September 2014: Seasonably Warm & Dry To End The Month

[srainhoutx]

Update from Jeff:

Flash Flood Watch issued through 700pm Thursday.

Ingredients coming together to produce multiple rounds of excessive rainfall this afternoon through Thursday afternoon. Moisture levels have increased to between 150%-200% of normal for this time of year as moisture from the remains of 92L in the Gulf of Mexico and TS Odile over NW MX pour into the region. A favorable trough axis oriented NW to SE across the area has become established while aloft disturbances eject out of Odile and cross MX into and across TX.

Rainfall over the past two days has been excessive in isolated spots (upwards of 3 inches per hour) over NW Harris County yesterday and today over SE Harris County and northern Brazoria County. Grounds are gradually saturating and with global and meso scale models show strong support for additional excessive rainfall tonight-Thursday flooding is becoming a more serious threat.

Rainfall Amounts:
Hard to be too accurate on the amounts at this point given the scattered nature of the rainfall thus far. Appears more concentrated and organized excessive rainfall is possible on Thursday. Additional average amounts of 1-3 inches will be possible with isolated amounts of 5-7 inches. Air mass is very capable of 3-5 inch per hour rainfall rates which will lead to rapid urban flash flooding and significant rises on area watersheds. I do not see any reason to favor one region over another at this time as there is no well defined surface boundary in place to focus storms along. Storms may end up generating their own surface outflow boundary and focus along that at some point, but when and if that happens is impossible to predict at the moment.

Rainfall Last 24 hours:

09172014 Jeff image001.png

[srainhoutx]

FLOOD ADVISORY
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
351 PM CDT WED SEP 17 2014

TXC339-172145-
/O.NEW.KHGX.FA.Y.0145.140917T2051Z-140917T2145Z/
/00000.N.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
MONTGOMERY TX-
351 PM CDT WED SEP 17 2014

THE NATIONAL WEATHER SERVICE IN LEAGUE CITY HAS ISSUED A

* FLOOD ADVISORY FOR...
CENTRAL MONTGOMERY COUNTY IN SOUTHEASTERN TEXAS...

* UNTIL 445 PM CDT

* AT 351 PM CDT...DOPPLER RADAR INDICATED HEAVY RAIN DUE TO
THUNDERSTORMS. THIS WILL CAUSE MINOR FLOODING IN THE ADVISORY
AREA. 1 TO 2 INCHES OF RAIN HAS FALLEN IN THE LAST 60 MINUTES.

* SOME LOCATIONS THAT WILL EXPERIENCE FLOODING INCLUDE...
CONROE...WILLIS...THE WOODLANDS...OAK RIDGE NORTH...PANORAMA
VILLAGE...SHENANDOAH...CUT AND SHOOT...MONTGOMERY...WOODLOCH...LAKE
CONROE DAM...PORTER HEIGHTS AND CHATEAU WOODS.

[jasons2k]

Dang. It is pouring something else here at the office by the waterway. Still missing the house though.

It's arcing/backbuilding to the west into The Woodlands. Will be interesting to see how this evolves.

[unome]

Dang. It is pouring something else here at the office by the waterway. Still missing the house though.

It's arcing/backbuilding to the west into The Woodlands. Will be interesting to see how this evolves.

you must be happy now ? http://www.findu.com/cgi-bin/wxpage.cgi?CW2840

[jasons2k]

Dang. It is pouring something else here at the office by the waterway. Still missing the house though.

It's arcing/backbuilding to the west into The Woodlands. Will be interesting to see how this evolves.

you must be happy now ? http://www.findu.com/cgi-bin/wxpage.cgi?CW2840

That's a few miles to my NW - actually closer to my office than home.

[jasons2k]

1.10" - I've now had more rain in September than the whole month of August.

[Kludge]

1.10" - I've now had more rain in September than the whole month of August.

"kairful whacha axe for". This seems like the real deal.

[jasons2k]

Indeed, some locations off to the West and Northwest are getting some incredible rainfall tonight.

[srainhoutx]

Anyone heading W on I-10 tonight heads up. Flash Flooding reported in Schulenburg and Flatonia.

[BlueJay]

My rain gauge says 0.02 inches for the day. All of those sprinkles added up!

[srainhoutx]

The 00Z short term meso guidance are suggesting some worrisome rainfall rates across portions of Central and SE Texas over the next 24 to 48 hours. If they are correct, some locations could see an additional 5 to 10 inches of rain which certainly would lead to Flash Flooding issues.

[Ptarmigan]

Quite a rainy day. I would not be surprised if there is more rain while we sleep.

[srainhoutx]

Portastorm reports water rescues underway in the Austin Area with multiple building fires from lightning strikes. WPC has expanded High Risk into W Texas for Excessive Rainfall and mentions potential core rain event possible over the next 24 hours across portions of Central/SE Texas.

[unome]

feels like a wet blanket outside, but at least I don't have to water the lawn !

http://earth.nullschool.net/#current/wi ... 28.68,1306

[Katdaddy]

The Austin area was hit hard with torrential flooding rains early this morning with up to 6" with 4-6" per hour rainfall rates. Most of the very heavy rains fell within an hour creating numerous road closures and swift water rescues. Light rains moving into Houston metro currently. Flash Flood Watch remains in effect for Central and SE TX. Some areas could see 5-6" totals later today. The weekend still looks to dry out with only a 30% chance of thunderstorms each day. Weak cold front still looks possible Monday.

[srainhoutx]

Morning Update QPF Outlook for our Region:

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
609 AM EDT THU SEP 18 2014


FINAL DAY 1...DAY 2 AND DAY 3 QPF DISCUSSION
VALID SEP 18/1200 UTC THRU SEP 21/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


...DAY 1...

...SOUTHWEST INTO THE SOUTHERN ROCKIES...SOUTHERN GREAT
PLAINS...AND ALONG THE WESTERN/CENTRAL GULF COAST...

WIDESPREAD HEAVY TO IN SOME AREAS EXCESSIVE RAINFALL IS EXPECTED
DURING THIS PERIOD...AS THE REMNANT LOW FROM ODILE DISSIPATES
WHILE IN ITS WAKE A FAIRLY ELONGATED AXIS OF ABOVE NORMAL PW
VALUES WILL PERSIST DURING THE PERIOD. CONDITIONS OVER WESTERN AZ
AND POINTS WEST WILL CONTINUE TO IMPROVE DURING THIS TIME AS MUCH
LOWER PWS (TIGHT BACK EDGE OF PW AXIS) SHIFTS EAST FROM CA/NV
AHEAD OF THE APPROACHING UPPER TROUGH. WPC MAINTAINED GOOD
CONTINUITY FROM PREVIOUS FCSTS WITH THE QPF...INCORPORATING SOME
OF THE BETTER PERFORMING HIGHER RESOLUTION GUIDANCE (NAM CONEST
AND WRF-ARW)...WHILE CONTINUING TO LEAN HEAVILY TOWARD THE
HIGH-RES ECMWF GUIDANCE WHICH ALSO MAINTAINED GOOD CONTINUITY FROM
ITS PREVIOUS RUN.

A HIGH RISK OF EXCESSIVE RAINFALL CONTINUES OVER AN AREA FROM
SOUTHEAST AZ AND MUCH OF SRN NM...THOUGH ANTICIPATE AN EASTWARD
SHIFT IN THE BACK EDGE (EAST OF AZ) BY 12Z OR SHORTLY THEREAFTER.
RAINFALL RATES HAVE COME DOWN A BIT EARLY THIS AM...HOWEVER AT THE
SAME TIME THE 1/3/6 HR FLASH FLOOD GUIDANCE CONTINUES TO LOWER
OVER THIS REGION WITH THE CONTINUED WIDESPREAD RAINFALL. WHILE THE
POTENTIAL FOR AREAS OF LONG DURATION FLOODING REMAINS A
CONCERN...THE HIGHLY ANOMALOUS PW AVAILABILITY (3-3.5 STANDARD
DEVIATIONS ABOVE NORMAL) AND WIDESPREAD RAINFALL/HIGH
AREAL-AVERAGE AMOUNTS (1-3.5 INCHES) WILL CONTINUE TO LOWER THE
FFG AND ELEVATE THE FLASH FLOODING RISK. THIS DESPITE THE LIMITED
INSTBY AND MODEST RAINFALL RATES (1.5 TO 2.5 INCHES WITHIN 3
HOURS) DIRECTLY ASSOCIATED WITH ODILE'S REMNANT CIRCULATION.

FARTHER EAST INTO TX...A SECONDARY AXIS OF HIGHER PWS (AOA 2.25
INCHES) POOLING ACROSS THE WRN GULF INTO CENTRAL AND EASTERN TX
WILL COMBINE WITH GREATER INSTBY (MUCAPES 500-2000 J/KG) TO
PRODUCE GREATER RAINFALL RATES...TO THE TUNE OF 2.5-3 INCHES/HOUR
AND/OR AS MUCH AS 3-5 INCHES WITHIN 3 HOURS WITHIN ISOLATED
HEAVIER CONVECTIVE CORES.


DAYS 2/3...

...SOUTHWEST TO SOUTHERN PLAINS...

SOUTHERLY FLOW OUT OF THE GULF OF CALIFORNIA WILL AID IN BRING
PRECIPITABLE WATER VALUES OF 1.25 INCHES INTO THE SOUTHWEST
THROUGH SUNDAY MORNING. IN ADDITION ... SOUTHWESTERLY FLOW OFF
THE GULF OF MEXICO WILL BRING PRECIPITABLE WATER VALUES OF 1.75
INCHES INTO THE SOUTHERN HIGH PLAINS THROUGH FRIDAY AFTERNOON.
THE FLOW WILL BECOME MORE SOUTHERLY FRIDAY EVENING INTO SATURDAY
MORNING THAT WILL USHER THE 2.00 INCHES PRECIPITABLE WATER VALUES
INTO THE CENTRAL PLAINS BY SATURDAY MORNING. THE INTENSITY OF THE
FLOW WILL BEGIN TO WANE ON SUNDAY. THE HEAVIEST QPF AMOUNTS WILL
BE OVER THE SOUTHERN HIGH PLAIN/SOUTHERN ROCKIES ON FRIDAY INTO
SATURDAY MORNING WITH MAXIMUM QPF AMOUNTS NEAR 2.00 INCHES. THE
AREA OF HEAVIEST QPF WILL MOVE TO THE TEXAS PANHANDLE AND VICINITY
ON SATURDAY INTO SUNDAY MORNING. MAXIMUM QPF AMOUNTS WILL BE NEAR
1.50 INCHES. THE MANUAL QPF USED THE ECMWF AS A STARTING POINT IN
THE FORECAST PROCESS.

...CENTRAL TEXAS TO THE TEXAS GULF COAST...

SOUTHWESTERLY FLOW OFF THE GULF OF MEXICO WILL STREAM PRECIPITABLE
WATER VALUES OF 2.00 INCHES OVER THE REGION THROUGH SUNDAY
MORNING. MAXIMUM QPF AMOUNTS WILL BE RANGING FROM 0.50 TO 0.75
INCHES ON FRIDAY SUNDAY MORNING. THE MANUAL QPF USED THE ECMWF AS
A STARTING POINT IN THE FORECAST PROCESS.



HURLEY/ZIEGENFELDER

[srainhoutx]

SE Texas radar is beginning to light up. The overnight meso low that brought flooding to the Austin Area and across Central Texas is allowing inflow at the lower levels to increase of the Gulf. Additional storms are positioned across the Caprock of the Panhandle and SE New Mexico associated with the remnants of Odile and additional embed upper air impulses should drop SE in the NW flow aloft throughout the into tonight.

[srainhoutx]

Updated Excessive Rainfall Outlook will place portions of Central Texas in a Moderate Risk with a Slight Risk continuing for SE Texas and SW Louisiana. The High Risk will continue across Southern New Mexico.


EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
749 AM EDT THU SEP 18 2014

...VALID 12Z THU SEP 18 2014 - 12Z FRI SEP 19 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


AZ/NM/CENTRAL TX
~~~~~~~~~~~~~~~~
A LARGE EXCESSIVE RAINFALL AREA REMAINS FROM SOUTHEAST AZ THROUGH
SOUTHERN NM AND A BELT OF CENTRAL TX IN ASSOCIATION WITH THE
REMAINS OF ODILE, WITH A HIGH RISK OF EXCESSIVE RAINFALL
CONTINUING FOR SOUTHERN NM. THE 1/3/6 HR FLASH FLOOD GUIDANCE
CONTINUES TO LOWER OVER THIS REGION WITH THE CONTINUED WIDESPREAD
RAINFALL. WHILE THE POTENTIAL FOR AREAS OF LONG DURATION FLOODING
REMAINS A CONCERN...THE HIGHLY ANOMALOUS PW AVAILABILITY (3-3.5
STANDARD DEVIATIONS ABOVE NORMAL) AND WIDESPREAD RAINFALL/HIGH
AREAL-AVERAGE AMOUNTS (1-3.5 INCHES) WILL CONTINUE TO LOWER THE
FFG AND ELEVATE THE FLASH FLOODING RISK. THE EXPECTATION IS THAT
INSTABILITY SHOULD BUILD ACROSS PORTIONS OF CENTRAL AND WESTERN TX
ALONG WITH ADJACENT PORTIONS OF NORTHERN MEXICO DUE TO DAYTIME
HEATING WITHIN A PARTLY CLOUDY REGION -- RECENT RAP RUNS INDICATE
CAPE VALUES RISE INTO THE 1000-2000 J/KG RANGE ACROSS TX AND
SOUTHEAST NM BY THIS AFTERNOON. PER COORDINATION WITH THE SJT/SAN
ANGELO TX FORECAST OFFICE, CONSTRICTED THE MODERATE RISK A BIT
ACROSS CENTRAL TX.


EASTERN TX/SOUTHWEST LA
~~~~~~~~~~~~~~~~~~~~~~~
AT PRESENT, THE INSTABILITY LINGERS ACROSS EASTERN TX, WITH
LOW-LEVEL INFLOW SLOWLY FADING. THE EXPECTATION IS THAT
INSTABILITY SHOULD BUILD ACROSS PORTIONS OF TX ALONG WITH ADJACENT
PORTIONS OF NORTHERN MEXICO DUE TO DAYTIME HEATING WITHIN A PARTLY
CLOUDY REGION -- RECENT RAP RUNS INDICATE CAPE VALUES RISE INTO
THE 1000-2000 J/KG RANGE ACROSS TX AND SOUTHEAST NM BY THIS
AFTERNOON. PER COORDINATION WITH THE SJT/SAN ANGELO TX FORECAST
OFFICE, CONSTRICTED THE MODERATE RISK A BIT ACROSS CENTRAL TX.
THE MESOSCALE GUIDANCE CONTINUES TO INDICATE LOCALLY HEAVY
RAINFALL SCATTER-SHOT WITHIN A TRIANGLE BOUNDED BY EXTREME
SOUTHWEST LA, THE MIDDLE TX COAST, AND THE EASTERN EDGE OF THE TX
HILL COUNTRY DURING THE DAY TODAY WITHIN AN AREA OF >2"
PRECIPITABLE WATER VALUES AND UPPER-LEVEL DIFFLUENCE. LOCAL
AMOUNTS OF 4-8" ARE ADVERTISED IN THIS REGION, SO KEPT SOUTHEAST
TX AND EXTREME SOUTHWEST LA WITHIN THE SLIGHT RISK.


ROTH/HURLEY

09182014 1150Z Excessive Rainfall Day 1 94ewbg.gif

[Portastorm]

Colossal storm here in Austin earlier this morning. Areas received anywhere from 3-6" if rain. 50+ roads closed at daybreak due to flooding and, sadly, one rumored fatality. More than a half dozen lightning strikes causing fires to himes/businesses. Power out at my house and scattered outages in west/south Austin. Quite a storm, folks...quite a storm.

[srainhoutx]

Morning Update from Jeff:

Several ingredients in place to produce a rather wet day across SE TX.

Flash Flood Watch remains in effect until 700pm this evening.

Current radar is showing a cluster of slow moving/near stationary heavy rainfall WSW of Austin with a large light rain shield having expanded ESE into SE TX from this cluster. Recently showers have begun to develop from College Station to Houston. These showers appear to being forced by weak lift from a NW to SE laying trough axis along/near US 290 and incoming lift from short waves over NC TX and W TX.

Yesterday evening sounding at CRP came in with PW of 2.38 inches which is 200% of mid-September values while LCH was at 2.16. Soundings were saturated from the surface up to about 400mb suggesting little room for evaporation. Freezing level was around 16,000ft yielding a large layer of warm rainfall production. All these ingredients point toward excessive rainfall rates from slow moving and training convection.

The main factor that still appears missing is any well defined surface boundary. The weak trough axis laying along US 290 could help to act as a focus for development as well as any left over outflow boundaries. For a significant flood threat I would like to see a well defined boundary to help force and then anchor convection. It is certainly possible to have flooding rainfall without such a boundary, but it tends to be more scattered and not concentrated.

Expect a gradual increase in convection this morning as lift increases from the approaching short waves and very modest heating creates even more instability. Nearly the entire area is at risk for development. Storm motions will be slow toward the E or SE which is a favorable setup up for cell training with good SE Gulf inflow. Backbuilding of convection will be toward the WNW or NW.

See no reason at this point to change the expected rainfall amounts from 1-3 inches widespread to isolated amounts of 5-7 inches. Hourly rainfall rates of 2-3 inches are likely which will lead to quick flash flooding of roadways, underpasses, and areas of poor drainage. Current thinking is that most watersheds will be able to handle the rainfall.

Drying begins to take place starting Friday, although still expect decent coverage of activity. May be a little harder to dry things out over the weekend as well with moisture from Odile still moving across the area. PWS remain near 2.0 inches and the area will be in a weakness in the sub-tropical ridge so additional scattered storms seem at least possible. Early next week frontal passage is becoming less certain as models have been gradually backing away from the idea of pushing the front through the area.