May 2015 Record Setting May Rainfall Totals For Region

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djjordan
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Looks like a nice weekend to kick off May 2015 after a very stormy and unsettled April. What will May bring us as we edge even closer to summer and Hurricane Season? Let's begin the May thread!!!! :)
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srainhoutx
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A quick update regarding the potential pattern as we begin May across the Region. The Climate Prediction Center Day 8+ and Day 11+ Analogs based on the ensemble guidance suggests cooler and wetter weather may well be the theme as a broad area of lower pressures establish across the West and Southwest. Typically as wavelengths become longer and we transition to a more zonal flow, convective activity is suggested to increase as the Polar jet retreats North and the sub tropical jet becomes very noisy which is typical of an El Nino pattern.
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Ptarmigan
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Some of the analog dates stand out like 1972.
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GBinGrimes
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Ptarmigan...would you tell us what stands out about 1972? You've have me curious.

Thanks!
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srainhoutx
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I'll let Ptarmigan provide the details, but a Major Central Texas Flood event occurred May 11th and 12th, 1972. ;)
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GBinGrimes
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Hmmm...I was 11 at the time, grew up in Houston and this has faded from my memory. What a brutal flood! Here's a brief writing of the details of the flood, copied from the good part of the internet:
Heavy rain began falling in Comal County around 8 PM on May 11. At midnight, sixteen plus inches poured upon the Guadalupe River midway between New Braunfels and the Canyon Lake Dam. The first flood waters rushed into New Braunfels from Blieders Creek and flowed into the Comal River at Landa Park. The flood waters filled the Comal and overflowed into the Guadalupe River, where they roared towards Seguin. Recent construction of Canyon Dam located twenty five miles upstream gave residents a false impression that they would be secure from any flooding. However, the storm waters fell almost perfectly into the Guadalupe River watershed just below the Canyon Dam. Homes were uprooted by the rushing waters and washed downstream at New Braunfels towards Seguin. Nighttime mass evacuations were initiated, as families scrambled to shelters in the area. Many homes and vehicles were seriously damaged and destroyed in the floodplains along Lake Dunlap, Geronimo Creek, and Lake McQueeney. All the homes on Treasure Island and in Glen Cove basin were underwater. The river finally crested near 33 feet at Seguin. Fifteen persons were found to have drowned during this event
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srainhoutx
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A quiet benign weather pattern that brought unseasonably cool weather to end April will begin to slowly transition to that of a split flow. The cool high pressure ridge will shift E during the weekend allowing a return flow of the Gulf to become established and moisture slowly increases throughout the first weekend of May. In the upper levels, an upper ridge that has been in place will begin the process to flatten out and a Western short wave organizes near the Baja Peninsula and meanders slowly west into Northern Mexico. A series of disturbances are expected to drop south into Northern Mexico carving out a Western trough across the Four Corners Region of the SW Untied States. As the shortwave develops and the Western trough takes hold, the upper trough currently across the Gulf of Mexico will begin to retreat north ushering in mid/upper level moisture from the Eastern Pacific. Moderate to strong convection has been ongoing off the Pacific Coast of Central America associated with the monsoonal trough. There are some indications that the monsoonal trough will be tugged north as the Western trough organizes. Deep tropical moisture from both the Eastern Pacific and the NW Caribbean Sea should begin to surge north and increase scatter rain/storm chance as we begin next week. The morning Quantitative Precipitation Forecast (QPF) that extends into early next Tuesday suggests increasing rain chances mid next week.
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The 04/29/2015 Climate Prediction Center Update continues to advertise a wet and stormy pattern is possible as we enter the first full week of May during mid next week period in the Day 8+ range. Indications via the ensemble guidance suggest severe storms may be possible next week across the Great Plains with some possibility of heavy rainfall returning to Texas and Oklahoma. Further East in the extended range, the various computer model schemes are suggesting a sub-tropical low may develop near the Bahamas and East of Florida.
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Looking ahead to next week, the mid-level subtropical ridge centered over the four corners region will begin to flatten out as models hint that a more active pattern could be on the horizon. Models are really struggling with the PNA , indicating a negative dip could occur next week, but both the ECMWF and GFS have a lot of variability in their respective ensembles. With that said, both of the globals do indicate that another pacific shortwave could cross the baja region early next week and slow down as it enters the state of Texas. A strong high centered over the Eastern U.S. look to amplify this shortwave as it begins to make a negative transition tilt on Monday. Models become split after this point on how fast they eject the wave north, but parts of the central and southern plains could be under the gun as strong return flow and low level winds could advect deep gulf moisture north. Still a lot of uncertainties in respect to timing and intensity as sampling of the shortwave is still really low right now but hopefully by the weekend more will be known.
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srainhoutx
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A quick morning update looking ahead to next week. The ensemble guidance though struggling with the various features in the mid to upper levels and what will actually be the sensible weather we can expect mid to late next week are suggesting a potential heavy rainfall event across our Region. The severe threat remains uncertain this morning due to the evolution and the eventual movement of the Northern Mexico shortwave as well as a strong upper air disturbance arriving along the NW Pacific Coast. It does appear a Western upper trough will develop with embedded disturbances riding from the SW to the NE within the upper flow across the Texas and the Great Plains. PW’s are expected to steadily increase to near or above 2 Standard Deviation above normal with the reforecast Quantitative Precipitation Forecast derived from the 12Z guidance yesterday (4/30/2015) exceeding the 99th percentile which raises an eyebrow particularly across Central Texas on North into Oklahoma. If the trends continue throughout the weekend, attention will turn to the Flood potential mid to late next week.
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jasons2k
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It seems over the last few years, and this year especially, every storm system that moved across pushed moisture into the "99th percentile". By definition that's supposed to be a rare event. But it's not. At what point does the "99th" percentile become the new normal? When does the curve get re-evaluated and shift?
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