Saturday, June 30, 2012

Hot High Pressure System to Settle In for Next 10 Days (Or More)

The high pressure system currently over much of the United States that is providing for high temperatures and drought conditions looks like it is settling in for at least the next 10 days. Let's take a look at two different ensembles from two agencies.

This image is from the NCEP Ensembles of the National Centers for Environmental Prediction (NCEP). This image is valid for 9 days out, and you can see that the ridge remains in place over a week from today. However, notice the low pressure system just north of the upper Great lakes. This disturbance is forecast by the NCEP ensembles to push south and essentially evacuate the high pressure system to the Western US. This disturbance's southward movement would happen 10 days from now.

This next ensemble set is the Earth System Research Laboratory (ESRL)'s Physical Sciences Division (PSD) Ensembles. You may notice that this image says hour 240 and the previous image says hour 216. That is because the NCEP ensembles initiated at 0z last night, while the PSD Ensembles above initiated at 0z 2 nights ago. Either way, both images end up at 9 days from today. The PSD Ensembles still show the ridge of high pressure over the US, but a low pressure system appears to be dipping into the Northeast rather than the NCEP's idea of a disturbance dipping into the Great Lakes. However, in both cases, the high pressure system is pushed west. It should be noted that the PSD ensembles are weaker with the ridge than the NCEP Ensembles.

So what does this all mean?
I expect the hot temperatures to continue to flourish across the nation. Thunderstorm location along the Ring of Fire is in the air. The reason? the 5880 line. It is common that storms cannot form above the 5880 line in the 500mb part of the atmosphere. So, the 5880 line can be used to forecast thunderstorms. That is why the location is up for grabs, as the 5880 line differs in the ensembles.



Randy the Random Dude said...

Oh yeah, the 5880 trick. I saw Henry margusity mention it last year, I believe. A very old and well known forecasting tool.

carolmc said...

Sorry, new to the site. What is the 5880 line?

Andrew said...

No biggie- it's basically what is considered the maximum level in the 500 millibar part of the atmosphere that storms will usually form in. When there are big high pressure systems like now, one can look to the 5880 line to see where storms may form.