Strong to Severe Thunderstorms Possible Pre-Dawn Sunday

• Thunderstorms are expected to move West to East across the area from around 3am on Sunday morning through about 6am on Sunday morning
• Locally heavy downpours of rain and frequent lightning can be expected in association with all of this activity
• As the activity initially approaches a given location, strong to possibly damaging wind gusts are possible, and some spotty instances of hail are also possible in some parts of the area
• There is a non-zero chance of an isolated tornado in some parts of the area, but this will strongly depend on the structure of the activity as it approaches

...Timing and Likely Impacts...
Thunderstorms are expected to move West to East across the local area from around 3am on Sunday morning through about 6am on Sunday morning. Locally heavy downpours of rain and frequent lightning can be expected in association with most all of this activity.

...Possible Wind and Hail Impacts...
As the activity initially approaches a given location, strong to possibly damaging wind gusts may occur in at least some parts of the area. Spotty instances of hail are also possible in some parts of the area, but strong, gusty winds are likely to be the primary concern by the time the activity reaches the local area based on present indications.

...Concerning the Possibility of an Isolated Tornado...
When thunderstorm activity initially develops to our West tonight, it will be more isolated/cellular with respect to organization. During this phase, the activity will have the greatest potential to produce a tornado, out to our West over the Hill Country and toward the Big Bend region. As the activity moves Eastward, present indications suggest that it will congeal into more of a band or line, which will reduce the threat of a tornado. So, while a non-zero threat of an isolated tornado does exist locally during the pre-dawn hours of Sunday morning, if the activity congeals into a line or band prior to arrival as currently expected, it will mainly pose a threat of strong to possibly damaging wind gusts as it enters the local area.

...Primary Areas of Uncertainty...
Should the thunderstorm activity that forms to our West tonight not congeal into a line or band before reaching our area during the pre-dawn hours of Sunday morning, the threat of at least isolated tornado activity would increase across the local area. While not currently expected to become a trend overall, we will continue monitoring the situation closely.

...Exit of the Activity...
The thunderstorm activity is expected to shift East out of the area by around 6am or shortly afterward on Sunday morning.

We will continue monitoring the situation and issue updates and/or specific alerts/warnings as conditions warrant.

Majority of Rain with Tropical Disturbance will Remain East of the Metro...

Scattered showers and isolated thunderstorms will continue across the area today. It won't rain all of the time, nor is rain likely to be particularly widespread at any given time. Locally heavy downpours of rain are possible at times with any scattered heavier showers and/or any isolated thunderstorms.

As we've been forecasting throughout this event, we do not expect any significant and/or widespread flooding concerns across the local area with this event. If heavier showers happen to impact a particularly troublesome low water crossing across a specific portion of the area more than once in a short time period, localized/isolated issues may develop at that specific location. Otherwise, the type of activity we're expecting, along with the scattered coverage of that activity, suggest that any local impacts will likely be zero to minimal overall.

Please note that shower and thunderstorm activity will be more widespread, and heavier, further to the East of the local area today, over east-central and southeast Texas.

For the local area, scattered activity is expected to decrease in number after Sunset today, and then end during the pre-dawn hours of Thursday morning, in association with this fetch of tropical moisture anyway.

Scattered Showers & T-Storms Are Possible Tonight/Pre-Dawn Thursday

Scattered to numerous showers and scattered thunderstorms are possible after 10pm this evening (and more likely toward/after Midnight tonight) into the pre-dawn and early morning hours on Thursday.

Locally heavy downpours of rain and lightning are possible with any scattered thunderstorms tonight/pre-dawn Thursday.

While we cannot completely rule out an isolated stronger thunderstorm with strong, gusty winds and/or spotty hail during the overnight hours tonight and/or the pre-dawn hours of Thursday morning, widespread and/or organized severe weather appears unlikely for the local area at this time, as the activity will likely be undergoing a weakening trend due to the time of night.

The activity is expected to shift East/Southeast out of the area by around 6-7am on Thursday morning, based on present indications.

Scattered thunderstorms are possible across the area this afternoon...

...Synopsis...
An area of showers and thunderstorms currently over west-central and northwest Texas will continue moving Eastward and Northeastward throughout the day today. If we were to consider only the present location and movement of this activity, all of it would remain to the North of the local area, with no local impacts of any kind. However, a boundary associated with this activity will move East/Southeast into the local area between the hours of 12 Noon and 6pm this afternoon. The potential exists for at least scattered thunderstorm development in association with the passage of this boundary during the above mentioned time period.

...Local Forecast...
There are 3 possible scenarios that could unfold for the local area at this time, all of which would occur sometime (as indicated below) during the 12 Noon-6pm time frame:

1. With the majority of the energy associated with the parent storm system passing to the North of the local area, thunderstorms are unable to develop locally, and all of the thunderstorm activity remains to the North of the local area. Probability of occurrence: 30 percent.

2. Scattered thunderstorms develop across the area between 12 Noon and 6pm this afternoon. Probability of occurrence: 60 percent. Please note: this doesn't mean that 60 percent of the area will have thunderstorms, but rather, there's a 60 percent chance of scattered thunderstorms across the local area. Some locations may receive rain and/or a thunderstorm while others, possibly very nearby, do not. Based on present indications, under this scenario we would place the probability of a thunderstorm impacting any given location at about 40 percent.

3. A line of thunderstorms moves from West/Northwest to East/Southeast across the area between 12 Noon and 3pm, with scattered activity behind it through 6pm this afternoon. Probability of occurrence: 10 percent.

With the above in mind, we currently expect scattered showers and thunderstorms from around or shortly after 12 Noon through about 6pm this afternoon. Locally heavy downpours of rain and lightning can be expected with any scattered thunderstorms, and an isolated to scattered stronger thunderstorm may also produce strong, gusty winds and/or hail in the affected portion(s) of the area. Present indications suggest the activity will be more numerous, and heavier, to the immediate North of the local area during the period.

...Locally Heavy Rainfall...
Although widespread, heavy rainfall does not currently appear likely across the local area, any isolated to scattered concentrations of heavier downpours could result in minor, mostly localized flooding of low lying and poor drainage areas in the affected portion(s) of the region. The potential for more numerous issues will likely increase as you move further to the North of the local area.



We will continue monitoring the situation and issue updates and/or specific alerts/warnings as conditions warrant.

Details on the Blanco River in southern Hays County....

A Flood Warning continues for the Blanco River in Hays County.  Details by location are as follows:


...At Fischer...
Current stage: 12.3 ft
Flood stage: 17.0 ft

The river is expected to crest just above flood stage later this evening, then recede overnight, falling just below flood stage during the pre-dawn hours on Thursday.

Applicable flood guidance based on previous history (note that guidance for 1 level above the current forecast crest is provided for precautionary/preparedness purposes):

At 23 feet: Lowest homes are threatened. Water begins to cut off secondary roadways near the river.

At 17 feet: Roadways and low bridges along the river are flooded. Vehicles cannot pass. Livestock can be stranded.

At 12 feet: Overbank conditions may cut off livestock in low areas.



...At Wimberley...
Current stage: 8.7 ft
Flood stage: 13.0 ft

The river is expected to crest near 20 feet later this evening, then recede overnight into pre-dawn Thursday. The river is expected to drop just below flood stage near dawn on Thursday.

Applicable flood guidance based on previous history (note that guidance for 1 level above the current forecast crest is provided for precautionary/preparedness purposes):

At 21 feet: Water recreation is very dangerous above Blanco to the San Marcos River confluence, including John Knox Camp and Dudley Johnson Park at Five Mile Dam above San Marcos.  Secondary roads and bridges in the flood plain are very dangerous to motorists. Hydraulic jumps behind low dams are dangerous to canoeists and kayakers as they may become trapped.

At 17 feet: Water recreation in the Blanco river is dangerous from above Blanco to the San Marcos river confluence. Secondary roads and bridges in the flood plain are flooded and dangerous. Much of Dudley Johnson park at Five Mile Dam is flooded.

At 13 feet: Minor lowland flooding reaches secondary roads. Low bridges and crossings from the headwaters to the San Marcos River confluence near San Marcos flood and are dangerous. Property in low lying areas of the Blanco and San Marcos Rivers should be moved to higher ground. Swimming and tubing are life threatening due to turbulence. Hydraulic jumps behind low water dams can trap canoeists and kayakers between the dam and the hydraulic jump and can be life threatening.

At 10 feet: A fast moving rise down the Blanco River can make swimming and canoeing dangerous above Blanco to below San Marcos. Especially in areas where steep banks make getting out of the river dangerous. Low dams create hydraulic jumps which can trap canoeists and kayakers between the dam and the jump.

At 7 feet: Overbank conditions begin to threaten swimmers and tubers in recreation areas above Blanco to the San Marcos River confluence below San Marcos.

At 6 feet: Low lying areas and crossings of secondary roads flood near and below Blanco to below Wimberley including Farm to Market 178 just above Wimberley.



...At San Marcos...
Current stage: 10.32 ft
Flood stage: 18.0 ft

The river is expected to crest near 22.5 feet during the pre-dawn hours of Thursday morning, then recede during the daytime hours on Thursday, falling just below flood stage near 12 Noon.

Applicable flood guidance based on previous history (note that guidance for 1 level above the current forecast crest is provided for precautionary/preparedness purposes):

At 24 feet: Lowest homes are threatened. Water beings to cut off secondary roads near the river.

At 18 feet: Roadways and low bridges along the river are flooded. Vehicles cannot pass. Livestock can be stranded.

At 13 feet: Overbank conditions may cut off livestock and low bridges near the river.



***PLEASE NOTE: ALL of the above forecasts are based on current conditions and short term forecast information. Should additional heavy rainfall occur upstream earlier or in greater quantity than currently expected, the forecast levels and timing could change. We will continue to monitor the situation and issue additional updates as warranted.

Also, additional heavy rainfall later this week will result in additional and/or renewed flooding issues at times across the area through this coming weekend.  We will continue monitoring the situation and issue updates as conditions warrant.

Scattered Heavy Downpours Possible Beginning Today, Increasing Through the Week....

Expected impacts:

• Periods of showers and thunderstorms will produce locally heavy rainfall at times from this afternoon through midday Saturday
• With ground conditions already saturated and stream levels running high across the region, flooding will likely result at least at times during the Watch period
• Initially, the typical problem low water crossings and other typically flood prone areas will be the primary concern, with stream and river flooding then possible over time as we move through the period
• On average, rainfall of 4-6 inches is expected for much of the area mainly from this afternoon through midday Saturday
• Locally higher amounts are possible in spots depending upon exactly where the heaviest rainfall recurs during the period

Discussion:
Periods of showers and thunderstorms will produce locally heavy rainfall at times across the area from this afternoon through midday Saturday. With ground conditions already saturated and stream levels running high across the region, flooding will likely result at least at times during the period. Initially, the typical problem low water crossings and other typically flood prone areas will be the primary concern, with stream and river flooding then possible in parts of the area over time as we move through the period. Please see below for a general overview of our present thinking for each day during the period:

...Today...
Scattered showers are possible this morning, becoming more numerous at times this afternoon into early this evening. Scattered thunderstorms are likely this afternoon into early this evening. The activity is expected to decrease near Sunset.
Low Water Crossing Flood Risk: Low to Moderate (Not widespread, but localized depending upon specific locations of thunderstorms)
River/Stream Flood Risk: Low

...Wednesday...
Scattered to numerous showers and thunderstorms. The activity appears likely to be most numerous during the midday and afternoon hours.
Low Water Crossing Flood Risk: Moderate to High (mainly p.m.)
River/Stream Flood Risk: Low to Moderate (mainly later p.m.)

...Thursday...
Scattered to at times numerous showers and thunderstorms. The activity appears likely to be most numerous during the afternoon and evening hours.
Low Water Crossing Flood Risk: High
River/Stream Flood Risk: Moderate to High on a localized basis

...Friday...
Scattered to at times numerous showers and thunderstorms.
Low Water Crossing Flood Risk: High
River/Stream Flood Risk: Moderate to High on a localized basis

...Saturday...
Scattered to at times numerous showers and scattered thunderstorms. The activity appears likely to be most numerous during the pre-dawn and morning hours.
Low Water Crossing Flood Risk: High (especially a.m.)
River/Stream Flood Risk: Moderate to High on a localized basis

...Expected Rainfall Amounts...
In general, rainfall of 4-6 inches appears probable for most of the area on average throughout the period from this afternoon through midday Saturday. A few locations that receive particularly frequent bouts of heavier rain could see greater than 6 inches, while a few locations that don't receive as many heavy downpours could see less than 4 inches. It is also important to remember that ground conditions are already saturated going into this event, and stream/river levels are already running above normal levels across many parts of the area. Both of those factors indicate that it will take less rain than normal to cause flooding issues across the area.
We will continue monitoring the situation and issue updates as conditions warrant.

Periods of locally heavy rainfall may result in new/renewed flooding this week....

Expected impacts:

• Periods of showers and thunderstorms will produce locally heavy rainfall at several different times mainly from Tuesday afternoon through Saturday morning
• With ground conditions already saturated and stream levels running high across the region, flooding will likely result at least at times during the period
• Initially, the typical problem low water crossings and other typically flood prone areas will be the primary concern, with stream and river flooding then possible in parts of the area over time
• On average, rainfall of 4-6 inches is expected for much of the area from mainly Tuesday afternoon through early Saturday morning
• Locally higher (and in some cases, lower) amounts are possible in spots depending upon exactly where the heavier thunderstorms track throughout the period

Discussion:
Periods of showers and thunderstorms will produce locally heavy rainfall at several different times across the area from Tuesday afternoon through Saturday morning. With ground conditions already saturated and stream levels running high across the region, flooding will likely result at least at times during the period. Initially, the typical problem low water crossings and other typically flood prone areas will be the primary concern, with stream and river flooding then possible in parts of the area over time. Please see below for a general overview of our present thinking for each day during the period:

...Today...
There is a chance for an isolated or widely spaced shower or thunderstorm across some portions of the local area mainly this afternoon or early this evening. While any such activity is expected to be isolated in nature at this time, if locally heavy downpours with an isolated thunderstorm occur in just the wrong place, then some mostly minor flooding issues could result in the adjacent low lying areas. Present indications suggest activity is more likely to occur to the immediate South of the local area today, but we'll continue to monitor trends closely.

...Tuesday...
Scattered to at times numerous showers and scattered thunderstorms. The activity appears likely to be most numerous during the afternoon hours, from 12 Noon to 6pm.
Low Water Crossing Flood Risk: Moderate
River/Stream Flood Risk: Low

...Wednesday...
Scattered to numerous showers and thunderstorms. The activity appears likely to be most numerous during the midday and afternoon hours.
Low Water Crossing Flood Risk: High
River/Stream Flood Risk: Moderate

...Thursday...
Scattered to at times numerous showers and thunderstorms. The activity appears likely to be most numerous during the afternoon and evening hours.
Low Water Crossing Flood Risk: High
River/Stream Flood Risk: Moderate to High on a localized basis

...Friday...
Scattered to at times numerous showers and thunderstorms. The activity appears likely to be most numerous during the morning hours.
Low Water Crossing Flood Risk: High
River/Stream Flood Risk: Moderate to High on a localized basis

...Saturday...
Scattered to at times numerous showers and scattered thunderstorms. The activity appears likely to be most numerous during the pre-dawn and early morning hours.
Low Water Crossing Flood Risk: High (pre-dawn/early a.m.)
River/Stream Flood Risk: Moderate to High on a localized basis

...Expected Rainfall Amounts...
In general --to repeat-- in general, rainfall of 4-6 inches appears probable for most of the area on average throughout the period Tuesday (mainly afternoon) through Saturday morning. We emphasized the "in general" detail because of the fact that actual amounts will widely vary based on thunderstorm tracks throughout the period. A few locations that receive particularly frequent bouts of heavier rain could see greater than 6 inches, while a few locations that don't receive as many heavy downpours could see less than 4 inches. It is also important to remember that ground conditions are already saturated going into this event, and stream/river levels are already running above normal levels across many parts of the area. Both of those factors indicate it will take less rain than normal to cause flooding issues at least at times across the area.
We will continue monitoring the situation and issue specific updates, alerts and/or warnings as conditions warrant.