Saturday, January 24, 2009

Bad sounding data 12Z 24 Jan 2009

There is a severe superadiabatic layer aloft in this morning’s TWC sounding due to wetbulbing when the wetted sensor moved into a dry layer aloft. This transition was just below 700 mb and the “observed” 700 mb temperature is at least 5C too cold. See figures.

Wednesday, January 21, 2009

Model Comment from Art Douglas

I agree with your comments on the GFS and ECMWF tendencies over the past two years. I would add that in major pattern changes the ECMWF seems to do a better job in capturing that pattern change before the GFS finally switches. It appears now that the deep trof in the East will soon be replaced by a broad ridge in the Southeast. This pattern change is connected to the retrograding ridge in the Northwest that will be replaced by broad troughing along the Pacific Northwest Coast.

Until Sunday, the GFS was the model that was holding on to a very cold East while the ECMWF was starting to show the reversal with the building heights in the Southeast.Then the 12Z GFS on Sunday looked like last night's 0Z GFS run. Both runs had deep closed lows off California and a building ridge in the Southeast third of the country. This morning's new 12Z GFS has a closed low near Point Conception. As you point out the ECMWF has not been leaning this direction with a coastal system............but it suddenly changed last night with a deep trough down the California coast with similar 552 HTS near Point Conception (but not a closed low in any of the ECMWF ensembles). I bet the 12Z ECMWF will have some members with a closed low.

The current 12Z GFS and older 0Z ECMWF both have >0.50" in southeast AZ for the next 5 days and almost 1" on the Rim northwest of Phoenix. So the models are now converging and this time the GFS is the bold model per the pattern change. What happens on the plains is still a crap shoot given how far out it is.

Performance of the GFS versus the ECMWF

AJ from the NWS has suggested that it might be useful to start a thread on the blog focused on the mid-range performance of the GFS in comparison to that of the ECMWF. So this post is in response to his request.

First, some qualifiers:

I am not a model expert and all of my comments result from subjective appraisal of the various forecasts. I have not attempted to keep any kind of quantitative verifications, and the degree to which I examine the model forecasts at 3 to 7 days depends upon my level of interest and time available. Thus, my inputs are purely informal. I do not have access either to the ECMWF quantitative precipitation forecasts at this time, nor to many of the products from the GFS that are available at NWS offices. I tend to examine products at the NCEP web page and at the PSU electronic wall. I usually examine the 00Z runs, since sometimes the GFS goes into a flip-flop mode where the forecasts are quite different at 12 GMT than at 00Z GMT – I never bother to examine the runs at the 6-hour off times. I usually look most closely at the model forecasts over the Southwest and am thus regionally biased. All of that said, I note the following:

During this winter, and especially last winter, the mid-range ECMWF has seemed to catch important systems, and moisture influxes, better than the GFS. This has been a distinct enough difference that I routinely examine the ECMWF out to 168 hours before I check the GFS forecasts. I have noticed this winter that the GFS operational run is often quite similar to the ECMWF operational run (I don’t have access to, or know where, to examine the ECMWF ensemble members). However, the runs from last night at 00 GMT on January 21, 2009 are VERY different. Thus, today is a good day to try to start a new blog thread.

Note that at 168 hours from last evening (valid time 00 GMT on January 28th) the GFS indicates a quite cold cutoff west of southern California with a distinct 500 mb ridge over western Canada.. The GFS indicates significant precip over much of the West and Southwest and does not indicate precip over the central and northern Plains. On the other hand, the ECMWF indicates the two most important short-waves to be over Colorado and western Canada, with trailing vorticity across southern California into the east Pacific. The ECMWF indicates a frontal like band of precip across the Southwest. But the ECMWF forecasts an intense lee low and strong baroclinic zone over the Plains. Indeed the ECMWF indicates that near blizzard conditions would be impacting the central and high Plains at 168 hours.

I suspect that when the ECMWF performs better than the GFS that it is because its initialization over the Pacific, and also at low latitudes, is capturing features of key importance more accurately. This is sometimes especially noticeable with subtropical features and moisture fields. I think that it is well known that the GFS tends to be too dry over the Southwest.

I have also noticed that if the GFS ensemble members come into sync and consistently forecast precip over southeast Arizona in 10 to 12 of the members, then precip is almost certain to occur. This is true even at low elevations (the 00Z run indicates precip over SE Arizona in only 5 of the 12 members at 168 hours). Note that I have seen a couple of cases during the past two winters where the GFS forecasts were better than those of the ECMWF, but my subjective conclusion remains that I should examine the ECMWF first and then consider and contrast the other models.

What do readers think?

Sunday, January 11, 2009

Happy New Year !

The blog has been a bit quiet lately, but we do have some news:

MADWEATHER has been listed as one of the 100 Best Blogs for Earth Science Scholars !!


Thanks to all of our blog readers and contributors!