Tuesday, March 17, 2009

Wednesday cold fron...Gary Lezak's in-depth Spring forecast!

A cold front will push through Wednesday morning, and temperatures will fall slowly throughout the day. Temperatures in the morning will likely be in the 50's and 60's, before falling to the 40's by evening, and by Thursday morning, lows will be in the 30's. So, this is not a strong front by any means, but it will cooler.

I am expecting the front to push through dry, but I wouldnt rule out a sprinkle or shower. Thursday should rebound into the 50's for highs.

Now onto the big part of this entry - The 2009 Spring forecast issued by Gary Lezak (NBC Action News Chief Meteorologist) based on his theory, the LRC or Lezak's Recurring Cycle! Here are the main components of the LRC:

**A unique weather pattern sets up every year between October 1st and November 10th
The weather pattern cycles, repeats, and continues through winter, spring and into summer.

**Identifying the cycle length is critical to making accurate predictions on when storm systems are likely to hit a local area.

**“Long term” long-wave troughs and ridges become established and also repeat at regular times within the cycle. These dominant features can be used to identify where storm systems will strengthen and weaken most often throughout the year.

**There is a pattern. It isn’t just one long-wave trough, storm system, or ridge. It is a sequence of troughs and ridges that are cycling across the Northern Hemisphere.

Now here is the detailed forecast!

The “long term” long-wave troughs and ridges that set up last October and November still exist today as we move into the spring months. By July and August this weather pattern (LRC 2008-2009) will finally break down and go through a transition. Between now and mid-summer we see a continuation of the same pattern that is cycling around every 60 days, give or take a few days. This has been a unique weather pattern and some spots have had many storm systems, like Chicago and Boston, whereas there are other locations that have been missed almost every time, like Denver and Dodge City. Will this continue to be the case as we move into spring? Let’s look at the dominant features that have created the wet, dry, cold and warm scenarios during the past few months.

The features that dominated the winter will continue, but there could be some differences in how they affect what we experience at the surface. Forecasting these surface reflections is a rather difficult task and this is what we are attempting to do in this spring forecast:

Dominant feature #1:

As discussed in the winter forecast there has been one strong “long term” long-wave trough extending from Hudson Bay south through the Great Lakes (eastern Michigan) down into the Alabama/Georgia line. This is a major feature in the cycling pattern, as it has really been the dominant feature returning many times through each cycle. There will be some subtle changes to this trough as the jet stream retreats, the temperature contrasts weaken, and summer approaches. The cold fronts will begin to weaken and eventually end up stalling somewhere from the mid-Atlantic states back into the plains. Where these fronts stall will be a critical factor into forecasting exactly where the heaviest precipitation will fall this spring and into early summer. This map below shows the "long term" long-wave trough as it will be lifting farther north as we move closer to summer:

Weaker feature #2

In the winter forecast we discussed a second “long term” long-wave trough that was located somewhere in the western plains. But, after going through the past few cycles of this years LRC we have noticed that it really isn’t a western plains trough, but rather a stretched out positively tilted trough in the mean stretching from the Pacific Northwest southeast into the plains before it phases with dominant feature #1 above. As the mean “long term” long-wave eastern trough weakens and shifts north there will be a strong potential of this secondary feature becoming a somewhat bigger force than it was during the winter months. This energy source was responsible for 13 rather strong surface lows tracking across the central plains states during the winter, many of which went through this region and didn’t produce much, unless you were in the Dakota’s that got the benefit of the center of these trough tracking south of this region. What will this mean for this spring forecast? This is another big challenge for this spring forecast. The same anomalies that happened during the winter may shift a bit as we move through the spring. But, this shift should only be slight.

Feature #3:

There has been a mean “long term” long-wave ridge over western Canada north of Washington and Idaho extending into northwest Canada and it has directed Gulf of Alaska energy southeast under this feature into the western states, and there is a “long term” long-wave ridge near Southern California that tends to drift off shore at times, but it has still been one of the reasons for some dryness out west.

Feature #4:

As described in the winter forecast there has been some splitting of the flow through the western states but very rarely has any organized storm system made it into the Rocky Mountain states and this is one of the reasons Denver, CO had their first February in their recorded history with no measurable snow.

This map below shows the weak split flow that has been evident through much of this pattern. When the eastern trough weakens this has been the dominant flow allowing for some storm systems to break through into the western states. Some of these storm systems have been quite strong affecting the northern plains, but most of them have been positively tilted and somewhat disorganized. When this pattern develops within the 60 day cycle severe weather outbreaks will be possible through the plains states. But, this is not the major part of this pattern and we expect severe weather to be much less active than in 2008 when Kansas lead the nation in severe weather reported and number of tornadoes.

The above map shows how complex this weather pattern really is and how difficult it will be to forecast this springs anamolies. When we have had the split flow, energy coming into the plains almost always goes into confluent flow as it approaches the mean trough through the Great Lakes states. I drew this map to show the likely flow for a two week stretch in April and again sometime in June before summer settles in. This part of the pattern could bring some of the drier areas some rain before summer arrives.

This next two maps are our rainfall and temperature outlooks for spring 2009:


Post a Comment

Subscribe to Post Comments [Atom]

<< Home