Update on Texas Heavy Rainfall, Severe Weather Event for Tuesday and Wednesday...

All of the ingredients necessary for a widespread heavy rain event are coming together in central and eastern Texas late this afternoon, including the Austin-San Antonio corridor region along I-35.

Above is the latest surface weather map, with the green shaded areas showing rich moisture building up in the Gulf of Mexico.  Surface winds (as noted by the purple lines) are shifting to the East/Southeast, which will pull the moisture Westward into the region overnight tonight and into Tuesday.

Later tonight, a "low level jet stream" will form just above the surface across southcentral and southeast Texas, pulling moisture into the region at speeds of around 50 mph, which will further make the atmosphere moist and unstable for the upcoming event.

Meanwhile, in the upper levels of the atmosphere, a strong area of low pressure is currently located just South of Yuma, AZ, over extreme northwestern Mexico:

Strong jet stream winds are already spreading East ahead of the system across the Lone star state, as indicated by the yellow arrows on the water vapor satellite image above.

The system is forecast to swing toward the Southeast tonight and move across Texas Tuesday and Wednesday, resulting in widespread shower and thunderstorm development.

Both locally heavy rainfall and severe thunderstorms are likely in association with this system.  Computer forecast model guidance is suggesting a total of 2-4 inches of rain will be common along the Austin to San Antonio corridor, with localized amounts up to 6 inches possible, and I agree with that assessment.

Here is how the latest high resolution NAM computer forecast model is forecasting the precipitation situation to shape up over the next 24-48 hours, and I agree with the overall trends that are depicted by this model.  First, accumulated rainfall from 6am to 6pm CST on Tuesday:

...through 6am CST Wednesday:

...and through 6pm CST Wednesday:

As you can see, the model is depicting a maximum rainfall swath of 5-6 inches along and East of I-35 between Austin and Dallas.  Widespread 3-5 inch rainfall amounts are indicated surrounding that bullseye.

The heavy rain may cause flash flooding in the urban areas of Austin and San Antonio, particularly tomorrow night and Wednesday morning.

In addition to the threat of heavy rainfall and flash flooding, severe thunderstorms will be a distinct possibility across mainly southcentral, southeastern and east-central Texas, including the Austin/San Antonio corridor, the Corpus Christi area and the Houston Metro area.

Below are the latest severe weather outlooks for Tuesday into Tuesday night (first) and Wednesday (second), from the Storm Prediction Center (SPC) in Norman, OK:

Severe weather will primarily take place along and to the South of a surface warm front across Deep South and southcentral Texas on Tuesday afternoon.  This threat will spread Northward into the Austin/San Antonio region on Tuesday night, and then shift East into southeastern Texas (including the Houston area) on Wednesday.

Damaging wind gusts and hail up to 1 inch in diameter will be the primary severe weather threats during both periods of time.  Isolated tornadoes are also possible, including during the overnight hours on Tuesday night in the Austin / San Antonio area.

If you live across the severe weather threat areas for Tuesday and Wednesday, please be alert.  Listen to NOAA Weather Radio, local media or other trusted sources for the latest information, watches and warnings.  If you live in the Austin/San Antonio and adjacent areas, please make sure that you have a way to receive severe weather warnings at night.

Stay tuned for more on this situation tomorrow and Wednesday.  If you don't already follow me on facebook, Google+ or twitter, please do so as I am likely to make more frequent, short posts on those outlets during an ongoing severe weather situation.

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Update on Widespread Heavy Rain and Localized Severe Weather Event for Texas / Lower MS Valley...

An upper-level low pressure system is swirling about just to the Northwest of Las Vegas, NV at this hour (as shown on the water vapor satellite image above).  This system will dive toward the South/Southeast tonight and Monday, the make a move toward the East across Texas on Tuesday and Wednesday.

Widespread, heavy rainfall can be expected in association with this system, particularly across central and eastern portions of Texas (especially along and to the East of I-35, including the Austin-San Antonio corridor).  Total rainfall amounts for the two day period will average 2-4 inches with locally heavier amounts near 6 inches possible.

Here is how I expect the heavy rainfall threat to pan out for Tuesday:

...and for Wednesday:

As much of this region is currently in a moderate to extreme drought condition, the rainfall will be very welcome, even though some of it may run off quickly during strong to severe thunderstorm activity.

Along with the good will come a threat of the bad, in the form of severe thunderstorm activity.  As I've been pointing out for several days now, this situation looks very similar to the one on January 25, 2012, which produced widespread heavy rainfall, damaging wind gusts and at least 1 tornado along the Austin/San Antonio corridor of I-35.  That trend has not changed as of this update, and strong to severe thunderstorms will indeed threaten the region on Tuesday and Wednesday:

The severe weather and heavy rainfall threat will shift East/Northeastward into portions of the lower Mississippi Valley region on Thursday.

If you live across the heavy rain and severe weather threat areas outlined for Tuesday and Wednesday of this week, please stay alert.  Take the time now to review your severe weather safety and preparedness tips so that you are ready to go if severe weather threatens.

At least some of the threat of severe weather will take place during the nighttime hours.  Make sure that you have a way to receive weather warnings when you are asleep at night, and identify your best sheltering option at home, work or school so that you can move there quickly if threatening weather is observed or a warning is issued.

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Update on Heavy Rain / Severe Weather Event for Texas and the Lower MS Valley...

I wanted to give a quick update on the storm system that I detailed in a post yesterday, and its potential impact on Texas and at least the lower Mississippi Valley region for the early to middle of next week...

First things first, a significant (and much needed) rain event will take place across the central and eastern two thirds of Texas, southeastern Oklahoma and much of Louisiana and Arkansas.  Most of this rain will fall during the period Tuesday through Wednesday:

As you can see on the cumulative rainfall forecast image above, widespread rainfall amounts of 2-4 inches are expected, with localized amounts of 4-6 inches possible across much of the region.  This rain will be very welcome indeed, as the vast majority of this region continues with a severe to extreme drought situation:

As I mentioned in a post yesterday, the European computer forecast model has been the most consistent thus far in forecasting this storm system, and I believe that it continues to be the most reliable with its depictions through today.  The latest run of that particular model is forecasting 4 inches of rain to fall in Austin, mainly from 12 Noon Tuesday through 12 Noon Wednesday, as shown on the graph below:

While the rain will certainly be welcome across the region, on the negative side of the coin, a threat of severe weather will come along with it as well.

While some of the severe weather details still need to be worked out (mainly with respect to timing), the area shown in red on the image below is likely to have the highest threat of severe weather on Tuesday, which includes the Austin-San Antonio corridor along I-35, "The Valley" in Deep South Texas, the Texas Coastal Bend and the Houston metropolitan area:

I still believe that the situation for Tuesday looks very similar to that of the heavy rainfall and severe weather event that took place across the Austin-San Antonio corridor area during the early morning hours of January 25, 2012.  That particular event produced widespread heavy rainfall (in excess of 6 inches in some locations), damaging wind gusts and at least 1 tornado.

While it is still too early to pinpoint some of the details as to the severe weather threat, if you live across the region shown in red on the map above, please pay attention to the weather on Tuesday and Tuesday night.  Make sure that you a have a way to receive severe weather warnings and identify your best sheltering option in case threatening weather approaches your area.

The threat of severe weather will shift East/Northeast into Louisiana, southern Arkansas and still the Northeast part of the Texas coast (including Houston) as well as east-central Texas for Wednesday.  More details on the Wednesday severe weather threat will be available tomorrow as the situation becomes more clear.

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More on Heavy Rainfall Across Southcentral Texas Yesterday...

As expected, rainfall was widespread and heavy across much of the central and Eastern two-thirds of Texas on Tuesday night and Wednesday. The above image depicts rainfall totals through 6am CST Yesterday morning, which roughly corresponds to the time that heavy rains were ending across the Austin-San Antonio corridor.  Additional heavy rain fell later in the day further East across east-central and southeast Texas.

At my home near Kyle, TX, we received 6.75 inches of rain Tuesday night.  I know that sounds impressive by itself, but to drive the point home even further, you have to know that we didn't receive that much rain in the first 5 months of 2011 combined!

The official observing station for Austin, located at Bergstrom International Airport, received 5.66 inches of rain, which was a new record for the day.  The old record was a mere 0.99 inch set back in 1973.  The 5.66 inches yesterday also set a new single day rainfall record for the month of January, and was also the 8th wettest day ever recorded in Austin.  (The all time daily rainfall ever recorded in Austin was 8.70 inches on November 23, 1974).  

The image below is a zoom-in of the first image, centered on the Austin/San Antonio area.  You can see that very heavy rains of 5-8 inches were widespread from northeast San Antonio through southeast Austin, and points just to the East of that line:

In San Antonio, 2.94 inches of rain was measured at the official observing station at the airport (which was also a daily record), but as you can see on the map above, much heavier amounts fell just to the East of there across much of eastern San Antonio.

The rains were certainly very welcome, as we've been suffering from an extensive drought across the region for the last year.  As is typical when you receive that much rain in such a short period of time (i.e., 6 hours or so), flash flooding and small stream flooding were widespread across the region yesterday morning.

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Lack of Snow Cover Beginning to Raise Eyebrows...

Recent images from NOAA indicate that only 22% of the nation has snow cover on the ground. The last time that there was less than 30% snow cover at this point in January was back in 2007, which came in at 27%.

The series of images below show the observed snow cover (via the NOHRSC) for today, January 5, for each of the last 5 years, beginning with today's image:

...and here is the image from 6 years ago, with 27% snow coverage in 2007:

Particularly after last year's heavy snow season across the West, the "snow drought" (as some are calling it) is striking.  Take a look at this image of snow cover across the Great Basin today (with a mere 4% of the ground covered):

...versus last year on the same date, when over 80% of the ground was covered:

A similar "snow drought" is noted across the central Rockies when you compare the snow coverage today:

...with that of last year on the same date:

Not only is there far less snow cover present, but the depth is far less this year as well, which is beginning to take a heavy toll on ski season.  

There are other impacts to be considered with regard to the lack of snow:  a very important one being the potential for damage to the winter wheat crop.  You see, snow cover actually acts somewhat like a "blanket" to help protect the Midwest and northern Plains wheat crops from being damaged by cold, arctic airmasses in January and February.  As you can see on the images below, the lack of snow cover in the winter wheat belt is astounding:

The snow cover itself, as well as the associated moisture that soaks into the ground, help to keep ground temperatures from reaching potentially damaging levels.  Such a barrier may not be in place should arctic air invade the region later this season (and at least one such invasion appears likely next week).

On the positive side of the coin, the lack of snowcover, and the resulting lack of moisture, would tend to lessen the impacts of some of the river flooding that typically takes place each year as a result of the snowmelt in the spring.  This is particularly the case across portions of the upper Mississippi River Valley region.  While this is good news, at the same time, moisture from the snowfall also contributes to a significant portion of the winter and early spring precipitation totals across much of the region.

If the entire winter season indeed ends up with below normal snowfall, and as a result, below normal water equivalent precipitation, this could lead to some real problems with warm season crops in some areas of the Plains and Midwest.  This will particularly be the case if rainfall also trends below normal during the spring and summer months.

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System In Gulf Classified as Tropical Depression 13...

The system we've been talking about in the Gulf this week was classified as the 13th Tropical Depression of the Atlantic season yesterday evening.  The above satellite image shows the system currently centered about 250 miles Southeast of Port Arthur, Texas, and remaining nearly stationary.  I wouldn't be too concerned about the exact location of the center, nor about the movement in the near term (24-36 hours), as there is likely to be quite a bit of fluctuation in both.

The main story with this system in the short term will be extremely heavy rainfall along adjacent portions of the Gulf Coast (unfortunately not Texas at this time), as shown on the latest rainfall forecast images below.  The first image is valid today and tonight, and the second for the 3 day period today through Sunday:

The "official" NHC forecast track is below and is generally a consensus of the major models at this time, however I wouldn't fixate on the exact track, especially in the short term, as there is still quite a bit of uncertainty:

I will have a more detailed post on this system by midday...

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Relief Headed for Texas...in One Form or Two?

After setting record high temperatures of 110+ in many areas (some of which were all time records, or tied for all time records) since Saturday, has the intense heat finally peaked in the Lone Star state this summer?  I think it may have (or it is in the process of, depending on exactly where you're located).

Today will be another scorcher, with high's of 100-105+ in many areas, and many records to be set again, but several changes are about to take place in the atmosphere that will lead to some temperature relief - and possibly some relief in the drought department, as well!

The above satellite image was taken just a few moments ago.  I have highlighted a tropical disturbance located roughly between Cuba and the Yucatan.  It is just drifting very slowly Westward at the moment, with not a lot in the way of organization taking place at the present time, however that is likely to change in a few days...

Below is a snapshot of the latest Global Forecasting System (GFS) computer model, valid 1am CDT this morning.  I have circled the aforementioned tropical disturbance in yellow on that image as well:

The same GFS computer model shows the disturbance becoming better organized out over the northwest Gulf of Mexico (yellow circled area again) in this image valid 7pm CDT this Saturday:

...and by 1am CDT Monday, Labor Day, morning, it is forecasting what looks like either a Tropical Depression, or perhaps even Tropical Storm "Lee" along the Texas or Louisiana coast: 

At the same time on the image above, I've noted a rather decent cold front that is forecast to be moving Southward into Texas.  A combination of cooler air behind the front, as well as increased cloud cover and possibly, dare I say it, rain from the tropical disturbance will lead to a dramatic cool down across much of the region by Labor Day.

Of course, we'll have to watch the progress of the tropical disturbance to see exactly what impact it may have, rain-wise or otherwise, on Texas and surrounding states, but at least we have something to look forward to, and the first decent looking chance of some widespread rain for at least part of the state in a long time.

I'm sure you also couldn't help but notice the large "blob" on the GFS model out over the Atlantic.  By that time we'll be dealing with Hurricane Katia, and likely a major hurricane at that.  The $64,000 question, of course, is whether she'll track more toward the West, the Northwest or turn out to sea as she approaches the U.S. East coast later next week (see notations on the image below, valid at the same time as the one above):

Stay tuned...we've got a lot to watch in the upcoming days!  If you have plans for this Labor Day Weekend (particularly the 2nd half of it) along the Texas or Louisiana coasts, keep a close eye on the latest updates...

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Much Needed Rain Slowly Moving South into Central Texas...

A complex of thunderstorms, which originated over Kansas and Oklahoma last night, continues to sag very slowly Southward into northern and central Texas this morning.  As you can see by the above radar image, the leading edge of the activity currently extends from near Hillsboro to San Angelo.

Much needed rains are currently falling in drought stricken areas, but the $64,000 question is - how many more folks further South will get a much needed break, too?  

The following images show the HRRR computer model radar forecasts valid at 1pm and 4pm this afternoon:

As you can see, while the model does slowly weaken the system, it does bring rain into the Austin/San Antonio corridor by 4pm.  It also hints that additional, isolated to scattered, new thunderstorm development will take place ahead of the decaying larger area of rain, which makes a lot of sense.

So, residents of southcentral Texas, keep your fingers crossed and say an extra prayer this morning - and we may finally get some rain in a few much needed spots this afternoon as well!

Oh, by the way, someone at the NWS in Austin/San Antonio might want to wake up and revise their current forecast:

Maybe they're afraid they'll scare away the rain???

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