Archive for March, 2007

FRIDAY’S FOLLY
March 31, 2007

For about the past two days a few of the long range forecasting models have been hinting at a cool down for the end of next week. This much is plausible. So far, this months average high temps have been warm, with Fort Smith averaging 72.2º and Fayetteville averaging 68.9º. These figures are both 8.2º and 9.9º degrees above monthly averages, respectively.

The above map, which is a model forecast for late Easter night shows not only cold air being in place but, low and behold, there’s a storm too! A few snow flakes could be flying if (and that is a huge “if”) things panned out as the map is showing. *It should be stated that 9-10 days out is what we like to call “fantasy land” with computer model data, though any type of snow in April, whether cloud or computer generated, is amusing enough and certainly worthy to be this week’s FRIDAY’S FOLLY blog entry.

FYI: Could we actually see some winter precipitation in April? Climatologically the latest measurable snow event happened on April 15th where just under an inch fell.

The Severe Weather Threat Has Ended……
March 30, 2007

Showers and storms have diminished in intensity across northern Texas, and we don’t anticipate any more severe weather for tonight. A few rumbles of thunder along with scattered showers remain in the forecast, mainly across eastern Oklahoma. The complex of storms has been cutoff from the warm humid air, so it will likely rain itself out over the next couple of hours.

Outflow boundaries from this complex may serve as a focus for more storms by Friday afternoon. We’ll watch those storms carefully, especially for large hail and gusty winds.

Heavy rain and storms are expected to redevelop across our area late Friday night into Saturday morning. This pesky storm system will move to our east by Sunday.

*9:30 UPDATE
March 30, 2007

The wind field aloft is becoming interesting. For most of the day, winds from the surface up through 500mb (18,000’) have been out of the due south. Subsequently, thunderstorm activity has remained in a convergent zone through central TX and OK. Winds are now displaying a slight kick to the east. Storms that were pushing through Dallas some two hours ago have been moving to the NNE at some 25 to 30 mph.

We’re just now starting to pick up on some lightning over Stigler and Sallisaw, OK. These storms are likely being kicked up by outflow winds from storms to the west. At this point it’s a good bet that the greater Fort Smith area will at least get wet. We’re continuing to monitor developments for severe weather though the strongest storms remain south of the latest batch of convection in an area that is untapped. If this activity holds together it will likely pass by to the south of the River Valley.

We are also now under a Flood Watch which is in effect through Saturday. A training effect of thunderstorms may produce localized flash flooding with amounts as a high as 2-4” of rain in our aqrea. Not to sound like a broken record but, please remember that if in doubt about the depth of a covered road, it’s best to turn around and find another route. Just a foot and a half of swiftly moving water can float your car and just half a foot can knock a person down. Be smart and be safe!

Newly Issued Tornado Watch:
March 30, 2007

The Storm Prediction Center has issued A Tornado watch which will extend through 1:00 AM Friday morning. This encompasses most of our counties in Eastern Oklahoma and stretches further to the south and west.

Most of the activity today has been confined to central Oklahoma and Texas. The parent Low pressure system has moved very little today as it is near vertically stacked in the atmosphere, meaning that from the surface to about 40,000 feet there is one broad scale circulation. Waves of low pressure have been spiraling around this Low. A wave that’s now pushing into the Dallas area looks to provide the necessary lift to initiate storms to a rather unstable atmosphere later tonight across the area affected by the watch.

Timing wise for our area, the later part of tonight into the early morning looks to be the most favorable for the threat of severe weather. Imbedded thunderstorms may also contain high wind gusts as well as hail. We’ll be tracking all developments throughout the entire event and will be making cut-ins as deemed necessary.

Classic Dryline Storms Tonight
March 29, 2007

All was quiet on the western front early this afternoon. Slowly, the clouds started to break, and the instability started to increase ahead of the dryline. The cap was still in place during the early afternoon, holding off convection until around 4:00 p.m. Surface heating and convergence along the dryline wasn’t enough to break the cap; however, a shortwave rotating around the upper level low helped to break the CAP late this afternoon. Convective initiation started near Plainview Texas, and the storms quickly moved north into Kansas and Nebraska.

Storm movement along the dryline was from the south to the north along the eastern side of the upper level low. The low isn’t moving very quickly east, but a kicker system across the Pacific northwest will slowly help to drive the low toward our area.

Look for Thursday as a whole to be quiet, but storms across central Oklahoma will move our way by Thursday night. Some of those storms may contain large hail and gusty winds. If we destabilize during the afternoon, expect a moisture rich environment for the storms to thrive on. The CAP will likely be an issue for us throughout the day on Thursday, but a shortwave at 500 mb could help crack the CAP if we have enough surface heating during the afternoon. We’ll watch everything closely for you!

Severe Storms for Thursday?
March 28, 2007

Our next big weather maker is moving across the southwest, however, a warm southwesterly flow aloft will dominate our weather pattern for Wednesday afternoon. Look for highs in the upper 70s and lower 80s thanks to warm 850mb temps. So will this trough yield any severe weather?

Computer model guidance suggests that the dry line will fire late Wednesday afternoon and evening across western Oklahoma, but those storms should remain west of our area for Wednesday night.

The dry line is forecast to set up across central Oklahoma during the day on Thursday, setting the stage for showers and storms to roll our way by Thursday evening. Temperatures will likely warm throughout the day on Thursday, but more than likely we’ll have a pretty stout CAP in place. A couple of ingredients will be needed to fire severe storms…

1. Extensive Surface Heating for Destabilization
2. Convergence along the dryline
3. An Upper level Wave to Help Bust the CAP

If the CAP can erode, supercell storms will have a chance to develop and roll our way. Wind shear isn’t very impressive, so the tornado threat will remain low, but large hail and damaging winds can’t be ruled out especially if we have a lot of sunshine!

Ring Around the Moon
March 27, 2007

I know many people have called and e-mailed about the ring around the moon. It was a glorious sight, with a fairly easy explanation.

Typically you see these optical displays when high cirrus clouds precede a storm system from the west. High cirrus clouds are composed of ice crystals, and they help refract the moon’s light. This refraction causes the halo look around the moon. Since the ice crystals have a fairly uniform hexagonal shape, the moon ring is usually the same size.

Once a moon ring is spotted, weather folklore says that rain will be possible over the next few days. We’ll have to see if this folklore is fact or fiction…………

A DEVELOPING LA NINA
March 27, 2007

Over the winter there was an anomalous warming of the waters off the equatorial Pacific Ocean off the South American coast. This is referred to as El Nino conditions. NOAA’s Climate Prediction Center, which is part of the National Weather Service, declares the onset of an El Nino episode when the 3-month average sea-surface temperature departure exceeds 0.5oC in the east-central equatorial Pacific [between 5oN-5oS and 170oW-120oW].

As we head into spring the opposite conditions look to be developing; there is now anomalous cooling of the waters over the same region and this is referred to as La Nina conditions. One of the best correlations between weather events and an El Nino or La Nina pattern exists with Hurricanes.

La Nina produces easterly wind departures at upper levels of the atmosphere and westerly wind departures at lower levels, across the eastern tropical Pacific Ocean and tropical Atlantic. Over the eastern Pacific these wind patterns are in phase with those normally seen in the region, resulting in higher vertical wind shear. The eastern Pacific hurricane season is typically less active during La Niña because of the expanded area of high vertical wind shear.Across the tropical Atlantic these same wind patterns are opposite to those normally observed, and result in lower vertical wind shear. There tend to be more Atlantic hurricanes during La Niña because of this expanded area of low vertical wind shear.El Niño and La Niña also influence where the Atlantic hurricanes form. During El Niño fewer hurricanes and major hurricanes develop in the deep Tropics from African easterly waves. During La Niña more hurricanes form in the deep Tropics from African easterly waves. These systems have a much greater likelihood of becoming major hurricanes, and of eventually threatening the U.S. and Caribbean Islands.

Last year early forecasts were for a severe hurricane season, this was made before El Nino conditions developed. This is now the most attributable factor, as to why last year was so non-eventful. Hurricane season starts in June.

OMNIPRESENT POLLEN & TWO CHANCES FOR RAIN
March 26, 2007

If you are suffering from the sneezing, the itchy eyes, the runny nose, the sinus pressure and the fatigue caused by the blooming season… you are not alone! Many, many people are at about wits end with the pollen. It has been a bad year so far. Pollen counts have been in ALERT status and with the absence of rain, relief has been hard to come by. But, this week as opposed to last is a little more promising in the rain department.

Today a few sprinkles popped up across the Ouachita Mountains, though many of us remained dry. This should change by tomorrow. We’re looking at a developing wave across Texas right now that may bring in as much as an inch of rain for a few lucky areas that get thunderstorms. This should provide widespread showers and thunderstorms across our entire area and pull out late Tuesday. A few localized heavy downpours are possible.

The bigger show for the week looks to affect us as early as late Wednesday in eastern OK. A trough, digging out west looks to carry a few systems into the continental US. The first will likely go well to the north of us but, a secondary low is slated to develop just east of the Rockies and pass through our area. It’s looking like it will have some Jet energy to work with and the wind profile may support some longer lived thunderstorms. We’re monitoring developments closely as it looks like we may have our next round of severe weather in a mere three to four days.

PLIGHT OF A CLOSED-LOW
March 25, 2007

Six days ago a trough was digging, or amplifying if you wish, off the Pacific Coast. With great consistency over some two days, long-range forecast models had this swinging through our area and giving us copious amounts good ol’ H2o. Did this happen? Well, no, not even close! Just take a look around at the ever pervasive green film that has settled on our cars, roads, driveways and has now even moved into our homes. Pollen is what we got and we certianly could use some rain to help wash it away.

So, what went wrong? A closed-low as we’ve mentioned before is a weatherman’s woe or to be PC a forecaster’s woe! This trough dug a hole in the southwestern United States and said “Hasta la vista baby!” as it broke off from the main flow. There an upper level low sat and did it’s spinning thing for most of the past week, while the Jet stream remained north of us and left us in no rain land. Last night part of this closed low pulled north and dished out some fifteen tornados across eastern New Mexico and western Texas. The other part is still spinning, but now this remaining “piece of energy” looks to be picked up by the southern branch of the Jet stream or the sub tropical Jet and pass through our area late Monday and into Tuesday.

What does this mean for us? Say your prayers and keep your fingers crossed, hopefully we’ll finally get some rain. We’re down by some three inches for the month but for the year we’re still hanging tough thanks to a wet January. In the long range we still are looking at a system to impact us on Wednesday night which will likely carry into Thursday. This could be our next round of severe weather. So, we’ll cling to what rain chances we’ve got and hope for the best.