Hand Analyzing VS Pre-analyzed Maps

[Andrew Pastore]

Which method does everyone use, and is there any benefit/drawback to one or the other?

 

[Robert Dewey]

Some people, myself included, feel that hand analysis will allow you to kind of get a "feel" for the atmosphere, since your paying extra attention. Whether your doing hand analysis on a piece of paper, or a hand analysis drawn out on a computer (programs such as GEMPAK, or even MS Paint, where you can draw the iso-lines using the mouse), its' the same... As far as pre-analyzed, that is certainly good too, for situations where you can't take the time to do a standard hand analysis...

 

[rdale]

The drawback to machine analysis is primarily that the computer doesn't ignore bad data... The advantage is 1) time and 2) if you don't know how to draw! The advantages to hand analysis are numerous:

http://www.cimms.ou.edu/~doswell/human/Human.html
http://www.cimms.ou.edu/~doswell/sfcanal/s...e_analysis.html

 

[Andrew Pastore]

I ask because I cannot seem to get ahold of hand analysis. I will draw out the map and compare them to computer analyzed maps and find that they are wrong. My biggest problem is not knowing where to start on the maps, then it is where do I go! Lets say I am drawing a 80 knot isotach, well which 80 knot isotach is next? I am sure I will figure it out, as I have not been doing it long, but any advice would be of help.

 

[PaulChambers]

Tim Vasquez (Weather Graphics) puts out at least 2 books that have helped me understand mapping better. One is "Storm Chasing Handbook" and the other is "Weather Map Handbook"

You might check his website for others.

 

[Tim Vasquez]

Isotachs are usually drawn on the odd tens digit, i.e. 30, 50, 70, 90, etc. But that's just standard convention.... I say use whatever works for you. As long as it presents the information for you coherently but isn't too tedious, it's all good.

As an aside I will say that I am a militant advocate of hand analysis, and if I don't challenge anyone to a duel over the issue it's just because I don't have time. There's a world of difference in just glossing carefully over premade maps and actually digging yourself into the trenches of the meteorological fields. Also the objective is not to draw the lines, but to use the lines to formulate a "visualization" of what is happening meteorologically. I think my visualization skills are outstanding but even I have trouble picking out subtleties just looking at preplotted/preisoplethed maps -- usually any map crossing my desk doesn't escape without a few pencil streaks here and there. Plus... word on the streets these days is that boundaries are all-important for demarcating an area of tornadic storms. Those rarely jump out at you, and are often annoyingly embedded/hidden in the data.

If you're seriously short on time, or the chase or forecast is not that important, then hand analysis probably isn't necessary. But if it's an important chase, time MUST be found to analyze (i.e. diagnose) the current weather. It comes down to time management -- the coats of Rain-X and organizing the camera gear can always be done at another time, like on the road. In chasing, being in the right place is like holding a royal flush.

Tim.

 

[Andrew Pastore]

I have the storm chasing handbook, and my woman got me the forcasting handbook, but I still have not yet got to reading it. I have a repreve coming up from work, and I am going to tackle the book then.

 

[mikedeason]

Several important points I'll add:

1) You will get frustrated at times, but don't give up. Hand analysis is not something most folks are born with the talent to perform. It's takes lots of practice to gain confidence in what you're doing, but you have to start somewhere. Even after almost 15 years, I still feel the urge to occasionally throw my hands up and admit defeat. ;-)


2) Give 5 people the same data plots and I'll bet the farm you get 5 different, if only subtle, analyses. Sure there are times when there could be gross errors in someone's analysis and sometimes important mesoscale features may be missed if you're not using all the resources available (especially satellite and radar imagery), but when done properly, there will still be variations among analyses. This is an inherent fact of life in subjective analysis. The important points to remember is data validation/QC and using ALL resources to ensure you create the most accurate representation of the state of the atmosphere.

3) If you are doing a series of analysis over a temporal range, continuity is very important. Many mesoscale and almost certainly all synoptic scale features do not just randomly disappear and reappear in a short range of time (say, 3 to 12 hours), but sometimes they do become "hidden" in the data, such as when the surface observation network is not dense enough to resolve an outflow boundary that may have appeared on a previous analysis. It is important to consult your previous analysis to refer to these items and, as in point 2, use other resources to provide clues as to their current location.

I know it's not much, but to me, these are important items to remember when doing subjective analysis.

Regards,

Mike

 

[Tim Vasquez]

Here's how my time budget breaks down when analyzing the charts on a typical storm day, and generally how I go through them in order:

1. 300 mb - About 2 minutes... find jet axes, outline a band of the most important isotachs, look for unusual patterns that may be associated with strong synoptic-scale vertical motion.

2. 200 mb - About 1 to 2 minutes... same as #1 but subtropical jets become more of a factor.

3. 500 mb - About 2 minutes... looking for jet axes and cores, and short waves (dampened in #1 and #2). Vorticity fields and satellite may be of some help in finding them.

4. 700 mb - About 1 minute... analyze the thermal field, maybe lay down isotherms every 2 deg to get a feel for the distribution of the cap. This layer usually intersects right through the cap.

5. 850 mb - About 2 minutes... analyze for fronts (sometimes more obvious here than at surface), quickly extract dewpoints and perhaps quickly isopleth those to see moisture distribution (gives some sense of depth/richness and what to expect on the soundings). It's important to keep in mind that the AGL height of this surface drops as you go west in the Plains, and intersects the ground near the Front Range.

6. Surface - About 5 to 20 minutes. Find obvious boundaries, lightly sketch in. Plot isobars. Synthesize with radar, 1 km vis, upper level charts, soundings, continuity. Look for interesting qualitative features (i.e. air masses, character of cloud layers, etc) that may reflect on the forecast. Harden in boundaries.

Tim

 

[Matthew Havin]

Time permitting, go for hand analysis, it is superior and rewarding as you can see from what others have posted. Got 20 seconds? Go for pre.

 

[Scott A. Kampas]

I'm curious as to what maps people use to do manual analysis. Digital Atmosphere, GEMPAK, etc. can produce suitable maps, and there are various maps available on internet sites like UCAR and COD. What do other people use, or prefer?

Scott