With La Niña conditions expected to stay at current strength or get stronger, the people of Oklahoma and Texas are rightfully concerned about their water conditions.  The map below is an interesting look at how many inches of rain are needed to break the drought.

Notice the two areas that desperately needed the rain this weekend got it.

Comparing this map to a couple of accumulated rainfall maps from Texas and Oklahoma, it’s easy to see that although this rainfall event hasn’t done away with the drought conditions across these areas, a nice dent was put into some of the anomalies.  Look at these maps that show accumulations of  3 + inches across parts of Texas and Oklahoma.

Courtesy of the Texas Mesonet

And in Oklahoma,

Not quite as descriptive as the data from the mesonet, but still gives the idea.

I’m sure that the people of Texas and Oklahoma who do not know what a dryline will still be thanking God for them.  Bring it on drylines!

As I mentioned yesterday, the HPC models tend to overdo forecasted precipitation totals, expecially for long-term periods.  The new 5-day totals still show a significant change to drought conditions in the north Texas/south Oklahoma areas, and also a significant flash-flooding threat.

Notice that the hot-spots are still in the same areas as yesterday, but the forecasted rainfall totals are less than they were.

This is great news for Texas.  A dryline is serving as the main focus of thunderstorm activity today, evident from the map below.

See the tight PWAT gradient west of Midland and Lubbock

As this dryline swings eastward, it will continue to meet up with moisture advecting in off of the Gulf of Mexico.  Some severe weather is possible out of these storms, with strong moisture convergence along the boundary forming (shown in red), upper level divergence in the right exit region of the jet streak and fairly strong low-level helicity values (also shown below).  Isolated tornadoes are possible tonight in the area, but the major concern will be flooding issues.

A cold-front is developing here

The trough over the Four Corners region is helping to bring much needed rain...

This is great news for Texas and Oklahoma.  After this rainfall event has completed, it will be interesting to look at how drought conditions have changed for the area.

Over the weekend, the extremely drought stricken areas of Oklahoma and Texas could potentially get some help from mother nature.  Thanks to the blocking pattern that’s currently in place over the eastern United States, any storms that move into the country are forced to go up and over this ridge that’s kept much of our weather pleasant and unseasonably warm.  As long as the blocking pattern stays in place, which only looks to be for about the next 5 days, any forward movement will be halted, placing areas that desperately need some rain under the influence of a cold front.

Currently we can see that almost the entire area contained within Texas and Oklahoma are and have been under an exceptional drought.

Much of the area that looks to be "on fire" may have some of those flames put out.

The models at the NOAA Hydrometeorological Prediction Center, at times over-predicting rainfall totals, still  show two distinct hot-spots for precipitation for the next 5 days.  The 5-day precipitation total published on their website shows a staggering 10.8 inches of rain forecasted for an area near Witchita Falls, TX.

Notice the extremely high numbers over Florida, Oklahoma and Texas

Any totals such as this are way off base given the conditions in the area.  The lack of soil moisture available will inhibit the sustenance of any convection that develops along the boundary.  However, persistent southeasterly flow off of the Gulf of Mexico provides the moisture advection necessary to allow for what will likely be persistent rain showers with some isolated thunderstorms.  Flash-flooding will be a major concern this weekend over the area.

Current surface conditions show the synoptic setup for this weekend.  The main feature causing the HPC models to pick up on the significant rainfall is the high pressure system at the surface, encompassing much of the east.  A tight pressure gradient is developing over Florida , allowing for strong easterly winds over Florida.  Along a stationary boundary located south of Florida, an area of rotation is expected to form in the wake of this tight pressure gradient and the enhanced easterly flow.  This looks to be the source of our next chance of rain in the Bluegrass State, most likely around Tuesday or Wednesday.

Note the position of the frontal boundary from Kansas southward toward New Mexico.

High pressure is still dominating weather in Kentucky through this weekend.

The frontal boundary has not moved much by Sunday morning

The frontal boundary is marked south of Florida.

We’ll have to wait and see how the ridge in the east moves, because that will be one of the steering mechanisms of any rotation and moisture that advects northward from the Caribbean.

Now that we’ve finally passed the peak of the hurricane season and almost the entire eastern half of the country will experience nice weather for a while, it’s a good idea to take a look at the tropics to see what may be brewing there.

As of now, the Atlantic basin has one active tropical system, tropical storm Phillipe.

This storm should transition to post-tropical within a few days.

Phillipe is the only notable area of convection in the Atlantic and Caribbean at the moment.  From the graphic below, a few fronts are evident, and Phillipe is marked.

Notice the large cloud shield moving toward Phillipe. This front is forecast to become quasi-stationary, but will keep Phillipe from impacting land as a tropical system.

The main area that forecasters watch at this time of the year is the Caribbean Sea and the Gulf of Mexico.  These areas are showing little to no activity at the moment, but model forecasts hint at a possible storm within the next 10-14 days.  See the area of vorticity just east of Florida.  The rotation is more pronounced at the 850 mb level.

This is forecast for 300 hours out, so this is something we'll have to wait on and see if it pans out.

With all of that said, it is still important that we’re entering back into La Niña conditions in the Pacific Ocean and that we can expect an active pattern with regards to the Madden-Julian Oscillation.  Under La Niña conditions, vertical wind shear in the areas that hurricanes form within is much less than during an El Niño year.  This is important in allowing the storms to grow.  In addition to that, with a more active Madden-Julian Oscillation, increased latent heat flux provides necessary energy to the atmosphere for the storm to tap into.

So, what is the Madden-Julian Oscillation?  The Madden-Julian Oscillation is a global scale wave occurring within the tropics that promotes areas of enhanced or suppressed rainfall.  It typically lasts between 30 and 60 days, begins in the Indian Ocean and propagates eastward from there.  The phase of the oscillation is characterized by the spatial location of the center of enhanced convection (rainfall).  When we enter the later phases of the cycle, the center of convection reaches closer and closer to the U.S. Pacific Coast.  Relative humidity, westerly winds and other variables increase ahead of the center.  When the conditions are in this phase, tropical cyclones are 4 times more likely to occur (Maloney and Hartmann, 2000).

Below is the GFS forecast of the MJO.  Follow the green and yellow lines to see where the center would be located and read off the magnitude from the plot.

We’ll have to wait and see how the forecast turns out, but in the short-term we could potentially see another storm form within two weeks, this one being more likely to impact the United States.

SOURCES:

– Maloney, E.D., and D.L. Hartmann, 2000: Modulation of hurricane activity in the Gulf of Mexico by the Madden-Julian Oscillation.  Science,287,2002-2004.

– Wheeler, M.C. and H.H. Hendon, 2004: An all-season real-time multivariate MJO index: Development of an index for monitoring and prediction.  Monthly Weather Review,132,1917-1932.

It is not often when an 8-12″ snowstorm can be considered a “surprise”, but that was the case Sunday in SE Iowa and parts of NW Illinois. Continue reading →

My previous post outlined some caveats that represented uncertainty over the pattern evolution over the 2nd half of January. Recent data has diminished the uncertainty which means that a wickedly cold pattern should begin across the northern plains later next week that will eventually plunge much of the northern tier states into a similar pattern as the December 1-15, 2007 period. In fact, it is possible that for many northern tier states, which currently are around 10F above normal for the first 10 days of the month, January’s early anomalous warmth could be canceled out by anomalous cold. Continue reading →

NWS forecast for the higher elevations outside Mammoth Lakes, California for January 4.

Today: Periods of snow. The snow could be heavy at times. High near 25. Strong and damaging winds, with a south wind 100 to 105 mph decreasing to between 80 and 85 mph. Winds could gust as high as 145 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 45 to 51 inches possible.

Tonight: Periods of snow. The snow could be heavy at times. Low around 13. Strong and damaging winds, with a southwest wind 75 to 80 mph decreasing to between 55 and 60 mph. Winds could gust as high as 130 mph. Chance of precipitation is 100%. New snow accumulation of 39 to 45 inches possible.

The official hurricane forecast from NOAA is for 13-17 named storms including 7-10 hurricanes. These numbers are very similar to what would be expected from the statistical average of a La Nina summer. Over three months ago I posted here that a simple statistical analysis suggests that the 2007 Atlantic hurrican season should be above average based on the idea that a weak La Nina was expected to form during the summer. The most recent ENSO diagnostic discussion continues to suggest a weak La Nina is expected. Here is that original post.

Original Post: February 22, 2007
While it is still early to project what type of hurricane season the Atlantic basin will have in 2007, it is worth nothing that computer models anticipate that La Nina conditions are expected to rapidly develop over the next few months. What does this mean for the 2007 hurricane season? Continue reading →

Some of you may be wondering what exactly subtropical storm Andrea was and how it was different from a typical tropical storm. A subtropical storm is a hybrid between a tropical and extratropical storm that exhibits characteristics of each. Continue reading →