All Weather News

Flooding Due To “Retrograding” Low Pressure Center (What does that mean, and where will it go?)

15 Jul 2013, 11:39 am

Let’s start with a quick definition:  What does the term “retrograding” mean?


[re-truh-greyd]adjective, verb, ret·ro·grad·ed, ret·ro·grad·ing.


1. moving backward; having a backward motion or direction; retiring or retreating.

2. inverse or reversed, as order

That is according to – you can click here for more on that…

There IS a reason, however, that we talk about it.  We are talking retrograding low pressure centers, and that area of low pressure is kick-starting flash flooding risks all over regions that would typically be a little bit drier and hotter this time of year (Dallas saw triple digits last week, but was down to the low 80s yesterday and likely will be again today).

Flash Flood Watch
Flash Flood Watch


That image above shows the flash flood watches in effect, in many spots through tomorrow.  It matches up quite well with where we’re already seeing storms moving back into the area.

In fact, take a look at today’s jetstream forecast:


Jetstream Today (Monday)
Jetstream Today (Monday)


The shaded areas represent regions of high wind near the top of the troposphere (the bottom section of the atmopshere, where weather occurs).

Look at where there is the low (the large “L” in a red circle).  That is an area cut-off from the main jetstream region, which is located in the Northwest and also in southern Canada.  Now look back at the flash flood watches over Texas… Interesting, huh?  That is no coincidence!

Luckily, things are going to change – and fairly soon.  Already by Wednesday that area of low pressure continues to retrograde westward… eventually getting sucked in by the monsoonal high pressure circulation over the Rockies.  It gets pulled northward after that.  Check out Wednesday’s jetstream forecast – you’ll easily see the difference:


Jetstream Wednesday
Jetstream Wednesday


Notice also, that slight dip in the jetstream in eastern Canada – that is a cooldown about to moderate things by the weekend across the East/Northeast.

By Friday we’ll start to see some cooler air moving into the Midwest and the Northeast – but that will also kick-start some strong storm chances as the cooler air progresses.


Friday Outlook
Friday Outlook


So – we’ll be on the lookout!

For now, just stay tuned!  More information to come in the next few days!

WeatherNation Meteorologist Aaron Shaffer @ashafferWNTV

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