Good morning, folks! Let’s take a look at what this week has to offer for the Coastal Central Gulf States.
Synoptic Picture
Currently, the Southeast is under a weak ridge with 500mb heights approaching 5,900m – about average for this time of year. This ridging, along with model-estimated precipitable water values around 2″ across the region, has been responsible for hot and muggy conditions throughout much of June and into early July – with the only relief coming in the form of rain and the occasional shot of drier air.
Ridge Once Again Building in the Southeast
While the ridge across the Southern United States is weak now, models are in good agreement that this ridge will only get stronger by the end of this week.
Taking a look at what the GFS has to offer, the ridge will continue to strengthen over the Southeast to a moderately strong 5,900+ m upper-level high pressure. This closed circulation will help to direct a synoptically east-southeasterly flow off of the Gulf of Mexico that will keep the air full of moisture through at least the end of this week.
This ridge doesn’t just here though, through the rest of the week, it continues to build and shift westward, taking hold of most of the United States by Saturday afternoon. However models are not entirely in agreement in this setup, as the ECMWF has a much stronger ridge over the Central United States, while the GFS shows a weaker ridge, and even some weak troughing in Southeast as a result of a stronger cut-off low in northeastern Canada.
Compared to the ridge that we dealt with for most of last month, this is looking like it will be weaker, and temperatures don’t look like they’ll reach as high as they had during the heat wave in June. The images below show the comparison between the average surface temperature anomalies between the American and the European weather models through Thursday afternoon. While there are still some differences between the models, such as the European model keeping the coastal regions a bit cooler than average, the takeaway is that, despite the presence of the anomalous ridge, temperatures will not reach as high as they had in a similar synoptic setup last month.
Why is this? Some increased chances for rain and thunderstorms, especially in the first half of this week, will help to keep the temperatures relatively cool.
Continued Chances for Rain, Thunderstorms for the First Half of the Week
A weak disturbance, visible in the 500mb vorticity fields, is currently located in northern Louisiana and southern Arkansas. This feature will drift southeastward this afternoon, increasing our chances for some showers or thunderstorms, particularly along the Mississippi and Alabama coasts. Let’s also make note of a fairly broad region of enhanced vorticity offshore of Southeast and over portions of Central Florida.
By Monday afternoon, the GFS shows this region enhanced vorticity along the coast of the Central Gulf states, with the other region of disturbed weather not too far behind it over Central Florida. By this time, the GFS also develops an upper-level high pressure, creating an anticyclonic wind flow that helps to bring some of the disturbed weather from offshore of the Southeast toward our region.
By Tuesday, most of this energy will be passing through the region, once again increasing the chance for showers and thunderstorms.
As is the case for convective precipitation, it can be difficult to estimate just how much rain will fall through Tuesday afternoon, with the GFS and the ECMWF showing some very different solutions:
The ECMWF shows heavier totals across the region, with a local maximum right along the Gulf Coast; meanwhile, the GFS outputs notably less precipitation for this region, especially in southeastern Louisiana.
To achieve some more clarity, I thought it would be useful to look at how a short-range model is handling this setup, and once again we’re treated to another very different solution:
This run of the NAM shows no rain for parts of Southern Mississippi and Alabama, and some hints of scattered thunderstorms right along the coast, with some locations receiving as much as 2″ of rain, particularly around the Mississippi River Delta.
Amongst this model uncertainty, one take-away that we can make is that the greatest threat for showers and thunderstorms is along and near the Gulf Coast, with rain on the order of a couple inches in the most persistent thunderstorms or downpours.
Day-to-Day Forecast
Sunday
Partly to mostly cloudy skies with a 60-percent chance for a shower or thunderstorm throughout the day. Expect highs in the mid-to-upper 80s.
Monday – Independence Day
Mostly cloudy skies with an 80-percent chance for showers or thunderstorms throughout the day. Expect highs in the mid-to-upper 80s.
Tuesday
Cloudy with an 80-percent chance for showers or thunderstorms throughout the day. Expect highs in the mid-80s.
Wednesday
Partly to mostly cloudy skies with a 60-percent chance for a shower or thunderstorm throughout the day. Expect highs in the mid-to-upper 80s.
Thursday
Partly cloudy skies with a 40-percent chance for an afternoon shower or thunderstorm. Expect highs in the mid-to-upper 80s.
Friday
Partly cloudy skies with a 40-percent chance for an afternoon shower or thunderstorm. Expect highs in the upper 80s.
Saturday
Partly to mostly cloudy skies with a 50-percent chance for a thunderstorm throughout the day. Expect highs in the upper 80s.
