Archive for September, 2008

Another Cool Shot of Air is Coming…
September 30, 2008

This is always a busy time of the year in the upper level wind department.  Large temperature contrasts across the northern hemisphere are causing the winds aloft to intensify, and that means a  more active pattern with fast moving fronts.  Look at some of the wind speeds at 30,000 ft!

We just had a front move through yesterday; another one is on the way for Wednesday night.  This next front will usher in cooler air, while keeping highs on Thursday into the upper 60s and lower 70s!  Some spots on Friday morning may approach the upper 30s.

Here’s the culprit, a cut-off feature across the northeast.  This low will be responsible for a northerly flow aloft through Friday.  Translation, cooler than average temperatures, and a relatively dry airmass.  This low will finally move east, and warmer temperatures will build our way toward the weekend under a ridge.

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October Averages…
September 30, 2008

September is just about over, so here are the averages for the month of October.  This is a great time of the year across our area; just wait until the leaves really start changing!  We’ll be updating those changes as the reports start to come in, so stay tuned to the weather blog over the next several weeks.

Subtropical or “Extratropical” storms / Laura
September 29, 2008

The two blue circles highlight the remnants of “Kyle” to the north and the newly named tropical storm or more aptly titled “subtropical” storm “Laura”.  Laura shares both characteristics of a mid-latitude storm system and a tropical system.  It is a hybrid storm of sorts.  Here’s a more formal definition from the AMS Glossary:

 

subtropical cyclone—A cyclone in tropical or subtropical latitudes (from the equator to about 50°N) that has characteristics of both tropical cyclones and midlatitude (or extratropical) cyclones.

 

They occur in regions of weak to moderate horizontal temperature gradient and extract the associated available potential energy, as do baroclinic cyclones, but they also receive some or most of their energy from convective redistribution of heat acquired from the sea, as do tropical cyclones. These storms usually have a radius of maximum winds that is larger than what is observed in purely tropical systems, and their maximum sustained winds have not been observed to exceed about 32 m s−1 (64 knots). Subtropical cyclones sometimes become true tropical cyclones, and likewise, tropical cyclones occasionally become subtropical storms. Subtropical cyclones in the Atlantic basin are classified by their maximum sustained surface winds: Subtropical depressions have surface winds less than 18 m s−1 (35 knots), while subtropical storms have surface winds greater than or equal to 18 m s−1. While these storms are not given names, forecasters do issue warnings for them.

Laura is on the edge of the northward extent of warm Atlantic and is questionably over water below the 26 C temperature threshold usually associated with a strengthening tropical storm.  Interestingly, the official forecast calls for Luara to strengthen to just below a category I storm, with max sustained winds of 60 Kt. by 5:00 PM Tuesday.  The storm will more than likely still look quite impressive as it moves across the northern Atlantic in the days to come.

Average First Freeze Date…..
September 29, 2008

Many people have been wondering when the average first freeze happens across our viewing area.  Ask and you shall receive.  Even though we’re going to be cool this week, freezing temperatures do look to stay away.

Cold Front Coming Through…..
September 29, 2008

It’s been a beautiful day across the entire area; however, some cooler changes are very evident behind a cold front highlighted in blue.  Most impressive are the dewpoints to our northwest.  Look at the dry air across Kansas and Nebraska; dewpoints have fallen into the upper 20s and low to mid 30’s.  In response to the dry air there are frost advisories across northern Kanasas and southern Nebraska.

This dry air will move our way throughout the next several days.  This air mass will allow for great cooling on light winds overnight.  We won’t see freezing temperatures, but the 40’s look to be a good bet throughout the rest of the week.

FINALLY FALL WEATHER!
September 29, 2008

The big cold front that we have been waiting for to cool our temperatures down finally arrives later today.  When we are looking at the movement of cold air, the best way to follow the temperature trends is from the 850 millibar map.  The 850 millibar map is about 6000 feet above sea level and takes out the effect of friction.  Here is a look at the 850 temperature maps for the next 48 hours and you will be able to visually see the movement of the cold air out of the north.

MONDAY AFTERNOON (850 MILLIBAR TEMPERATURE)

TUESDAY MORNING (850 MILLIBAR TEMPERATURE)

TUESDAY AFTERNOON (850 MILLIBAR TEMPERATURE)

Way on out…
September 28, 2008

If you’ve ever been to the beach and done some body surfing or perhaps boogie boarding or surfing, you know that waves come in sets.  The same can almost be said for the atmosphere; sometimes a quiet weather pattern is followed by a set of waves (weather disturbances in this sense), which can successively intensify, only to peak and then become quiet again for a period of time.

 

The above maps are at the outer fringes of a model run.  Little imperfections in the initial assessment of the atmosphere at this point (384 hours out) can become monsters of erroneous bunk junk!  What’s interesting here though is that the above maps are within the realm of possibilities for early fall weather.  If such a scenario were to develop as the maps above depict, then a potential severe weather event would be knocking on our door!  As we move into October we’ll have to be watching out for such a set up or two where the clash of the air masses meets up with some significant jet stream energy and a sharp cold front is in place to make it all happen.

KYLE… lopsided!
September 26, 2008

Kyle is struggling to maintain intensity and / or strengthen! Part of the problem is a steady stream of 20 Kt. westerly winds, shearing the storm apart.  In fact, most of the strong thunderstorms and highest winds are on the right hand side of the storm.  Most of the left hand side is just marked by clouds spiraling around the center.  As Kyle continues on a northerly track, this “wind shear”, which is keeping the storm looking so asymmetrical, should lessen, providing a more favorable environment for strengthening.  As Kyle continues northward however, warm water which serves as fuel for the storm will become a scarcer commodity. Present winds are at 60 mph, just 14 shy of hurricane strength.

 

 

WIND SHEAR

 

FALL FRONT ON THE WAY!
September 26, 2008

We have been warmer than average over the past several days and everyone is wondering when it’s finally going to feel like fall.  Well, the wait will soon be over as a cold front will be moving in out of the west and northwest by Tuesday.

TUESDAY MORNING SURFACE MAP

This front won’t have that much moisture to work with and that means shower chances will be very low.  This front will be strong enough to drop our temperatures anywhere from 5-10 degrees for afternoon highs.

TEMPERATURE FORECAST TUESDAY AFTERNOON

and then there was… KYLE!
September 25, 2008

Over the past several days, a weather disturbance near Puerto Rico has been flirting with tropical characteristics and organization; it has now officially become “Kyle”, the eleventh named storm of the 2009 Tropical Atlantic season.  For a while, a coastal Low which is now impressively “spun-up” off the southeast coast looked like it was going to grab the name.  The shot above is of Kyle and the one below is of the un-named Low.  As far as looks go, certainly the coastal Low has more of the classic appearance of what one typically envisions at the mention of the word tropical cyclone, but the storm to the south got the name.

 

The composite wider-range view highlights both storms.  Interestingly, winds on the backside of the coastal Low at mid-levels of the atmosphere are Northeasterly.  This will keep us dry and temperate through the weekend.

 

The latest model tracks have Kyle taking an almost due northerly track, though a few take the storm into the coast.  A front looks to scoop up the retrograding Low by late in the weekend and carry it off to the Northeast.