August 2016: Rain Chances Continue.

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jasons2k
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From the morning NWS-AFD - shows just how lucky those folks are who saw some rain the last few weeks - most of us continue to toast:

.Climate...

Rainfall totals so far for August are...
-College Station - trace
-Houston Intercontinental Airport - 0.00
-Houston Hobby - trace
-Galveston - trace
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srainhoutx
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The 12Z GFS suggests a very complicated and difficult forecast is likely regarding where the heaviest rain may fall and which neighborhoods could see the highest totals. Let me point out that the NWS Houston/Galveston Forecasters fully understand the challenges ahead and that folks are getting anxious because of what they are seeing unfolding just a short 300 miles to our East in Lafayette and Baton Rogue. Please understand that our Professional Forecasters DO feel pressure to "get it right", so let's be mindful that they are our neighbors and those of us that are weather savoy understand that weather forecasting is not an exact science. Also know that some of us personally know these Professional Forecasters in real life and that they are big supporters of our efforts here in the KHOU Weather Forum. We are fortunate to have so many folks that are paid to forecast the weather supporting and following what we do here, and for that we ALL can be proud.
08122016 12Z 54 gfs_z700_vort_scus_10.png
08122016 12Z 54 gfs_z850_vort_scus_10.png
08122016 12Z 54 gfs_z500_vort_scus_10.png
08122016 12Z GFS 108 qpf_acc_us_sc.png
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BlueJay
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Sure looks promising! We are toasty up here in the Woods...
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Yep, the GFS has been and continues to be the most aggressive with rain totals for our area this weekend. Regardless of the exact track of the low, PWats will be exceedingly high in SE Texas over the next few days and ANY storm that develops in that atmosphere has the potential to dump 2"+ rain per hour. Will it be exactly on YOUR neighborhood...? No one can tell. Stay close to weather updates this weekend. We'll be watching it here at KHOU11 closely.
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08122016 mcd0552.gif
MESOSCALE PRECIPITATION DISCUSSION 0552
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 PM EDT FRI AUG 12 2016

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

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

VALID 121720Z - 122330Z

SUMMARY...DANGEROUS AND LIFE-THREATENING FLASH FLOODING/RUNOFF
FROM EXTREMELY HEAVY RAINFALL WILL CONTINUE THROUGH THIS AFTERNOON.

DISCUSSION...VERY INTENSE CONVECTIVE RAINFALL CONTINUES AROUND THE
SOUTHWEST FLANK OF A LOW TO MID LEVEL LOW CENTER OVER SOUTHWEST MS
WHICH CONTINUES TO SLOWLY DRIFT WEST. CLOUD TOPS HAVE WARMED EVER
SO SLIGHTLY OVER THE LAST COUPLE OF HOURS AS SEEN IN 1-MINUTE
GOES-14 IR ANIMATIONS...BUT CLOUD TOPS ARE STILL ABOUT -75C FROM
FAR SOUTHWEST MS INTO SOUTH-CENTRAL LA WHERE PROLIFIC RAINFALL HAS
BEEN OCCURRING THROUGHOUT THE MORNING HOURS.

THE CONVECTION REMAINS HIGHLY PERSISTENT WHILE FOCUSING WITHIN A
VERY MOIST/UNSTABLE AND CONFLUENT LOW LEVEL FLOW REGIME. PWATS ARE
VERY HIGH AND NEAR ALL-TIME RECORD LEVELS CURRENTLY OVER CENTRAL
AND SOUTHERN LA AS INDICATED BY THE 12Z LIX RAOB WHICH HAD A 2.78
INCH PW OF RECORD. LOW PRESSURE AT LEAST IN THE 850/500 MB LAYER
HAS BEEN SHOWING EVIDENCE OF STRENGTHENING THIS MORNING WHICH IS
HELPING TO FURTHER CONCENTRATE AND ORGANIZE THE CONVECTION WHILE
ALSO ENHANCING THE CONFLUENT LOW LEVEL FLOW AROUND THE SOUTHWEST
FLANK OF THE LOW CENTER.

THE 16Z HRRR/HRRRP GUIDANCE INDICATES THE POTENTIAL FOR AN
ADDITIONAL 4 TO 8 INCHES OF RAIN...WITH ISOLATED HEAVIER AMOUNTS
THROUGH LATE-AFTERNOON ACROSS PORTIONS OF CENTRAL AND SOUTHERN LA.
IN SOME CASES...THIS WILL BE ON TOP OF ALREADY EXTREMELY HEAVY
RAINFALL AMOUNTS THAT HAVE OCCURRED. DANGEROUS AND
LIFE-THREATENING FLASH FLOODING/RUNOFF WILL BE LIKELY AS A RESULT.

ORRISON

ATTN...WFO...JAN...LCH...LIX...SHV...
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unome
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:cry:


Area Forecast Discussion
National Weather Service Houston/Galveston TX
1246 PM CDT Fri Aug 12 2016

.AVIATION...
Main change to the forecast is to pull mentions of showers and storms - it appears subsidence over our area due to the low over Louisiana will be too strong to allow much in the way of convection. While it may not be totally dry, any showers that manage to pop up will be few and far between, if one will be over any site, it's impossible to say with confidence. Otherwise, should look for MVFR cigs over the usual suspects again tonight. End of period may start to be influenced by encroaching rainfall from Gulf low, but will leave fleshing out the specifics to future
cycles.
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Inconceivable! :x :x
unome wrote::cry:

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1246 PM CDT Fri Aug 12 2016

.AVIATION...
Main change to the forecast is to pull mentions of showers and storms - it appears subsidence over our area due to the low over Louisiana will be too strong to allow much in the way of convection. While it may not be totally dry, any showers that manage to pop up will be few and far between, if one will be over any site, it's impossible to say with confidence. Otherwise, should look for MVFR cigs over the usual suspects again tonight. End of period may start to be influenced by encroaching rainfall from Gulf low, but will leave fleshing out the specifics to future
cycles.
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Rip76
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Puts sprinklers back out.
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srainhoutx
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ECMWF is somewhat similar in tracking the 850mb Vort, but a tad NW of the GFS. Will need to watch things very closely beginning tomorrow and continuing throughout Sunday into early Monday.
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08122016 12Z 72 ecmwf_uv850_vort_scus_4.png
08122016 12Z 72 ecmwf_T850_scus_4.png
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unome
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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
240 PM EDT Fri Aug 12 2016

Valid 00Z Sat Aug 13 2016 - 00Z Mon Aug 15 2016

...Significant flash flood potential expected to continue for portions of the Gulf Coast and lower Mississippi valley...

...Hot and humid conditions expected to continue into the weekend for much of the East Coast...

An area of low pressure that originated in the tropics will continue to drift slowly west across the lower Mississippi valley through Saturday morning before merging with a frontal system Saturday afternoon. The area of low pressure will continue to focus widespread showers and thunderstorms across the Gulf Coast and lower Mississippi valley through Saturday, with the continued threat of heavy rains over areas that have already received copious amounts of rainfall. The result will be a continued significant flash flooding potential across these areas through Saturday. After the low merges with the frontal boundary Saturday afternoon, the threat of heavy rainfall is expected to expand along the front from Saturday afternoon into Sunday, extending from the southern plains to the Northeast. The most substantial risk of flash flooding on Sunday is forecast to be across portions of the mid-Mississippi valley.

Along the Eastern Seaboard, high pressure at the mid and upper-levels will expand through the weekend, keeping hot and humid conditions in place with only very isolated showers and thunderstorms during the afternoon and evening. High temperatures are forecast to be 5 to 15 degrees above average across much of the eastern U.S. on Saturday and Sunday, with manyareas rising well into the 90s. These temperatures will combine with the high humidity to result in dangerous heat index values. Heat advisories as well as excessive heat watches and warnings have been issued for portions of the Mid-Atlantic and Northeast.

High pressure will also remain place across the West through the weekend, keeping most areas dry with above average temperatures. Afternoon high temperatures are expected to be 5 to 15 degrees above average.

Ryan

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Ptarmigan
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unome
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insane rain totals...

WPC Storm Summary for the Southeastern U.S. and Gulf Coast Heavy Rainfall.
Last Updated: 1120 AM EDT FRI AUG 12 2016

http://www.wpc.ncep.noaa.gov/discussions/nfdscc2.html

THE NEXT STORM SUMMARY WILL BE ISSUED BY THE WEATHER PREDICTION CENTER AT 400 PM CDT. PLEASE REFER TO YOUR LOCAL NATIONAL WEATHER SERVICE OFFICE FOR ADDITIONAL INFORMATION ON THIS EVENT.
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Ptarmigan
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srainhoutx wrote:You have to remember that the actual air temperatures back in 1962 were in the 112F to 115F range on this date across SE Texas. Let that sink in for a minute. Many of us didn't have Air Conditioning at that time. Just those hot attic fans circulating the steamy air throughout the house. ;)
The highest temperature in 1962 was on August 9, which reached 106°F at Houston Weather Bureau Office. Of course Houston was less developed back than. If that happened today, I suspect the air temperature would be much higher, likely around 110°F to 115°F.

There is also a high of 108°F on August 18, 1909. Back than, Houston was way less developed like today or in 1962. I suspect if that happened today, the high could be easily 115°F.

August Records
http://www.srh.noaa.gov/hgx/?n=climate_iah_normals_aug
davidiowx
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Ptarmigan wrote:
srainhoutx wrote:You have to remember that the actual air temperatures back in 1962 were in the 112F to 115F range on this date across SE Texas. Let that sink in for a minute. Many of us didn't have Air Conditioning at that time. Just those hot attic fans circulating the steamy air throughout the house. ;)
The highest temperature in 1962 was on August 9, which reached 106°F at Houston Weather Bureau Office. Of course Houston was less developed back than. If that happened today, I suspect the air temperature would be much higher, likely around 110°F to 115°F.

There is also a high of 108°F on August 18, 1909. Back than, Houston was way less developed like today or in 1962. I suspect if that happened today, the high could be easily 115°F.

August Records
http://www.srh.noaa.gov/hgx/?n=climate_iah_normals_aug

Gotta love June 5th and 6th back in 2011. Sheesh what a summer that was.

And that 106 on August 11 of last year as well.
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By looking at some of the models posted by Srain, et al, that this Low pressure would probably never get west of Houston, so we wouldn't be getting the dirty side of the low, hence gobs of rain like what Louisiana is experiencing. Is that somewhat accurate?

Granted, we should get some rain, but not the 9" forecast in central La. Thanks.
A.V.

Ptarmigan wrote:The highest temperature in 1962 was on August 9, which reached 106°F at Houston Weather Bureau Office. Of course Houston was less developed back than. If that happened today, I suspect the air temperature would be much higher, likely around 110°F to 115°F.

There is also a high of 108°F on August 18, 1909. Back than, Houston was way less developed like today or in 1962. I suspect if that happened today, the high could be easily 115°F.

August Records
http://www.srh.noaa.gov/hgx/?n=climate_iah_normals_aug
Austin's record high is 112F. Thus, 115F for Houston, even with UHI, is quite overdone.
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A.V. wrote:
Ptarmigan wrote:The highest temperature in 1962 was on August 9, which reached 106°F at Houston Weather Bureau Office. Of course Houston was less developed back than. If that happened today, I suspect the air temperature would be much higher, likely around 110°F to 115°F.

There is also a high of 108°F on August 18, 1909. Back than, Houston was way less developed like today or in 1962. I suspect if that happened today, the high could be easily 115°F.

August Records
http://www.srh.noaa.gov/hgx/?n=climate_iah_normals_aug
Austin's record high is 112F. Thus, 115F for Houston, even with UHI, is quite overdone.
The urban heat island increases temperatures by 5 degrees.

The 112°F record happened at Camp Mabry in 2000 and 2011.

There was 108°F on July 11, 1917, 109°F on July 26, 1954 at Camp Mabry.
http://threadex.rcc-acis.org

Since Austin is less humid, if those highs back than happened today, they could go well over 115°F, possibly even close to 120°F.
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srainhoutx
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Friday afternoon briefing from Jeff:

Tropical low over southern Louisiana to bring heavy rains back to SE TX this weekend.

Life threatening flash flood event continues to unfold across southern Louisiana where rainfall totals since 400am this morning have exceeded 15 inches in some locations. Surface low of 1009mb located inland north of Baton Rouge is drifting toward the west slowly with a large swath of very heavy rainfall on its SW flank extending westward to east of Lake Charles. It is certainly possible that some locations over southern Louisiana could approach 20-25 inches of rainfall in 48 hours with this system.

Upper level ridge over TX is in the process of breaking down and shifting WSW as a trough advances into the state from the NW this afternoon. Moisture from former TS Javier over the eastern Pacific is advecting NE along this trough/frontal boundary into NW TX where numerous showers and thunderstorms are starting to develop. Mid and surface low pressure system over southeast Louisiana will continues its slow drift westward this weekend and be located somewhere near/over SE TX by Sunday. Will see a marked increase in rain chances starting later on Saturday as rain bands approach from the ENE and pivot into the region. Subsidence from the ridge aloft will decrease and tropical moisture will surge into the region with PWS values over SW/SC Louisiana currently in the 2.5-2.8 inches range which is near maximum values for summer. Hence there is little surprise in the rainfall rates and amounts that have fallen over Louisiana today.

GFS maintains a very well defined 850mb vort center into SE TX Sunday and this would be very concerning as core rains will focus around this center while the ECMWF and other models are not as defined with the 850mb center and show a more elongated trough of low pressure moving in from the east. Given that the surface pressure has actually fallen to 1009mb today is interesting…almost like the surface center is intensifying even though it is inland…we have seen this before with decaying tropical systems close to the Gulf of Mexico which are able to feed off the very moist air mass and maintain their definition in defiance of land interaction. Not ready to jump on the GFS solution just yet which is showing some impressive totals over the region since there is little model support from the other major models. Will just have to watch how activity to our east unfolds over the next 24-36 hours and how defined the circulation remains. If other models begin to show what the GFS is showing then a significant increase in QPF will be required along with likely flash flood watches…a bit difficult to digest given KBDI values are 650-750 over many counties indicating very dry conditions.

Will go with widespread rainfall of 2-4 inches NE of a line from College Station to Katy to Galveston and 4-6 inches around Lake Livingston with lower amounts to the SW around Matagorda Bay which will be well removed from the track of this feature. With that said…we need to be aware that the SW flank of this system has been the active side and if this continues this may bring higher totals across a larger part of the area. Think these totals may be on the conservative side, but not enough confidence just yet to bump them up.

Onset of tropical air mass and saturated air column certainly will support very heavy rainfall rates of 2-4 inches per hour under the heavy rain cores which will quickly lead to rapid run-off even with generally dry grounds…it will just be raining too hard and fast to give the ground time to absorb much water. End result will likely be street flooding and flooding of underpasses…and now is a good time to remind residents not to drive into those high water locations…stated more bluntly if water is over the road do NOT drive into it!

Will see how things unfold over the next 24-48 hours before placing much stock into next week…but the overall pattern remains a wet one with no upper ridging returning and moisture values remaining high…will likely need at least 40-50% chances each day after Monday.
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A.V.

Ptarmigan wrote:The urban heat island increases temperatures by 5 degrees.

The 112°F record happened at Camp Mabry in 2000 and 2011.

There was 108°F on July 11, 1917, 109°F on July 26, 1954 at Camp Mabry.
http://threadex.rcc-acis.org

Since Austin is less humid, if those highs back than happened today, they could go well over 115°F, possibly even close to 120°F.
The effect of UHI is dependent of geographic/climate factors, as well as level of build. Houston Hobby is more built up, and is more in the center of the urban core compared to many areas of inland/northern Houston metro (College Station, Tomball, Woodland, etc), but, because it is in the sea-breeze zone, it has lower 100F frequency than those places.
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srainhoutx
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Today looking at the Climate Prediction Center updated Day 8 to 14 Outlook and the Day 11+ Analogs, it appears we are indeed seeing a significant pattern change and the hot days of summer may be slowly coming to an end.
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814temp.new (6).gif
814prcp.new (7).gif
814analog.off (8).gif
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