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Let's get the fall convective season started!


weatherwiz

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With the passage of a very potent reinforcing cold front through the region we are experiencing our first real cool shot of the late summer season as we are only days away from the official beginning to the Autumn season. As we move through September and the sun angle rapidly decreases and wave lengths shorten this reminds us that the hot/humid weather from summer is just about behind us and we can start looking forward to much cooler/drier and more comfortable weather. This isn't to say we still won't see warm or even humid weather, all very possible but the longevity and duration of these events is usually short-lived. Just b/c we are on the move towards cooler weather doesn't mean convective season is done though, while we are done with those juicy cape events we now move onto the season where you can get some fairly nasty squall lines in the form of low-topped thunderstorms as the low cape/high shear season begins to kick in.

Over the next few days it will be rather chilly thanks to the strong cold front that just pushed through the region. As we begin the upcoming work week, however, a warm front will slowly begin to lift northward in response to an approaching cold front/sfc low off to our west. As the front nears and eventually pushes through the region, or at least part of the region...(remember, this time of year models can start having trouble depicting where the warm fronts usually make it), the winds will eventually **** to the south and southwest. This will slowly advect some warmer and slightly more humid air into the region. As of now models seem to indicate a warm frontal passage of about Tuesday. Where the front does pass through temperatures should range from the mid 70's to about the lower 80's with dewpoints creeping into the lower 60's...perhaps even near the mid 60's.

It appears as if the next cold front will cross the region sometime next Thursday. This is also the day the GFS is indicating the most instability (right now around 500-700 J/KG of SBCape) along with LI values of -3C to -4C. With 500mb temps of around -12C and 700mb temps of around +3C and surface temps well into the 70's this should yield to some fairly steep lapse rates. We could see ML lapse rates up around 6.5 C/KM in this instance.

Along with some modest instability we will be dealing with a highly sheared environment. In fact, the GFS is indicating vertical shear values of 35-50 knots out ahead of the front and as much as 40-60 knots of vertical shear right along the front! With some decent forcing along the front coupled with fairly steep mid level lapse rates and modest instability this could be enough to generate some decent updrafts and perhaps form a low-topped squall line out ahead of the front or a forced line right along the front.

With this setup we'd be looking at the potential for strong gusty winds and perhaps some small hail given the lower freezing levels.

These types of setups can be fun, especially considering the temp gradients usually associated along the fronts. We'll see what happens!

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But in all honesty, I love the fall convective season. You can get some reeeally good wind events with these ... also followed by damaging winds behind the front.

The alert maps can get pretty colorful in these cases, with severe thunderstorm watches, warnings, maybe a tornado warning or two, high wind warnings, freeze warnings, maybe a lake effect snow advisory thrown in for good measure by later in the season :)

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:weenie:

No storms this week AMOUT

:weenie:

Still potential for storms out ahead of the front...still looks like the possibility of perhaps a forced low-topped elevated line out ahead of the front, unless we can get some instability which would increase the risk for sfc-based storms and gusty winds. Always difficult though this time of year to get much sun to break out with the way the wind trajectory will be out ahead of the front with ample moisture working northward and lots of cloud debris streaming overhead from the west.

Still have to watch for the front stalling though which could give us a few days of on and of heavier bands of rain.

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