March: Warm Days To End The Month With Isolated Showers

[Ptarmigan]

Here's a meteogram based on the just-out 12Z GFS. Good weather for ducks this weekend, bad weather for any outdoor activities. Of course, it dries up and warms up AFTER the weekend. Guess it'll be a movies weekend for us vs. cycling.

Looks to be a rainy and stormy night. That means I will be awaken by thunder.

[srainhoutx]

The over night guidance has converged to a solution that suggest a more consolidated closed upper low solution represented by the Euro/UKMet/Parallel GFS 3D ~vs~ a GFS operational/NAM split or dual U/L solution lending credence to the non NCEP (American) guidance which would stall the U/L over New Mexico/TX Panhandle through Saturday. A very shallow cold front will approach the Houston Area over night tonight into Friday morning becoming stationary and acting as a focal point for rounds of very heavy rainfall through Sunday before lifting N decreasing rain chances as the U/L finally ejects NE.

The SPC has a Slight Risk for severe storms for portions of Central TX, mainly along and ENE of the I-35 Corridor for today and these storms will move into SE TX overnight tonight and likely transition to elevated storms on Friday-Sunday bring waves of potential training cells with very heavy rainfall along and N of the stalled boundary. While continuous rains seem unlikely, short wave energy that cannot be forecast well appear to be the trigger for bouts of rain chance and may be mesoscale driven as a weak surface low develops on Saturday near Corpus. The guidance does suggest a general 3-4 inch rainfall amounts with isolated 6-8 inch or higher for areas mainly N and E of Houston near the ARKLATX Region.

As HGX mentioned yesterday afternoon, there are some missing ingredients suggesting some bust potential and with lack of full model convergence, expect changes to the forecast with further 'fine tuning' over the next day or two. As we saw earlier the year, these U/L are a forecasting challenge at best and with a split flow and deep separation from the mean jet stream flow across the US/Canadian border, expect those changes. Stay tuned and we'll see what the afternoon guidance offers and watch develops in Central TX as storms begin to fire and move toward the area later today.

[MontgomeryCoWx]

[srainhoutx]

Morning e-mail from Jeff:

Short wave approaching the area from the southwest early this morning sparking a few thunderstorms.



And so it begins….large upper level storm system has dropped into the SW US and is becoming cut off from the main upper level flow over the US. At the surface a strong cold front is surging through NW TX while ahead of this feature a strong 40-55kt low level jet extends from the western Gulf across much of eastern TX. Corpus VAD data showing winds just off the surface of 40-50kts including around 56kt on the 600am sounding around 2500 ft. Some of the wind energy has been mixing down to the surface in the developing thunderstorms around the Victoria area this morning. Storms over Calhoun County WSW to near Alice, TX appear to be developing under the core of the low level jet and strong moisture convergence with the aid of a weak mid level short wave. No meso scale models showed this development this morning. Storm motions are toward the ENE to NE or generally up the US 59 corridor, but storms have thus far been weakening as they move across Wharton into Fort Bend Counties. These storms will be capable of producing brief very heavy rainfall and very strong winds of 50-55mph as they transport down the strong wind energy just above the surface.



Cold front will cross the area tonight and then stall over the coastal waters Friday. A shallow dense cold air mass will filter into the region behind this front while the upper level storm system over the SW US remains stalled. This will result in tremendous Gulf moisture advection northward over the surface cold dome Friday-Sunday. Incoming flow off the western Gulf will be very moist with PWS of 1.5-1.7 inches being forced up and over the surface cold dome…an overrunning event. This pattern in itself will linger widespread rains behind the front, although the short term models are showing more scattered nature type stuff on Friday versus widespread constant rains. Past event have been more scattered and will trend toward that thought for Friday.



Where things really start to get interesting is in the timing of the short waves (disturbances) ejecting out of the main upper level storm to our SW. Each disturbance will move across the area from SW to NE over the weekend and work with the moist air mass, stalled surface front, and favorable upper level divergence to produce periods of showers/thunderstorms. Still looks like the 850mb front will stall and become oriented SSW to NNE from NW of Victoria to near College Station to Texarkana and along and east of this feature appears to be where the greatest threat for training thunderstorms may be over the weekend. It is one of these event that will have to be watched hour by hour to see where and for how long any cell training sets up. Models are not able to always grasp the meso scale banding and boundaries that can set up and produce very heavy rainfall in a local area.



While the red flags are there for a heavy rainfall/flood event with this set up, I am not confident in the location nor the duration of any sustained training heavy rainfall which is typically what causes the most problems in this area. Moisture levels nearing the +2 SD for this time of year along with excellent inflow of rich moisture off the western Gulf, stalled surface and mid level synoptic scale boundaries, upper level flow parallel to the boundaries, and broad 250mb divergence are all pointing to training heavy rains. However this does not appear at this point to be a continuous rainfall event for the next 72 hours, but instead rounds of thunderstorms every 4-6 hours as the disturbances mentioned above eject across the region. The question then becomes how long does the heavy rainfall last with each round and how long are the breaks between rounds to allow rainfall to run-off and additionally does the heavy rainfall hit the same area each round. None of these questions can be answered more than about 12 hours out in this type of a pattern so it becomes a watch and see type situation.



Will continue with widespread rainfall amounts of 2-4 inches across the entire area with isolated totals of 5-6 inches especially north of I-10 and west of I-45. A few locations over E and NE TX could see totals even higher by Sunday evening. Will need to keep a very close eye on rainfall totals over the weekend and the run-off that is being generated. Flash Flood Guidance is in the 4-5 inch range for the 3 hr time period for nearly all of our SE TX counties…while this is high now, rains today and Friday will greatly reduce these values and saturate grounds, so it will be the rains over the weekend that will need to be watched. Long duration of the event and widespread nature suggest some rises on area rivers are likely going into the late weekend and next week. Given the amounts of rainfall forecasted over a fairly large area could produce some rises on area rivers to near flood stage.



Severe Threat:

SPC has expanded their slight risk area overnight to include much of our northern counties (roughly north of HWY 105). With the front not reaching our area until after midnight, there appears to be only modest instability in place by that point to produce much in the way of severe storms. Isolated wind damage will be possible and a few hail reports, but widespread severe weather is not expected. Elevated thunderstorms in the cold air mass over the weekend could produce some hail.



Note: Temperatures will fall into the 50’s behind the cold front on Friday and with NE surface winds, clouds and rainfall through the weekend temperatures will likely be locked in the 50’s for much of the period.



SPC (Day 1) Severe Weather Outlook):

[srainhoutx]

The 12Z NAM (WRF/NMM) suggests a potential meso (MCS) developing tomorrow afternoon very close to the Metro Houston area. We'll need to monitor the short range meso models to see if that trend continues...

[weatherguy425]

Quite the rude awakening up here in the Panhandle. Yesterday's high was near 80, right now its in the mid 30's with winds gusting well over 50 mph. Most models indicated precipitation starting to break out in the Panhandle region by now, but so far I'm not noticing much...perhaps because the low is moving even slower than models anticipated?

[Andrew]

Houston NWS thinking for tonight:

[weatherguy425]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1001 AM CST THU MAR 8 2012

.DISCUSSION...
JUST MINOR & INSIGNIFICANT TWEAKS TO THE 1ST PERIOD GRIDS BASED ON
LATEST TRENDS. STILL LOOKING FOR FRONT TO PUSH THRU OVERNIGHT.
WHILE EXPECTING SHRA/TSTMS...NOT THAT CONCERNED WITH FLOODING WITH
THIS INITIAL SHOT OF PRECIP. THAT`LL COME OVER THE WEEKEND. 06Z &
SOME INCOMING 12Z DATA SUGGESTING THAT FRONT WILL GRADUALLY
TRANSFORM INTO AN N-S LLVL ORIENTED BOUNDARY OVER SE TX THAT WAS
ABSENT IN MOST OF YDAYS DAYTIME RUNS. THIS WAS ONE OF THE MISSING
FCST PARAMETERS FOR HEAVY RAIN WE TALKED ABOUT YDAY. MORE ABOUT THIS
LATER THIS AFTN AS ALL THE 12Z MODELS COME IN AND ARE ANALYZED.

[texoz]

Is there a place on the NWS site, or anywhere else, where you can find the forward motion of cold fronts?

I see the cold front is dipping southward and has just passed Lake Buchanan at 1:15pm, but not Waco yet. Trying to figure out when it will pass through Austin.

[Kludge]

Is there a place on the NWS site, or anywhere else, where you can find the forward motion of cold fronts?

I see the cold front is dipping southward and has just passed Lake Buchanan at 1:15pm, but not Waco yet. Trying to figure out when it will pass through Austin.

Try this... http://www.wunderground.com/wundermap/? ... &wmo=99999

Move the map to your location, and note the weather station wind directions.

[srainhoutx]

The latest from HGX explains what we have been talking about for several day here on the board. This will be an event that will bring bouts of rainfall for several days and there still is some uncertainty regarding exactly who and where the heavier rainfall totals will fall....

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
354 PM CST THU MAR 8 2012

.DISCUSSION...
COLD FRONT IS MAKING FAST SWD PROGRESS. THIS BOUNDARY SHOULD BE
MOVING INTO NORTHERN PARTS OF SE TX AROUND 6PM...TO THE HWY 59
CORRIDOR AROUND 10PM AND OFF THE EXTREME SE COASTLINE SHORTLY
AFTER MIDNIGHT. MODELS DON`T HAVE THE BEST HANDLE OF THIS SHALLOW
COLD AIRMASS AND TRENDED FCST TIMING, WINDS, AND TEMPS CLOSER TO
THE FASTER TX TECH AND LOCAL WRF. HAVE A FEELING TEMPS MIGHT NEED
TO BE FURTHER LOWERED ESP NW ZONES. SHRA/TSTMS HAVE DEVELOPED
ALONG THE BOUNDARY AND EXPECT THESE TO MOVE INTO SE TX THIS EVENING.
MAY HAVE A SHORT TIME PERIOD FOR AN ISOLATED STRONG TO SEVERE STORM
ACROSS NRN COUNTIES THIS EVENING WITH HAIL BEING THE MAIN THREAT.
HIGHER RAINFALL TOTALS WILL LIKELY BE ACROSS NE PARTS BUT AM NOT
EXPECTING MUCH IF ANY OF A FLOOD THREAT WITH THIS FRONT. PERIODS
OF -RA WILL PERSIST THROUGH FRIDAY WITH MOISTURE OVERRUNNING THE
SHALLOW COLD AIR. NORTHERN PARTS OF THE AREA MAY SEE ANOTHER
1/4-1/2" DURING THE DAY AS THERE SHOULD BE A LLVL CONVERGENT ZONE
IN THE AREA WHICH COULD PROVIDE A FOCUS.

BASED ON THE MANY PHONE CALLS TODAY...THERE SEEMS TO BE QUITE A
BIT OF CONFUSION AND/OR MISCOMMUNICATION REGARDING RAINFALL &
FLOOD POTENTIAL THROUGH THE WEEKEND. LET`S SEE IF WE CAN BEGIN
CLEARING SOME THINGS UP. I BELIEVE MANY PEOPLE ARE SEEING POTENTIAL
4-DAY RAIN TOTALS BEING ADVERTISED AND POSSIBLY CONFUSING THAT
WITH THAT OF RAINFALL OCCURRING ON A SINGLE DAY OR SHORT TIME
PERIOD. THEY ARE DIFFERENT ANIMALS.

WE ARE CURRENTLY EXPECTING 2...AND POSSIBLY 3 ROUNDS...OF MODERATE
TO OCCASIONALLY HEAVIER RAINFALL EPISODES BETWEEN NOW AND SUNDAY
NIGHT:

1. TONIGHTS FRONT WILL BE ROUND NUMBER ONE.
2. MAY SEE AN UPPER LEVEL DISTURBANCE PUSH SW-NE ACROSS THE STATE
SATURDAY AFTERNOON AND SATURDAY EVENING. THE LATEST GUIDANCE
SUGGESTS THIS DISTURBANCE WILL PASS CLOSE TO (AND MORE LIKELY
JUST NORTH) OF THE NORTHERN PARTS OF SE TX.
3. EXPECT PROBABLY THE MORE SIGNIFICANT RAINFALL EPISODE TO OCCUR
ON SUNDAY IN ADVANCE OF THE MAIN UPPER TROF THAT WILL BE
APPROACHING THE AREA.

SO...THE GROUND WILL PROGRESSIVELY BECOME WETTER WITH TIME WITH
EACH SUBSEQUENT RAINFALL EPISODE. THE LOCATIONS THAT SEE THE
HIGHER RAINFALL AMOUNTS EARLY WILL BE MORE PRONE TO RUNOFF AND
FLASH FLOODING DURING THE LATER TIME PERIODS. AT THIS TIME
LOCATIONS GENERALLY NORTH AND WEST OF HIGHWAY 59 APPEAR TO BE IN
THE MORE FAVORABLE POSITION TO SEE THE HIGHER RAINFALL AMOUNTS
THROUGH THE WEEKEND.

FORECASTING PRECISE RAINFALL ACCUMULATIONS 3/4 DAYS OUT ARE JUST
AN EDUCATED GUESS AND WILL UNDOUBTEDLY EVOLVE WITH TIME. SLIGHT
DEVIATIONS OF SURFACE AND UPPER LEVEL FEATURES, TIMING AND
MOISTURE AVAILABILITY COULD ALTER RAINFALL AMOUNTS ONE WAY OR THE
OTHER. AVERAGE RAINFALL ACCUMULATIONS THRU THE WEEKEND (ADDING UP
#1-3 ABOVE) WILL PROBABLY AVERAGE ONE TO THREE INCHES. DUE TO
FORECAST UPPER LEVEL CONDITIONS...LOCALIZED 4-7" AMOUNTS (AGAIN
ADDING UP #1-3) ARE A POSSIBILITY DUE TO TRAINING.

AT THE CURRENT TIME...IT LOOKS LIKE SUNDAYS EVENT MAY CAUSE THE
HIGHER RAINFALL AMOUNTS AND WOULD BE THE DAY MOST CONCERNED ABOUT
POTENTIAL FLOODING - DUE TO POTENTIALLY SATURATED GROUNDS AT SOME
LOCATIONS. WE WILL CONTINUE TO MONITOR THE SITUATION AND EVALUATE
THE NEED FOR ANY WATCHES, ETC.

THIS SYSTEM SHOULD PUSH EAST OF THE REGION EARLY MONDAY BRINGING
AN END TO THE RAINFALL AND SETTING UP A WARM SPRING BREAK WITH
JUST A SLIGHTLY POSSIBILITY OF SOME ISO DAYTIME SHOWERS.

[Andrew]

Is there a place on the NWS site, or anywhere else, where you can find the forward motion of cold fronts?

I see the cold front is dipping southward and has just passed Lake Buchanan at 1:15pm, but not Waco yet. Trying to figure out when it will pass through Austin.

Also here are some good ones:

US_T.GIF

2012030822_metars_abi.gif

http://www.atmo.arizona.edu/products/wx ... 0mbwv.html

[Ptarmigan]

Looks like rain is developing west of Houston. Should be an interesting night.

[Belmer]

Upper 30s low 40s forecasted here in and around San Marcos tomorrow morning. I certainly wouldn't mind seeing a sleet pellet or two before I head to Houston tomorrow afternoon to begin my Spring Break!

[MESOMAN]

Total Bust so far. Hope it gets going overnight.

[Ptarmigan]

Total Bust so far. Hope it gets going overnight.

The calm before the storm. Not a bust yet. The January 9, 2012 storm did not form until after past midnight.

[Andrew]

Total Bust so far. Hope it gets going overnight.

Not a bust at all so far. The front was not supposed to spark widespread showers. It is when the system out west get closer and swings storms around when we will see all our rain.

[srainhoutx]

The over night guidance suggests and bit more close core upper low will remain well to our W with embedded short wave energy rotating beneath that U/L in the SW flow aloft for the next 48 to 60 hours. Over running showers with a chance of some stronger elevated storms look to increase mid day Friday near SE TX before another break in the action on Saturday. The 'heavier rains Saturday appear to be focused further W over Central TX and the Hill Country Lakes where the past events have missed and should benefit that region of our drought parched State, and that is a good thing.

The guidance had suggested that heavier storms/rains of Thursday, with the cold front passage, would remain to our N and E and that has be exactly what has happened and where Flood Advisories are in effect near Lufkin and on N and E. The NAM (WRF/NMM) continues to advertise a round of heavier elevated storms moving near the Houston Metro area Friday as short wave energy swings across the region heading ENE along the boundary. On Saturday, a surface wave of low pressure looks to develop near Rock Port and traverse NNE as the U/L creeps slowly E toward the Texas Panhandle. Additional short wave energy streams in from the W with over running showers developing again Saturday night into Sunday. As the U/L finally begins to trek NE across N TX/OK, a line of heavier showers/elevated storms appears to swing through as the frontal boundary begins retreating N decreasing aerial coverage of rains by Sunday evening, if guidance is correct. All in all things are unfolding as generally expected and we'll need to watch radar trends later today to see if training cells set up mainly along and W of the HWY 59 corridor.

[srainhoutx]

HGX Morning Update:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
416 AM CST FRI MAR 9 2012

.DISCUSSION...
COLD FRONT MOVED OFF THE COAST EARLY THIS MORNING AND COOLED US ALL
DOWN. SPOTTY AREAS OF LIGHT TO MODERATE RAIN ARE FOUND ACROSS PARTS
OF SOUTHEAST TEXAS AT 4 AM. HAVE MADE VERY LITTLE CHANGES TO THE FORECAST
PACKAGE WHICH CALLS FOR PERIODS OF RAIN/RAIN SHOWERS AND EMBEDDED THUNDERSTORMS
THROUGH SUNDAY. ALTHOUGH LOCALLY HEAVY RAINFALL WILL BE POSSIBLE WITH
ANY OF THE HARD TO TIME DISTURBANCES THAT MOVE ACROSS OUR AREA...IT APPEARS
THE STRONGEST DISTURBANCE AND BEST CHANCE FOR HEAVY RAIN SHOULD COME LATE
SATURDAY NIGHT THROUGH SUNDAY AFTERNOON AS THE MID/UPPER LEVEL LOW CURRENTLY
SPINNING ACROSS NEW MEXICO FINALLY EJECTS OFF TO THE NORTHEAST AND
HEADS TOWARDS THE GREAT LAKES AREA. SO FAR...HEAVIEST RAINFALL AMOUNTS
HAVE BEEN UP NORTH WITH TOTALS OF 2 TO 3 INCHES FROM AROUND THE CROCKETT
AREA EASTWARD TO THE APPLE SPRINGS AREA. STILL THINK THAT THROUGH
SUNDAY MOST OF SOUTHEAST TEXAS WILL AVERAGE 1 TO 3 INCHES WITH ISOLATED
AMOUNTS IN A 4 TO 7 INCH RANGE. WE WILL BE WATCHING FOR WHICH AREAS RECEIVE
THE MOST RAINFALL AS THESE EVENTS UNFOLD AND CONSIDER POSSIBLE FLOOD
WATCHES. ONCE THIS EVENTS COMES TO AN END...THE AREA WILL SEE A RETURN OF
WARM SPRING TIME WEATHER FOR MUCH OF NEXT WEEK WITH LOWS GENERALLY IN
THE 60S AND HIGHS GENERALLY IN THE UPPER 70S TO AROUND 80 AND LOW RAIN
CHANCES EACH DAY.

HERE ARE SOME RAINFALL RECORDS THAT HAVE THE POTENTIAL TO BE BROKEN OVER
THE NEXT THREE DAYS.

LOCATION TODAY SATURDAY SUNDAY

CLL ... 1.73 IN 1913 ... 1.51 IN 2008 ... 1.68 IN 1921
IAH ... 1.50 IN 1903 ... 3.23 IN 1926 ... 1.20 IN 1903
HOU ... 1.20 IN 1994 ... 1.03 IN 1944 ... 0.74 IN 1970
GLS ... 1.75 IN 1880 ... 3.97 IN 1903 ... 1.17 IN 1914

[unome]

their multimedia briefing today http://www.srh.weather.gov/hgx/?n=briefing should be updated either sat or sun