September. Heavy Rainfall Event/Flooding Possible 9/28-30th

Tue Sep 11, 2012 7:39 am

Morning e-mail from Jeff...he must have been reading my mind...

Nice and dry weather of late will be ending over the next 24 hours as Gulf moisture returns.

Stalled frontal boundary over the Gulf of Mexico is washing out and dissipating this morning as surface high pressure moves to the eastern US. This will allow ESE to SE winds to begin to return deep tropical moisture to the region starting late today and in earnest on Wednesday. Not sure how quickly the air mass will modify, but suspect dewpoints will rebound into the lower 70’s south of I-10 on Wednesday and showers/thunderstorms may affect the coastal counties by Wednesday afternoon.

Moisture begins to surge northward on Thursday as a trough deepens over the high plains. Expect scattered showers/thunderstorms as deep SSE wind flow pumps moisture into the region. Friday appears to be the wettest day with deep moisture in place and increasingly large scale lift from an approaching cold front. Front does not look to plow through the area like the last front, but slow and possibly stall either along the coast or offshore. Rain chances will continue into the weekend (especially Saturday) with the boundary in the area.

CMC and ECMWF try and develop a broad surface low over the central/western Gulf of Mexico late this weekend/early next week. This low could help drive the front further offshore. CMC drifts the low over the western Gulf while the ECMWF has the feature caught up in the trough and pulled toward Louisiana. GFS does not show this feature as much and is not nearly as well defined as the CMC and ECMWF.

With deep tropical moisture returning, scattered rainfall amounts of 1-2 inches will be possible Thursday-Saturday. Would not be surprised to see a few higher totals (3-5 inches) under areas of more organized convection. Dry spell of late with high KBDI values suggest this rainfall should be easily handled.

Tue Sep 11, 2012 9:31 am

srainhoutx wrote:Morning e-mail from Jeff:

. We might just be done with the really oppressive heat of the summer…highs near 100. [/i]

I think so too. Just an opinion from a weather weenie...

Tue Sep 11, 2012 9:39 am

I always feel sad this time of year. The peak of hurricane season has passed. Days are getting shorter. Temps are dropping. Nothing to look forward to until next April/May when the average high tops 80F again...

Tue Sep 11, 2012 12:40 pm

MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
118 PM EDT TUE SEP 11 2012

VALID SEP 11/1200 UTC THRU SEP 15/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

12Z NAM/GFS/CANADIAN/UKMET EVALUATION INCLUDING MODEL PREFERENCES
=================================================================
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.

SHORTWAVE/LOW MOVING THROUGH WESTERN CANADA FRIDAY
==================================================
PREFERENCE: CANADIAN/UKMET/ECMWF COMPROMISE WITH AVERAGE
CONFIDENCE

THE 12Z NAM WAS A SLOW OUTLIER WITH THIS SYSTEM'S PROGRESSION
THROUGH WESTERN CANADA. AS IT IS EMBEDDED WITHIN A
QUICK-MOVING/ZONAL FLOW PATTERN WITH MINIMAL AMPLITUDE, A QUICKER
SOLUTION IS MORE LIKELY TO VERIFY. HOWEVER, THE 12Z GFS IS THE
WEAKEST/QUICKEST WITH THIS SYSTEM. SINCE THE GEFS ENSEMBLE MEAN
SOLUTION SHOWS GREATER AMPLITUDE THAN THE GFS, ITS SOLUTION IS
LIKELY TOO WEAK ALOFT/QUICK AT THE SURFACE. THE 12Z UKMET IS
LIKELY TOO STRONG WITH THIS SYSTEM, DUE TO THE ZONAL NATURE OF THE
FLOW PATTERN. WITH THE SURFACE LOW HOWEVER, A 12Z UKMET/12Z
CANADIAN/00Z ECMWF COMPROMISE APPEARS BEST. THE PREFERENCE IS FOR
A 12Z UKMET/12Z CANADIAN/00Z ECMWF COMPROMISE HERE WITH AVERAGE
CONFIDENCE CONSIDERING ITS QUICK MOVEMENT.

UPPER LOW MOVING SLOWLY ACROSS THE WEST/SOUTHWEST
=================================================
PREFERENCE: NON-GFS COMPROMISE WITH ABOVE AVERAGE CONFIDENCE

THE GUIDANCE IS IN GENERAL AGREEMENT WITH THIS SYSTEM'S SLOW
MOVEMENT INTO NEW MEXICO BY LATE FRIDAY, WITH THE NON-12Z GFS
GUIDANCE STRONGER AND SLIGHTLY SLOWER WITH THIS SYSTEM. AS THERE
IS A PROGRESSIVE NORTHERN STREAM RIDGE MOVING OVER THE TOP OF THE
SYSTEM, A STRONGER AND SLOWER SOLUTION STANDS THE BEST CHANCE OF
VERIFYING. A NON-GFS COMPROMISE IS PREFERRED HERE WITH ABOVE
AVERAGE CONFIDENCE CONSIDERING ITS QUICK MOVEMENT.

Wed Sep 12, 2012 7:48 am

The overnight guidance continues to paint a wet picture for our area and most of Lone Star State. The HPC 5 Day QPF Forecast has increased the rainfall potential to a general 1-2 inch rainfall with isolated higher amounts nearing the 4 inch mark for a lucky few. Those totals may be a bit too low as the frontal boundary stalls along Coastal Texas and a surface wave of low pressure develops and rides the boundary ENE. Again, the fly in the ointment will be just where that boundary actually stalls as the guidance has been flip flopping with the upper air disturbance developing across Texas and just how quickly or slowly it translates E.

Another interesting turn of events is a tropical system that some of the models have been ‘sniffing’ developing in the Bay of Campeche early next week. The GFS finally latched on to that idea overnight and brings that disturbance N to near the SE Texas/SW Louisiana Coast as the boundary washes out and yet another perhaps stronger cold front dive S into the area and finally picks up that disturbance and clears us out. There are also hints of yet another area of disturbed weather developing in the Western Caribbean later next week that begins to lift NW further complicating things. All in all it truly appears we are entering a more active period and showers/storms chances will become the theme and an active flow that we tend to expect in late September with fronts progressing S and plentiful tropical moisture available. We will see.

Wed Sep 12, 2012 7:59 am

While we have enjoyed the nice weather the last several days, I am glad to see more active pattern taking shape for SE TX. We could use some additional rains however its looking a little more like a few of us will more than we might need especially should models continue to trend toward a potential tropical system in the WGOM.

Wed Sep 12, 2012 8:48 am

Morning e-mail from Jeff:

Wet period expected for the region today-Sunday

Gulf moisture is making a return to the region with overnight dewpoints rising into the 60’s and 70’s and scattered showers developing on radar south of I-10 this morning. This increase in moisture is in response to the washing out of the frontal boundary offshore and low pressure developing over the central plains encouraging southerly winds to bring the deep tropical moisture over the western Gulf northward. Feel the wetter guidance is on the right track for today given the amount of development noted on the radar at this time. Most favorable are for showers/thunderstorms will be along the coast where moisture values are greatest this morning and then spreading inland today as the seabreeze and moisture surge northward.

Expect scattered rains today and Thursday with better coverage and chances on Friday and Saturday as a weak diffuse frontal boundary sags into the area and stalls near the coast/just offshore. More organized thunderstorms will be possible during this period as the front provides lift along with the slow progression of an upper level low over the SW US. Front should limp off the coast before stalling while the main upper level trough/low remains west of the area into the weekend. This will produce an overrunning pattern and additionally force surface low pressure to form along the frontal boundary. Could see a break in the more organized rainfall Saturday afternoon, before the coastal low moves NE up the frontal slope providing another good shot at rainfall Saturday evening/night. Best rain chances over the weekend may focus closer to the coast or even offshore depending on where the frontal boundary pulls up stationary.

With PWS forecast to reach 2.0 inches heavy rainfall will be likely. Fast storm motions today and Thursday along with very dry grounds should mitigate any flooding threat. Friday-Saturday more widespread and organized heavy rainfall could present some problems in the urban areas, but forecasted QPF totals remain below the thresholds that would cause widespread problems. Widespread amounts of 1-2 inches with isolated totals of 3-4 inches appear possible from today-Sunday. Best chances of rainfall and highest QPF should be south of I-10.

Fire Weather:
KBDI values a starting to reach critical levels across the region as vegetation had dried under weeks of hot weather and lack of rainfall…especially north of I-10. 500 acre wildfire in Walker/Houston County yesterday suggest the fire potential is high in those areas mainly north of HWY 105. Luckily, RH will be much higher today and winds weaker and this should preclude any rapid fire growth. Wetting rains appear likely over the next several days and this should greatly reduce the wildfire threat.

Wed Sep 12, 2012 9:22 am

wxman57 wrote:I always feel sad this time of year. The peak of hurricane season has passed. Days are getting shorter. Temps are dropping. Nothing to look forward to until next April/May when the average high tops 80F again...

No offense, but your tears are my CHEERS! Bring on the cool/cold weather.

Wed Sep 12, 2012 11:03 am

was surprised to see this
Special Weather Statement

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1008 AM CDT WED SEP 12 2012

TXZ200-213-214-226-227-235>238-121900-
LIBERTY-HARRIS-CHAMBERS-WHARTON-FORT BEND-JACKSON-MATAGORDA-
BRAZORIA-GALVESTON-
INCLUDING THE CITIES OF...LIBERTY...CLEVELAND...DAYTON...
HOUSTON...PASADENA...KATY...TOMBALL...HUMBLE...WINNIE...
MONT BELVIEU...ANAHUAC...EL CAMPO...WHARTON...PIERCE...
SUGAR LAND...MISSOURI CITY...RICHMOND...ROSENBERG...EDNA...
BAY CITY...PALACIOS...PEARLAND...LAKE JACKSON...ALVIN...
ANGLETON...FREEPORT...LEAGUE CITY...TEXAS CITY...FRIENDSWOOD...
GALVESTON
1008 AM CDT WED SEP 12 2012

....FUNNEL CLOUDS POSSIBLE TODAY...

RAPIDLY DEVELOPING THUNDERSTORMS COUPLED WITH A VERY BUOYANT
ATMOSPHERE AND INTERSECTING BOUNDARIES WILL YIELD BRIEF FUNNEL
CLOUDS THIS MORNING INTO THE EARLY AFTERNOON. THESE FUNNEL CLOUDS
WILL BE SHORT LIVED AND DIFFICULT TO DETECT ON RADAR. THESE FUNNEL
CLOUDS COULD BRIEFLY EXTEND TO THE GROUND AND BECOME A SHORT LIVED
TORNADO. STAY ALERT FOR RAPIDLY CHANGING CONDITIONS AS THESE
FUNNEL CLOUDS WILL DEVELOP AND DISSIPATE QUICKLY. A FUNNEL CLOUD
WAS REPORTED BETWEEN ANGLETON AND DANBURY ALONG HIGHWAY 35 AT 957
AM.

$$

Wed Sep 12, 2012 11:09 am

Getting a nice little shower here...hope it keeps up for a while

Wed Sep 12, 2012 11:12 am

wxman57 wrote:I always feel sad this time of year. The peak of hurricane season has passed. Days are getting shorter. Temps are dropping. Nothing to look forward to until next April/May when the average high tops 80F again...

Hurricane season coming to a close means a sigh of relief from me...now we can watch for cold fronts and later freeze warnings... and listen for the "S" word

Wed Sep 12, 2012 1:36 pm

I am also glad the peak of hurricane season is passing by harmlessly and looking forward to a wet weekend. Picked up .61" at the house in League City so far today.

Wed Sep 12, 2012 5:52 pm

Updated HPC 5 Day QPF Forecast continues to slowly increase across Texas...

Thu Sep 13, 2012 6:20 am

A very complex and complicated forecast is unfolding across the Southern half of the Lone Star State for the next 4-6 days. A frontal boundary will push S and stall while an upper trough meanders over New Mexico to our W and lingers. Add to the mix TS Kristy along the offshore Pacific Waters of Mexico and you have a recipe for a potential heavy rainfall event over Texas.

Showers and storms will increase in aerial coverage today as deep tropical moisture surges inland from the Gulf. PW's of 2.0+ will sweep inland as the frontal boundary sags S and stalls. The upper level support then collapses and brings S Cetral/SE TX into a very favorable region for a heavy rainfall potential. Several waves of low pressure look to develop along the Coastal Waters of the Gulf and move slowly ENE over the weekend. The fly in the ointment will be the meandering upper trough to our W. The overnight Euro and the 06Z GFS now suggest this feature will be with us until another cold front and mid latitude trough drops S from Canada late next Tuesday or Wednesday. Kristy moisture from the EPAC continues to be entrained over NE Mexico and Texas throughout the period to further complicate things. I wouldn’t be too surprised to see 3-5 inches of rainfall throughout this wet pattern with some isolated 6-8+ amounts possible. Stay Tuned!

Thu Sep 13, 2012 7:39 am

Morning e-mail from Jeff:

Showers and thunderstorms already ongoing this morning over the region.

Moisture has increased over the past 24 hours leading to scattered showers and thunderstorms moving northward off the western Gulf of Mexico. Storms have been prodigious lightening producers which is somewhat unusual given the very tropical air mass in place. Little change is expected for the next 24 hours as moisture continues to stream northward and showers/thunderstorms will become most numerous with a little bit of morning heating and then weaken toward the late afternoon hours only to re-develop again early Friday morning.

On Friday, the frontal boundary over NW TX currently will move slowly southward and into our region toward the afternoon hours. This boundary will interact with the abundant tropical moisture in place and weak upper air disturbances associated with a deep layer trough over the SW US to produce a good chance of widespread showers/thunderstorms. Unlike the current scattered activity, the period from Friday afternoon-Saturday will feature more organized storms with greater potential for sustained heavy rainfall.

Forecast for the weekend is difficult as competing weather factors will be in place. The slow moving front looks to cross into the near shore Gulf waters at some point late Saturday into Sunday morning and expect this to act as the main focus for rainfall on Saturday. NAM attempts to bring in drier air from the east this weekend shutting down rain chances, but with the main upper trough axis still west of the area and the GFS showing more moisture hanging in behind the front think the wetter solutions is what will likely pan out. Feel the GFS is heading in the right direction keeping high rain chances on Saturday and only slowly lowering chances into early next week. Models really diverge by early next week with some indicating ridging building into the area and others keeping the trough located across the region.

Rainfall amounts of the next 2-3 days will average 1-3 inches with isolated totals of 4-5 inches possible. This tropical air mass is very capable of producing some very heavy short term rainfall rates of 1-2 inches in an hour or less. While grounds are generally dry, multiple rounds of rainfall along with the potential for more organized rains on Friday/Saturday do raise some red flags especially with PWS at or above 2 inches.

Thu Sep 13, 2012 8:37 am

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
547 AM EDT THU SEP 13 2012

FINAL DAY 1...DAY 2 AND DAY 3 QPF DISCUSSION
VALID SEP 13/1200 UTC THRU SEP 16/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR

DAY 1...

06Z CYCLE UPDATE...
THE FINAL DAY 1 QPF WAS ADJUSTED FOR SATELLITE/RADAR TRENDS AND TO
BLEND WITH THE 00Z ECMWF/06Z NAM/06Z GFS/03Z SREF MEAN QPF.

...CENTRAL AND SOUTHERN PLAINS/TX GULF COAST
TO THE SOUTH...CNVCTV RAINS WILL DVLP INVOF THE CDFNT LYING ACROSS
THE SRN PLAINS
WHILE THE TRAILING PORTION OF THE FRONT FM THE S CNTRL PLAINS IS
ACTED UPON BY PIECES OF ENERGY EMBEDDED WITHIN BROAD
WEST-SOUTHWEST FLOW. THE MODELS CONTINUE TO SHOW DEVELOPMENT OF A
CLOSED 700 MB LOW IN WESTERN OK. SEVERAL SREF MEMBERS FCST
LOCALLY HEAVY DOWNPOURS IN THE VICINITY OF THE LOW. THE GFS MOVED
ITS MAXIMA NORTH TOWARDS THE KS/OK BORDER BUT MANUAL PROGS STAYED
FURTHER SOUTH IN CENTRAL OK NEAR WHERE THE GFS 300 MB DIVERGENCE
MAXIMA AND DEEPER MOISTURE AXIS/HIGHER PW VALUES AREA...WHICH IS
CLOSE TO WHERE THE WRF ARW MAXIMA IS 06-12Z FRI. CONVECTION IS
FCST TO TO DVLP SEWD ACROSS TX UNDER A REGION OF WEAK DIV FLOW
ALOFT WHILE LOW LVL SELY CONTINUES TO ADVECT MSTR INTO THE
ADVANCING SFC BNDRY. A WELL DEFINED 850-700 MB CONVERGENCE/300 MB
DIVERGENCE MAXIMA COUPLET DEVELOPS IN THE RIO GRANDE
VALLEY...WHERE SEVERAL MODELS/ENSEMBLE MEMBERS FCST LOCALLY HEAVY
RAIN TO DEVELOP. MANUAL PROGS BLENDED THE 21Z SREF MEAN/12Z
ECMWF/00Z GFS/12Z-00Z UKMET QPF WITH CONTINUITY.

Thu Sep 13, 2012 8:53 am

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
825 AM CDT THU SEP 13 2012

TXZ200-213-214-235>238-131430-
LIBERTY-HARRIS-CHAMBERS-JACKSON-MATAGORDA-BRAZORIA-GALVESTON-
INCLUDING THE CITIES OF...LIBERTY...CLEVELAND...DAYTON...
HOUSTON...PASADENA...KATY...TOMBALL...HUMBLE...WINNIE...
MONT BELVIEU...ANAHUAC...EDNA...BAY CITY...PALACIOS...PEARLAND...
LAKE JACKSON...ALVIN...ANGLETON...FREEPORT...LEAGUE CITY...
TEXAS CITY...FRIENDSWOOD...GALVESTON
825 AM CDT THU SEP 13 2012

....FUNNEL CLOUDS POSSIBLE TODAY...

RAPIDLY DEVELOPING THUNDERSTORMS COUPLED WITH A VERY BUOYANT
ATMOSPHERE AND INTERSECTING BOUNDARIES WILL YIELD BRIEF FUNNEL
CLOUDS THIS MORNING INTO THE EARLY AFTERNOON. THESE FUNNEL CLOUDS
COULD BRIEFLY EXTEND TO THE GROUND AND BECOME A SHORT LIVED
TORNADO. STAY ALERT FOR RAPIDLY CHANGING CONDITIONS AS THESE
FUNNEL CLOUDS WILL DEVELOP AND DISSIPATE QUICKLY.

Thu Sep 13, 2012 9:19 am

Ominous skies outside my window in La Marque.

Thu Sep 13, 2012 10:48 am

From Nesdis:

SATELLITE PRECIPITATION ESTIMATES..DATE/TIME 09/13/12 1543Z
SATELLITE ANALYSIS BRANCH/NESDIS---NPPU---TEL.301-683-1404
LATEST DATA USED: GOES-13 1515Z JBN
.
LOCATION...TEXAS...
.
ATTN WFOS...LCH...HGX...FWD...CRP...EWX...
ATTN RFCS...WGRFC...
.
EVENT...DEVELOPING CONVECTION OVER SERN TX/NWRN GULF OF MEXICO
.
SATELLITE ANALYSIS AND TRENDS...LATEST GOES IR/VIS IMAGERY SHOWS A GROWING
CLUSTER OF CONVECTION OVER THE NWRN GULF OF MEXICO/SERN TX. CONVECTION
APPEARS TO BE MIGRATING NWWD WITHIN CORRIDOR OF DEEPER MOISTURE VALUES
NOSING NWWD INTO CNTRL TX. WITH ADDITIONAL DAYTIME HEATING TAKING PLACE
AND SOME WEAK UL DIVERGENCE IN PLACE, WOULD EXPECT CONVECTION TO CONTINUE
TO DEVELOP AND PERHAPS FORM EITHER SOME MORE ORGANIZED BANDS THAT COULD
TRAIN OR A LARGER CLUSTER THAT WORKS NWWD FROM THE COAST. MANUAL SATELLITE
ESTIMATE TECHNIQUES SUGGEST RAIN RATES OF 1-1.5"/30 MIN MAY BE OCCURRING
WITH THE CONVECTION. COULD SEE 1-3" AMTS OF RAIN THE NEXT FEW HRS WHERE
CONVECTION PERSISTS THE LONGEST/CAN TRAIN OVER SERN TX.
.
SHORT TERM OUTLOOK VALID 1545Z-1945Z...MEDIUM CONFIDENCE FACTOR IN SHORT
TERM OUTLOOK...MAY SEE A FEW MORE ORGANIZED NW TO SE ORIENTED BANDS
TAKE SHAPE ACROSS SE TX THE ENXT FEW HRS THAT SHOULD WORK NWWD ACROSS
THE DISCUSSION AREA. THIS COULD LEAD TO SOME TRAINING/ISOLATED HIGHER
RAIN FALL AMTS THE NEXT COUPLE OF HRS MAY PRODUCE SOME MAINLY POOR
DRAINAGE/URBAN TYPE FLOODING PROBLEMS ACROSS THE DISCUSSION AREA. GREATER
THREAT FOR SOME FLOODING WOULD OCCUR IF BANDS CONTINUE TO ORGANIZE AND
EXTEND INTO GULF OF MEXICO AND FEED NWWD FOR SEVERAL HRS. COULD SEE
A SLIGHT CHANCE OF THIS HAPPENING IN A FEW SPOTS AS IT LOOKS LIKE THE
CONVERGENCE ZONE INITIALLY RESPONSIBLE FOR THE CONVECTION EXTENDS PRETTY
FAR SEWD INTO THE GULF IN VIS IMAGERY. THIS ZONE REMAINS PRETTY ACTIVE
WITH CONVECTION STILL DEVELOPING OVER THE WATER IN ATTM.
.

Thu Sep 13, 2012 11:10 am

Radar starting to light up here (Austin) west of y'all. Showers increasing in coverage and intensity. And these are moving north ... we still have the large convective blob approaching associated with the vort max out west and the cold front in north Texas. We would LOVE to see 2-3 inches here and especially in the Hill Country.

September. Heavy Rainfall Event/Flooding Possible 9/28-30th

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