August 2016: Rain Chances Continue.

[srainhoutx]

Sunday morning briefing from Jeff:

Rainfall events continues over C/SW/SE TX this morning.

Flash Flood Watch is in effect until 700pm for the western counties of SE TX.

Excessive rainfall overnight of 6-9 inches SE of San Antonio has resulted in the formation of a well defined meso low as seen on radar midday between San Antonio and Victoria. This warm core feature is drifting very slowly toward the NNE with activity developing along its eastern inflow flank from Matagorda Bay to Grimes County. Expect showers and thunderstorms to continue to develop and translate NNE to N across SE TX today as meso low tracks toward our western counties.

Moisture levels remain extremely high with PWS of 2.2-2.5 inches over the region and this will support excessive short term rainfall rates of 2-3 inches per hour. Rainfall rates overnight near Gonzales, TX were upwards of 5.5-6.0 inches per hour. Meso scale factors continue to drive the pattern of heavy rainfall while upper level divergence and general overall lift remains favorable over the region for storm generation. Again today it will be watching the radar to see where any sustained training of cells develops and will favor this potential west of I-45. Widespread rainfall amounts of 2-3 inches will be possible with isolated totals of 8 inches or more especially in the Flash Flood Watch area. Will see another day of potential heavy rainfall on Monday especially along the seabreeze, before drier air spreads across the region from the Gulf of Mexico Monday night.

Drier weather will build into the region Tuesday-Wednesday as the sub-tropical ridge off FL builds west along the US Gulf coast. By the end of the week the ridge shifts slightly northward placing the northern Gulf under a tropical easterly flow. Tropical disturbances within this flow will arrive into the area enhancing rainfall Thursday-next weekend. Will need to continue to watch the potential development and track of Atlantic tropical wave 99L just in case it is able to become trapped under this building ridge.

Hydro:
Heavy rainfall overnight has resulted in significant rises on rivers flowing toward the coastal bend out of central TX including the San Antonio River and the Guadalupe River. Flood flows are likely into Lake Somerville from Yegua Creek. A rise on the Brazos River is expected, but not expected to reach flood stage. Additional heavy rainfall today will likely result in changes to the current river forecasts and additional rises of some basins to flood stage will be possible.

[Katdaddy]

MESOSCALE PRECIPITATION DISCUSSION 0589
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
856 AM EDT SUN AUG 21 2016

AREAS AFFECTED...SOUTH TEXAS AND ADJECENT NE MEXICO

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 211300Z - 211800Z

SUMMARY...CONVERGENCE BAND WITH HIGHLY EFFICIENT RAINFALL
PRODUCTION MAY POSE ISOLATED FLASH FLOOD CONCERNS DUE TO HIGH
RATES AND WET ANTECEDENT CONDITIONS.

DISCUSSION...RADAR AND SATELLITE MOSAIC LOOPS INDICATE A STRONG
MCV OVER S GONZALES COUNTY WITH A BROAD CONFLUENCE ZONE/TROF
EXTENDING NORTHEASTWARD ACROSS EASTERN TEXAS TOWARD FRONTAL ZONE
NEAR/ALONG LA/AR BORDER. UPPER LEVEL JET STREAK SPEED MAX
ENHANCED BY LAST NIGHT'S MCS ACTIVITY IS EXITING TOWARD THE
NORTHEAST AND SUPPORTING BROAD ASCENT ACROSS SE TX ATTM. THIS
COMBINED WITH NORTHERLY CHANNEL OF EARLY MORNING ENHANCED ONSHORE
FLOW SUPPORTS STRONG MST CONVERGENCE ALONG A N-S BAND FROM
ROBERTSON COUNTY TO CALHOUN COUNTY ALONG THE EASTERN PERIPHERY OF
THE MCV. DEEPLY SATURATED PROFILE (PARTICULARLY WESTWARD) WITH
TPWS ABOVE 2.0" WITH DOWNSTREAM AVAILABLE INSTABILITY DENOTED BY
CAPES UP TO 2000 J/KG (CLOSER TO THE COAST) SHOULD PRESENT THE
OPPORTUNITY FOR VIGOROUS CONVECTIVE UPDRAFTS WITH EFFICIENT WARM
CLOUD RAINFALL PRODUCTION FOR RATES IN THE 2-2.5"/HR RANGE. SHORT
TERM CELL MOTIONS HAVE A SLIGHT NORTHERLY COMPONENT THAT MAY
SUPPORT SOME ISOLATED REPEAT ALLOWING FOR COMPOUNDED TOTALS...BUT
MOST HI-RES GUIDANCE SUPPORTED MOST STRONGLY BY THE 00Z WRF-ARW
SUGGEST EASTWARD ADVANCEMENT ACROSS SE TX THOUGH 19-20Z...LEADING
TO STREAKS OF 2-3" TOTALS. VERY HIGH FFG VALUES WOULD SUGGEST
THIS IS NOT A THREAT...THOUGH AHPS INDICATES MUCH OF THE AREA WELL
ABOVE NORMAL (400% AND GREATER) OVER THE WEEK AND SHOWING A WET
MONTH AS WELL SUPPORTING THE NOTION OF ISOLATED FLASH FLOODING
CONDITIONS LIMITED TO STRONGEST CORES.

[unome]

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1027 AM CDT Sun Aug 21 2016

.DISCUSSION...
Corridor of higher moisture at 700 mb was over the western and northern counties of the forecast area corelated well with the RAP PW analysis of 2.1 to 2.4 inches. This moisture axis was over a frontal boundary that was located at 7 am from near KLFK to just east of KCLL. An MCV between Columbus and San Antonio will slowly drift northward as well. HRRR and the RAP13 agreed with a rainfall potential of 1 to 2 inches over the northern counties. However, both models differed on the rainfall potential over the south. With an outflow moving eastward through metro Houston, think that some locations over the coastal areas may experience isolated amounts of 1 to 2 inches as well.

Tweaked the rain chances for the rest of the day. Also lowered the temperatures slightly due to the cloud cover and rainfall potential.

[srainhoutx]

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1126 AM CDT SUN AUG 21 2016

TXZ237-238-211715-
GALVESTON TX-BRAZORIA TX-
1126 AM CDT SUN AUG 21 2016

...STRONG THUNDERSTORMS ACROSS NORTHWESTERN GALVESTON...NORTHEASTERN
BRAZORIA AND SOUTHEASTERN HARRIS COUNTIES THROUGH 1215 PM CDT...

AT 1126 AM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM
OVER BONNEY...OR 11 MILES NORTH OF ANGLETON...MOVING NORTHEAST AT 25
MPH.

WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH THIS STORM.

LOCATIONS IMPACTED INCLUDE...
SOUTHEASTERN PEARLAND...LEAGUE CITY...TEXAS CITY...FRIENDSWOOD...
ALVIN...DICKINSON...LA MARQUE...SANTA FE...WEBSTER...HITCHCOCK...
MANVEL...NASSAU BAY...IOWA COLONY...HILLCREST...LIVERPOOL...BONNEY...
CHOCOLATE BAYOU AND ROSHARON.

[Rip76]

Wow, that was a lightning show over here in the Pearland area.

[DoctorMu]

9.5 in of rain for the entire event IMBY. Finally getting a break after on and off showers since 7 pm last night.

[Texaspirate11]

7 inches so far since last Saturday down by the bay

[djmike]

8" IMBY here in Beaumont since last Saturday! Im loving it! So is my plants and yard. Perfect rainy lazy sunday. Put on a movie and doze!

[unome]

MESOSCALE PRECIPITATION DISCUSSION 0590
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT SUN AUG 21 2016

AREAS AFFECTED...PORTIONS OF SOUTH-CENTRAL/SOUTHERN AND SOUTHEAST
TX

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 211837Z - 220000Z

SUMMARY...ADDITIONAL CLUSTERS OF HEAVY RAIN ARE EXPECTED THROUGH
THE AFTERNOON. ADDITIONAL FLASH FLOODING CONCERNS WILL EXIST GIVEN
THE WET ANTECEDENT CONDITIONS.

DISCUSSION...IR SATELLITE IMAGERY HAS BEEN SHOWING COOLING
CONVECTIVE TOPS OVER PORTIONS OF SOUTH-CENTRAL AND SOUTHEAST TX IN
ASSOCIATION WITH A WEAK SURFACE LOW RIDING NORTHEAST UP ALONG A
FRONT DRAPED ACROSS THE REGION THAT IS FOCUSING DOWN TOWARD THE
GULF COAST.

THERE REMAINS A DEEP POOL OF TROPICAL MOISTURE IN VICINITY OF THE
FRONT...WITH PWATS AS HIGH AS 2.25 INCHES. MEANWHILE...THE LATEST
RAP ANALYSIS SHOWS A FAIR AMOUNT OF INSTABILITY POOLED ALONG THE
BOUNDARY WITH THE PERSISTENCE OF A MODEST LOW LEVEL SOUTHERLY
FETCH IN OFF THE GULF OF MEXICO THAT IS INTERACTING WITH AND
OVERRUNNING THE BOUNDARY.

THE FRONT SHOULD REMAIN ACTIVE WITH CONVECTION THROUGH THE
AFTERNOON AND INTO THE EARLY EVENING HOURS. THE LOW TO MID LEVEL
SOUTHERLY FLOW AHEAD OF THE SURFACE WAVE WILL PROMOTE SOME MODEST
N/S ORIENTED BANDS OF CONVECTION THAT WILL BE CAPABLE OF PRODUCING
ADDITIONAL HEAVY RAINFALL GIVEN THE INSTABILITY GRADIENT AND FOCUS
OF DEEP MOISTURE.

THE CIRA-LPW PRODUCT SHOWS MOISTURE HIGHLY CONCENTRATED IN THE
500/300 MB LAYER WHICH WILL ENHANCE RAINFALL EFFICIENCY AND THUS
THE RAINFALL RATES WHICH WILL LIKELY EXCEED 2.5 INCHES/HR WITHIN
THE STRONGER CORES. THE N/S ORIENTATION OF SOME OF THE BANDS WILL
ENHANCE THE POTENTIAL FOR TRAINING CELLS...AND THEREFORE THIS MAY
RESULT IN ADDITIONAL VERY HEAVY RAINFALL TOTALS.

AS PER RECENT HRRR/HRRRP GUIDANCE...EXPECT ADDITIONAL RAINFALL
AMOUNTS THROUGH 00Z OF AS MUCH AS 3 TO 5 INCHES...WITH ISOLATED
HEAVIER AMOUNTS. THESE RAINS WILL IMPACT SOME AREAS THAT SAW VERY
HEAVY RAINS LAST NIGHT...ESPECIALLY SOUTH AND EAST OF AN AREA FROM
AUSTIN TO SAN ANTONIO.
THUS...ADDITIONAL FLASH FLOODING WILL BE POSSIBLE GIVEN THE WET
ANTECEDENT CONDITIONS.

ORRISON

ATTN...WFO...BRO...CRP...EWX...HGX...

ATTN...RFC...WGRFC...

LAT...LON 30519775 30379683 30089649 29259620 28589636
27849700 27089746 26299779 26239832 26489876
27109875 27829850 28559842 29679838

[unome]

Area Forecast Discussion
National Weather Service Houston/Galveston TX
256 PM CDT Sun Aug 21 2016

.DISCUSSION...
Because the threat of widespread flooding has diminished, will cancel the flash flood watch. That does not mean that the chances for rain have diminished. Even there was a bit of a lull in the rain activity over most of SE Texas at 2:30 PM, another area of moisture was moving in from the Gulf and helping in the development of showers and thunderstorms. These will likely move inland through the remainder of the afternoon. PW/s have decreased and the outflow boundary that was across the area has moved out to the east and offshore. Decent storm motions will also limit the rainfall potential.

Rain chances will diminish tonight as the deep layer moisture axis moves further inland and the entrance region of the upper level jet moves out of the state. However, the rainfall over the past few days will lead to at least patchy fog tonight and early Monday morning.

The trend during the next several days will be for the upper level ridge to build overhead. This can be seen on the GFS and ECMWF 500 mb height forecast. Warmer daytime temperatures will result. Also, with an onshore flow and some residual upper level moisture, a diurnal cycle of mainly afternoon and evening thunderstorms should persist through the week. Best chances will be on Monday with mainly isolated chances thereafter through Thursday. A weakness in the upper level ridge should aid in the return of better rain chances by Friday.
40

&&

.MARINE...
Outflow boundary pushed into the nearshore waters and is currently serving as a focus for some tstms. Expect this boundary to gradually washout and onshore flow to resume. Other than scattered storms again late tonight and in the morning - no significant marine concerns thru the period. Light/moderate onshore winds and seas 2-4 ft should continue. 47

[unome]

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Sun Aug 21 2016

Valid 00Z Mon Aug 22 2016 - 00Z Wed Aug 24 2016

...Heavy rain could lead to flash flooding in southern Texas through tonight...

...Cooler and drier air will move in behinds showers and thunderstorms over the eastern U.S...

...Cooling trend expected for the Pacific Northwest...

A cold front moving steadily eastward across the Appalachians this Sunday afternoon will bring a round of showers and thunderstorms along the Eastern Seaboard through tonight. New England will see these showers Monday morning before cooler and drier air behind the cold front overspreads much of the eastern U.S. under mostly sunny skies. The cooler temperatures will extend southwestward across the Mississippi Valley into Texas and southern Rockies where the trailing end of the cold front becomes stationary. Thunderstorms that form in southern Texas are expected to be slow-moving, and thus could lead to locally heavy rain and flash flooding through tonight. The stationary front will remain across the same areas on Monday and Tuesday but will begin to gradually weaken. Showers and thunderstorms should become more scattered in nature as the dissipating front slowly lifts northward into Oklahoma and Arkansas on Tuesday.

Meanwhile, an upper-level trough is expected to amplify as it moves across British Columbia over the next couple of days. Cooler air associated with this trough will filter into and across the Pacific Northwest behind a cold front. The warm air ahead of the cold front will be pushed eastward into the northern Plains, where afternoon highs could approach the century mark on Monday. Little precipitation is expected ahead of the front until Tuesday afternoon when some strong thunderstorms could form in the Midwest. Meanwhile, monsoonal showers and thunderstorms are expected to continue in the central/southern Rockies.

Kong

Graphics available at http://www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php

[BlueJay]

This summer has been brutal to many. OUr Texas summer is on the down slide.

We should not be expecting any more 100F+ temperature days for the remainder of 2016...?

[unome]

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
713 PM CDT SUN AUG 21 2016

TXZ199-212-213-220100-
WALLER TX-HARRIS TX-MONTGOMERY TX-
713 PM CDT SUN AUG 21 2016

...STRONG THUNDERSTORMS ACROSS NORTHEASTERN WALLER...SOUTHWESTERN
MONTGOMERY AND NORTHWESTERN HARRIS COUNTIES THROUGH 800 PM CDT...

AT 711 PM CDT...DOPPLER RADAR WAS TRACKING A MERGER OF THUNDERSTORMS
OCCURRING NEAR HOCKLEY...OR 9 MILES NORTH OF KATY...MOVING NORTHEAST
AT 15 MPH.

WINDS IN EXCESS OF 30 MPH WILL BE POSSIBLE WITH THIS STORM.
ALSO...TORRENTIAL RAINFALL IS POSSIBLE AS THE MULTIPLE CELLS
COMBINE. 0.92 INCHES OF RAIN HAVE BEEN OBSERVED IN THE PAST HOUR BY
THE HARRIS COUNTY FLOOD CONTROL DISTRICT GAGE ON LITTLE CYPRESS
CREEK AT BECKER ROAD.

LOCATIONS IMPACTED INCLUDE...
TOMBALL...PINEHURST...HOCKLEY...MAGNOLIA...STAGECOACH AND CYPRESS.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD
TO LOCALIZED FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

[unome]

quick rise, Little Cypress at Becker "Water level is 1.38 feet below Top of Bank"

http://www.harriscountyfws.org/GageDetail/Index/1230

[worrybug]

Drier weather will build into the region Tuesday-Wednesday as the sub-tropical ridge off FL builds west along the US Gulf coast. By the end of the week the ridge shifts slightly northward placing the northern Gulf under a tropical easterly flow. Tropical disturbances within this flow will arrive into the area enhancing rainfall Thursday-next weekend. Will need to continue to watch the potential development and track of Atlantic tropical wave 99L just in case it is able to become trapped under this building ridge.[/i]

Jeff, are you saying that the door is being opened for tropical wave 99L to (possibly) come into the Houston/Galveston area? I hope you're not.

[Ptarmigan]

Drier weather will build into the region Tuesday-Wednesday as the sub-tropical ridge off FL builds west along the US Gulf coast. By the end of the week the ridge shifts slightly northward placing the northern Gulf under a tropical easterly flow. Tropical disturbances within this flow will arrive into the area enhancing rainfall Thursday-next weekend. Will need to continue to watch the potential development and track of Atlantic tropical wave 99L just in case it is able to become trapped under this building ridge.[/i]

Jeff, are you saying that the door is being opened for tropical wave 99L to (possibly) come into the Houston/Galveston area? I hope you're not.

Too early to tell. Just keep an eye on the weather.

[Katdaddy]

A few scattered showers and thunderstorms down to coast near Victoria this morning. Additional scattered shower and thunderstorm development this afternoon but less widespread than previous days. The atmosphere dries out a little more Tuesday and Wednesday before additional deep moisture and a disturbance arrives Thursday and Friday.

99L and 90L looking better this morning with a moderate to high chance for tropical development the next 5 days.

[Texaspirate11]

From the HGX NWS Disco

ECMWF keep a couple of tropical/hybrid looking systems in
the offing but over the Atlantic with the Western Caribbean and
Gulf quiet.

[houstonia]

Morning briefing from Jeff (1 hour ago, no graphics):
Jeffrey

Additional rainfall today before a few “drier” days followed by increasing rain chances for the end of the week into the weekend.

Atlantic tropics becoming active as we near the peak of the hurricane season.

Tropical air mass remains in place this morning with the radar showing scattered showers and thunderstorms west of I-45. With heating this morning the air mass will become increasing unstable and expect to see numerous showers and thunderstorms develop across the region. Storm motions of 10-15mph will keep rainfall amounts manageable today, but could still see a quick 1-2 inches under the heaviest rainfall cores.

Drier air mass over the western Gulf of Mexico will advect into the region tonight into Tuesday and expect to see a downward trend in rainfall coverage. Additionally, upper level ridge will intensify and expand westward from the mid-Atlantic and SE US toward TX Tuesday and Wednesday, but upper level heights are not overly strong for August over TX and suspect we will still be able to generate showers and thunderstorms along the seabreeze both Tuesday and Wednesday afternoons…will keep 30% for both of those days.

Upper ridge takes hold over the SE US into the end of the week with TX laying near the western edge of this feature. Another shear axis looks to develop over the southern plains by the end of the week helping to break down the western edge of the ridge. Global models are showing a tropical wave or inverted trough moving west across the northern Gulf and into TX Thursday and Friday along with a surge in tropical moisture. Will bring up rain chances on both Thursday and Friday to at least 50% at this point…but may need to go higher and introduce heavy rainfall again with PWS likely above 2.0 inches.

Tropics:

99L:
A tropical wave located about 900 miles east of the Lesser Antilles Islands is moving toward the W to WNW at 15-20mph. Satellite derived moisture profiles show continued decent vorticity with this wave and a large envelop of tropical air even though the feature currently lacks overall deep convection. Conditions are not overly favorable for development for the next few days, but as the feature arrives into the Bahamas late this week conditions look to become more favorable for development. At that time the system may come under the influence of the large scale deep layer ridging which should be in place over the US east coast stretching westward toward the middle Gulf coast. However influences to the east including the weakening of TD Fiona and the potential development of a significant tropical system out of 90L may become important in the upper air pattern over the SW Atlantic by this weekend. NHC is giving this wave a 50% chance of development over the next 5 days.

90L:
A well defined tropical wave with likely a closed surface circulation and deep convection around the center is located about 400 miles SW of the Cape Verde Islands. Advisories will likely begin at 1000am this morning on a tropical depression. Global and hurricane track model guidance is in good agreement on this system moving WNW then NW toward a weakness in the sub-tropical ridge located over the central Atlantic Ocean downstream of the US east coast ridge. Factors appear overall favorable for development of this system as it tracks toward the WNW and NW over the open Atlantic and it is likely that the system will become a hurricane. NHC is giving this wave a 100% chance of development.

[Katdaddy]

Special Marine Warning continues for Galveston Bay.

BULLETIN - IMMEDIATE BROADCAST REQUESTED
SPECIAL MARINE WARNING
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1139 AM CDT MON AUG 22 2016

THE NATIONAL WEATHER SERVICE IN LEAGUE CITY HAS ISSUED A

* SPECIAL MARINE WARNING FOR...
GALVESTON BAY...

* UNTIL 1245 PM CDT

* AT 1138 AM CDT...STRONG THUNDERSTORMS WERE LOCATED ALONG A LINE
EXTENDING FROM DOWNTOWN HOUSTON TO ELLINGTON FIELD TO SANTA
FE...MOVING NORTHEAST AT 20 KNOTS.

HAZARD...WIND GUSTS 34 KNOTS OR GREATER.

SOURCE...RADAR INDICATED.

IMPACT...SMALL CRAFT COULD BE DAMAGED IN BRIEFLY HIGHER WINDS AND
SUDDENLY HIGHER WAVES.

* LOCATIONS IMPACTED INCLUDE...
GALVESTON BAY...SCOTT BAY...TABBS BAY...BURNET BAY...MITCHELL
BAY...TRINITY BAY...UPPER SAN JACINTO BAY...EAGLE POINT...CRYSTAL
BAY AND BLACK DUCK BAY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

FREQUENT LIGHTNING IS OCCURRING WITH THESE STORMS. IF CAUGHT ON THE
OPEN WATER STAY BELOW DECK IF POSSIBLE...KEEP AWAY FROM UNGROUNDED
METAL OBJECTS.