August 2016: Rain Chances Continue.

[unome]

both CIMSS Satellite Blog and GOES-R JPSS Satellite Liason Blog are posting on the flooding event in Louisianna

http://cimss.ssec.wisc.edu/goes/blog/archives/21729

https://satelliteliaisonblog.wordpress. ... od-threat/

[srainhoutx]

1030Z Surface Chart analysis suggest a stalled frontal boundary near College Station extending back to the West near San Antonio. Deep mid/upper level Eastern Pacific moisture somewhat associated with the remnants of once TS Javier that moved inland along the Baja Peninsula is being funneled ENE along and North of that boundary. Cloud tops are cooling across Arcadia in Louisiana associated with the area of tropical like low pressure and should be an effective heavy rainfall maker as the freezing levels are around 16K feet. Expect very heavy rainfall rates to develop in the 2.5+ PW's that are slowly shifting West toward SW Louisiana/SE Texas today and additional deep tropical moisture surging NW into the Southern/SW Gulf with a westbound tropical wave axis located near the Yucatan Peninsula.

[srainhoutx]

MESOSCALE PRECIPITATION DISCUSSION 0556
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
702 AM EDT SAT AUG 13 2016

AREAS AFFECTED...CENTRAL/SOUTHERN LA...SOUTHWEST MS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 131100Z - 131700Z

SUMMARY...EXTREMELY HEAVY RAINFALL WILL CONTINUE THIS
MORNING...WITH DANGEROUS AND POTENTIALLY LIFE-THREATENING FLASH
FLOODING EXPECTED.

DISCUSSION...A VERY SLOW-MOVING LOW TO MID LEVEL LOW CENTER WEST
OF NATCHEZ MS CONTINUES TO DRIFT EVER SO SLOWLY TO THE
WEST-NORTHWEST THIS MORNING...AND CONTINUES TO FOCUS EXTREMELY
HEAVY RAINFALL ACROSS PORTIONS OF CENTRAL AND SOUTHWEST LA WITH
THE PERSISTENCE OF MULTIPLE WELL-DEFINED CONVECTIVE BANDS.

AREAS OF SOUTHWEST LA IN PARTICULAR ARE SEEING A SET-UP CURRENTLY
OF A WELL-DEFINED FETCH OF DEEP MOISTURE AND INSTABILITY OUT OF
THE NORTHWEST GULF OF MEXICO AND SOUTHEAST TX WHERE THE LOW LEVEL
FLOW IS QUITE CONFLUENT. MLCAPE VALUES ARE ALREADY OVER 1500 J/KG
IN SOME CASES AND COINCIDING WITH A DEEP TROPICAL AIRMASS OVER THE
REGION. PWATS EMBEDDED WITHIN THE BROADER LOW CIRCULATION REMAIN
VERY HIGH WITH VALUES GENERALLY ABOVE 2.5 INCHES.

THE BEST FORCING SHOULD REMAIN AROUND THE SOUTHWEST FLANK OF THE
LOW CIRCULATION AND THIS WOULD FAVOR PORTIONS OF CENTRAL AND
SOUTHWEST LA SEEING EXTREMELY HEAVY RAINS PERSIST. TRAINING
CONVECTIVE BANDS WITH HOURLY RAINFALL RATES OF UP TO 3 INCHES/HR
WILL FAVOR VERY HIGH RAINFALL TOTALS THROUGH MIDDAY.

EXPECT ADDITIONAL RAINFALL AMOUNTS OF 4 TO 8 INCHES WITH THE
HEAVIEST FOCUS GENERALLY NEAR AND JUST EAST OF A LINE FROM
ALEXANDRIA TO OAKDALE TO LAKE CHARLES. FARTHER SOUTHEAST OVER
TOWARD BATON ROUGE AND LAFAYETTE...THE RAINS HERE WILL BE MODERATE
TO HEAVY AS WELL...BUT WITH LOWER RAINFALL RATES.
NEVERTHELESS...EVEN THESE ALREADY SEVERELY HARD HIT AREAS WILL SEE
THE POTENTIAL FOR ADDITIONAL AMOUNTS OF 2 TO 4 INCHES.

DANGEROUS AND POTENTIALLY LIFE-THREATENING FLASH FLOODING WILL
REMAIN LIKELY ON THE ADDITION OF THESE VERY HEAVY RAINS AND
ESPECIALLY OVER AREAS OF SOUTH-CENTRAL LA WHERE STORM TOTALS ARE
BEGINNING TO EXCEED 20 INCHES FOR THE EVENT IN SOME AREAS.

ORRISON

ATTN...WFO...JAN...LCH...LIX...SHV...

[BlueJay]

We had a one minute down pour about 10 minutes or so ago-not enough to get the whole driveway wet, though. I'll stay tuned!

[BlueJay]

Liquid gold! Now the driveway is all wet!!
Happy Dance!

[jasons2k]

They should copy those bullet points and paste them at the bottom of every AFD before a system like this, just to remind folks. Good discussion.

[srainhoutx]

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0757 AM CDT SAT AUG 13 2016

VALID 131300Z - 141200Z


...PORTIONS OF LA/EAST TX...
A VERY MOIST AND DIURNALLY UNSTABLE BOUNDARY LAYER SHOULD EXIST ON
THE WESTERN PERIPHERY OF THE PERSISTENT LOW ACROSS LA AND NEAR A
SLOW-SOUTHEASTWARD-MOVING FRONT ACROSS THE ARKLATEX/SOUTHEAST TX.
WHILE VERTICAL SHEAR WILL BE QUITE WEAK...STEEPENING LOW-LEVEL LAPSE
RATES THIS AFTERNOON IN CONJUNCTION WITH AMPLE MOISTURE MAY BECOME
CONDUCIVE FOR A COUPLE INSTANCES OF MICROBURSTS CAPABLE OF LOCALIZED
WIND DAMAGE.

..GUYER/PICCA.. 08/13/2016

[srainhoutx]

The Weather Prediction Center slightly extends the Moderate Risk for Excessive Rainfall West into more of SE Texas with their Update Day 1 Outlook. Folks in most of Southern Louisiana remain in a High Risk.

08132016 1320Z Excessive Rainfall Day 1 94ewbg.gif

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
943 AM EDT SAT AUG 13 2016

...VALID 15Z SAT AUG 13 2016 - 12Z SUN AUG 14 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...



LOUISIANA, MISSISSIPPI, AND EASTERN TEXAS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...ADDITIONAL SIGNIFICANT RAINFALL EXPECTED ACROSS MUCH OF
LOUISIANA AND SOUTHWEST MISSISSIPPI...

THE SLOW-MOVING CONVECTIVE LOW IS EXPECTED TO BE PULLED GRADUALLY
NORTHWEST ALONG THE SOUTHERN PERIPHERY OF THE APPROACHING CENTRAL
U.S. TROUGH AND WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE.
ANOTHER ROUND OF HEAVY TO EXCESSIVE RAINFALL IS EXPECTED ACROSS
MUCH OF LA...EAST TX...AR...AND WESTERN MS. RECENT RADAR IMAGERY
SHOWS A CONNECTION IN THE CONVECTIVE PATTERN ASSOCIATED WITH THE
FRONTAL ZONE TO THE NORTH AND THIS CYCLONE. THE ATMOSPHERE
REMAINS SATURATED OVER THE CENTRAL GULF REGION...WITH PRECIPITABLE
WATER VALUES OF 2.25-2.5" OR 3-3.5 STANDARD DEVIATIONS ABOVE
NORMAL FOR MID-AUGUST. THE MORE ANOMALOUS PW PLUME WILL SHIFT
INTO EAST TX AND THE UPPER TX COAST AS THE WEAK LOW-MID LEVEL
CIRCULATION LIFTS SLOWLY NORTHWARD. DEVELOPING INSTABILITY TO THE
WEST AND NORTH OF THIS SYSTEM DUE TO DAYTIME HEATING WILL TEND TO
LURE THUNDERSTORMS WITH HEAVY RAINFALL IN THOSE DIRECTIONS.
PROLIFIC SHORT-TERM RAINFALL RATES REMAIN POSSIBLE, WITH HOURLY
RAIN RATES MAXIMIZING IN THE 3-4" RANGE PARTICULARLY ACROSS
WESTERN AND CENTRAL LA. THE TALL SKINNY CAPE PROFILES PER MODEL
FCST SOUNDINGS ALONG WITH THE ABNORMALLY HIGH WET BULB ZERO LEVELS
(DEEP WARM CLOUD LAYERS) ALSO FAVOR HIGHLY EFFICIENT WARM RAIN
PROCESSES...AS EVIDENCED FROM THE POCKETS OF MUCH HIGHER QPF (24
HR AMOUNTS OF 10+ INCHES) FROM THE LATEST GUIDANCE, ESPECIALLY THE
00Z ECMWF AND HIGH-RESOLUTION GUIDANCE. AREAS DEPICTED REMAIN
VIRTUALLY UNCHANGED FROM THE 09Z ISSUANCE.


TEXAS
~~~~~
THE INCREASED MOISTURE ADVECTION FROM THE EAST ALONG AND AHEAD OF
THE SLOW-MOVING FRONTAL BOUNDARY FROM THE DIRECTION OF THE
CONVECTIVE LOW WILL SPONSOR MORE WIDESPREAD SHOWERS AND
THUNDERSTORMS WITH HEAVY RAINFALL ACROSS CENTRAL-EASTERN TX.
AREAL-AVERAGE TOTALS BETWEEN 1.5-3.0" ACROSS EAST TX AND 0.5-1.5"
ELSEWHERE OVER CENTRAL TX ARE EXPECTED. THE SATURATED ENVIRONMENT
AND MODEST DEEP-LAYER INSTABILITY SHOULD ALLOW FOR LOCALIZED
HIGHER TOTALS GIVEN THE VERY WEAK 850-300 MB FLOW AND SLOW CELL
MOTIONS (LIGHT CORFIDI VECTORS). THE LACK OF LOW LEVEL INFLOW AND
OVERALL WEAK 0-6KM BULK SHEAR SHOULD LEAD TO A MORE PULSE-TYPE
EVOLUTION WITHIN THE STRONGER CELLS...WHICH ALONG WITH THE
INITIALLY HIGH FLASH FLOOD GUIDANCE VALUES WILL LEAD TO A LOWER
FLASH FLOOD THREAT COMPARED TO AREAS TO THE EAST. THE
ANTICIPATED ROBUST HOURLY RAINFALL RATES OF 2-4" UNDERNEATH THE
STRONGEST CORES WARRANT A SLIGHT RISK FOR EXCESSIVE RAINFALL. THE
AREAS IN CENTRAL AND WESTERN TX REMAIN UNCHANGED FROM THE 09Z
ISSUANCE.

[redneckweather]

I'm pretty confident that moderate risk area will continue to expand more to the west as the system continues meandering to the West.

[Cromagnum]

When is the event supposed to fire up in Houston?

[DoctorMu]

With the ridge broken down and boundary established across east Texas, expect daytime heating to crank up the cells as CAPE increases. Moderate movers with localized burst of rain for most of us over the weekend.

Action beginning this morning along the frontal zone.




Lots of uncertainty during the week as the mid level low in LA slips toward TX. Further complicated IF the boundary eases into the Gulf

[DoctorMu]

When is the event supposed to fire up in Houston?

Not a single event. Expect showers around NW Houston area first this afternoon

[Cromagnum]

I just hope northern Brazoria county gets some much needed rain. We have had less than a quarter inch at my house since June.

[Rip76]

From satellite it appears that area of weather (surface low) is losing some of its punch.

[mckinne63]

With all this cloud cover will we have daytime heating to fire off storms? I sure hope we get some rain. I am holding off putting the hose in the pool.

[unome]

a science reminder from NWS' Flood Safety http://www.floodsafety.noaa.gov/

http://www.nws.noaa.gov/os/water/tadd/p ... hysics.pdf

[jasons2k]

Area Forecast Discussion
National Weather Service Houston/Galveston TX
950 AM CDT Sat Aug 13 2016

.DISCUSSION...
Still looking for increasing shower and thunderstorm coverage across
parts of Southeast Texas later today and especially tonight and tomorrow
as significantly higher moisture levels partly associated with the nearly
stationary Louisiana storm system move into our area. The chances for
locally heavy rainfall will be increasing, and we might need to issue
a flash flood watch some time in the next 24 hours. Increasing cloud
cover and rain chances will help to bring our area`s afternoon high
temperatures down over the next several days.

[Rip76]

And appears to be moving SW instead of West.

http://www.nhc.noaa.gov/mobile/sat_zoom ... _loop.html

But I'm looking on my phone, so it's tough to tell.

[TexasBreeze]

http://radar.weather.gov/radar_lite.php ... TP&loop=no

We don't need this kind of rainfall here. That is the most widespread 12+ inches I have seen for only a couple days worth!!!

[houstonia]

Update from Jeff:

Tremendous rainfall event continues over southern Louisiana…shifting slowly toward E/SE TX.

Threat for heavy rainfall will increase this afternoon and remain into Monday.

Prolific rainfall event over southern Louisiana along and south of a “tropical” low pressure system has resulted in 24-hr storm totals of 15-22 inches with an isolated max of 27.47 inches near Brownfields, LA. Dangerous flash flood event continues to develop and shift westward along I-10 and the Louisiana coast with strong low level WSW confluent flow over SE TX and the upper TX coast feeding a near continuous shield of very heavy rainfall and significant training bands. Hourly rainfall rates of 2-4 inches have been observed under these “feeder” bands. Center of mid level low appears to be located over C LA with a surface reflection over SC/SE LA. Massive rain shield continues to favor the SW flank of this system as has been the case for the last 2-3 days.

At the same time a surface trough and weak front is approaching SE TX from the NW while western flank of approaching LA system is crossing the Sabine River. Banding features have started to develop within the last few hours from eastern Harris County to near Lake Charles and off the coast south of Sabine Pass. Record breaking moisture profile over Louisiana with PWS of 2.5-2.8 inches will shift west into SE TX later today…New Orleans sounding had a shattering 2.79 inch PW last evening which is the second highest I have ever seen at an actual sounding site. “Super” tropical air mass will shift into SE TX this afternoon and remain in place into Monday. The mid and low level centers embedded in this tropical air mass continues feed energy into these lows and they are behaving very much like a decaying tropical system…and that is how they should be treated.

Model guidance continues to insist that the defined low will open into a westward moving trough and the heavy rainfall will become less concentrated over SE/E TX compared to Louisiana…however this process has yet to happen and radar data out of Lake Charles continues to show a well defined circulation to the reflectivity.

Expect an increase in showers and thunderstorms this afternoon as moisture increases and heating destabilizes the air mass. Will have to watch trends closely tonight to see if sustained banding develops on the SW flank of the circulation center again…similar to the last several nights which would be near/over our eastern set of counties or roughly from Lake Livingston to Galveston Bay. Given extraordinarily moist air mass excessive rainfall rates under the stronger storms will be likely with 2-4 inches per hour common.

Will maintain widespread rainfall amounts of 2-4 inches across the area NE of a Line from College Station to Katy to Galveston and I am tempted to go higher with these amounts…but if the system opens into a wave of low pressure instead of the more concentrated low then 2-4 inches is reasonable. If the system maintains a defined low center rainfall will need to be greatly increase along and south of that center track. Isolated totals of 6-8 inches or higher is certainly possible given slow storm motions and high moisture levels.

A flash flood watch may be required later this afternoon or tonight as trends unfold even with the very dry ground conditions currently in place.

Lake Charles Radar Estimates: Note the massive area over 12 inches
Click for latest Storm Total Precipitation radar loop from the Lake Charles, LA radar and current weather warnings