calculated from the skew-T by adding up the area between the parcel trajectory (along a moist adiabat) and the environmental temperature profile. So, if there's a lot of room between the two, you can know the CAPE is high before looking at the calculated parameters directly.

The "opposite" of CAPE is CIN (convective inhibition) and is also measured in J/kg. CIN occurs when the parcel trajectory will lead it to be colder than the environmental temperature. If the parcel is colder, it's not buoyant in the free atmosphere and needs to be forced to a height in the atmosphere where it is bouyant before it can freely begin to rise. When people speak of a "cap", there means the atmospheric profile has a certain amount of CIN to overcome.

The easiest way for me to understand cap was to think of the atmosphere as a pot with a lid on it. The lid being the cap that needs to come off before any storms can develop and grow in size.

[Bob Chill]

Speaking of CAPE and following up about the skew-T discussion, the amount of CAPE can be directly calculated from the skew-T by adding up the area between the parcel trajectory (along a moist adiabat) and the environmental temperature profile. So, if there's a lot of room between the two, you can know the CAPE is high before looking at the calculated parameters directly.

The "opposite" of CAPE is CIN (convective inhibition) and is also measured in J/kg. CIN occurs when the parcel trajectory will lead it to be colder than the environmental temperature. If the parcel is colder, it's not buoyant in the free atmosphere and needs to be forced to a height in the atmosphere where it is bouyant before it can freely begin to rise. When people speak of a "cap", there means the atmospheric profile has a certain amount of CIN to overcome.

Very good explanation. I found this skew diagram while reading through the links that trix posted. I don't think there could be a better visual to go along with your explanation.

[ohleary]

CAPE is an acronym for Convective Available Potential Energy, and is used as a metric when identifying the potential for convection (thunderstorm activity). It must be stressed that CAPE is the end all for determining severe weather risk, but is certainly important. Remember that air must have buoyancy (ability to rise) and then condense to form clouds, rain, hail, etc and CAPE provides a measure of this buoyancy. The higher this buoyancy, the quicker air will rise and begin the formation of thunderstorms. The CAPE value is measured in Joules per kilogram (J/Kg) and, generally, you need a minimum of 1,000j/kg of CAPE to see severe weather (Blanchard, 1998). CAPE can reach values of up to 5,000J/Kg, but that is reserved for rare events, such as large scale severe weather outbreaks. Here in the Mid Atlantic a good day is when CAPE gets to ~2,000J/Kg. There are two other types of CAPE talked about in forecast discussions and severe weather outlooks: MLCAPE (Mixed Layer CAPE) and SBCAPE (Surface-Based CAPE). Unfortunately I am not adept at explaining these two terms, but if you were to Google: SPC + MLCAPE or SPC + SBCAPE there are several good snippets of information. Hope this helps!

Reference:

Blanchard, D. O. (1998). Assessing the Vertical distribution of Convective Available Potential Energy. American Meteorological Society, 13, 870 - 877.:

MLCAPE and SBCAPE are just two different ways of initially lifting the parcel. With MLCAPE you average the temp and dewpoint in the lowest 100mb and lift from where they intersect. With SBCAPE, you lift from the surface temp and dewpoint to get your parcel trajectory. For example, in Bob's post above, the parcel looks to be SBCAPE where the traces start at the surface temp/dewpoint. If you try lifting from the average of the lowest 100mb temp/dewpoint, it looks like you would get slightly less CAPE.

[Bob Chill]

Ellinwood and other severe guys, could you provide a little tutorial on what you guys look for irt t-storms and severe? I have a handle on some of the basics but I thought it was pretty cool that you identified today's threat pretty easily in advance. I'm interested in which charts and models you use.

Thanks!

[Ellinwood]

Ellinwood and other severe guys, could you provide a little tutorial on what you guys look for irt t-storms and severe? I have a handle on some of the basics but I thought it was pretty cool that you identified today's threat pretty easily in advance. I'm interested in which charts and models you use.

Thanks!

Soundings, available moisture, dynamics and jet streaks are the most important things to look at... I'll get something drawn up this weekend but for now it's chase day!

[Bob Chill]

Soundings, available moisture, dynamics and jet streaks are the most important things to look at... I'll get something drawn up this weekend but for now it's chase day!

Excellent. No rush of course. Thread won't be going anywhere and I'm looking forward to expanding my brain this year. Winter analysis is getting kinda boring in these parts. lol

Bring your camera and don't pull a Dorothy and Oz on us!

[TalcottWx]

Sometimes i think the things that inhibit severe can be better to know; dry air, cap, stable marine LL BL, too much shear, lack of mid level lapse rates, no trigger/lift, no cold pool aloft, bad timing, no curved hodo signature, no favorable jet... some obviously already mentioned

[ohleary]

Sometimes i think the things that inhibit severe can be better to know; dry air, cap, stable marine LL BL, too much shear, lack of mid level lapse rates, no trigger/lift, no cold pool aloft, bad timing, no curved hodo signature, no favorable jet... some obviously already mentioned

Not sure "better" is accurate. Alot of these are just the opposite of features you assess for severe risk...so if you learn what causes severe wx, knowing these is a no-brainer.

We are taught to assess severe parameters and look for severe where they overlap, like on a severe composite map. Then once the threat area is outlined, you assess the features that would hinder it. At least, that's what I'd do.

For example, if you look at severe parameters and find an area where they all overlap, there likely won't be a stable marine layer/lack of ML lapse rates/lack of shear/lack of trigger/no favorable jet/lack of hodo sig/etc there in the first place. You initially found an environment where the opposite of all of these are present. Make sense?

[Fozz]

I found this link (http://www.wunderground.com/radar/help.asp) which nicely explains how radars work, but I do have a noob question:

I sometimes see people talking about level 3 or level 2 radars, which I assume refers to NEXRAD's data, but what is the difference between those "levels"? From what I've seen, people talk about level 3 data as if it's inferior, but why?

[NOVAForecaster]

I found this link (http://www.wundergro.../radar/help.asp) which nicely explains how radars work, but I do have a noob question:

I sometimes see people talking about level 3 or level 2 radars, which I assume refers to NEXRAD's data, but what is the difference between those "levels"? From what I've seen, people talk about level 3 data as if it's inferior, but why?

http://www.grlevelx.com/ this is what is being referred to by the "levels" of radar...

[dtk]

http://www.grlevelx.com/ this is what is being referred to by the "levels" of radar...

In many data sets, particularly for observations, the "level" usually is in reference to the amount of processing that has been done to the raw measurement. For NEXRAD, you can find descriptions for

Level2 Here: http://www.roc.noaa.gov/WSR88D/Level_II/Level2Info.aspx

and

Level3 Here: http://www.roc.noaa.gov/WSR88D/Level_III/Level3Info.aspx

[thunderman]

Great resource for comparing soundings and overall synoptic patterns to verified events.

http://www.spc.noaa.gov/exper/archive/events/

[thunderman]

Mesoscale book that I would highly recommend. Served me well at Millersville and has a fair amount of pictures/diagrams if you are a more visual learner. It doesn't really make a hard effort to avoid the mathematics, but it also tries to break things down conceptually so if you have the interest you will likely enjoy it.

http://www.amazon.co...r/dp/0470742135

BTW, this a GREAT thread!

[Bob Chill]

This is probably a good thread to post all our favorite weather links. I'm terrible about organizing my own. I almost feel like paying someone to send me an organized bookmark folder with all the good ones.

Here's a few I really like:

Making composites for analog years:

http://www.esrl.noaa.gov/psd/cgi-bin/data/getpage.pl

Major teleconnection forecasts and historical data:

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/teleconnections.shtml

One Stop Enso:

Nino: http://www.elnino.noaa.gov/index.html

Nina: http://www.elnino.noaa.gov/lanina.html

Historical Data: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

MJO ensemble forecast (GFS):

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/foregfs.shtml

Aweome climate data site (especially for historical location snowfall):

http://climate.usurf.usu.edu/products/data.php

Favorite MD radar (great resolution with temp overlay):

http://www.marylandwx.com/radar/lwx/flashklwxstatebr.php

Favorite Model Links:

GFS/NAM/GEFS/RUC/SREF: http://mag.ncep.noaa.gov/NCOMAGWEB/appcontroller?prevpage=index&MainPage=index&cat=MODEL+GUIDANCE&page=MODEL+GUIDANCE

Euro: http://www.wunderground.com/wundermap/?zoom=4&rad=0&wxsn=0&svr=0&cams=0&sat=0&riv=0&mm=1&mm.mdl=GFS&mm.type=SURPRE&mm.hour=0&mm.opa=100&mm.clk=0&hur=0&fire=0&tor=0&ndfd=0&pix=0&dir=0&ads=0&tfk=0&fodors=0&ski=0&ls=0&rad2=0

There are 100's of other great links out there. Please share your faves. I need to get my stuff organized and I'm always looking for the best links out there. I'm sure there are many other board members who would like to add to their list as well.

[LocoAko]

Mesoscale book that I would highly recommend. Served me well at Millersville and has a fair amount of pictures/diagrams if you are a more visual learner. It doesn't really make a hard effort to avoid the mathematics, but it also tries to break things down conceptually so if you have the interest you will likely enjoy it.

http://www.amazon.co...r/dp/0470742135

BTW, this a GREAT thread!

Seconded suggestion for this book! Great, comprehensive resource for all things mesoscale.

[Bob Chill]

Bumpity bump. New folks, ask any and all questions about models, storm setups, what to look for, etc. 

[Thanatos_I_Am]

Bob, what kind of 500 map would be perfect? Too good to fail kind of perfect.

[psuhoffman]

1 hour ago, Thanatos_I_Am said:

Bob, what kind of 500 map would be perfect? Too good to fail kind of perfect.

These 3 were pretty much locks given the h5 heading into them.

Notice the lower heights to our northeast on all 3.  That is the most consistent feature across all our big snow events.  Also notice the higher heights up to our north in general.  In 1996 it was breaking down (not uncommon) but the damage was done.  That "blocking" tends to help in several ways.  It can displace the PV south and aid in cold pressing down to our latitude.  It promotes lower heights to develop under it, which we need.  And by forcing systems under it it prevents systems from cutting up toward the pole and promotes the sliding under which usually gets them into the 50/50 position.  Called the 50/50 low (its near 50 lat and 50 long) that is the lower heights to our northeast.  That is important because it creates flow out of the north into New England.  This promotes cold transport into our area and when combined with the return flow of the approaching system creates confluence (where two streams merge) which promotes high pressure there. 

Now below is a closer look at 1996 over the CONUS.  Looking at h5 is better because that is about the mid level of the atmosphere in terms of thickness and tends to be the level that has the most influence on driving the pattern.  Think of it like currents in flowing water, or waves.  Troughs and ridges slide around within the flow usually finding the path of least resistance.  And within the flow you get buckling where a major areas of low and high heights can build up and become road blocks that divert and influence everything around them.  Kind of like a whirlpool in the water.  Looking at h5 is looking at the steering currents. 

On the H5 below I highlighted some of the key features that made this a can't miss classic setup.  There are several things to check off.  50/50 low to suppress the flow enough to prevent cutting.  Higher heights over the top leading up to displace things south.  Then a monster system digging into the TN valley with enough room to pump ridging in front and allow it to amplify and ultimately cut off completely and bomb a system up the coast.  But with the 50/50 and suppressed flow across Canada it cant lift north so its forced east under us.  That's also why the western atlantic ridge or WAR is such a problem for us, put a ridge where we want that 50/50 low and a system that digs in and amplifies will simply lift north and the low will cut to our west usually.  As a system amplifies it wants to lift poleward along the east side of the trough, so if you don't have a blocking feature were in trouble unless we get perfect timing.  On the other hand, put a road block to our north, get a strong system trying to come north but being blocked right at our latitude and suddenly were getting crushed.  More resistance means more "convergence" and more lift and thus more potential for heavy precip and in these cases with cold in place feet of snow. 

[Thanatos_I_Am]

Thanks PSU. Another question, what is vort? What should we want around here in regards to that? 

[BTRWx]

50 minutes ago, Thanatos_I_Am said:

Thanks PSU. Another question, what is vort? What should we want around here in regards to that? 

"Vort" is short for vorticity, the spin of the flow.  In practically any weather event, you want vorticity to be as strong as possible for good results.  Stronger vorticity = stronger lift = stronger storms.  Ideally, we'd want the strongest vorticity just ahead of an approaching weather system for the greatest impacts (just as it rolls through).  Here is the nws glossary definition. "A measure of the rotation of air in a horizontal plane. Positive (counter-clockwise or cyclonic) vorticity can be correlated with surface low development and upward vertical motion (in areas of positive vorticity advection)."

Most such maps have the intensity of vorticity shaded yellow as weaker flow, orange-ish for more moderate flow, and red for the strongest vorticity. 

Maybe psu can elaborate more on specifics of vorticity maps.

[psuhoffman]

3 hours ago, Thanatos_I_Am said:

Thanks PSU. Another question, what is vort? What should we want around here in regards to that? 

Usually when we say vort we mean a vorticity maximum embedded in the 500 mb flow. It's a measure of vertical vorticity or spin along a vertical plane. Positive vorticity advection or pva is important in a basic sense because it enhances lift which is what causes precip. 

The h5 map below shows a vort max. The specifics can get complicated and I am tired but this is a really good explanation I found a while ago. 

http://www.weather.gov/source/zhu/ZHU_Training_Page/Miscellaneous/vorticity/vorticity.html

if you still have any specific questions I'd be glad to try to answer them