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

[Ounce]

I'm just wondering if there's any cooler air up in Alaska that's going to get released for a cooler snap in SE Texas in 2 weeks?

[Belmer]

I'm just wondering if there's any cooler air up in Alaska that's going to get released for a cooler snap in SE Texas in 2 weeks?

Not very likely. Temps in Alaska right now are running somewhat average (mid 50s or so). Next week a storm is expected to come through dropping temps into the lower 40s with Fairbanks seeing its first snow of the season possibly by next weekend. However, as of now, no huge drop in temps for us folks in south TX. We should stay in our mid to upper 80s with a few places reaching lower 90s.

[Portastorm]

I'm just wondering if there's any cooler air up in Alaska that's going to get released for a cooler snap in SE Texas in 2 weeks?

Not very likely. Temps in Alaska right now are running somewhat average (mid 50s or so). Next week a storm is expected to come through dropping temps into the lower 40s with Fairbanks seeing its first snow of the season possibly by next weekend. However, as of now, no huge drop in temps for us folks in south TX. We should stay in our mid to upper 80s with a few places reaching lower 90s.

The 0z GFS shows a swath of below to well below normal temps from Alaska across the Canadian prairies into the Great Lakes region in the 11-15 day period. But as Belmer indicated, it doesn't appear like south central and southeast Texas will be the recipient of that "air" in the next two weeks.

Edit update: The 12z GFS continues the trend, and in fact, shows a strong Canadian cold front coming down into the southern Plains/Texas late in the period (Oct. 6-8). We shall see.

[JackCruz]

There is some chatter on the accuweather forum about a possible mLa Nina redevelopment....Joe Bastardi tweeted something about one model going with a quick nino n then a la moms comeback. I hope this doesn't happen

[srainhoutx]

As we head toward the last week of September, another complicated and complex pattern is developing as rain chances once again enter the picture beginning Wednesday along our Coastal Counties. PW’s appear to increase to near the 1.8 range as a return flow becomes established and tropical moisture begins to pool across the Western Gulf.

Along the West Coast of Mexico, Hurricane Miriam will begin to turn N to NNE as an advancing trough and 500mb upper low develops off the California Coast. A series of short waves (upper air disturbances) begin to enter the picture on Thursday and tap into that mid/upper level moisture associated with Miriam and the 500mb low begins to slowly meander E across the Four Corners Regions on Thursday/Friday and the onshore flow across Texas increases with PW’s nearing the 2.2 range by Friday. Showers/storms appear rather likely in the 50%+ range at this time. The fly in the ointment will be just how quickly all these feature move along to our E. The GFS appears to be too aggressive and ends rain chances Saturday evening, while the ensembles and the operational Euro and Canadian are slower suggesting rain chances continue into Sunday and even Monday.

While it is too far out to know with any certainty, all and all it does appear that some remnants of Miriam and a myriad of upper air disturbances will enter the picture as an active period weather wise replaces the pleasant pattern of the past week and ½.

[srainhoutx]

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
959 AM EDT MON SEP 24 2012

VALID 12Z FRI SEP 28 2012 - 12Z MON OCT 01 2012

...SYNOPSIS...

WHAT AMOUNTS TO SPLIT FLOW WILL CONTINUE THROUGH THE MEDIUM
RANGE...IN THE AREA BETWEEN A STRONG TROUGH IN THE GULF OF
ALASKA...AND MEAN TROUGH IN EASTERN NORTH AMERICA. THE SOUTHERN
STREAM IS MORE WEAKLY DEFINED...BUT WILL DRIVE MUCH OF THE
PRECIPITATION IN THE FORECAST. DEEP MOISTURE REMAINS CONFINED TO A
FRONTAL ZONE STRETCHING FROM THE DESERT SOUTHWEST...TO THE
SOUTHEAST STATES...CURVING UP OFF THE NEW ENGLAND COAST. HURRICANE
MIRIAM IN THE EASTERN PACIFIC WILL SEND INCREASING MID LEVEL
MOISTURE DOWNSTREAM TOWARD WEST TEXAS/SOUTHERN NEW MEXICO...AND
MOISTURE ACCOMPANYING THE CIRCULATION CENTER WILL EVENTUALLY
INCREASE TOWARD AZ/NM AS THE CYCLONE LIFTS AHEAD OF A SOUTHERN
STREAM TROUGH.

...NORTHERN STREAM...

A SHORTWAVE TROUGH WILL MOVE THROUGH THE MEAN RIDGE POSITION IN
WESTERN CANADA BEFORE DROPPING INTO THE MEAN LONGWAVE TROUGH
POSITION FARTHER EAST. THIS WAS EARLIER THOUGHT TO KICK/WEAKEN THE
LONGWAVE TROUGH...BUT OPERATIONAL RUNS HAVE SHOWN A TREND TOWARD
MORE OF A RE-LOADING PROCESS SINCE THE 12Z/23 CYCLE. LOW LEVEL
FORCING WILL BE HAMPERED AS THE AMPLIFYING SHORTWAVE MOVES ATOP
GENERALLY STABLE AND DRY AIR OVER EASTERN NORTH AMERICA...BUT
CYCLOGENESIS COULD OCCUR CLOSE ENOUGH TO SHORE TO BRING BRING A
PRECIPITATION EVENT TO NEW ENGLAND BY DY 6/7.

...SOUTHERN STREAM...

AWAY FROM NRN STREAM FLOW... DIFFUSE ENERGY OVER THE WEST IS FCST
TO DRIFT ACROSS THE PLAINS TOWARD THE MS VLY. THIS PATTERN WILL
SEE A FRONTAL ZONE LAY OUT WEST TO EAST...EXTENDING FROM THE
SOUTHERN ROCKIES TO THE EAST COAST. THE ZONE MAY SAG AS INDIVIDUAL
WAVES ALOFT AND PRECIPITATION FORCE THE BOUNDARY SOUTHWARD.
MEANINGFUL DIFFS EXIST AMONG MODELS AND ENSEMBLES FOR EACH
SIGNIFICANT FEATURE SO OVERALL CONFIDENCE IN THE SPECIFICS OF THE
MEDIUM RANGE FCST IS AVERAGE TO BELOW AVERAGE. INCREASINGLY
MOIST/HIGH PW ENVIRONMENT OWING TO HURRICANE MIRIAM RAISES THE
POSSIBILITY OF SOME LOCALLY HEAVY RAINS ALONG THE FRONT.

...MODEL CHOICE...
PREFER A 00Z GFS/ECMWF BLEND IN EASTERN NORTH AMERICA TO REFLECT
AN INTERMEDIATE SOLN FOR THE CLOSED LOW AND ACCOUNT FOR TENDENCY
OF OPERATIONAL MODELS TO HAVE A BETTER HANDLE ON DETAILS VERSUS
ENSEMBLE MEANS EARLY IN THE PERIOD. SFC IMPACT BECOMES
INCREASINGLY UNCERTAIN BY DAYS 6-7 SUN-MON. CURRENTLY ENSEMBLE
MEANS INCL THE 12Z CANADIAN MEAN KEEP ANY SFC LOW PRES OFFSHORE
VERSUS THE 00Z ECMWF AND EVENTUALLY GFS WHICH WRAP LOW PRES
INLAND. FOR NOW WILL FAVOR THE ENSEMBLE MEAN SCENARIO FOR DAYS
6-7 BUT WITH LOW CONFIDENCE... BASED ON POSITIVE HGT ANOMALIES
FCST OVER ERN CANADA LATE IN THE PERIOD NOT BEING VERY SUPPORTIVE
OF A VERY DEEP MID LVL LOW SO CLOSE TO THE S AS DEPICTED IN THE
GFS/ECMWF.

ACROSS THE SRN TIER THE GFS APPEARS TOO FAST/STG WITH ITS SYSTEM
THAT STARTS OVER THE SRN PLAINS. THE 00Z ECMWF IS SLOWER AND
SUPPORTED TO SOME EXTENT BY THE ENSEMBLE MEANS.

BASED ON THE ABOVE CONSIDERATIONS AND GFS/ECMWF PREFS IN THE SHORT
RANGE... THE DAYS 3-5 THU-SAT FCST STARTS WITH A GFS/ECMWF BLEND
WEIGHTED SLIGHTLY MORE TOWARD THE ECMWF DUE TO QUESTIONABLE
HANDLING OF THE GFS WAVE STARTING OVER THE PLAINS DAY 3. THE LACK
OF CONFIDENCE IN DAYS 6-7 DETAILS OVER/NEAR NOAM LEAD TO FAVORING
A SOLN CLOSE TO AN EVEN BLEND OF THE 00Z GEFS/12Z ECMWF ENSEMBLE
MEANS.

BURKE/RAUSCH

[srainhoutx]

HGX is beginning to ramp up the chatter regarding the late week/weekend pattern. I would expect the HPC to slowly increase the QPF forecast over the next couple of days as well. The upcoming pattern is not all that different from what we experienced a week and 1/2 ago where some folks saw some much needed rainfall while others received little.

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
448 AM CDT TUE SEP 25 2012

.DISCUSSION...
ONE MORE FAIR WEATHER AND UNSEASONABLY WARM DAY CAN BE EXPECTED
ACROSS SE TX AS A HIGH PRESSURE RIDGE CONTINUES OVERHEAD. OVER THE
NEXT FEW DAYS THE MODELS ARE CONSISTENT IN PUSHING THE RIDGE EAST
AND SOUTH WHILE AN UPPER LEVEL LOW PRESSURE AREA DEEPENS OVER THE
ROCKIES AND BEGINS TO MOVE EASTWARD. MOISTURE ALONG AND AHEAD OF
THE TROUGH WILL BE ENHANCED FROM TROPICAL MOISTURE STREAMING
NORTHEASTWARD FROM MARIAM OFFSHORE OF THE BAJA CA COAST. ALTHOUGH
THE MODELS ARE CONSISTENT IN THE DEVELOPMENT AND MOVEMENT OF THE
UPCOMING SYSTEM...THEY ARE NOT IN AGREEMENT WITH THE TIMING. THE
GFS IS A BIT FASTER THAN THE ECMWF. THIS FORECAST TAKES IN ACCOUNT
A SLOWER SOLUTION LATE IN THE WEEKEND BUT LEANS HEAVILY TOWARD
THE GFS.

AS FOR DETAILS...MOISTURE ADVECTION WILL HELP TEMPER THE
TEMPERATURES AND PROVIDE A SLOW INCREASE IN THE CLOUD COVER TODAY
AND WEDNESDAY. THE RIDGE ALOFT HANGS AROUND LONG ENOUGH TO KEEP
THE DEEPER LAYER MOISTURE OUT OF THE AREA UNTIL FRIDAY. THE
CURRENT MODEL ACTUALLY AGREES FAIRLY WELL WITH THE CURRENT
FORECAST EXCEPT FOR A BIT LESS COVERAGE ON FRIDAY. THE ARRIVAL OF
THE TROPICAL MOISTURE ALOFT WILL COINCIDE WITH THE GULF MOISTURE
TO BRING THE BEST CHANCES AND MOST COVERAGE LATE FRIDAY INTO
SATURDAY. THE GFS ACTUALLY RAISES PW/S INTO THE 2 TO 2.5 INCH
RANGE OVER THE CENTRAL AND SOUTHERN COUNTIES FRIDAY NIGHT INTO
SATURDAY EVENING. IF THIS TREND CONTINUES...THE POTENTIAL FOR
LOCALLY HEAVY RAINFALL MAY DEVELOP AND WILL ADDRESS THIS CONCERN
OVER THE NEXT DAY OR SO IF NEEDED. THE MODELS END THE RAINFALL
CHANCES BY LATE SUNDAY.

[srainhoutx]

Morning e-mail from Jeff:

After over a week of nice fall weather, changes are on the way.

High pressure aloft over the region and ridging SW from the eastern US has kept a fairly dry and warm air mass in place for the past several days. However high pressure at the surface is moving eastward and low pressure is developing in the lee of the Rockies ahead of a slow moving upper level trough over the SW US. This is resulting in an increase in the southerly flow and slight increase in surface moisture. At the same time powerful Hurricane Miriam is moving NW off the western coast of MX under the influence of ridging over N MX and the developing trough over the SW US. High level moisture plume is clearly noted extending NE from the circulation of Miriam spreading ENE to NE into central MX and toward the TX border.

Parameters are slowly coming together for a period of very wet weather Fri-Sun as the upper trough over the SW US interacts with eastern Pacific hurricane Miriam. The overall setup will likely produce an excessive rainfall event for some location across the state of TX late this week/this weekend. Current upper level trough will slow with lift reaching TX by late this week, while both Gulf and mid/high level moisture increase across the area as Miriam sheds moisture and energy NE. PWS increase toward 1.5 inches on Thursday and 2.0 inches by late Friday and then into the 2.0-2.4 inch range on Saturday with soundings becoming increasingly saturated. Upper level jet dynamics come into play by Friday as a 250mb jet streak is progged over NC TX increasing large scale lift over C and SE TX. Expect to see scattered showers and thunderstorms develop and move inland along the TX coast with more organized rainfall over C and N TX on Friday. With moisture levels running very high expect areas of very heavy rainfall.

Upper trough and moisture plume from Miriam sag eastward over the weekend with SE TX coming increasingly under the influence of both the lifting by the trough aloft and high level moisture/energy from the tropical system. Expect more widespread and organized rainfall potential Saturday into Sunday. With moisture levels in the “excessive” range heavy rainfall is likely, but at this time there is no well defined surface boundary to focus/anchor convection at least not at the present time. One would think that with upstream convection some sort of outflow boundary could/would be present on the following days and this potential will need to be watched.

Since we are still over 48 hours from the onset of any event, there is plenty of time to fine tune and nail down the location that looks most favorable for heavy rainfall. Only recently have model guidance come into decent agreement on the phasing of the moisture of Miriam and the upper level trough so some additional changes are likely.

[srainhoutx]

Morning e-mail from Jeff:

Widespread rainfall event increasingly likely this weekend

Ingredients continue to come together for a period of wet weather from Friday-Sunday. Moisture is returning to SE TX this morning as noted by the isolated inland moving showers on radar over the coastal waters into the coastal and inland first tier counties. These showers appear to be in response to a sliver of higher moisture being transported northward on increased southerly flow of the past 48 hours. With a little heating this morning expected a continuation of these showers today.

Of more importance is the late week period into the weekend as parameters are coming together to produce a potential widespread rainfall event. Low pressure formation ahead of a deepening SW US trough will help transports low level tropical moisture over the southern Gulf of Mexico northward into the region starting Thursday. May see slightly better rain chances on Thursday than currently being indicated, but the better chances should hold off until Friday when the tropical moisture reaches the area. Expect numerous showers and thunderstorms on Friday pulling northward off the western Gulf of Mexico. At the same time, mid and high level moisture is already spreading NE across MX into TX from EPAC tropical system Miriam. This moisture along with the increasing Gulf moisture will become entrained in the slow moving trough producing widespread rainfall from SW TX into E TX over the weekend.

Surface frontal boundary currently over NW TX will only slowly drag SE over the next 2 days and gradually enter the area early Saturday…more importantly this boundary adds a focus for deep convection that was largely absent yesterday in the model guidance. This change does raise some concern for more significant rainfall over the weekend as the slow moving trough, a slow moving surface boundary, saturated air column, and extremely high moisture levels (PWS 2.2-2.4 inches) all combine to produce some very heavy rainfall. Still not overly confident on where the heavy rains will set up although the southern half of TX appears to be in the best location south of the 250mb jet streak and near/south of the surface boundary. The “tropical like” air column will support some very heavy rainfall rates in a short period of time and this will need to be watched especially if any cell training or slow storm motions are noted. Would not at all be surprised to see some 2-3 inch per hour rainfall rates with this set up. Models are really keying in on Saturday afternoon-Sunday morning as the best time for organized heavy rainfall spreading from SW to NE across the region.

[srainhoutx]

This is looking more and more like the event we experience during mid September where areas of Central Texas saw some isolated 8 inch amounts and NW Harris County receive 6+ inches while areas down S in Galveston/Brazoria Counties saw little if any rainfall. Perhaps the areas that have been lacking will benefit this time around. The fly in the ointment is the lack of a stronger frontal boundary as a focal point close for our part of the world and as always, any meso features that cannot be forecast at this range.

HPC:

DAYS 2 AND 3

...CENTRAL/SRN PLAINS TO TN VLY/SRN OH VLY...

AS MENTIONED ABOVE... A QUASI-STATIONARY FRONT WILL BE THE MAIN
FOCUS FOR QPF ON THURS AND FRI. THIS FRONT WILL GRADUALLY PRESS
SOUTH FROM THE CENTRAL PLAINS/MID MS VLY AND OH VLY INTO THE
CENTRAL PLAINS AND TN VLY... WHILE SIGNIFICANT MOISTURE POOLING IS
ANTICIPATED OVER TX/SRN PLAINS FOR FRI. THE FOCUS ON THURS WILL BE
WITH A MID-LEVEL DISTURBANCE SLIDING FROM CO TO THE CENTRAL PLAINS
OR ALONG THE FRONTAL BOUNDARY AND GRADUALLY DECAYING... WHILE
MID-LEVEL VORTICITY AHEAD OF ERN PAC TROPICAL ENTITY MIRIAM
ADVECTS INTO WEST TX. A SOLID SURFACE RIDGE OVER THE SOUTHEAST
WILL ALLOW DEEP SERLY FLOW FROM THE GULF OF MEXICO TO RETURN NORTH
INTO TX AND KS/OK AND INTERACT WITH FEATURES FOR ORGANIZED
SHOWERS/STORMS. THIS APPEARS LIKELY ACROSS WEST TX INTO OK/KS AND
DOWNSTREAM INTO SRN MO/NRN AR... ESPECIALLY NEAR THE DECAYING
MID-LEVEL VORT TRACKING SOUTH AND EAST ALONG THE FRONTAL ZONE OR
FROM WRN TO SOUTH CENTRAL KS. THE MOISTURE POOLING REALLY BECOMES
ANOMALOUS ON FRI... AS THE GLOBAL MODELS SUGGEST PWS INCREASING
SIGNIFICANTLY TO AOA 2.25 INCH PWS ACROSS TX. THIS IS WHEN THE
FRONT WILL DRIFT SOUTH SOME AND THE MID-LEVEL FEATURES BLEND WITH
EACH OTHER FOR RATHER ORGANIZED HEAVY RAINFALL ACROSS WRN/CENTRAL
TX INTO OK AND POSSIBLY SPREADING DOWNSTREAM WITH THE WSWRLY 850MB
FLOW INTO THE TN AND SRN OH VLY. HPC GENERALLY FOLLOWED THE
OPERATIONAL ECMWF AS A BASE FOR THE QPF FCST WITH ADDITIONAL
GUIDANCE FROM THE GFS AND INTERNAL PSEUDO BIAS CORRECTED GUIDANCE.

[spadilly]

looks like rain at my A&M tailgate this weekend

[srainhoutx]

The HPC seems to believe the Euro may be more correct in handling the upper air pattern and various disturbances at the lower and upper levels and are not confident in the various GFS solutions due to convective feedback issues. The 12Z Euro suggests some fairly significant rainfall totals with increasing coverage during the day on Saturday and develops a coastal low very near the Matagorda Bay area before existing E on Sunday. Should that scenario develop, Saturday night could provide for some heavy rainfall potential. We will see.

MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
256 PM EDT WED SEP 26 2012

VALID SEP 26/1200 UTC THRU SEP 30/0000 UTC

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

12Z NAM/GFS EVALUATION INCLUDING THE ECMWF AND PREFERENCES

...FRONTAL ZONE EXTENDING FROM THE GREAT LAKES INTO THE CENTRAL
PLAINS...

MODELS SHOW GOOD LARGE-SCALE AGREEMENT WITH THE TIMING AND
STRENGTH OF THIS FRONT.

...CLOSED LOW OVER THE CENTRAL ROCKIES...

PREFERENCE: EQUAL BLEND OF THE OPERATIONAL ECMWF AND ITS OWN
ENSEMBLE MEAN
CONFIDENCE: AVERAGE

THE NAM DEPICTS THE CENTER OF THE LOW 40-50 NM EAST NORTHEAST OF
THE ACTUAL CENTER AND APPEARS STRONGER THAN INITIALIZED...WHILE
THE GFS APPEARS TO INITIALIZE THE BEST AND IS SUPPORTED BY THE NEW
ECMWF. REGARDING MODEL DIFFERENCES...THE NAM BECOMES
PROGRESSIVELY SLOWER ENTERING THE SOUTHERN PLAINS COMPARED TO THE
GFS AND 00Z ECMWF...WITH ITS SLOWER MOVEMENT PARTIALLY DUE TO
WORSE INITIALIZATION AND SUSPICIOUSLY SLOW INTERACTION WITH MID
LEVEL PORTIONS OF WEAKENING TROPICAL STORM MIRIAM IN THE PACIFIC.
AMONG THE REMAINING SOLUTIONS...THE GFS AND ECMWF ARE MOSTLY
SIMILAR...EXCEPT BOTH APPEAR TO SUFFER FROM EPISODES OF CONVECTIVE
GRID-SCALE FEEDBACK WITH THE GFS THE WORST...WHICH IS MOST
NOTICEABLE OVER TEXAS BY LATE SATURDAY. FOR THESE
REASONS...THROUGH A PROCESS OF ELIMINATION THE ECMWF APPEARS TO
PROVIDE THE BEST STARTING POINT TO THE FORECAST...BUT IT MAY BE
MORE PRUDENT TO BLEND ITS FORECAST WITH ITS OWN ENSEMBLE MEAN TO
ADDRESS THE GROWING SOLUTION SPREAD...PARTICULARLY BY FRIDAY.

[wxman57]

12Z GFS still not very bullish on any heavy rain here, though it's now forecasting a little over an inch of rain on Saturday - which is way higher than it was forecasting 24 hrs ago (a tenth of an inch or so). Not looking like a good weekend to be outdoors. Got in 100 miles of biking last weekend, though.

[Katdaddy]

A wet weekend continues to look possible which we need:

THE GFS AND ECMWF AGREED BETTER FOR THE UPCOMING RAIN EVENT. BOTH
DEVELOP A SURFACE FRONT/TROUGH OVER THE INLAND AREAS FRIDAY NIGHT
AND SATURDAY AS A SURFACE LOW DEVELOPS OVER SOUTH TEXAS AND MOVES
UP THE COAST. WIDESPREAD RAIN AND THUNDERSTORMS LOOK LIKELY ON
SATURDAY WITH THE BEST CHANCES DURING THE AFTERNOON AND EVENING.
PW/S REACH INTO THE 2 TO 2.25 INCH RANGE...INDICATING THE
POTENTIAL FOR LOCALLY HEAVY RAINFALL. THE ECMWF IS NOW A BIT
SLOWER IN ENDING THE RAINFALL ON SUNDAY THAN THE GFS.

[jasons2k]

I hope I get nailed this time. I really do but I'll believe it when I see it. I feel like Harold Taft and his famous quote: "Never forecast snow in Texas until you see it falling outside your window" except replace snow with rain...hehe.

[srainhoutx]

I hope I get nailed this time. I really do but I'll believe it when I see it. I feel like Harold Taft and his famous quote: "Never forecast snow in Texas until you see it falling outside your window" except replace snow with rain...hehe.

We have a dinner party planned Saturday evening. Book it...

HPC:

DAYS 2 AND 3

...SRN PLAINS/LWR MS VLY TO TN VLY/SOUTH...

A LARGE SCALE AND WIDESPREAD RAIN EVENT APPEARS LIKELY ACROSS
TX/OK AND SPREADING DOWNSTREAM TOWARDS THE LWR MS VLY INTO THE
SOUTH ON FRI AND SAT. THE COMBINATION OF MERGING UPPER DYNAMICS
FROM CO AND MEXICO WILL INTERACT WITH THE QUASI-STATIONARY FRONT
AND A SIGNIFICANT INCREASE AND ANOMALOUS BATCH OF DEEP TROPICAL
MOISTURE WILL SPELL HEAVY BUT MOSTLY BENEFICIAL RAINFALL. THE
FOCUS ON FRI WILL BE NEAR THE FRONT BASED WEST TO EAST FROM OK TO
TN... AS UPPER HEIGHTS LOWER WITH VORTICITY SLIDING SOUTH AND EAST
FROM WRN KS TO OK/NRN TX... AND ACROSS WEST CENTRAL TX AS POSSIBLE
TROPICAL MID-LEVEL DYNAMICS SLIDE NORTH AND EAST FROM MEXICO. AS
THIS OCCURS... DEEP SERLY FLOW FROM THE GULF OF MEXICO WILL
INCREASE MOISTURE CONTENT FROM 1.5 TO 2 INCH PWS ACROSS TX AND
KEEP 1.75 INCH PWS INTACT NEAR THE FRONTAL BOUNDARY. EXPECT 1 TO 2
INCH QPF AMOUNTS WITH LOCALLY HEAVIER AMOUNTS ACROSS WEST CENTRAL
TX AND UP TO 1 INCH AMOUNTS FROM SWRN KS THROUGH OK INTO NRN AR
AND MUCH OF TN. THEN ON SAT... A POSSIBLE WAVE DEVELOPS ALONG THE
FRONT THAT SLIDES ACROSS TX AND THE DEEP TROPICAL MOISTURE BEGINS
TO ADVECT DOWNSTREAM TOWARD THE LWR MS VLY AND DEEP SOUTH. ONCE
AGAIN... EXPECT WIDESPREAD HEAVY RAIN WITH A VERY SLIGHT CHANCE OF
EXCESSIVE AMOUNTS FROM CENTRAL TO SERN TX ON SAT... AS A LARGE
PLUME OF 2.25 INCH PWS IS AOA THE WAVE AND FRONTAL ZONE. THE
MODELS GENERALLY SHOW THIS BUT ALSO POTENTIAL FEEDBACK... HPC
ATTEMPTED TO ELIMINATE THE FEEDBACK WHILE FOLLOWING A BLEND OF THE
ECMWF/GFS FOR QPF AMOUNTS OR 1 TO 3 INCHES FROM CENTRAL TX TO SRN
LA/MS.

[wxman57]

I hope I get nailed this time. I really do but I'll believe it when I see it. I feel like Harold Taft and his famous quote: "Never forecast snow in Texas until you see it falling outside your window" except replace snow with rain...hehe.

Back when I was in school (A&M) around 1979, I spent the summers at my father's house in Ft. Worth. Had a friend (fellow met student at A&M) who's father worked at KXAS. We went over to the station to meet Harold Taft and watch him prepare for his weathercast. He made his own charts with large U.S. maps and colored chalk. A true artist.

As for this weekend, the new GFS bumps up the rain to about 1.75" during the day on Saturday. Heaviest rain indicated from mid morning to late afternoon.

[srainhoutx]

Morning e-mail from Jeff:

Active weather period expected Friday-Sunday.

Upper level storm system over the western US will move slowly eastward into TX over the next 48-72 hours. High pressure aloft will be pushed southward and at the surface eastward allowing a more favorable influx of both Gulf and Pacific moisture and lowering heights aloft. General subsidence will be replaced with general lift as the upper trough and impulses rotating around the trough move into the state. Increasing moisture today will likely cause a few streamer showers west of I-45 and south of I-10 similar to yesterday. Rain chances begin to creep upward on Friday as surface high shifts eastward allowing the pool of deep tropical moisture over the southern Gulf of Mexico to surge northward. At the same time mid and high level moisture from weakening tropical system Miriam will move across TX from the SW. With the air column becoming increasingly saturated and hard to time or ill defined disturbances approaching from the SW by midday Friday expect showers and thunderstorms to begin to develop and overspread the region from the Gulf waters. Coverage should be on the lower side for most of Friday, but where it rains it will be heavy.

Main event looks to be Saturday into Saturday night as the main upper trough ejects into SW TX and forces surface low pressure formation over SW TX. GFS/ECMWF/NAM model all generally agree on the development of thunderstorms over SW TX late Friday night/early Saturday in a region of strong lift ahead of the upper trough which then moves eastward across SC TX on Saturday. GFS and NAM QPF bullseyes suggest some sort of MCS feature may develop and track ESE toward the middle TX coastal plain by Saturday evening. Air mass ahead of the upper trough and surface low completely saturates with PWS pushing 2.3 inches and favorable low level inflow. The extreme moisture levels (pushing 2 std above early October normals) combined with slow moving organized thunderstorms raises flash flooding red flags. Given the saturated air column warm rainfall production will be likely with little dry air entrainment leading to excessive short term rainfall rates. Tropical like MCS systems tend to slow in the overnight hours some especially as they near the TX coastal plains where the low level inflow increases after dark and this raises the threat for extended heavy rainfall into Sunday morning.

Both models agree that the best lift and rainfall will be focused south of I-10 and west of I-45 or toward the coastal bend into our SW counties where the models are showing the greatest QPF. While the models are in agreement on this placement, that does not mean that is where the threat will be greatest and it is possible that more of the area could be under the gun Saturday night for excessive rainfall. Will likely not be able to firm the threat area up any more than broadly prior to Saturday morning. Widespread rainfall amounts of 2-3 inches are likely with isolated amounts of 4-5 inches especially over those SW counties. Given the moisture profiles I would not be surprised to see a few locations pick up a quick 6-8 inches but these should be fairly small is spatial coverage…hopefully. Grounds are generally dry over much of the area and will be able to handle much of this rainfall, but urban areas will respond quickly to the high short term rates and some flooding or ponding is likely where rainfall rates exceed 1.5 inches in less than 30 minutes. While widespread rains are likely, most rivers are at or below base flow levels, so there is plenty of capacity to handle the expected amounts of run-off.

[Canebo]

I hope I get nailed this time. I really do but I'll believe it when I see it. I feel like Harold Taft and his famous quote: "Never forecast snow in Texas until you see it falling outside your window" except replace snow with rain...hehe.

I know the feeling and couldn't agree more. Those of us who have missed out lately really need something good from this system!
I am going to wash the car and plan a BBQ for Saturday. At least I can say I put in the effort!

[wxman57]

Looking like widespread 1-2" of rain on Saturday. Latest GFS has just over 2" for IAH on Saturday. Close to 2" as far north as College Station. No biking for me on Saturday, that's for sure.