Archive for May, 2007

The Low Level Jet and Nocturnal Storms…….
May 31, 2007

You will often hear us mention on television the formation of a low level jet that feeds into thunderstorms; moreover, LLJ’s serve as a great initiator for overnight thunderstorm complex development, and locating them can be a key to pinpoint thunderstorm formation. Last night we saw a complex of storms called a Mesoscale Convective Complex (MCC) initiate across western Oklahoma and move southeast all the way into Louisiana. This organized complex of storms was responsible for 20 severe wind reports. Could we see these types of storms in our area?

Our current weather pattern has a broad upper level low spinning around the upper Midwest. Low level moist air is surging into this low from the south, creating a favorable environment for these complexes to develop. Let’s take a look at some of the latest model data that suggests a possible scenario for nocturnal storms by Friday morning.

This 850 mb forecast chart above let’s us know where to start looking. Notice the winds are moving north toward our low pressure area across the upper Midwest. This ribbon of strong air around 5,000 ft is responsible for transporting rich moist air from the Gulf of Mexico. We call this ribbon of air the “low level jet (LLJ). It’s typically a wind at 850 mb that’s stronger than 35 knts that can provide moisture and lift for storms to form.
The maximum wind speed appears to be close to 50 knts across west Texas into western Oklahoma around midnight. The LLJ becomes stronger at night due to less friction in the lower part of the atmosphere we call the boundary layer. Radiation from the sun stops, so the ground begins to cool rapidly. Air aloft remains warmer, so the boundary layer becomes stable. Since friction drops off on top of the boundary layer, the winds become faster, and transport more moisture north. LLJ’s are almost always apart of MCC development, so this is our first clue, but now we need to find a disturbance aloft to kick all of this off.

This is a 500 mb chart. We look for atmospheric waves aloft to indicate areas of rising air. We want to find a point where the 500 mb wave intersects the 850 mb LLJ. If we can find a correlation, then we’ll have an idea on where convective initiation will occur. Look at the wave over west Texas and Oklahoma that’s created by our main storm to the North. This is where the LLJ pools in from the south. This disturbance aloft is depicted by the WRF model at Midnight on Friday morning.
Most likely convective initiation will occur across western Oklahoma/Texas, and eventually move southeast. The stronger the cold pool, the faster the MCC movement. We’ll have to watch our eastern Oklahoma counties closely as we head into the early morning hours on Friday.
Advertisements

Added Moisture Means Fog……
May 30, 2007

This picture was taken from Poteau, Oklahoma from our recent saturated weather pattern. Of course we have all of the ingredients coming together, not only for the rain, but for foggy conditions as well. At 850 mb look at the dominant high over the SE. This high is responsible for pumping moisture off the Gulf of Mexico and straight into our area.

That southerly feed has provided us ample chances for rain during the afternoon; however, at night, the winds have been going calm, and the temperature has quickly cooled to the dewpoint under a partly cloudy sky. This has been the recipe for overnight fog development; moreover, the added rainfall only helps to saturate the layer of air right above the surface, so fog tends to quickly develop where the rain falls.

HAVES & HAVE-NOTS
May 29, 2007

It was another day of the “haves” and the “have-nots”; where it did rain, there was plenty, where it didn’t, it just remained warm and muggy! A viewer from Heavener, OK was most certainly among the “haves”. I spoke with her earlier in the evening and she said that around 7:45 PM or so she heard a loud “whoosh”. This was while it was raining hard with lightning and thunder, but she just thought that it was an afternoon t-storm… that is, until she heard the “whooshing” noise, which seemed to last for about a minute. When she looked out her front door, much to her dismay, a tree had fallen on her Pathfinder!

Elsewhere, one complex of storms that pushed through Benton County prompted a short-lived t-storm warning for McDonald County in MO. As we lost the heat of the day, the activity dwindled.

The pictures tell a nice story. Plenty of moisture along with significant daytime heating can produce some impressive storms, capable of gusty winds, small hail, dangerous lightning as well as profuse amounts of rain! We’re definitely in spring, and with any one thunderstorm, a significant threat arises.

ANOTHER SLOW LOW… (a look at the week ahead)
May 28, 2007

… is going to make you mow!

Look over Texas at the blue L. Note how it’s sitting in a carved out green line and this line is by enlarge, alone across the southern half of the country as opposed to being among several others, as is the case in the northen half of the states. These lines are isobars, or lines of equal pressure, and the close proximity of the lines along the US / Canadian border represent the region of the fastest moving winds otherwise known as the jetstream. Mr. Texas blue L (TbL) is far removed from this speedy high way. Think of it like this; instead of cruising along, making time, doing 90+ mph, Mr. TbL is lost on a dirt road and struggling to go 5 mph!

TbL spells “trouble” if you’re hoping for a dry start to the week ahead.

The dip in the jetstream over Washington, Oregon and Idaho looks to be the saving grace from the rather muggy pattern we’ve been in for sometime now. This storm system, with a little luck and a prayer, will hopefully drag a cold front across our area by Friday, ushering in a much cooler and dryer air mass. It may not be too long lived, but we’ll save that thought for another blog entry. Until then, it’s on / off shower and thunderstorm activity, ramped up by daytime heating and a few waves spinning around TbL, throughout most of the week.

If you happen to take a peak at our superdoppler radar and see a window of clear, then start that engine and mow away, either that or wait until the weekend!



STORM PICTURES May 27, 2005
May 28, 2007

More photos taken by 4029 Storm Tracker Brian Emfinger… THANKS BRIAN!

Loosely quoting him:

“This one was taken NE of Ozark. A wall cloud look alike kinda – it’s where a wall cloud should be (sw corner of storm – pic is looking east) but it wasn’t connected to the tower…so it’s a far less impressive shelf cloud.”

“Same storm looking north now into heavy rain core.”

“and again same storm actually showing a bit of the structure (looking Northwest now). It was really short but plenty of available moisture allowed it to put down some really heavy rain. AND of course there is the look alike Tornado there below the updraft which is just scud. The scud was going up but not very fast at all…however technically speaking the lowering below that updraft base from where the fake tornado is coming down from would be a wall cloud.”

A FEW STRONG STORMS TODAY…
May 27, 2007

4029 Storm Chaser Brian Emfinger sent this photo in today. Thanks!

We saw quite a few terrain induced thunderstorms pop up as we neared peak heating in the mid afternoon. A complex that pushed through regions of Benton and Carroll counties passed right over Beaver lake gathering steam as it pushed into southern MO. A few warnings were issued some time later as the storms continued to move to the north.


The above picture shows a nice rain shaft or perhaps a small-scale wet micro burst, a concentrated area of rain cooled air that falls rapidly from a decaying thunderstorm. In this case not all of the rain was evaporated. There may have been some embedded small hail too.

There is an upper level storm system now over Texas. This is moving very slowly and interaction with a few faster moving waves may likely develop a complex of storms that drops heavy rain across portions of south eastern OK. Just in the last hour, interaction of the upper level low with a wave that has pushed into the pan-handle has exploded into region of heavy rain with embedded thunderstorms.

Remember that just a foot and a half of swiftly moving water can float your vehicle away and just a mere half foot of moving water could knock you down. Please do not try to cross flooded roadways. TURN AROUND DON’T DROWN!

FRIDAY’S FOLLY
May 26, 2007


So here we are at the unofficial start of summer with the arrival of Memorial Day weekend, but perhaps you’re not quite ready for the hazy, hot and humid stuff and you just didn’t get enough winter… well head south!

High up in the Andes mountains of South America there is snow and plenty of it! Winter is just beginning! Check out the beautiful pictures from Las Lenas, a resort in Argentina… (I’m crying a little that I can’t get a day on those slopes). According to their snow report LAS LENAS, they already have a base depth of 158 inches at the top and 121” at mid-mountain. Ok, enough dreaming, back to home…


We received anywhere from a ¼” to an inch of rain today and this has helped bring rainfall totals for the month even closer to average. We are presently running about a half an inch to an inch shy. This should not be too hard to make up by June 1st.

Yet another wave, cycling around an upper level storm system, is putting down more rain on the Texas panhandle. This complex is moving to the North East an will weaken by morning, though a stray outflow boundary may be a focal point across NE OK tomorrow for a few afternoon t-storms. We’ll be muggy and mild over the course of the holiday weekend with a slow rise in high temps. A few showers and storms will be scattered about in the afternoons, firing off with the heat of the day, though don’t let them spoil your plans. Most will be short lived.

We’re watching a developing system which had promised to cool us down and dry us out by the end of the upcoming week, though the cool-down is now looking less and less likely. There’s still plenty of time to work on that forecast, so for the time being…

HAVE A GREAT HOLIDAY!

More Impressive Pictures…
May 24, 2007

A Storm Chaser Killer…..

Look at the inflow……..

This is a great picture of a mesocyclone
Thanks to 40/29 Storm Chaser Brian Emfinger for these shots!

Oklahoma Panhandle Storms
May 23, 2007

Take a look at these pictures from 40/29 Storm Chaser Brian Emfinger. They were taken from his web camera near Canadian, Texas. He’s seen many wall clouds tonight, and that area looks to be active throughout the evening with supercell thunderstorms. The CAP busted around 4 this afternoon, and the storms exploded! There was even a report of softball size hail.

Outflow Boundary….
May 23, 2007

Look at the outflow boundary from the satellite photo above. On this visible image it shows up as a thin cloud line that is well ahead of the surface cold front which remains in western Oklahoma. This cool air has rushed hundreds of miles ahead of the storms along the front; moreover, it could be the key to future thunderstorm development across our area this afternoon.

With sunshine already breaking out, we’ll need to watch where this boundary goes, in order to pinpoint where convective initiation will occur. This is a great example of how satellite data can be very useful when creating a forecast.