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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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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I'll let Ptarmigan provide the details, but a Major Central Texas Flood event occurred May 11th and 12th, 1972. ;)
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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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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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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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04302015 CPC 610prcp_new.gif
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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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jasons wrote: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?
Anything above 95th percentile is an outlier. I am sure they will re-evaluate the curve.
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Our string of pleasant weather days will begin to transition to a somewhat unsettled weather pattern next week. The overnight ensemble guidance continues to advertise the upper ridge that has been responsible for the quiet weather pattern this week will flatten out and be replaced with a developing Western trough and increasing onshore flow off the Western Gulf of Mexico.

The first in a series of shortwaves is moving east from the Eastern Pacific and will be near Northern Mexico as the weekend ends. Leeside cyclogenesis across the Central/Southern Rockies in response to the pressure falls out west will increase the onshore flow Monday and continue ushering in increasing moisture as the week progresses. A second upper air disturbance is expected to begin dropping SE into the Great Basin from the Gulf of Alaska early next week and meander as a split zonal flow develops. That upper low appears to become trapped across the Great Basin as a stout upper ridge develops across the Mississippi Valley and the Southern flow becomes stagnant or slow moving. The Northern jet continues to remain well up into Canada setting the stage for strong and possibly some severe thunderstorms to develop east of the Continental Divide into the Great Plains. This stagnant flow across the West and Central United States appears to linger into at least next weekend.

There are still indications via the various computer model schemes that a subtropical/extra tropical low pressure system may develop next week near the Bahamas and meander offshore of the Southeastern US Coastline as upper ridging builds north of that feature. The greatest concern for heavier rainfall looks to be focused from Texas across the Southern/Central Plains into Minnesota and across Southern Florida.
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Some of the analog dates are interesting like 1957 and 1989.
Paul Robison

Will this help?

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And then there's this little tidbit from SPC:
PRIOR TO THE EMERGENCE OF THE LEAD IMPULSE FROM THE SOUTHWEST...
MODELS CONTINUE TO SUGGEST THAT THERE WILL BE SUBSTANTIVE LOWER/MID
TROPOSPHERIC COOLING AND STABILIZATION OF MID-LEVEL LAPSE RATES
ACROSS THE PLAINS...WITH THE POSSIBLE EXCEPTION OF AREAS NEAR THE
LOWER RIO GRANDE VALLEY. WITH RICH...TROPICAL BOUNDARY LAYER
MOISTURE PROBABLY REMAINING CONFINED TO MEXICAN GULF COASTAL
AREAS...THE CARIBBEAN AND SOUTHWESTERN ATLANTIC INTO AT LEAST EARLY
PORTIONS OF THE PERIOD /DUE TO THE CONTINUING PRESENCE OF UPPER
TROUGHING ACROSS THAT REGION...SEVERE WEATHER POTENTIAL STILL SEEMS
LIKELY TO REMAIN SEASONABLY LOW. MORE SUBSTANTIVE DESTABILIZATION
DOES APPEAR POSSIBLE IN THE WAKE OF THIS LEAD IMPULSE...ACROSS PARTS
OF THE PLAINS AND MISSISSIPPI VALLEY...LATE THIS COMING WEEK INTO
NEXT WEEKEND. HOWEVER...DUE TO THE LOW PATTERN
PREDICTABILITY...SEVERE PROBABILITIES CURRENTLY REMAIN BELOW 15
PERCENT THROUGH THE PERIOD.
Sorry I couldn't include the whole thing, but SE TX will not get very much rain out of this, if it verifies. Any severe likely in the area Tues-Wednesday, BTW?
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The overnight guidance continues to struggle with the evolving pattern and how the leading shortwave ejecting out of Northern Mexico will affect the sensible weather across Texas, Eastern New Mexico and Oklahoma. The Storm Prediction Center has outlined a Slight Risk for severe storms across portions of West Central Texas and Eastern New Mexico as the shortwave meanders ENE and convective activity along the dryline could increase. The various computer model scheme are not in very good agreement as to the strength of this shortwave, so expect day to day changes. Meanwhile, the upper ridge that has brought our pleasant weather of late continues to slide E and we should begin to see moisture returning off the Gulf of Mexico increasing daily as a persistent Western trough develops and lingers as several upper low features drop SE into the Great Basin at least through next weekend...if not longer.
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1151 AM EDT SUN MAY 03 2015

VALID 12Z WED MAY 06 2015 - 12Z SUN MAY 10 2015


...MULTI-DAY HEAVY RAINFALL EVENT FOR THE SOUTHERN AND CENTRAL
PLAINS...

A BLOCKING PATTERN IS PROGGED TO TAKE SHAPE ACROSS NORTH AMERICA
THIS WEEK, WITH A MEAN TROUGH SETTING UP IN THE WESTERN UNITED
STATES. USED A BLEND OF THE 00Z/03 ENSEMBLE MEANS AS A SYNOPTIC
GUIDE THIS FORECAST, AS THE EVOLUTION OF THE FLOW HAS BEEN WILDLY
HANDLED BY THE VARIOUS OPERATIONAL MODELS. DID INCORPORATE SOME OF
THE 00Z/03 GFS TO ADD SOME DEFINITION TO THE POSSIBLE SUBTROPICAL
LOW OFF THE SOUTHEAST COAST, WHICH THE NATIONAL HURRICANE CENTER
ESTIMATES AS HAVING A 30 PERCENT CHANCE OF DEVELOPMENT PAST 48
HOURS IN THEIR SPECIAL TROPICAL OUTLOOK. A DEEPER WESTERN TROUGH
MEANS A GREATER CHANCE OF BACKDOOR MARITIME POLAR FLOW INTO THE
NORTHEAST AND MID-ATLANTIC, SO NOT SURE HOW FAR NORTH ANY LOW OFF
THE ATLANTIC COAST WILL BE ABLE TO ULTIMATELY DRIFT.

THE STAGNATION OF THE PATTERN MEANS THAT WHAT YOU SEE IS WHAT YOU
WILL GET FOR SOME TIME TO COME. THE GREATEST IMPACT OF THE BLOCK
SHOULD BE OVER THE SOUTHERN AND CENTRAL PLAINS, WHERE PROLONGED
INFLOW FROM THE GULF OF MEXICO SHOULD FUEL DAY AFTER DAY OF
SOAKING SHOWERS AND THUNDERSTORMS. EVENTUALLY, THE MOISTURE SHOULD
WRAP BACK INTO THE HIGH PLAINS OF NORTHEASTERN COLORADO AND
EASTERN WYOMING WHEN THE UPPER LOW OVER THE SOUTHWEST BEGINS TO
KICK OUT.

THE SOUTHEAST SHOULD GRADUALLY MOISTEN UP AS THE OFFSHORE
DISTURBANCE TENDS TO RETROGRESS IN THE TIGHTENING BLOCK--MAINLY
SOUTH OF VIRGINIA.


CISCO
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Do the factors mentioned here in this HGX disco reduce the chances of severe weather in the Houston region? Read:

ISSUED 427 AM CDT SUN MAY 3 2015/


WATER VAPOR IMAGERY STILL SHOWS ONE UPPER LEVEL LOW WEST OF
CALIFORNIA AND A MORE POTENT SYSTEM IN THE GULF OF ALASKA. ALL OF
THE SYNOPTIC MODELS ARE IN GOOD AGREEMENT WITH BRINGING THE FIRST
UPPER LOW ACROSS THE S ROCKIES WITH A BIT OF A NEG TILT ON TUE.
THERE IS A BROAD AREA OF DIFFLUENCE ALOFT OVER TX ASSOCIATED WITH
THE TROUGH AND JET STREAM COMING INTO TX FROM ACROSS MEXICO. WITH
850MB FLOW LARGELY FROM THE SE/S...THERE SHOULD NOT BE MUCH OF AN
EML FOR CAPPING. MODEL SOUNDINGS SHOW THAT AN EML NEVER REALLY
ESTABLISHES ITSELF OVER THE REGION FOR THE COMING WEEK. THIS MEANS
THAT EVEN SYNOPTIC SCALE LIFT MAY BE ENOUGH TO INITIATE CONVECTION
OVER THE AREA ESPECIALLY WITH DAY TIME HEATING SUPPORTING MAX
TEMPS IN THE MID 80S.

THE BIGGEST DIFFERENCE IN MODEL DATA FROM YESTERDAY TO TODAY IS
THAT LARGE SCALE LIFT DOES NOT APPEAR TO BE AS FAVORABLE. THE JET
STREAM IS MORE ANTICYCLONICALLY CURVED OVER THE REGION THAN
YESTERDAY WITH SUGGESTS SOME SUBSIDENCE. DIFFLUENCE ALOFT DOES NOT
LOOK A GREAT AND JET STREAKS ASSOCIATED WITH THE UPPER LOW OVER
THE GREAT BASIN DO NOT LOOK TO MAKE AN IMPACT UNTIL LATER IN THE
WEEK ON FRI/SAT. DURING THIS TIME UPPER FLOW STILL HAS SOME
RIDGING OR AT LEAST SOME ANTICYCLONIC CURVATURE TO IT WHICH WOULD
LIMIT LARGE SCALE ASCENT. FINALLY THERE ARE REALLY NOT ANY STRONG
BOUNDARIES TO FOCUS CONVECTION WHICH MEANS THERE MAY NEED TO BE
SOME MESOSCALE FORCING TO FOCUS CONVECTION. SO THE FORECAST HAS
TRENDED DOWN A BIT IN RAIN CHANCES. FORECAST DOES KEEP MAINLY 40
POPS FOR TUE/WED BUT TRIMMED BACK CHANCES TO 30 PERCENT FOR THE
END OF THE WEEK.

Note that he mentions large scale ascent. What does that mean for severe WX?
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Scattered showers and thunderstorms should begin to increase this afternoon into tomorrow as low level moisture continues streaming inland off the Gulf of Mexico. A weak shortwave near Northern Mexico will begin the process of carving out an upper trough across the Great Basin as a series of upper air disturbances ride SE from the Pacific Northwest and eventually develop into a robust 500/700mb closed upper low near the Four Corners Region later this week. Meanwhile across the Northeastern United States, a strong upper ridge of high pressure develops creating a blocking pattern in the split zonal flow regime. The overnight guidance continues to advertise a subtropical or hybrid low pressure system will develop near the Bahamas and meander near or just offshore of the Southeastern United States Coastline basically trapped beneath the ridge to the north.

The mean upper flow looks very stagnant suggesting the next upper low to our West may dig a bit deeper and become stronger or more wrapped up Thursday into the weekend before ejecting into the Central Plains. The continuous onshore flow off the Gulf as well as increasing moisture from the Pacific Ocean may increase our rain chances again later in the week into the weekend...if not longer. As the wavelength pattern over the Pacific Ocean get longer, weather patterns across the Southern half of the United States can become very stagnant. The best chance for stronger storms in the short term appears to be W of the I-35 Corridor up into the Southern/Central Plains. Later in the work week and into next weekend, storm chances may increase further east across Texas and possibly into Louisiana.
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The afternoon Update from the Climate Prediction Center is advertising an unsettled pattern continues with a stagnant Southern stream allowing for a continued trough in West with above normal rain chances in the Day 8+ Range.
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Reading the afternoon AFD from the local NWS office...and they are not impressed. Maybe something tomorrow but mostly dry until at least Sunday or Monday. It keeps getting pushed further and further into the future.

Go back and read last week's discussions. It looked so promising.

So much for a wet week. Time to crank the sprinklers, at least for now.
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