Fun with Models...

[chrisbray]

Hello,

I thought for the first time, I would attempt to look at http://weather.cod.edu/forecast/ and look at the models myself, since I have been reading so much about them from the SPC over the years. I figured this would be the best spot to post this since I don't have nearly enough knowledge or experience to post in the target area.

So to begin, yesterday I noted that the SPC had Illinois (where I live) targeted in the day 4-8 outlook for Day 5, or Wednesday, May 2. Now, today when I look at it, they have no areas predicted for May 2. This is what they say:

...DISCUSSION...
MODEL CONSENSUS IS THAT A QUASI-ZONAL PATTERN WILL PERSIST THROUGH
AT LEAST DAY 5 WITH PRIMARY BELT OF WLYS OVER THE NRN THIRD OF THE
COUNTRY. THREAT OF SEVERE STORMS MAY PERSIST FROM PORTIONS OF THE
CNTRL PLAINS INTO MID-UPPER MS VALLEY...GREAT LAKES AND OH VALLEY
DAY 4-5 IN VICINITY OF NE-SW ORIENTED STALLED FRONT AND WHERE A
MOIST WARM SECTOR WILL HAVE ADVECTED NWD BENEATH THE STRONGER WLYS.
HOWEVER...CONSIDERABLE MODEL VARIABILITY EXISTS REGARDING TIMING AND
AMPLITUDE OF INDIVIDUAL WAVES MOVING THROUGH THIS FLOW REGIME. THIS
IN CONJUNCTION WITH AREAS OF ONGOING CONVECTION LOWER CONFIDENCE IN
WHERE A HIGHER COVERAGE OF SEVERE STORMS MAY DEVELOP.

So basically they agree there will be some systems moving through and some activity, but the models no longer agree exactly when or where. So I want to look at these models myself. Since I haven't done this before, I could use some assistance in knowing what to look for. So here are my questions:

1. If today is Sunday, April 29 at about 1530z, I assume for looking at May 2, I want to set the models for +72 hours from now, correct?

2. Since they are indicating uncertainty regarding the timing of the (short?)waves moving through the area, what chart is going to be the best for checking for these waves? I think my current guess would be the 500mb Vorticity and the 500mb Wind. Is that right, wrong or what else do I need to check in addition to that?

3. On the surface, the most imporant things would be to check for temp, dewpoint, and then look at CAPE and possibly the EHI?

Thanks in advance for the tips!

 

[chrisbray]

WEll, Wednesday is tomorrow now.....anyone willing to give me a few pointers on using the NAM/GFS?

 

[Jesse Risley]

WEll, Wednesday is tomorrow now.....anyone willing to give me a few pointers on using the NAM/GFS?

Chris, I would recommend that you grab a cup of coffee, block off a few hours of time, sit down, and start here:
http://www.theweatherprediction.com/winterwx/shortrange/interpret/
http://philadelphiaweather.blogspot.com/2008/01/weather-101-how-to-read-computer-model.html

 

[Zach Young]

1. If today is Sunday, April 29 at about 1530z, I assume for looking at May 2, I want to set the models for +72 hours from now, correct?

Regarding model times: Keep in mind that the medium and long range models (NAM, GFS, ECMWF, etc) are initialized 2-4 times per day at 00Z, 06Z, 12Z, and 18Z. After they begin to run, it will take at least a few hours for the model solution to come out. What you'll need to do is check which model run you're on and then figure out how far forward you need to go from there. In your example above, if it's Sunday at 1530Z then you'll probably be looking at the 12Z NAM (morning run), but you may still be looking at the 06Z GFS (midnight run) because the GFS takes longer to output. If you're trying to look at May 2 you'd want to look at between +78 and +84hrs on the NAM, and between +84 and +90hrs on the GFS. These times would be mid-day to evening on the 2nd.

 

[chrisbray]

Thanks for that clarification, Zach.

And Jesse, I have been looking through theweatherprediction.com, I guess I was just looking for validation if I am checking the right things. Thanks.