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Extremeweatherguy wrote:It has gotten nice out there! Dewpoints have fallen into the middle 40s and the air temperature is hovering somewhere in the upper 60s to near 70F here in northern Harris county at 10am. You cannot ask for much better weather than this on May 3rd in SE Texas!
Very active morning across the N ½ of the area.
Warm front moving northward combining with short wave moving out of Mexico to produce widespread thunderstorms along and N of I-10 this morning. Have already seen 2-3.5 inches of rainfall around CLL with a band of 1-2 inches spreading SE into N Harris County.
Parameters appear to be in place for a possible flash flood event over the northern ½ of SE TX today. Tremendous moisture return overnight has allowed PWS to climb to near 1.7 inches across the region with even deeper moisture poised to move into the area from the SW (PWS near the magic 2.0 in over the Matagorda Bay area). Weak warm front is moving slowly northward across the region….however per surface obs at IAH and CXO is appears the morning convection has laid down a surface outflow boundary that extends roughly from Humble to Greenspoint to Cypress to Brenham. Thunderstorms continue to fire along and north of this boundary and train ENE across the northern areas of SE TX.
Air mass is uncapped for a change and very moist with surface dewpoints approaching 70 and as mentioned above PWS approaching summer levels. Feel the air mass is capable for producing prodigious rainfall amounts in a very short period of time as the air column is nearly saturated and warm rain processes are likely occurring to some degree. Given the training along the boundaries in place coupled with a favorable upwind propagation vector to the NW which aligns nicely with the warm front orientation flash flooding will be possible especially along and NE of a line from Giddings to Hempstead to Humble. Will also need to closely watch ongoing MCS S of Laredo for any boundaries heading NE into our SW counties that may set things off this afternoon…given the lack of capping today.
Rainfall amounts of 2-4 inches are likely NE of the above mentioned line with lesser amounts to the SW of this line. Similar patterns of slow moving/training convection in a very moist air mass have produced some very high totals in the past. Using the PW rule for slow moving or training convection of multiplying the PW value by 2-4 gives rainfall values of 4-8 inches in the band of heavy convection. Luckily while the current band is training is also has some slow NE motion and storms are not feeding into the southern edge of the line. We shall see how this unfolds over the next several hours.
We should see somewhat of a break on Tuesday as the air mass dries a tad…however it remain cap free and the seabreeze/baybreeze may be enough to generate a few afternoon thunderstorms.
Upper trough ejects into the plains late Tuesday and into Wednesday with numerous thunderstorms expected along the W TX dry line. Models continue to point toward MCS formation to our W late Tuesday with some kind of weakening complex approaching our W counties Wed AM. Cap should begin to increase and widespread low clouds should limit heating on Wednesday so for now will go with fairly low rain chances…but these may need to be raised.
After Wed sprawling sub-tropical high builds over the region with summer heat as 850mb temps. climb toward +20-25. Very strong cap will develop and moisture levels will fall by Thursday. Will go ahead of show the first 90 on Thursday and warm the afternoons even more Friday and Saturday into the lower 90’s given 850mb temps. Onshore flow will continue with dewpoints hovering in the 60’s and lower 70’s…this will push heat index values into the low 100’s.
Very heavy rainfall moving into Harris County.
Band of excessive rainfall continues to train along a line from S of CLL to Hempstead to Spring. Rainfall totals since 400am are approaching 5.0 inches over Waller and Washington counties with 2-3 inches into southern Montgomery County. ALERT station at Spring Creek and FM 2978 recorded 1.12 inches in 12 minutes…suggesting rainfall rates are nearing 4.0 inches per hour under this band.
Storms continue to develop and train along this stalled outflow boundary. An additional 2-3 inches will be possible along this line over the next 1-2 hours.
Flash flooding and ponding may develop as grounds become saturated and rainfall begins to pond and run-off.
NWS has issued a Flash Flood Watch until 400pm for locations along and N of I-10.
Since 400am 4-6 inches of rainfall has fallen along a line from N of Hempstead to W of The Woodlands with 1-2 inches surroundings this narrow band. In the past 3 hours 5.09 inches of rain has fallen at ALERT station 1070 at Spring Creek and SH 249
Thunderstorms continue to develop and train E along this line and an additional 1-3 inches of rainfall will be possible this afternoon in the watch area.
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
210 PM CDT MON MAY 5 2008
THE NATIONAL WEATHER SERVICE IN LEAGUE CITY HAS ISSUED A
* FLASH FLOOD WARNING FOR...
EXTREME NORTHERN HARRIS COUNTY IN SOUTHEAST TEXAS...
SOUTHERN MONTGOMERY COUNTY IN SOUTHEAST TEXAS...
* UNTIL 415 PM CDT
* AT 206 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED
TO SHOW SHOWER AND THUNDERSTORM DEVELOPMENT ALONG A NEARLY
STATIONARY BOUNDARY DRAPED ACROSS THE REGION. WIDESPREAD RAINFALL
AMOUNTS OF 3 TO 5 INCHES HAVE OCCURRED IN THIS AREA TODAY...WITH
LOCALIZED AMOUNTS CLOSE TO 8 INCHES. CONTINUED MODERATE TO HEAVY
RAIN WILL RUNOFF TO CAUSE FLOODING OF STREETS AND LOW LYING AREAS.
IN ADDITION...SOME OF THE SMALLER CREEKS IN THE AREA ARE ALSO
RISING. DO NOT DRIVE ACROSS WATER COVERED ROADS!
* LOCATIONS IN THE FLOOD WARNING INCLUDE BUT ARE NOT LIMITED TO
SPLASHTOWN...PORTER...NEW CANEY...HOOKS AIRPORT...WOODLOCH...
WOODBRANCH...TOMBALL...THE WOODLANDS...SPRING...SPLENDORA...
SHENANDOAH...ROMAN FOREST...PORTER HEIGHTS...PINEHURST...PATTON
VILLAGE...OAK RIDGE NORTH...MAGNOLIA...KINGWOOD...CUT AND SHOOT...
CONROE AND CHATEAU WOODS.
PLEASE REPORT SEVERE WEATHER TO THE COUNTY SHERIFF...LOCAL POLICE...
OR DEPARTMENT OF PUBLIC SAFETY. THEY WILL RELAY YOUR REPORT TO THE
NATIONAL WEATHER SERVICE.
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