Several periods of showers and thunderstorms are likely across the local region this week. The above image shows the forecast total rainfall - on average - for the region for Monday through Friday. I point out "on average" because this doesn't account for pockets of locally heavier rainfall produced by thunderstorm activity, which is certainly possible in at least some parts of the area.
Precipitation will start out relatively light (in the form of drizzle and/or patchy showers) on Monday with the potential for heavier showers and thunderstorms developing by later Tuesday into early Wednesday. Additional showers and storms are then possible on Thursday and Friday, with Friday likely to be the more active of the last two days (locally heavy downpours are possible at times again with the activity on Friday).
We do have some concern for potential flooding of low lying and poor drainage areas (especially low water crossings and the like) across at least some parts of the local area during the period late Tuesday evening into the pre-dawn and early morning hours of Wednesday, as illustrated on the graph below:
The small white squares on the graph show the average rainfall forecast between the NAM and GFS computer models. As you can see, the period 9pm Tuesday thru 6am Wednesday is "targeted" as particularly active rainfall wise, and it is important to keep in mind that higher totals are possible with thunderstorm activity during the same time period.
We agree with that general timing for possible locally heavy rainfall based on the latest forecast trends that we're seeing. With that in mind, we'll need to keep an eye on the Wednesday morning commute for possible issues with low water crossings, etc. It is possible that the heaviest rainfall will occur to the East of I-35 during that specific time period, so folks in the Bastrop and Lockhart areas will particularly want to keep an eye on the low water crossings early on Wednesday morning.
As far as "severe" weather (i.e,. damaging winds, large hail, isolated tornadoes, etc.) is concerned, while we cannot rule it out across some parts of the local area, the situation is far from certain and is somewhat complex. We'll attempt to explain why below...
As of now there appear to be two time periods that we need to watch for the possibility of strong to severe thunderstorm development across the local area:
(1). Late Monday night into early Tuesday morning
(2). Late Tuesday evening into Tuesday night
At this time, we do not expect significant strong or severe thunderstorm activity locally on Tuesday morning (period one) due to the presence of a strong "capping inversion" across the local area. This should tend to limit thunderstorm development overall across the local area during that time period (and this trend is also supported by the computer model data shown on the above graph). If an isolated strong or severe storm were to be able to develop during this time, it could produce strong, gusty winds and hail on at least an isolated basis in some parts of the local region.
The second time period appears more favorable for at least isolated to scattered strong to severe thunderstorm activity across the local area as a strong upper air disturbance will likely help "break the cap" to our West, which could lead to more extensive thunderstorm development locally late on Tuesday evening or early on Tuesday night.
The image below shows a simulated weather radar forecast (by the NAM computer model) valid at 6pm on Tuesday. As you can see, it suggests that scattered strong thunderstorm activity will be developing around or shortly after that time to our West, out over the Hill Country:
This activity would then likely move and/or develop toward the East/Northeast and some of it could impact the local region mainly after 9pm on Tuesday, into Tuesday night. The primary concerns for any locally severe weather by that time would likely be in the form of strong, gusty winds and spotty hail, along with the heavy rainfall threat noted earlier in this post.
So, to sum things up: Most everyone can expect some much needed rainfall across the area this week. We need to keep an eye on the period from late Tuesday evening into early Wednesday morning for possible low land flooding in at least some parts of the area (especially in low water crossings and especially along/East of I-35). While we cannot rule out some strong to severe thunderstorm activity (mainly during that same late Tuesday-early Wednesday period), there are more variables at play there, and we need to watch the latest trends for more clues on what is likely to happen. Friday is another day to watch for possibly locally heavy downpours in at least some parts of the area.
Stay tuned here on the blog as well as on twitter and we'll keep you updated throughout the week...
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