Of course, in my days off, a powerful nor'easter swamped the east coast with rain and heavy snow. Blizzard conditions were experienced in New York City. It was quite the event.
But I kind of missed that. So, instead I'm turning to the potent trough that models are indicating should move through the country late this week.
What trough is this? Here's the 96 hour GFS 500 mb height forecast for Friday morning--
|Fig 1 -- 96 hour GFS forecast of 500 mb geopotential heights and winds for 12Z, Friday, Dec. 31, 2010. From the HOOT website.|
|Fig 2 -- 96 hour GFS forecast of surface temperature (shaded), sea-level pressure (contoured) and winds (barbs) for 12Z, Friday, Dec. 31, 2010. From the HOOT website.|
|Fig 3 -- HPC surface analysis from 15Z, January 7, 2008. From the SPC Severe Thunderstorm Event Archive.|
However, there are some noticeable differences between these two events (or rather, from this theoretical GFS forecast and this event two years ago). First, the surface temperatures are rather different. In the GFS forecast, northern Illinois is only in the upper 30s in the morning, where as in the map from January 7, 2008, the dewpoints (and consequently low temperatures) were in the 50s--so not only is it much cooler, there also doesn't seem to be as much moisture. In fact, looking at the GFS dewpoint forecast for the same time:
|Fig 4 -- 96 hour GFS forecast for dewpoint temperature (shaded) and winds at 12Z, Dec. 27, 2010. From the HOOT website.|
However, in looking at the 500mb chart from 12Z, January 7th, 2008, we see more differences:
|Fig 5 -- Objective analysis of 500mb heights, winds, and temperatures from 12Z, January 7th, 2008. From the SPC Severe Thunderstorm Event Archive.|
We can also look at the upper air temperatures to get a hint at possible instability. In figure 5 above, on January 7th, 2008, the 500mb temperatures over the surface baroclinic zone (over the fronts) ranged from the -10 to -15 degree range in the lower Mississippi valley to around -20 degrees Celsius over northern Illinois and southern Wisconsin. Looking at the GFS 500mb temperatures forecast for this Friday shows surprisingly similar numbers:
|Fig 6 -- 96 hour GFS forecast of 500mb temperatures (shaded), geopotential height (contoured) and winds for 12Z, Friday, Dec. 31, 2010. From the HOOT website.|
|Fig 7 -- BUFKIT GFS 108-hour forecast sounding for KRFD for 00Z, Jan. 1, 2010.|
Anyhow, just thought I'd do a quick run down comparing this long-term forecast to the January 7th event after noting the striking similarities in the surface patterns. However, as we can see here, just because the conditions look similar from being viewed one way doesn't mean that they are similar in other ways. We'll still see unusually warm temperatures throughout much of the middle of the country and probably some thunderstorms somewhere this Friday. But at this point it doesn't look like quite the severe weather event we had two years ago.
Things could change in the models, though. And they most definitely will. 96-hour forecasts are still way, way, way out there and there's no doubt that that GFS forecast will change in the days to come. Already there's disagreement with the ECMWF model. Here's the ECMWF 500mb chart for the same 96-hour forecast:
|Fig 8 -- 96 hour ECMWF 500mb forecast winds (shaded) and geopotential heights (contoured) for 12Z, Dec. 31, 2010. From the HOOT website.|
We'll just have to wait and see how this one all comes together.