Cooldown to Intensify; Wintry Precip for some Early Thurs/Fri - Likely Everyone Sunday night/Monday...

 

...Overview...

Increasingly cold, arctic air will continue to slowly invade the region through Friday and even more rapidly from Saturday through Tuesday before a moderation in temperature occurs beginning Wednesday of next week. Patchy, light wintry precipitation is possible in Western portions of the local area on Thursday and Friday morning. A more significant round of wintry precipitation is possible area-wide from late Sunday into Monday.

...Regarding Temperatures & Wind Chill Conditions...

Daytime high temperatures will average the 30s Thursday through Saturday, mainly the 20s on Sunday and Monday, and the 30s again by Tuesday and Wednesday. Nighttime/early morning low temperatures will average the lower 30s Thursday and Friday, the low to mid 20s Saturday and Sunday, and the teens on Monday and Tuesday.

Wind Chill values will average the 20s throughout most of the period, except for the single digits and teens from Sunday through Tuesday morning.

...Regarding Patchy, Light Wintry Precipitation on Thursday Morning & Friday Morning...

Patchy, light wintry precipitation is possible in Western parts of the local region (generally West of a line from Canyon Lake to Dripping Springs to Lakeway) mainly between 5am and 9am on Thursday morning, and in the same general area mainly between 4am and 8am on Friday morning. Within this part of the local region, patchy, light ice accumulation is possible especially on elevated, metallic and other colder types of surfaces.

...Regarding A More Significant Round of Wintry Precipitation from Late Sunday into Monday...

Wintry precipitation appears likely area-wide from late Sunday evening or Sunday night into Monday. The potential exists for both freezing drizzle/freezing rain and snow across much of the area during this time period, with potentially significant impacts in at least some parts of the area. We are continuing to monitor this aspect of the situation with more detailed updates to follow, likely beginning tomorrow.

Significant Cold Wave Likely Late Week into Next Week

We are closely monitoring a developing weather situation for the period Friday of this week through Wednesday of next week.  While changes to the forecast are still likely, we wanted to give you a heads-up so that you can prepare for the coming cold weather.

Expected impacts:

•A surge of arctic air is forecast to impact the local region beginning about Friday of this week and continuing through at least Wednesday morning of next week

•During this time period, temperatures will remain at or below freezing for extended periods of time with wind chill values mainly in the teens and 20s for extended periods of time

•Minimum early morning low temperatures will average 15-20 degrees across much of the area, centered on Sunday/Monday

•Daytime high temperatures will average the 30s on Friday/Saturday, the 20s on Sunday, and the lower to middle 30s on Monday/Tuesday

Some light, wintry precipitation is also possible at times from Sunday through Tuesday, but at this time it is too early to be precise with regard to potential impacts

Discussion:

A surge of bitterly cold, arctic air is forecast to impact the local region beginning about Friday of this week (2/12/21) and continuing through at least Wednesday morning of next week (2/17/21). While all details are not 100% certain, we wanted to provide as much notice as possible so that you can prepare accordingly for this event.

During the above mentiond time period, temperatures will remain at or below freezing for extended periods of time with wind chill values mainly in the teens and 20s for extended periods of time. Minimum early morning low temperatures will average 15-20 degrees across much of the area, centered on Sunday and Monday mornings. Daytime high temperatures will average the 30s on Friday/Saturday, the 20s on Sunday, and the lower to middle 30s on Monday and Tuesday.

In addition, several weak upper level weather disturbances are forecast to move across the region during the period Sunday through Tuesday, which will result in the potential for at least occasional, light wintry precipitation at times during that portion of the peirod. At this time it is too early to be precise with regard to potential impacts, but we will continue to monitor the situation closely.

The purpose of this alert is to provide advance notice that temperatures will be significantly colder and for a significant period of time during the above indicated period. We recommend that planning begin now to prepare for the upcoming cold weather, especially due to the relatively mild conditions that we've experienced for much of the winter to this date. We are still in the initial monitoring stages of this event, so expect additional changes to the forecast as we move through the coming days.

Additional Shower & T-Storm Activity Likely - Especially Tonight/Early Tuesday....

Expected impacts:

• Widely scattered showers and isolated thunderstorms are possible across the area today with coverage of around 30 percent likely at any given time
• Periods of showers and thunderstorms are likely from around Midnight or shortly after tonight through about 9am on Tuesday
• Scattered showers and thunderstorms are possible from 9am to 6pm on Tuesday
• Locally heavy rainfall is likely at times with thunderstorms, especially tonight into early Tuesday morning
• Additional rainfall of around 1 inch is likely with localized amounts of 1-2 inches possible in some parts of the area, which is likely to cause minor flooding of low lying and poor drainage areas at times during the period

Details:

...Today and This Evening...
Widely scattered showers and thunderstorms are possible. Coverage will likely average 30 percent throughout most of the period. Generally brief but locally heavy downpours of rain and lightning are possible with any isolated thunderstorms.

...Midnight Tonight thru 9am Tuesday...
Periods of showers and thunderstorms are likely from around Midnight or 1am tonight through about 8 or 9am Tuesday. Locally heavy rainfall can be expected at times during the period, and cloud to ground lightning can be expected with any thunderstorms. Mostly minor flooding of low water crossings and similar flood prone areas can be expected in at least some parts of the area in association with this activity.

There will also be a risk for gusty winds as the (expected) main band of thunderstorms initially approaches the area between Midnight tonight and 2am Tuesday. Present indications suggest the strongest winds will be to the immediate South of the local area, but we'll continue to monitor trends closely as the situation evolves.

...9am Tuesday to 6pm Tuesday...
Scattered showers and thunderstorms are possible during the daytime hours on Tuesday. Coverage will likely average 30 percent in the morning (after 9am) and then 40 percent during the afternoon hours. Generally brief but locally heavy downpours of rain and lightning are likely with any thunderstorms.

Total Rainfall for the Period:

Additional rainfall of around 1 inch is likely with localized amounts of 1-2 inches possible in some parts of the area, the majority of which will occur from Midnight tonight to 9am Tuesday.

Remainder of the Week:

A relative lull in precipitation (with mostly just spotty activity) is expected for Wednesday and Thursday, and then increasing chances of showers and thunderstorms are expected again toward Friday and into next weekend.

UPDATE on Shower/T-Storm Activity This Evening through Tonight (as well as beyond)....

Synopsis:

• Scattered showers and thunderstorms are possible across the area this evening, especially toward/after 8pm, with locally heavy downpours possible in the affected areas
• Periods of showers and thunderstorms are likely from around 10pm or shortly after this evening through about 6am on Monday, with locally heavy rainfall likely and strong, gusty winds possible initially
• Scattered showers and thunderstorms are possible during the daytime and evening hours on Monday
• Periods of showers and thunderstorms are likely from around 2-3am Tuesday through about 9am Tuesday, with locally heavy rainfall possible at times during the period
• Widespread rainfall of 1-2 inches is likely with localized amounts of 2-3 inches possible in some parts of the area, which may lead to at least minor flooding of low lying and poor drainage areas at times during the period

Details:
...Now through 10pm This Evening...
Scattered showers and thunderstorms are possible across the area this evening, especially toward/after 8pm, with locally heavy downpours possible in the affected areas. An isolated stronger thunderstorm could also produce gusty winds and/or hail in the affected portion(s) of the area, again, especially toward/after 8pm.

...10pm This Evening thru 6am Monday Morning...
Periods of showers and thunderstorms are likely. Locally heavy rainfall can be expected at times during the period, and cloud to ground lightning can be expected with any thunderstorms. As the initial main line of thunderstorms approaches a given location late this evening/early tonight (generally between 10pm and 1am), strong, gusty winds are possible in parts of the area.
Minor flooding of some of the typically more vulnerable low water crossings and similar flood prone areas is possible in at least some parts of the area, particularly near/adjacent to areas where downpours are more persistent.

...Daytime and Evening Hours on Monday...
Scattered showers and thunderstorms are possible during the daytime and evening hours on Monday. Coverage will likely average 40 percent throughout most of the period. Generally brief but locally heavy downpours of rain and lightning are likely with any thunderstorms.

...2am Tuesday through 9am Tuesday...
Periods of showers and thunderstorms are likely from around 2-3am Tuesday through about 9am Tuesday. Locally heavy rainfall can be expected at times during the period, and cloud to ground lightning can be expected with any thunderstorms. Mostly minor flooding of low water crossings and similar flood prone areas is possible in at least some parts of the area. This will be of greatest concern in areas that also receive heavy rainfall on Sunday night/Monday morning.

...9am Tuesday to 6pm Tuesday...
Scattered showers and thunderstorms are possible during the daytime and evening hours on Monday. Coverage will likely average 40 percent throughout most of the period. Generally brief but locally heavy downpours of rain and lightning are likely with any thunderstorms.

Total Rainfall for the Period:Widespread rainfall of 1-2 inches is likely with localized amounts of 2-3 inches possible in some parts of the area.

Remainder of the Week: Please be aware that periods of scattered shower and thunderstorm activity are expected again on Wednesday and especially on Thursday and Friday of this week. Depending upon how much rainfall is received beforehand, any additional heavy rainfall during the middle and latter portions of the week could further aggravate the low land flooding potential across the area, and this will need to continue to be monitored closely.

Periods of Showers & T-Storms to Bring Locally Heavy Rainfall Threat This Week

Synopsis/Key Points:

• Isolated to widely spaced showers and isolated thunderstorms are possible at times during the day today and into this evening
• Periods of showers and thunderstorms are likely from around or shortly after Midnight tonight through about 8am on Monday, with locally heavy rainfall possible at times during the period
• Scattered showers and thunderstorms are possible during the daytime and evening hours on Monday
• Periods of showers and thunderstorms are likely from around 2-3am Tuesday through about 9am Tuesday, with locally heavy rainfall possible at times during the period
• Widespread rainfall of 1-2 inches is likely with localized amounts of 2-3 inches possible in some parts of the area, which may lead to at least minor flooding of low lying and poor drainage areas at times during the period

Details by Time Period:

...Today and This Evening...
Isolated to widely spaced showers and isolated thunderstorms are possible at times during the day today and into this evening. Coverage of the activity will likely average 30 percent at any given time, possibly reaching 40 percent during peak afternoon heating. Generally brief but locally heavy downpours of rain and lightning are likely with any isolated thunderstorms.

...Midnight Tonight to 8am Monday Morning...
Periods of showers and thunderstorms are likely from around or shortly after Midnight tonight through about 8am on Monday. Locally heavy rainfall can be expected at times during the period, and cloud to ground lightning can be expected with any thunderstorms. Minor flooding of some of the typically more vulnerable low water crossings and similar flood prone areas is possible in at least some parts of the area, particularly near/adjacent to areas where downpours are more persistent.

...Daytime and Evening Hours on Monday...
Scattered showers and thunderstorms are possible during the daytime and evening hours on Monday. Coverage will likely average 40 percent throughout most of the period. Generally brief but locally heavy downpours of rain and lightning are likely with any thunderstorms.

...2am Tuesday through 9am Tuesday...
Periods of showers and thunderstorms are likely from around 2-3am Tuesday through about 9am Tuesday. Locally heavy rainfall can be expected at times during the period, and cloud to ground lightning can be expected with any thunderstorms. Mostly minor flooding of low water crossings and similar flood prone areas is possible in at least some parts of the area. This will be of greatest concern in areas that also receive heavy rainfall on Sunday night/Monday morning.

...9am Tuesday to 6pm Tuesday...
Scattered showers and thunderstorms are possible during the daytime and evening hours on Monday. Coverage will likely average 40 percent throughout most of the period. Generally brief but locally heavy downpours of rain and lightning are likely with any thunderstorms.

Total Rainfall for the Period:

Widespread rainfall of 1-2 inches is likely with localized amounts of 2-3 inches possible in some parts of the area.

Remainder of the Week:

Please be aware that periods of scattered shower and thunderstorm activity are expected again on Wednesday and especially on Thursday and Friday of this week. Depending upon how much rainfall is received beforehand, any additional heavy rainfall during the middle and latter portions of the week could further aggravate the low land flooding potential across the area, and this will need to continue to be monitored closely.

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.