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

[djjordan]

Seems like this weekend has been the hottest of the entire summer. Felt like it anyways. I'm ready for autumn as I'm sure everyone else around here is too.

[srainhoutx]

Morning e-mail from Jeff:

Summer heat will make a stand this week with high pressure in control both aloft and at the surface. Upper ridge will build into the area from the NW producing subsidence across the region and eliminating any chance of rainfall. At the surface high pressure centered over the Gulf of Mexico will continue to pump in a humid southerly flow keeping dewpoints on the high side. Lack of significant cloud cover will allow afternoon temperatures to top out in the 97-102 range each afternoon this week. High dewpoints and surface RH will result in afternoon heat index values at or above 105. Only relief will be a slight SSW to SW surface flow in the 10-15mph range. No chance of rainfall is expected through Thursday.

Toward the end of the week into the weekend, the ridge over the western US amplifies allowing a deep trough for this time of year to develop across the eastern US. Cold air for early September standards will begin to move southward down the plains this week and a cold front will arrive into TX by Friday/Saturday. Upper pattern looks fairly favorable for the first cold frontal passage of the upcoming fall/winter season in the Saturday time period. Moisture does begin to pool along and ahead of this boundary late Friday into Saturday, but GFS guidance is not overly impressive on rain chances (30-40%). This is still several days away, and better dynamics and moisture may be found over the next few days to raise rain chances. Bigger news will be the much drier and yes “cooler” air mass that will move into the area. Not ready to go as cool as some of the guidance as it is still early and such fronts tend to look stronger in the extended range only to show up in a much weaker state. For now will go with the front pushing off the coast late Saturday or early Sunday with gusty NW winds in its wake. Low temperatures look to fall into the low to mid 60’s for Sunday morning into early next week with high temps in the lower 90’s, could see cooler highs in the 80’s if the thrust of the cooler air is more southward than SE.

TS Leslie:
Large tropical storm continues to sit and spin over the open Atlantic waters north of the Leeward Islands. Leslie has been undergoing NW shear for the past 3 days which has continued to remove the thunderstorm activity to the south of the center of circulation. Leslie is also caught in a region of very weak steering with a trough bypassing her to the NNE and high pressure building down from the E coast of the US over the top of the system blocking any northward motion. In fact there is likely to be little motion over the next 3-4 days until the central/E US trough that drives the cold front into TX this weekend begins to affect the system by Day 5. At that time Leslie should begin to move at a slightly faster speed to the NNW or NW ahead of this approaching trough. The large wind field and slow storm motion will produce increasing swells along the entire US east coast over the next 5-7 days.

[wxman666]

Still way too early to tell but HGX hinted that they may need to monitor for any severe weather potential saturday.

OF COURSE THIS RECENT HEAT HAS THE NEWS OF THIS WEEKEND`S COLD
FRONTAL PASSAGE GENERATING MORE ATTENTION. IT`S STILL ON WITH ITS
SATURDAY PASSAGE INTRODUCING MODERATE RAIN/STORM CHANCES BUT...
MOST IMPORTANTLY...IT WILL USHER IN MUCH COOLER TEMPERATURES. A
SIGNIFICANT DIP IN MID-LEVEL TEMPERATURES FROM THE RECENT LOWER
20S TO (AS LOW AS) 11-12C BY SUNDAY...WITH EARLY WEEK SURFACE
TEMPERATURES RESPONDING BY AN AVERAGE 5-8 DEGREES COOLER UPON
AFTERNOON READINGS TO OVER 10 DEGREES COOLER IN THE MORNING (WHEN
COMPARING PRE-FRONTAL NUMBERS TO THOSE IN THE POST-FRONTAL). THE
UPPER TROUGH AXIS WILL DIG DOWN INTO THE EASTERN U.S...WITH TEXAS
FALLING WITHIN THE WESTERN LEG OF UPPER WEST-NORTHWEST FLOW...SO
THERE IS A QUESTION ON HOW EXTENSIVE ANY WEEKEND SEVERE WEATHER
WILL BE AHEAD OR ALONG THE BOUNDARY ITSELF. 31

[MontgomeryCoWx]

Please no. Saturdays in the Fall are the only time I don't want rain.

Cool, yes. Rain No. I have a huge tailgate to throw all day Saturday for the A&M/Florida game.

[mckinne63]

Seems like this weekend has been the hottest of the entire summer. Felt like it anyways. I'm ready for autumn as I'm sure everyone else around here is too.

It sure did seem that way! I looked like I just got out of the shower after doing yard work on Monday. Bring on those cooler temps!

[Andrew]

Please no. Saturdays in the Fall are the only time I don't want rain.

Cool, yes. Rain No. I have a huge tailgate to throw all day Saturday for the A&M/Florida game.

+1 for that one.

I will have to monitor the models/ radar over the next couple of days for sure.

[srainhoutx]

Morning e-mail from Jeff:

High pressure remains in control of the weather over the state.

High pressure aloft to the WNW of the area and at the surface over the central Gulf of Mexico is resulting in very warm conditions. Afternoon high temperatures have been topping out in the upper 90’s to low 100’s and this will continue for today and Friday. Cold front is still slated to cross the area on Saturday as the western US ridge amplifies and deepens the trough over the eastern US. The front with a significantly drier air mass will cross the area from Saturday morning through early evening. Moisture profiles increase ahead of the boundary, but model trends over the past 24-26 hours have been for less and less rainfall potential. This potential seems even more reasonable if a tropical system forms in the central Gulf of Mexico over the next 48 hours producing northerly flow ahead of the boundary. Still think there may be a think band of showers or an isolated thunderstorm along the front Saturday afternoon, but chances of widespread wetting rains is decreasing.

Front will be of the coast Sunday morning with a much drier air mass in place. Dewpoints should fall well into the 50’s at most locations giving the area its first reprieve from the summer humidity. High temperatures on Sunday will be 10-12 degrees cooler than Friday (the upper 80’s) and lows on Monday morning under clear skies and calm winds will fall into the low 60’s and upper 50’s. SE winds begin to return moisture to the area by Tuesday of next week with a gradual warming and moistening trend.

Fire Weather:
Lack of widespread rainfall over the past several weeks and intense heat has allowed vegetation to dry. Incoming frontal boundary this weekend will spread gusty winds and a drier air mass over the region. KBDI values range from 500-750 across many of the SE TX counties suggesting fire weather conditions could be near critical under the right weather conditions. For now it does not appear that wind speeds will reach Red Flag criteria on Saturday or Sunday and the onset of the drier air mass does not happen until after the stronger post frontal winds decrease. With that said, wildfire danger will be elevated from Saturday-early next week.

90L:
Weak low pressure is located over the northern Gulf of Mexico south of the AL/MS coast this morning. Numerous thunderstorms have develop well to the S and SW of this feature over the north-central Gulf of Mexico. This system is along the far SE edge of the ridge of high pressure over W TX which is producing a degree of N/NE wind shear across the system and preventing much development. Global models are in some agreement that the system may attempt to develop into a tropical cyclone as it moves southward and then ENE or NE this weekend ahead of the incoming frontal boundary across the western Gulf of Mexico. At this time, this system poses no threat to the TX coast.

[srainhoutx]

The pre frontal trough should sweep through most of the area in the early morning hour of Saturday. It appears the actual front will lag behind by about 6-8 hours. Increasing northerly winds and drier air should be the theme for the weekend and a few spots could see some lows in the low 60’s Monday morning. The front will not linger, so enjoy the weekend.

Looking ahead to later next week, the GFS and Euro are very suggestive of deep tropical moisture pooling across the Western Gulf as a return flow from the Gulf becomes re established. If guidance is correct, rain chances could increase by next Friday as an inverted trough/weakness develops across the Southern half of the Lone Star State and may well bring some badly needed rainfall to the area once again.

[srainhoutx]

The front is progressing nicely through the Panhandle at this hour...

[unome]

check it out here: http://hint.fm/wind/ it updates at the top of the hour

[srainhoutx]

Good morning. The cool front is nearing the Houston Metro and has just passed Bryan/College Station as of 11Z...

[ticka1]

srainhoutx can you post the link to the map showing temps and wind change for texas so i can save it on my ipad? thank you

[srainhoutx]

srainhoutx can you post the link to the map showing temps and wind change for texas so i can save it on my ipad? thank you

Here you go, ticka1. The wind just shifted out of the NNW at my location as well...

http://weather.rap.ucar.edu/surface/dis ... duration=0

[JackCruz]

Wow...it feels amazing outside. I don't want any weather over 92 degrees again for a longgggggggg time. Amazing weather in Houston. I can't wait for winter and all the winter warnings we'll have

[srainhoutx]

After a few days of cool nights and warm days, moisture returns to The Lone Star State as the 'cool front' washes out and deeper moisture pools in the Western Gulf. By Thursday, PW's should near the 2.0 range and a return flow will be estblished with increasing chances of showers and perhaps a few storms as well. There are differences between the GFS and the Euro as to just how far S the next front will push. The GFS is a tad more agressive with the next frontal boundary and 'wetter' while the Euro is slower and stalls the front to our N. After a period when many have seen little in the way of rainfall, a return to a bit 'wetter' pattern would be welcome for many.The next 'front doesn't look strong enough to make it this far S, so enjoy the cooler weather while it lasts. Sunday night could be one of those open the windows type of evenings we enjoy in Central/SE Texas in September...

[SusieinLP]

Quite a difference between Conroe and La Porte. 72 here 57 there. 66 dew point here and dew point in the 50s there....still feels nice, though

[srainhoutx]

MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
246 PM EDT SUN SEP 09 2012

VALID SEP 09/1200 UTC THRU SEP 13/0000 UTC


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

FINAL 12Z MODEL EVALUATION INCLUDING THE ECMWF

INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY IMPACT THE
LARGE SCALE FORECAST.


...BROAD LOW DEVELOPING OVER TEXAS/WESTERN GULF STATES...

PREFERENCE: BLEND OF 12Z GFS/12Z ECMWF
CONFIDENCE: AVERAGE

A SHORTWAVE RIDGE CENTER WILL REDEVELOP EASTWARD FROM THE ROCKIES
INTO THE MIDWEST. THIS LEAVES AN OPPORTUNITY FOR A WEAK DEPRESSION
IN THE HEIGHT FIELD TO FORM BENEATH THE RIDGE...GENERALLY FROM
TEXAS INTO THE SOUTHERN MISSISSIPPI RIVER VALLEY. THE MODELS
ADVERTISE THIS DEPRESSION TO BECOME WEAKLY DEFINED AS AN UPPER LOW
BY WEDNESDAY...AS VARIOUS SHEAR AXES DRIFT TOWARD ONE ANOTHER AND
BEGIN TO INTERACT. DETAILS VARY AMONG THE MODELS. THE 12Z NAM
SOLUTION IS WITHIN REASON...THOUGH IT MAY BE OVERDEVELOPED WITH A
VORTICITY LOBE IN THE GULF. THE 12Z GFS LOOKS MOST LIKE THE GEFS
MEAN AND EC ENSEMBLE MEAN...WITH ALL GENERALLY INDICATING A CENTER
OF CIRCULATION OVER LOUISIANA. THE 12Z UKMET AND CANADIAN MODELS
HAVE A REASONABLE SHAPE TO THE LOW...BUT HAVE MOVED IT FARTHER
EAST...AND AWAY FROM THE ENSEMBLE MEANS. THE 12Z ECMWF BETTER
SUPPORTS OUR THINKING TO KEEP THE LOW CENTER NEAR LOUISIANA UNTIL
THE FRONTAL SYSTEM ENTERING THE PLAINS COMES ALONG IN THE MEDIUM
RANGE. CONFIDENCE IS NOT HIGH IN THE DETAILS...BUT PREFER TO SIDE
WITH THE GFS/ECMWF...WHICH ARE CLOSER TO THE MEANS AND NEAR THE
MIDDLE OF THE OVERALL GUIDANCE.

[srainhoutx]

Morning e-mail from Jeff:

A refreshing change to the local weather this weekend as a cold front moved across the area Saturday.

Cool and dry morning in progress with lows into the upper 50’s and 60’s across the area under calm winds. Surface high responsible for the break in the late summer heat will be shifting eastward allowing onshore (ESE) winds to return by late Tuesday. Deep tropical moisture is lurking over the southern Gulf of Mexico and will make a return to the area starting on Wednesday. Noticeable change will be the increase in humidity and cloud cover followed by increasing rain chances. GFS 00Z run from yesterday evening has come in wetter in the Thurs-Fri time period with rain chances in the solid 40-50% range.

Another upper air trough and cold front will swing toward the area this next weekend, but the push behind this feature looks weaker than the one that just passes on Saturday. Still with tropical moisture in place, showers and thunderstorms should continue along and ahead of the slowing boundary into at least the first half of the weekend. While moisture and humidity will be returning by mid week, high temperatures do not warm much with lowered mid level heights and increasing cloud cover. We might just be done with the really oppressive heat of the summer…highs near 100.

[srainhoutx]

The 12Z suite of guidance still suggests some differences, but rain chances still look like a good bet beginning Wednesday and increasing into Friday. The GFS is the most aggressive with bringing a weak frontal boundary through SE Texas and stalling it offshore and remains rather wet. The Euro is still much slower with that boundary and virtually stalls it on top of SE Texas and keeps rain chances going throughout the coming weekend. The differences appear to be just how strong the short wave diving S from the Northern Plains will be as well as any meso features that cannot be determined at this range. What is interesting is the GFS suggests a rather wet pattern becoming established that may last until the end of September. We’ll see how all this shakes out over the next couple of days as the GFS Ensembles are rather suggestive of a general 1-2 inch rainfall with some potential for isolated higher amounts closer to the Coast. It is also noteworthy that the GFS and the Euro both agree that some areas of the Lone Star State that have been rather dry will have a fairly good chance of receiving some very beneficial rains.

[srainhoutx]

There still remain some differences between the overnight guidance, but the trend is looking a bit more favorable for rain chance increasing Thursday and extending into the weekend. The GFS and Euro are in some what better agreement regarding the potent short wave and mid latitude trough diving SSE into the Eastern US on Friday. A strong 500mb upper low develops over the Ohio Valley and the attending ‘cold front’ drops S into the Lone Star State. The potent short wave drops S into Texas and slowly meanders E providing lift in an unstable air mass with increasing moisture as the Gulf opens with a return flow. The fly in the ointment will be just where this boundary stalls. Another new wrinkle is a potential surface low developing in the Western Gulf that the Canadian, and to a weaker extent, the Euro are ‘sniffing’. The GFS does not show this feature, but does suggest lowering pressures in the Gulf, so that bears watching as well. All in all it does appear that some beneficial rains are ahead and we’ll need to monitor for any potential development in the Gulf. Stalled boundaries and lowering pressures in the Gulf always raise an eyebrow or two when we enter the month of September.