Tuesday Morning Forecast Thoughts

Early morning surface analysis shows high pressure just to our west along the Mississippi River. As expected, as that high moved directly overhead overnight last night, temperatures really bottomed out! We reached 59 degrees in Starkville...wow!! 

But, that dry air will not be here for too terribly long. That aforementioned high pressure will begin to weaken over the next couple of days, and as such, moisture will gradually return. Here's precipitable water off the 6z GFS valid for 4 pm Wednesday. Notice how in the GTR we are still 'relatively' dry, but areas just to our east over in Alabama are beginning the moistening trend. 

By Thursday, PW values increase to above 1.5" around the GTR area. It'll start to feel increasingly muggy through the next couple of days, and that heat index could become a real factor by late week. Here's why...

The upper-level ridge, while not overhead directly, is still remaining firm over the central and west-central US. Temperatures will begin to increase toward the end of the week, where mid 90s are certainly possible. 

Dew point temperatures for late week through the weekend will also be increasing. This map is for Saturday evening, and with a temperature in the mid 90s potentially and these dew point temperatures around 70, the heat index could definitely reach 100 in spots. 

IW 

Monday Morning Forecast Thoughts

We begin with a surface analysis as of 830 AM this morning. A relatively strong surface high pressure remains anchored to our northeast, with a refreshing easterly flow at the surface. This is helping keep somewhat drier air in our area right now, versus what a more southeasterly flow would mean-increasing moisture. 

Looking at the upper levels, a sprawling ridge of high pressure over the nation's mid-section is also influencing our weather. Subsidence underneath this ridge is helping our sky be very bright and sunny on this Monday morning! 

Here is a look at total atmospheric precipitable water valid at 4AM tomorrow morning from the latest run of the GFS (6z). Notice the values are below .75" and in some cases, are around or just below 0.5". For this time of the year, that's indicating very dry air. The aforementioned surface high is forecast to gradually weaken slightly, but the remaining core of the high should be collocated with the minimum in precipitable water as seen above. What this should mean for us here in the GTR is a very nice evening with lows ranging from 62 to 65. 

As we go throughout the week, the ridge of high pressure aloft is forecast to gradually contract/retreat back to the west. As this happens, moisture will increase by the latter part of the week; precipitable water values return  to around 2" by Friday. 

Here's an upper level map valid for Friday afternoon at the same time. Heights are a little bit lower versus today, but there doesn't appear to be any discernible upper level support to set off any storms, but surface heating will likely contribute to at least a few storms but the coverage should remain sparse. 

IW

Friday Morning Forecast Thoughts

It's a great start to our Friday morning across the GTR. Here's a look at the high-resolution RPM for 4pm this afternoon. Notice there should be only isolated coverage of showers and thunderstorms by this afternoon. The more concentrated areas of showers and thunderstorms should be over the far northern Gulf into the Florida Panhandle due to a weak tropical disturbance.

As advertised, the models continue to suggest a ridge of high pressure aloft will build in from the west by the end of the weekend persisting into the first part of next week. Normally, this would mean increasing surface temperatures across the area, but as high pressure at the surface noses in from the northeast, a more easterly to east-southeasterly flow is expected to prevail. As this happens, I think this will help keep temperatures mostly in check, i.e. not getting into the upper 90s. I think temperatures through the end of the weekend through the first part of next week should range from about 89 to 94. Also, rain chances should be minimal (at or below 20%) through the weekend into the first part of the week.

By the end of the week, the GFS model shows the ridge of high pressure shifting back towards the west and we come under a northerly flow aloft. The Euro shows this too, but has the trough axis a little farther to the east toward the Mid-Atlantic. In either case, I think rain chances will slowly creep back up to near seasonal/climatological levels by mid-week as upper heights begin to decrease ever so slightly.

Have a great Friday, and God Bless!

IW

Thursday Morning Forecast Thoughts

Here's a quick look at 850mb theta-e and wind fields valid early this afternoon. Notice, compared to yesterday, there isn't a clear defined axis of convergence (at least in my opinion). But still, a few isolated downpours could develop this afternoon once daytime heating is maximized.

The transition from general troughiness to a ridge beginning to build in from the west. The above image is a 500mb chart valid at 9pm this evening; notice the weakness in upper heights has shifted into New England, carrying the better rain chances with it. In its wake, notice the core of an upper ridge currently located over the OK/TX Panhandles. Most model guidance builds this ridge eastward over the weekend.

By Sunday, the ridge is expected to be fairly well established across the center of the country. Here locally in the GTR, as upper heights rise, we should feel the impacts of this ridge primarily in the form of increasing temperatures. However, at the same time, high pressure over the Appalachians will also influence our weather and the GFS is suggesting an easterly flow at the surface. This would imply that, despite the upper heights rising due to the aforementioned ridge, our temperatures may not exceed the mid 90s at worst.

Also, most model guidance suggests some drier air will begin to work into our area by the end of the weekend and persist into the first part of next week. This will be a little abnormal as it's rather unlikely that we can say with reasonable confidence that it may not rain for a couple days in August in Mississippi. But by the same token, it IS August in Mississippi, so stay tuned for potential changes!

Have a great Thursday, and God Bless!

IW

August 21, 2013 - Wednesday Morning Forecast Thoughts

Starting things off this morning, there's lots of clouds across the GTR area into northwest Alabama. Moisture remains abundant across the area, and we can definitely feel it this morning with dew point temperatures in the low to mid 70s. The map above shows 850mb winds and precipitable water at the 850mb level. In the oval area I delineated, notice how there are convergent winds. This convergence axis will be the focal point for showers and thunderstorms later this morning lasting through the afternoon hours.

Some showers are already developing, primarily across southern Middle Tennessee. I think they will continue developing southwest through northeastern parts of central Mississippi as well through the afternoon hours.

Another driving force for today's weather is the weakness in heights/weak trough of low pressure in the mid levels of the atmosphere. As we progress through the day, this feature is expected to lift slowly towards the northeast away from our area. However, a trailing ribbon of weak vorticity will be gradually advected over northeast MS/northwest AL primarily, so at least scattered showers and storms will be possible through the afternoon.

Looking into the future toward the weekend, the current ridge of high pressure over the western High Plains will slowly build/expand eastward. By Sunday, the core of the high pressure should be centered near Tulsa, OK, and surface high pressure will also build in from New England by the first part of next week. This should mean an overall decrease in rain coverage and a gradual increase in temperatures. We could see low, and mayyyybe mid 90s by the first part of next week. We'll have to see how the overall pattern evolves because for much of the summer, this ridge has been anchored over the western US with general troughiness across the eastern half of the country.

Enjoy your Wednesday, and God Bless!

IW