Archive for May, 2008

Another MCS for Sunday Morning?
May 31, 2008

Like clock work, it looks like another complex of showers and storms will roll across NW AR and the River Valley for Sunday morning.  The greatest severe threat will be large hail and damaging wind gusts; we just missed most of the severe weather this morning, however, we’re more in line for the strong to severe storms for Sunday morning.  Many people wonder why there won’t be a tornado threat with these storms.  While we can’t rule out an isolated tornado, these complexes are elevated in nature, and really aren’t close enough to the ground to ever form tornadoes.  Here’s the set-up on how these complexes form overnight…..

Upper Level Shortwave

These complexes have to be set off by something, and usually they are aided by a trough in the upper levels of the atmosphere.  Take a look at the 500 mb chart below.  The bright colors in red indicate great atmospheric lift; notice the bright colors across Oklahoma and Kansas; this wave will spark off the complex after midnight just to our west.

 

 

The 850 mb Low Level Jet

These complexes typically form at the intersection of the Low Level Jet and the upper level wave; since the CAP is strong overnight, the low level jet provides the lift for showers and storms to form above the inversion.  The “X” marks the greatest transport of warm air advection; this is the location where the greatest lift would occur and where storm initiation would likely take place.

Find the Surface Boundary

Mesoscale Convective Complexes always develop along a surface frontal boundary.  Here’s the model depiction on where the front will be at midnight.  Last night this same boundary was to our north, but it will be very close to our area for Sunday morning.  These storms follow the boundary until they develop a cold pool that makes them move further south.

 

 

 

By tomorrow morning the NAM paints the area with precipitation.  Severe weather will likely be a factor, so we’ll be on the air watching it for Sunday morning!

Mesoscale Convective Systems
May 31, 2008

Mesoscale Convective Sytems are the top of the food chain when it comes to nocturnal showers and storms.  These complexes typically develop along a frontal boundary overnight.  The low level jet at 5,000 ft aloft speeds up after midnight, and ultimately provides the fuel for the storms.  The trigger for these complexes is usually a shortwave aloft, typically between 700 and 500 mb.  Once the complex develops, it moves along the frontal boundary until it’s cold pool helps to push it south.

These complexes act like efficient engines; while they feed upon warm, moist, and unstable air, they also emit cool air like exhaust. 

 

 

 

 

Look at the picture above.  Notice the complex of storms within the bright white canopy of cold cloud tops.  As the storm produces more precipitation, it develops a cold pool of rain cooled air.  The cooling produces a small area of high pressure at the surface that’s called a “meso high”  This cold pool flows out the back of the system, just like exhaust from an engine; however, it can also create new thunderstorms on the southwest side of the storm.

Notice the new storm development on the backside.  Eventually, during the late morningthese storms weaken, but more storms south of the complex are always possible during the afternoon if the outflow boundary encounters warm and moist air!

10:00 a.m. Saturday Morning Update
May 31, 2008

 

 

A stationary boundary just to our north has become very active this morning.  A complex of showers and storms has developed across southern Missouri and Kansas along the front, and is moving southeastward toward NW AR.  These storms have produced quarter size hail across Kansas along with damaging wind gusts across portions of Oklahoma.

These storms may contain heavy rainfall, gusty winds to 50 mph, and dime size hail as they move across Benton, Delaware, and McDonald counties.

An outflow boundary has also fired up toward Tulsa, and that looks to move throughout NE OK and NW AR after 10:00 a.m.  These storms may also become strong to severe with hail and gusty winds.

 

 

   

SATURDAY SEVERE WEATHER…
May 30, 2008

We will be under a slight risk of severe weather Saturday. What kind of severe weather could be possible? Here is a look at some of the possible severe weather threats.

HELICITY MAP

This is a look at the Helicity forecast Saturday afternoon. What is helicity? The scientific definition: the transfer of vorticity from the environment to an air parcel in convective motion. This means the possibility of a fluid (in our case air) rotating in a corkscrew motion. So if the helicity is high then that means we could get some rotation with some of these storms. Rotating air could lead to possible tornado formation.

QUANTITATIVE PRECIPITATION FORECAST (QPF)

Here is a look at the quantitative precipitation forecast tomorrow afternoon. The strongest storms look to stay to the north, but a few isolated storms cells could develop over NE OK and NW AR. Rainfall totals don’t look to be too high.

Rainfall totals will range from 0.25″ to 1.0″; Now a few storms could produce heavy rain that could lead to some isolated flooding, but flooding is not the major weather threat tomorrow.

CONVECTIVE AVAILABLE POTENTIAL ENERGY (CAPE)

This map shows us the energy that could be available as the storms develop. We look at a CAPE map when we want to see how how intense thunderstorms could be. Whenever CAPE values are about 1500 J/kg or more; that means that severe storms could possibly develop. CAPE values over our area look to be greater than 1500 and some areas could have CAPE readings near 3000. That lets us know that some of the storms tomorrow could be strong and possibly severe.

SATURDAY’S SEVERE WEATHER THREATS

-DAMAGING WINDS

-LARGE HAIL

-A POSSIBLE TORNADO

Keep checking the best weather blog in the market all day for any changes (good or bad) for tomorrow’s storms.

blog posted by PATRICK CRAWFORD 5/30/2008 @ 7:36am

Weekend Severe Weather Possible?
May 30, 2008

 

Well, yesterday I wrote about the dominant area of high pressure that will grip us early next week; however, we may get some relief this weekend, but that relief could be in the form of showers and storms. 

The last couple of model runs have been consistent with a shortwave trough at 500 mb kicking a frontal boundary right over eastern Oklahoma and western Arkansas for the weekend.  That front, coupled with sunshine, could mean a focus for strong to severe storms.  CAPE values are forecast to run between 2500 and 3500 J/KG, and with some wind shear in place, large hail could be supported by the stronger cells.

We’ll be posting more updates as the new information becomes available!

 

Hurricane Preparedness Week
May 29, 2008

The clip above is of Hurricane Charley, which struck the Gulf side of Florida in August of 2004. 

NOAA has dedicated this week to Hurricane Preparedness.  We’re generally speaking, far enough away to dodge most of the wind from a Hurricane, though a CAT 5 storm traveling at 24 kts., could feasibly spread 50 to 65 kt. winds across our neck of the woods!  Rainfall and flooding potential though brings the threat closer; remnants of both Pacific and Atlantic storms on the right track could dump copious amounts of rain here.  We’ve already seen our share of flooding so far this year.  Remember, just a foot and a half of swifity moving water is enough to float most vehicles, including Pick-ups and SUV’s. 

 

The Death Ridge Returns….
May 29, 2008

 

 

Meteorologists always tend to nickname weather patterns; we always tend to get scared when the dominant ridge of high pressure returns; we call it the the death ridge.  Under the ridge, sinking air prevails, and that means compressional heating.  The jetstream’s circulation is responsible for the surface high pressure area, and that translates into dry and hot conditions.  This type of ridge is a little unusual for this time of the year; we typically expect it toward the summer months!

We’re looking at a ridge to set up over the central United States by the weekend.  The storm chances will remain north along the path of the jetstream.  These systems are affectionately nicknamed “ridge riders”.  If the ridge breaks down enough, we may see a chance of a complex of storms coming our way, but it doesn’t look very promising at this point. 

A Great Video For Storm Structure Fans
May 28, 2008

I wanted to post a video that is clearly not from this area.  This is a time lapse of a low precipitation (L.P.) supercell storm.  Notice how the base of the storm is void of precipitation.  Although no tornado was produced on this time lapse, you can clearly see the inflow on the left hand side of the video. 

If you are an avid chaser in our area, clear pictures like this will make you very jealous; however, to see storms like this, you need to be right along the dryline.

FRIDAY’S HEAT AND HUMIDITY
May 28, 2008

I have some good news and bad news about this Friday. The good news, well, it’s FRIDAY! The bad news, well, it’s going to be hot and humid. Here is a look at the temperature forecast for Friday afternoon. Temperatures will reach the lower 90s for the River Valley and the upper 80s in Northwest Arkansas. We can handle these temperatures…right? Well, there is something that we are going to have to add into the Friday weather stew…Moisture!

Dew point temperatures will be in the mid 60s and possibly in the lower 70s! That means heat index readings will be in the mid and upper 90s. We might be wishing it was Friday, but after the dry and crisp afternoon we will have today…maybe Wednesday is not so bad.

blog posted by Patrick Crawford 5/28/2008 @ 9:58am

3:30 P.M. Storm Update
May 27, 2008

The cloud cover continues to limit any thunderstorm development this afternoon.  This is the current visible satellite picture, and the overcast conditions still dominate.  Isolated storms will still be possible if we see sunshine during the late afternoon and evening; however, without the sunshine to help destabilize the atmosphere, we’re looking at a very small chance for redevelopment.  The SPC has shifted the severe threat for today south of our area, and that makes sense due to the cloud cover.

 Our next chance for more storms will be possible after midnight; however, no widespread severe weather’s expected overnight.  Strong gusty winds, heavy rainfall, and small hail will remain the threats!