April 2016 Recap: Regional Flood/Severe Weather

[BlueJay]

Tomball…Klein Tornado:
NWS survey team investigated the wind damage across northern Harris County yesterday and determined a weak tornado occurred 6 miles SW of The Woodlands along Willow Creek in the Willow Forest Subdivision. The tornado was .41 miles wide with a damage path of 40 yards and winds estimated near 70mph. Numerous large pines were snapped or uprooted with several trees impacted homes. 1 person was killed when a tree fell on their mobile home.

I think our area experienced some of those winds because there is evidence of large-ish branches that were torn off and thrown around. Driveways were cluttered with branches.

[houstonia]

Slightly off-topic, but in the interest of storm watching:
Interesting:
Anyone see that TVNweather has decided to discontinue it's live storm chasing service? I enjoyed watching the dashcam videos, but recently I noticed there were an increasing number of storm chasers and in the last storm event, it seemed like there were people using TVN to further their own interests. Also, with Facebook offering FB Live - maybe that would be strong competition.
Thoughts?
The notice is here: https://tvnweather.com/

[Katdaddy]

...FLASH FLOOD WATCH IN EFFECT FROM FRIDAY AFTERNOON THROUGH
SUNDAY MORNING...

THE NATIONAL WEATHER SERVICE IN HOUSTON/GALVESTON HAS ISSUED A

* FLASH FLOOD WATCH FOR A PORTION OF SOUTHEAST TEXAS...INCLUDING
THE FOLLOWING AUSTIN...BRAZOS...BURLESON...COLORADO...FORT ...
BEND...GRIMES...HARRIS...HOUSTON...MADISON...MONTGOMERY...
POLK...SAN JACINTO...TRINITY...WALKER...WALLER...WASHINGTON
AND WHARTON.

* FROM FRIDAY AFTERNOON THROUGH SUNDAY MORNING

* UNUSUALLY MOIST TROPICAL AIR WILL STREAM INTO THE REGION FRIDAY
AS SOUTHERLY WINDS INCREASE. AN UPPER LEVEL JETSTREAM WILL BRING
A SERIES OF DISTURBANCES INTO THE REGION AND SHOULD HELP TO
DEVELOP SHOWERS AND THUNDERSTORMS FRIDAY AFTERNOON OVER THE
WESTERN PORTIONS OF THE WATCH AREA THEN SHIFTING EASTWARD AND
NORTHWARD THROUGHOUT THE REGION FRIDAY NIGHT AND SATURDAY. THE
GROUND IS SATURATED AND ANY STORMS WITH HIGH RAIN RATES WILL
LEAD TO RAPID RUNOFF AND FLOODING. THE HEAVIEST RAINFALL THREAT
SHOULD PEAK FRIDAY NIGHT THROUGH SATURDAY AFTERNOON. ADDITIONAL
RAINFALL IS POSSIBLE AFTER THAT AND THE GROUND WILL BE SATURATED
AND STREAMS AND BAYOUS MAY ALREADY BE SWOLLEN OR FLOODING.
WIDESPREAD RAINFALL TOTALS THROUGH THE WATCH PERIOD WILL LIKELY
AVERAGE 2 TO 4 INCHES WITH LOCALIZED AMOUNTS OF 5 TO 8 INCHES.
MUCH OF THESE AMOUNTS COULD COME IN ONLY A FEW HOURS OF HEAVY
RAIN. AS WE APPROACH THE WATCH PERIOD CONFIDENCE IN TIMING AND
LOCATION WILL LIKELY IMPROVE THE FOCUS FOR WHERE THE HEAVY RAINS
WILL FALL.

* STREETS...BAYOUS...STREAMS AND RIVERS WILL LIKELY HAVE THE
GREATEST IMPACTS FROM THE HEAVY RAINFALL. MOTORISTS AND PERSONS
WITH OUTDOOR ACTIVITIES SHOULD STAY ABREAST OF THE LATEST
FORECASTS AND HAVE CONTINGENCY PLANS FOR WHEN THE HEAVY RAIN
ARRIVES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A FLASH FLOOD WATCH MEANS THAT CONDITIONS MAY DEVELOP THAT LEAD
TO FLASH FLOODING. FLASH FLOODING IS A VERY DANGEROUS SITUATION.

YOU SHOULD MONITOR LATER FORECASTS AND BE PREPARED TO TAKE ACTION
SHOULD FLASH FLOOD WARNINGS BE ISSUED.

[tireman4]

Yep, the mets (Wxman 57 and Srain) were hinting at this...I figured it was coming..

[srainhoutx]

The afternoon guidance suggests a stalling frontal boundary across the area generally across Waller, Grimes, Montgomery and San Jacinto Counties into early Sunday.

[houstonia]

The afternoon guidance suggests a stalling frontal boundary across the area generally across Waller, Grimes, Montgomery and San Jacinto Counties into early Sunday.

does this mean the possibility for heavy rain is less across Harris, Fort Bend, and Wharton counties?

[srainhoutx]

The afternoon guidance suggests a stalling frontal boundary across the area generally across Waller, Grimes, Montgomery and San Jacinto Counties into early Sunday.

does this mean the possibility for heavy rain is less across Harris, Fort Bend, and Wharton counties?

Need to monitor for training storms across all of our Region. Think that areas that received the most rain the 17-20th is the main reason for the Watch. Jeff just issued a briefing. Let me get that up.

[srainhoutx]

Thursday afternoon briefing from Jeff:

***Heavy rainfall and flash flood event possible Friday afternoon-Saturday***

NWS has issued a Flash Flood Watch from noon Friday until Sun AM for all of SE TX except the immediate coastal counties and Liberty County.

Incoming storm system will produce favorable lift across a very moist air mass which is already moving into SE TX. Concern is growing that slow moving/and/or training convection will develop Friday afternoon over the western counties of the region and slowly move ESE overnight into the US 59 corridor. Moisture levels support excessive short term rainfall rates of 2-3 inches per hour which on top of saturated grounds which will produce extensive run-off and likely lead to rapid flash flooding.

There is still uncertainty on exactly where significant cell training may develop which would indicate the greatest potential for high rainfall amounts and flash flooding. This will likely not be known until the event is underway…but the increasing 850mb flow off the Gulf into a potentially linear WSW to ENE line of thunderstorms is a classic overnight flash flood setup for SE TX. For what it is worth the EURO is seeming to favor the I-10 corridor from western Harris County toward Austin and Colorado Counties.

Severe threats including damaging winds and large hail will also be possible this this activity.

[ticka1]

The afternoon guidance suggests a stalling frontal boundary across the area generally across Waller, Grimes, Montgomery and San Jacinto Counties into early Sunday.

does this mean the possibility for heavy rain is less across Harris, Fort Bend, and Wharton counties?

Need to monitor for training storms across all of our Region. Think that areas that received the most rain the 17-20th

Is it possible the coastal counties like Chambers and Galveston will be added later or the threat not there for us?

[srainhoutx]

Possibly ticka. Remember there is a lot of uncertainty where the front stalls as Jeff mentioned. Additional rain is making expected Monday into Tuesday particularly along the coastal tier of counties. Likely will not have a good handle on things until we see where the training storms set up. Stay tuned folks. We'll be monitoring carefully.

[Cromagnum]

I would consider the entire viewing area under watch and wait. The Wednesday morning storm line was thought to stall out before Houston and then lift out, but the cap busted and it plowed all the way offshore.

[srainhoutx]

The afternoon updated Weather Prediction Center Day 2 Excessive Rainfall Outlook introduced a Moderate Risk for Excessive Rainfall across the Western portion of SE Texas.

[davidiowx]

Man it's so moist outside! just walked out of work and it's like walking into a wall!

[jasons2k]

GFS and Euro are a little different, but the Euro is pretty concerning. A pretty wide band of 7"+ rains from NC/NE Harris County, up through Central Montgomery County, and then arcing NE into San Jacinto County and extreme SE Walker County.

I'm a bit surprised Liberty County isn't in the FF watch with the models still wobbling around a bit. They seem to always get dumped on, and the Trinity River is prone to flooding too.

[nuby3]

been watching the severe storm moving only very slightly sw of Waco tonight. rainfall accumulations radar estimated at 2-3 inches per hour and over 4 inches accumulated there now. interesting little spot

[Texaspirate11]

been watching the severe storm moving only very slightly sw of Waco tonight. rainfall accumulations radar estimated at 2-3 inches per hour and over 4 inches accumulated there now. interesting little spot

There's an interesting blob in South Texas coming up from Mx that I'm watching....

[Texaspirate11]

Interesting blob in South Texas

[srainhoutx]

The Weather Prediction Center as outlined a large area of East, SE and NE Texas, West and NW Louisiana as well as portions of the Southern half of Arkansas with a Moderate Risk for Excessive Rainfall.

There remains a lot of uncertainty exactly how the sensible weather will play out with several scenarios that are possible due to lack of clear cut solutions via the guidance. We will need to monitor radar trends as the evolution of events today through Saturday night and possibly into early Sunday will be mesoscale driven and cannot be determined until the event is underway. What raises an eyebrow this morning is very high PW's surging N out of the NW Gulf with up to 2.2 inches of precipitable water values with its origins in the NW Caribbean. Radar detects showers with embedded storms offshore slowly creeping N as well as the sub tropical jet with its deep tropical moisture from the Eastern Pacific nosing N toward Coastal Texas. The upper trough with a cold core upper low is situated over New Mexico/Colorado where snowfall is expected across the front range and higher elevations. Water vapor imagery shows another shortwave nearing California that should round the base of the Western trough tonight into tomorrow.

To further complicate things, there are indications that the stalling Pacific frontal boundary may linger across the area just to the West of Houston until Tuesday morning. Best case scenario is for a mesoscale convective system to sweep across the area late tonight into tomorrow morning leaving a cold pool in its wake with some drier air and a stabilized atmosphere.

Another option is for the line of storms to pass to the N of Metro Houston and continue a highly unstable atmosphere over the Region with boundaries as focal points for heavy rainfall to train. At this time there is no clear cut solutions, so stay tuned to developments as they unfold. This is a very difficult forecasting challenge, so we encourage everyone to monitor the NWS and reliable weather information sources.

[Katdaddy]

Enjoy the quiet weather for now. Flash Flood and severe weather threat continues through the weekend so remain weather aware as Srain posted. Here is this morning's Houston-Galveston Area Forecast Discussion (AFD):

FAIRLY UNEVENTFUL MORNING ANTICIPATED. AN AREA OF DEEP TROPICAL MOISTURE (PW`S 2-2.2") SITUATED IN THE SW GULF WILL BE MAKING ITS WAY UP THE COAST AND INTO SE TX DURING THE LATE MORNING AND
AFTERNOON HOURS. BY EARLY AFTERNOON...THERE`S PRETTY GOOD AGREEMENT IN GUIDANCE SHOWING SHOWERS/STORMS BEING INITIATED ALONG DRYLINE IN CNTL TEXAS AND MAKING THEIR WAY EASTWARD INTO SE TX DURING THE LATE AFTERNOON AND EVENING HOURS. SHOULD BE ENOUGH INSTABILITY & SHEAR BY THAT TIME FOR SOME SEVERE STORMS TO BE A THREAT (HAIL, WIND, ISO TORNADOES ALL A POSSIBILITY). FLASH FLOODING IS ALSO A CONCERN IN ASSOCIATION WITH CONVECTIVE CELLS. THE MORE FAVORED LOCATION FOR THIS TO OCCUR APPEARS TO GENERALLY BE NORTHWEST OF HIGHWAY 59.

THIS EVENING INTO SATURDAY MORNING:
THIS IS WHERE CONSIDERABLE UNCERTAINTY ENTERS THE PICTURE ON HOW THINGS WILL EVOLVE. BEST CASE SCENARIO WILL BE FOR THE LINE/COMPLEX OF STRONG TO SEVERE STORMS TO CONTINUE MOVING ESE
ACROSS THE REMAINDER OF THE REGION WITH A BREAK IN THE PRECIP IN ITS WAKE. WORST CASE SCENARIO...WHICH CANNOT BE RULED OUT EITHER...IS FOR THE THE NORTH-TO-SOUTH ORIENTED PORTION OF THE LINE OF STORMS TO RACE EASTWARD LEAVING THE SOUTHERN PORTION OF THE LINE BEHIND AS IT TRANSITIONS INTO A MORE WEST-TO-EAST ORIENTATION SOMEWHERE ACROSS THE AREA. SHOULD THIS OCCUR...IT`LL BECOME SITUATED ROUGHLY PARALLEL TO THE UPPER FLOW AND MOVEMENT COULD SUBSTANTIALLY SLOW. FAVORABLE UPPER LEVEL DIVERGENCE OVERHEAD INTO MIDDAY SATURDAY WITH SUSTAINED MODERATE INFLOW FEEDING PERPENDICULAR TO SUCH A BOUNDARY COULD LEAD TO A SIGNIFICANT FF THREAT WHEREVER SUCH A BOUNDARY ENDS UP. AGAIN...THAT WOULD BE A WORST CASE SITUATION. ANYTHING IN BETWEEN IS POSSIBLE. UNFORTUNATELY...MANY TIMES THESE EVENTS PLAY OUT ON SMALLER SCALE DETAILS THAN WHAT MODELS DEPICT...SO OVERALL CONFIDENCE IN ANY ONE SOLUTION ISN`T VERY HIGH AND WILL HAVE TO KEEP AN EYE ON TRENDS. BOTTOM LINE IS GROUND IS NEARLY SATURATED FROM RECENT RAINS. EVEN 35-50 MPH WINDS WILL BE A RISK OF DOWNING TREES. STRONGER CELLS WILL ALSO PRODUCE EFFICIENT RAINFALL RATES. QUICK RUNOFF WILL PRODUCE A FF THREAT. WILL LEAVE FF WATCH AS/IS.

[srainhoutx]

Friday morning briefing from Jeff:


***Significant rainfall and flash flood event possible over SE TX this afternoon-early Saturday***

Discussion

An upper level storm system over the SW US is currently spreading lift across W TX. A very impressive pool of moisture over the western Gulf of Mexico (PWS 2.0-2.2 inches…record levels) is heading NNW toward the TX coast and will arrive later this morning. Upper level winds will gradually become divergent this afternoon and weak disturbances will approach from the SW. With a little heating the local air mass will be primed.

Expect a line of strong to severe storms to develop along the dry line over C TX early this afternoon and move eastward into SE TX by mid afternoon. Additionally, some of the meso scale models show development in a S to N or SSW to NNE line from Brazoria County into Harris County…not sure what the focus of this development is, but since a couple of the models show this activity…it certainly could happen.

Big concern is late this afternoon into the overnight hours as central TX line arrives into the region. Looks like the northern end of the line will move across our northern set of counties, but southern tail end slows and unfortunately becomes parallel to the upper level flow. Expect the outflow boundary to become oriented WSW to ENE over some part of the region and the flash flood threat will really go up with good potential for training convection. Tremendous Gulf inflow will be maintained into this boundary all night which will allow storms to be maintained. This is a highly classis overnight flash flood setup for SE TX.

Moisture levels near mid summer and at tropical like levels is very concerning. Expect intense rainfall rates in any stronger storms of 2-4 inches per hour. These kind of rainfall rates are very damaging for this area and will get areas into trouble very quickly….especially with the saturated grounds in place. Such rainfall rates over urban areas will cause rapid run-off and flooding.

Widespread rainfall amounts of 2-4 inches look likely with isolated amounts of 5-8 inches. Could see even higher totals if the storms train for an extended period of time. Will favor areas along and NW of US 59 (or areas so hard hit two weeks ago) for the highest rainfall totals…but there is still plenty of uncertainty as to where these maximum amounts will fall.

Severe:

There will certainly be a severe threat with all the instability and shear in place. Main threats will be wind damage…especially in any bowing segments and large hail. With extremely wet grounds…it will not take much wind to blow down trees…so even non-severe thunderstorms may produce damage. Think the highest severe threat will be from Huntsville SSW to near Victoria this afternoon with the overall threat lessening eastward tonight as the event transitions toward a heavy rainfall event.

Saturday-Tuesday:

Weak front will stall somewhere over the area with continued chances for additional rounds of thunderstorms. May get a break on Saturday if the air mass becomes worked over enough tonight…if not…thunderstorms will just continue to develop.

Next period of interest will be late Sunday-early Tuesday when the next strong disturbance comes out of Mexico and across TX. Looks like another heavy rainfall threat especially along the coast during this period.

Hydro:

Watersheds across the area are well above base flow and many rivers, while below flood stage, remain swollen. With saturated grounds and full lakes and rivers…there is just no place for the water to go. Expect rises on all watersheds and some will likely go into flood due to the rainfall over the next 24-48 hours. Residents along rivers, creeks, and bayous should remain alert to the threat for rapidly rising water and be prepared to act.

As a reminder…never drive into high water…of the 8 fatalities associated with the Tax Day Flood…all 8 were vehicle related. Remember…Turn Around Don’t Drown”