Monday, October 18, 2010

Southern Plains Weather To Become Active Again

After a week to 10 days of nearly non-existent (but beautiful) weather, a major pattern change is underway in the atmosphere that will bring much more active weather to the southern Plains (and much of the remainder of the nation for that matter) over the coming 2 weeks.  This is to be expected during the 2nd half of October and 1st part of November, so it's nice to see things moving along the meteorological calendar "on schedule" for a change...

If you live in central or south Texas, you've probably noticed the first element of this change this morning:  FOG.  As noted on the 7:43 a.m. surface map from this morning, dense fog is widespread across much of central & east Texas, into adjacent portions of Oklahoma, Louisiana and Arkansas (note the purple symbol that looks like a large equal sign "=", which depicts the observance of fog at the appropriate stations):

The development of widespread fog is indicative of low-level moisture surging back Northward from the Gulf of Mexico.  This moisture return will be an important ingredient in producing rain across the region on an increasing basis over the next week to 10 days.

The second part of the pattern change has to do with wind flow and disturbances in the middle & upper levels of the atmosphere.  Below is the latest computer forecast from the GFS Model, valid at 7pm CDT tomorrow evening, 10-19-10:

Note the panel on the upper left side of the 4-panel image.  This panel shows the expected wind flow at 500mb, which meteorologically speaking roughly corresponds to the "middle" of the atmosphere.  (For a more detailed tutorial on what each panel means and how to interpret the information, go here).

Note the large swirling area of low pressure over the southwest U.S.  This area of low pressure will begin ejecting disturbances to the Northeast into the southern Rockies & Plains this week, bringing increasing chances of precipitation.  Note the latest forecast rainfall map for today through Friday from the HPC:

By Friday, the low is expected to lift out into the Plains, bringing an even more widespread rain event (including an increasing potential for severe storms) to the region at that time:

Also note in the above image (which is the GFS computer model forecast valid at 7pm Friday, 10-22), that yet another piece of energy is already forming back over the Southwest where the original low pressure area had formed earlier). This suggests that an active pattern will continue even after the main low pressure area is ejected out to the Northeast later in the week.

Looking even further ahead, an even more vigorous scenario is forecast next week.  Below is the 240 hour forecast from the GFS Model, valid 7pm CDT Wednesday, 10-27-10:

Note another, even stronger, area of low pressure forecast over the same region in the southwest U.S.  Perhaps even of more interest is the very strong, arctic cold front that is forecast to be surging Southward into the Plains at about the same time (note the upper right panel in the same 4 panel image, which shows the forecast conditions at the surface level).

If this latter scenario verifies, it will be the first significant arctic cold front of the season to impact the U.S.  240 hours is obviously a long ways out, and a lot can change in the meantime, but it definitely bears watching.

Regardless of how all of the above scenarios actually pan-out, the bottom-line is that we're definitely going to see a return to a more active weather pattern over the coming week to 10 days.  Stay tuned!

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