Archive for November, 2007

F4 TORNADO NOV. 29, 1991
November 29, 2007

Tornadoes can happen any time of the year for us, though peak season is in the Spring when temperature contrasts between air masses is greatest. Fall brings about similar conditions, just not to the extent of Spring. It was on this day back in 1991 that our neighbors to the north had to contend with a tornado that produced F4 damage. The tornado traveled some ten miles between Nixa and Springfield, producing devastating damage and unfortunately claiming a few lives.

November 28, 2007

The Arkansas River Valley is many miles wide in eastern Oklahoma, though becomes narrow to almost a point 100 miles east of Fort Smith. Air, cooling across the Ozark and Boston Mountains to the North as well as Ouachita Mountains to the South, especially at night, funnels into the valley and travels westward, flowing towards the wider opening in the valley and thus creates an easterly wind.

In fact, Fort Smith has an easterly wind direction some 41% of the year and at night it is easterly 50% of the time. Precipitation maximum in a 24 hour period over the calendar year peaks at 10:00 PM, correlating well with the nocturnal easterly wind, which lifts warm moisture -laden air as it flows westward towards Oklahoma. One other unique feature of the easterly wind is that often Fort Smith will drop lower temperature-wise than Fayetteville. This type of a set-up is almost always accompanied by a warm southerly wind aloft which downslopes and warms into Drake field. Such was the case last night with Fort Smith dropping to 38 F and Fayetteville only to 45 F.

November 28, 2007

The cold front that will be sweeping through the area later on today is attached to an area of low pressure in the upper Midwest. As this low moves over the great lakes it will create some measurable snowfall. Areas of northern Michigan and northeastern Wisconsin will receive 3-6 inches and surrounding areas will be seeing 1-3 inches. The attached cold front that is moving through our region is very dry and will just give us some strong winds, clouds, and much cooler temperatures. This is a time when our location has really come in handy.

Windy & Mild Wednesday…….
November 28, 2007

We’re looking for more of a spring-like afternoon for Wednesday thanks to a nice southerly feed. Unseasonably mild highs in the upper 50s and lower 60s are in the forecast.

In addition to increasing temperatures, the winds aloft look to speed up by Wednesday afternoon. Look at the 850 mb map above. Notice how strong the winds are around 5,000 feet. 40 to 50 knt winds aloft are forecasted by the NAM. This is a clue that decent mixing will occur, which will translate into gusty winds at the surface.

Expect winds between 10 to 20 mph with wind gusts over 30 mph across NW AR! Unfortunately, cooler air will work back in behind the front toward the end of the week, with high temperatures only in the low to mid 50s.

November 27, 2007

The Santa Ana winds are returning to the southwest for Tuesday night and Wednesday. An area of high pressure system is setting up over the Great Basin and will create a strong flow out of the east and northeast. As the air flows through the mountains and valleys, it will pick up speed and force the dry air into the southwest. It’s this dry and strong wind that is ideal for allowing wild fires to intensify and grow. After what happened just a few months ago, this area is on a major alert for high fire danger. We will keep you posted as this weather scenario unfolds.

Clearing Line………..
November 26, 2007

After several days of clouds and chilly conditions, the sunshine looks to make a return this afternoon. The visible satellite picture shows the clearing line moving into eastern Oklahoma, and the dry air to our west should provide us sunshine and falling dewpoints.

Expect A chilly night with temperatures in the 20s and lower 30s before we warm back up on Tuesday and Wednesday.

November 26, 2007

The wintry mix stayed just to our north for Monday morning. That doesn’t mean we didn’t get any precipitation to start off the work week. Rain showers moved through the area late last night and early this morning leading to some patchy fog and slick roads. The great news is that this system will be out of our way this afternoon and we could actually see a little bit of afternoon sunshine, especially in northeast Oklahoma.

November 26, 2007

Just a little pocket of cold air remains in a semi cut-off area of Low pressure to our WSW. This Low is in what is known as “spin-down” stage. Cold air is no longer advecting (horizontally moving) into the system, and adding to it’s strength. It is filling in and becoming mixed with surrounding air. This process can take up to 5 days or so and the Low will be long gone by then.

But, for the time being, the system has been quite stubborn in going over to an all rain event! Note Abilene’s temperature in the observations (32F) and the snowy scene. As this system passes over our area tomorrow morning, we may see a little bit of a wintry mix and even some light snow. NE OK and possibly NW Benton county stand the best chance as the Low looks to track just south of I-44, though please use caution on all area-wide bridges and overpasses tomorrow morning. There could be isolated slick spots. Be sure to check in with Patrick tomorrow morning for any travel issues or concerns. By tomorrow afternoon we should see breaks of sun and Tuesday looks to be a fine day with ample sunshine and highs in the mid 50s… at this point, the gem of the week!

November 25, 2007

Throughout the day, we are predominantly looking at a cold rain. Temperatures may not break 40 degrees north of I-40. Just along the leading edge of precipitation this morning though, there have been pockets of sleet and possibly a little freezing rain. The ground is still relatively warm so slick spots will likely not be an issue, but with limited visibility and wet roads it would be wise to just take it easy if your traveling today.

As we clear out tomorrow morning, enough cold air on the western side of the Low may give us a brief period of wintry precipitation. Tune in tonight at 5:30 and 10:00 PM for the latest information and any impending travel concerns for your commute to work on Monday morning.

November 25, 2007

Check out the two model soundings for Fort Smith and Fayetteville at 6:00 AM on Sunday. The numbers on the bottom in yellow are temperatures in Celsius and they are “skewed” to the right up the chart, hence therefore the name “Skew-T chart”, which is what the diagrams are typically called.

Of particular note is how close the the red line (temperature) and dashed black line (dew point) are to zero degrees at the bottom of the chart (surface). The temperature profile actually warms aloft and is not below freezing until roughly 10,000 feet, but at the surface all it takes is a shallow layer of air below freezing to create a glaze, especially on bridges and overpasses.

We’ll be updating current conditions at 7:00 AM Sunday and will alert you to any travel issues or concerns.