Archive for December, 2008

LATEST ON WINTER WEATHER CHANCES…
December 31, 2008

The winter weather chances are still in the forecast next week (Monday/Tuesday/Wednesday), but the timing and the strength of that storm will continue to come into question.  Latest model runs keep the heaviest precipitation out of the area.  That is great news, but it only takes a little winter weather to create dangerous road conditions.

The jet stream…that river of flowing air over 25,000 feet in the atmosphere.  It’s always important to know what the jet stream is doing when we are forecasting the weather.  A trough (a dip in the jet stream) will develop over the western third of the nation and this trough will be over us early next week.  This weather set-up will give us a chance of winter weather…here is the very latest.

SUNDAY JET STREAM FORECAST

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Notice the trough digging down over the Gulf of California.  This indicates cold air moving all the way down into the 4 corners region.

TUESDAY JET STREAM

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Keep an eye on the movement of the trough…it should be over Texas and Oklahoma by Tuesday.  Now that we will have the cold air moving into the area…what are we looking at as far as precipitation chances.

PRECIPITATION FORECAST (SUNDAY AFTERNOON)

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That digging trough will bring some rain (and snow in the high elevations) into the Southwest.

PRECIPITATION FORECAST (TUESDAY MORNING)

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PRECIPITATION FORECAST (TUESDAY AFTERNOON)

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According to these forecasts the heaviest precipitation will just miss us, but we still have a chance for getting some winter weather.  Now the next question…what kind of winter weather will we get?

Here are the very latest precipitation type forecasts and these are what the colors stand for: Green-Rain, Blue-Snow, Yellow-Freezing Rain and Red-Ice Pellets.

PRECIPITATION TYPE FORECAST (MONDAY AFTERNOON)gfs144hr_sfc_ptyp2

PRECIPITATION TYPE FORECAST (TUESDAY MORNING)

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PRECIPITATION TYPE FORECAST (TUESDAY AFTERNOON)

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PRECIPITATION TYPE FORECAST (WEDNESDAY MORNING)

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First Winter Storm Of 2009 On The Horizon?
December 30, 2008

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There will be several fronts that will move through the area this week. The forth and final front will contain more moisture with an area of low pressure developing to our south. All of the ingredients seem to be coming together for this potential winter storm.

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There are still questions on the track of this system. Right now the models agree it will develop to our south and then move northeastward. However this storm system is still 6 days away, and many times computer models show storms developing to far to the south when the storm is still several days away. Therefore, the storm system could develop further north than what is currently projected. The other big question is the cold air. It is unclear how much cold air will be available. Perhaps the bigger question is how deep the cold air will be. All of the models agree on cold air in our area, however some of them only show a shallow cold air mass which could lead to freezing rain or sleet instead of snow.

GFS Computer Model For Monday Night

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The GFS (American Model) continues to show moderate to heavy amounts of precipitation Monday into Tuesday. According to the forecasted temperature profile. It starts this precipitation off as freezing rain and sleet and then changes it over to snow on Tuesday. The ECMWF (European Model) indicates a nearly all freezing rain event, while the GEM (Canadian Model) shows a nearly all snow event.

GFS 500mb Vorticity

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The mid level flow is forecasted to become very energized. The image above shows an upper-level storm developing right on top of the area. There is a lot of lift, rising air, with this storm system. Notice the jet stream map below. It shows areas of large divergence which forces rising motion.

GFS 300mb flow

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IS IT DECEMBER OR MARCH?
December 30, 2008

A big warm up for today and it’s going to feel more like March than December for the entire area.  Our winds will be strong (gusts over 25 mph) out of the South and Southwest and we will continue to have that sunshine.   A cold front arrives later today and that will put an end to the well above average temperatures; so make sure you try to get outside and enjoy the great weather!

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TUESDAY HIGHS

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WEDNESDAY HIGHS

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Old Man Winter Set To Return With A Vengeance
December 30, 2008

In light of the Football Bowel Seasons, the Super Doppler Weather Team is going deep down the field with this post. A look beyond the typical 7-day forecast. What will the first two weeks of January 2009 bring? Well it appears the latest maps and trends suggest more winter. First, here is the 8-14 day outlook by the Climate Prediction Center:

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After further review of not only the long range maps, but more importantly the short term climate guidance this makes sense. Most of November and December the eastern 1/3rd of the country has been battered by cold and snow but right before Christmas this all changed. The pattern shifted to the western part of the country. During this transition phase as the cold shifted west, major snow and ice storms occurred all over the country in time for Christmas. Seattle had a record snow, Blizzards developed across the

Midwest, and New England had a horrible ice storm. Here at home we had the coldest temperatures in 3 years, only to go to record highs 5 days later with severe weather. Now the pattern appears it will reverse next week. Winter weather patterns are often shaped around semi-permanent highs and lows across North America and the world. The three big ones that affect the United States are the NAO (North Atlantic Oscillation), AO (Arctic Oscillation), and PNA (Pacific North American teleconnection).

Here is the NAO (North Atlantic Oscillation) Forecast:

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Notice it has gone negative and is forecasted to stay there for the next two weeks. During negative events the eastern 1/3rd of the country is normally very cold and snowy.

Here is a look at the AO (Arctic Oscillation) forecast:

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It is trending negative over the past few days and should stay this way for at least a week or more. Negative events normally lead to Arctic invasions of cold air into the Midwest and eventually our area.

Here is a look at the PNA (Pacific North American Teleconnection):

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This is perhaps the most important factor. Notice the general trend upwards? During positive events the West coast is normally very warm, during negative events they are very cold. All three of the trends have the west coast warming and the east coast cooling. There is only one way to get the pattern to flip during that time frame and it is to have it happen gradually west to east during a transition phase. Not only will Northwest Arkansas feel the chill of winter again, but the first couple of weeks of January will likely be active with storm systems pushing through the area, much like Christmas week 2008. On the other hand, this week still appears to be a timeout in the active winter pattern. Lets enjoy it!

After One Of The Wettest Years, Drought?
December 30, 2008

Despite the very wet spring and summer, dry conditions have prevailed. The Climate Prediction Center updates their drought monitor weekly and now some of our area is officially in a moderate drought. Here is the latest information:

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Most of the area is listed in a D0, 1 step away from a drought. However, Latimer, Haskell, and Muskogee counties in Oklahoma are now under a moderate drought.

Calm Weather, But Active Space Weather
December 30, 2008

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If you look to the southwest sky tonight you will see 3 planets and the slim crescent moon. Some of the brightest objects in the sky are forming a conjunction. The bright light high in the sky is Venus. From there trace your way towards the horizon to find the moon,  Jupiter and Mercury.

(Courtesy of Spaceweather.com)

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The Moon is en route to Venus for a spectacular conjunction on Dec. 31st. On New Year’s Eve, the two brightest objects in the night sky will shine through city lights and even fireworks–so everyone can enjoy the show. What a nice way to end the year!

HIGH PRESSURE BRINGS SUNSHINE
December 29, 2008

MORNING SURFACE MAP

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An area of high pressure has set up shop right over Northern Louisiana and that means beautiful weather across the area today.  There are two reasons why we will be nice today: 1) South Winds 2) A Clear Sky

TEMPERATURE  (MONDAY 12:00 PM)

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CLOUD FORECAST (MONDAY 9 AM)

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CLOUD FORECAST (MONDAY 3PM)

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Very Active Week In Weather Comes To An End
December 29, 2008

The Christmas week weather roller coaster ride has come to an end. Here is a quick review of the weather events that played out.

Monday 22nd:Day began with the coldest temperatures in over 3 years. Fort Smith had a morning low of 13. Fayetteville had a low of 6, and Highfill XNA airport had a low of just 4 degrees. Wind chill values were below 0 to start off the day.

Tuesday 23rd: A big warm up wasn’t warm enough. Temperatures quickly warmed to freezing for the Tuesday morning’s commute. However, rain began to fall right as temperatures were at the freezing mark. Slick spots caused several accidents on I-40 and I-540.

Christmas Eve and Christmas Day: Calm and Pleasant

Friday 26th:Temperatures warmed to record highs in Northwest Arkansas with temperatures near 70 degrees. The mercury topped out in the mid 70s in the river valley and made a run at 80 degrees from Mena to Poteau.

Saturday 27th:The record highs didn’t last for long. Overnight lows were stuck in the 70s before a round of severe weather and heavy rainfall drenched the area. Rainfall totals between 1-3″ were common across the viewing area.

The last week of 2008 will be much calmer. It will be warm with lots of sunshine. However, late Thursday night and Friday morning is looking a little more interesting. Computer models are showing a cold front moving through the area with a wave of low pressure to our south. This could provide rain changing over to some light snowfall or a rain/snow mix. Here is the 12z GFS computer model:

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Severe Weather Threat Ending
December 27, 2008

The severe weather threat is moving out of the area. Here is a look around 12:30 pm. The cold front is sweeping through the region bringing a much cooler air mass into the area.

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Down tree limbs and pondering of water on the roadways have been the biggest threats. The severe weather threat will now shift into the Midwest. After Today’s heavy rainfall, we may stay dry through the end of 2008. A much more calm weather pattern will settle in after a very active week.

Tornado Watch Extended
December 27, 2008

A tornado watch has been extended across the area until 2 pm CST. The main threats this morning still look to be Damaging Winds and Heavy Rainfall. Also, penny sized hail and lightning will be a concern as well. Even though we are in a tornado watch the tornadic potential remains low. However, an isolated tornado can not be ruled out.

Strong thunderstorms will move out of the area around noon today. Behind the front temperatures will drop from the upper 60s to low 70s into the 30s.