March: Warm Days To End The Month With Isolated Showers

[srainhoutx]

The guidance is still struggling with the eventual evolution of a pesky cut off upper low over New Mexico during the Wednesday/Thursday time frame. The Euro now suggests a 'cold front' will stall just N and W of the Houston area keeping rain chances in the picture from Thursday through Saturday and even lingering into early Sunday. There appears to be embedded short wave energy rotating around the base of the U/L (H5) and a surface low developing in Central Texas creeping along the stalled boundary. The UKMet is in agreement with a slow ejecting U/L and with a split flow and a potent storm cut off from the mean flow further N, it make sense that a heavy rainfall scenario will play out over several days. What remains to be seen is exactly where the boundary stalls. That boundary will serve as a focal point for potential very heavy training cells with very heavy rainfall N of the boundary. The surface low will act as a trigger for stronger storms, with elevated storms N of the stalled front. All in all it does appear a large portion of the eastern half of Texas is setting up for a significant food potential and folks should monitor the weather news carefully the next several days.

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
151 PM EST TUE MAR 06 2012

VALID 12Z FRI MAR 09 2012 - 12Z TUE MAR 13 2012

...12Z MODEL UPDATE...

WITH MUCH OF THE 12Z MODEL GUIDANCE AVAILABLE...THE 12Z GFS
FOLLOWED SUIT WITH ITS EARLIER THREE RUNS AS IT CONTINUES CARRYING
A FASTER PRIMARY UPPER WAVE FOLLOWED BY A SECONDARY FEATURE
TRACKING THROUGH THE SOUTHERN PLAINS BY LATE IN THE WEEKEND.
MEANWHILE...THE 12Z UKMET MAINTAINED STRONG CONTINUITY ACROSS THE
SOUTH-CENTRAL U.S. WHILE IT HAS BECOME MUCH MORE PROGRESSIVE WITH
THE SYSTEM REACHING THE PACIFIC NORTHWEST BY DAY 5...SUNDAY WHICH
RESEMBLES THE SOLUTION OF THE 12Z GFS. THIS PARTICULAR THEME WAS
ALSO SEEN WITH THE 12Z CMC...ALTHOUGH IT IS FAR MORE AMPLIFIED
ALOFT AND FURTHER INLAND WITH THE WESTERN SYSTEM THAN ANY OF THE
OTHER DETERMINISTIC GUIDANCE. LOOKING AT THE 12Z ECMWF...IT SHOWED
THE MOST CHANGE FROM ITS PREVIOUS RUN WHEN ANALYZING THE SYSTEM IN
THE SOUTHERN PLAINS. THE BIGGEST DIFFERENCE IN THE 12Z RUN IS IT
IS SLOW IN BRINGING OUT A TRAILING PIECE OF ENERGY WITH IT
REACHING THE LOWER OHIO VALLEY BY DAY 7...TUESDAY. OVERALL...NO
CHANGES WERE MADE TO THE PRELIMINARY GRAPHICS.

[MontgomeryCoWx]

Damn, 10 inch totals in the ArkLaTex region! Wish they could move those down here, but I"ll take 2-3 inches.

We are having our first child on Saturday, so it will be a good day to be in the Hospital.

Congrats and best wishes, MCW.....!!!!

Fingers crossed that you take your new child to a drought-free home...

Thank you Kludge!

[Andrew]

The overnight models have come into more agreement on a slower ejection of the U/L. GFS along with the Euro and CMC keep rain in the forecast all the way into Sunday or even Monday. The amplification of the second/ split of the U/L is more evident in the 00z run for the gfs and a flooding type event looks more and more likely. Just from looking at the Euro saturation levels look strong across all levels of the atmosphere which is similar to events earlier this year that provided us with huge amounts of rain. It is good though to see a model consensus coming together.

[srainhoutx]

The over night guidance still offers little overall confidence with the evolution of a complex weather pattern that includes a cut off upper low near the 4 Corners Region, a shallow cold front and a split flow separation from the mean Polar Jet across Southern Canada/Northern Plains. The models are converging on a solution that does suggest very heavy rainfall with training cells near where the frontal boundary stalls. The SPC currently has a Slight Risk for severe storms for portions of N Central/NE TX into OK and AR for Thursday with large hail and damaging winds being the main threat with a transition to elevated post frontal training cells appear to be the 'bigger' issues as the frontal boundary stalls E of the I-35 Corridor Thursday night into Friday. The Upper Low will slow its eastward progression over New Mexico and the Texas Panhandle on Friday into Saturday before ejecting NE during the day on Sunday. There appears to be multiple waves of short wave energy rotating beneath the U/L making for a very complicated and wet forecast challenge. Another fly in the ointment is a developing surface low pressure system along the stalled frontal boundary in S Central TX Friday night into Saturday. The focal point for very heavy rainfall will be along and to the N of that stalled boundry. The $64,000 questions is exactly where the boundary will stall? Indications are areas from Columbus to just S of Lake Livingston will be the favored areas for heavy training cells, but a slight shift S and E by 20-40 miles may put the Houston Metro in line for a potential flood scerario. That will need to be monitored as events unfold. All in all a general 2-4 inches of rain with isolated 6-8 inch amounts or higher are not out of the question for the favored areas N of the boundary. The boundary should begin to retreat N as the U/L moves NE on Sunday decreasing rain chances as we head into Monday. Stay tuned and monitor further updates from the NWS and our weather forum in this complex and evolving weather headline maker...

[MontgomeryCoWx]

so 4-5 inches for Houston Metro.... NICE!

[srainhoutx]

Email from Jeff:

Strong storm system to affect the region Thursday-Sunday



An upper level storm system will drop into the SW US today and then slow/stall across this region of the US into the weekend. This will result in downstream wetter conditions over the state of TX starting late Thursday and continuing through much of the weekend. At the surface a cold front will surge southward on Thursday ahead of the upper level storm system reaching the TX coast between 300am-900am Friday. Ahead of this front moisture continues to deepen over the region on gusty southerly winds as a 35-45kt low level jet extends from the western Gulf across much of eastern TX. Moisture levels will saturate the low levels by later today and expect that a few showers will begin to develop and spread northward out of the Gulf of Mexico.



Front arrives Thursday night/Friday morning lifting the moist air mass and producing a band of showers and thunderstorms. SPC Day 2 slight risk area is getting close to our northern counties for Thursday afternoon, but feel the severe threat will be north of our region. Front will slow and stall out along the coast Friday with the large upper storm over the SW US ejecting frequent impulses ENE across the boundary Friday night through Saturday night. Moisture will be forced up and over the surface cool dome allowing of favorable lift. In fact the position of the surface front off the coast and the 850mb front draped near/along I-35 appears to be setting up a favored heavy rainfall event under a front jet aloft and good low level moisture convergence. Moisture levels increase to 2 standard deviations above normal for early March and this raises a red flag with respect to flooding.



Current thinking is that widespread rains will develop Friday evening post front and continue into Sunday morning with the focus being near/east of the 850mb front/trough axis and north of the surface front near the coast or in the area along and east of I-35 from near Austin into AR. I am not overly confident in this placement of the rainfall axis and it could just as easily be displaced further southward or eastward, some of the latest models are trending more in that direction.



Grounds have dried some in the last few weeks and most rivers have returned to near normal flow with flash flood guidance for 3-hr for most counties in the 4-5 inch range. Feel the area can handle some decent rainfall amounts. While the nature of this system is slow moving and extended, there does appear to be some breaks between rounds of thunderstorms allowing rainfall to run-off. Over time grounds will saturate leading to greater and greater amounts of run-off and so the flood threat will increase the later we move in time (over the weekend).



Rainfall amounts look to average 2-4 inches across the area with isolated amounts of 4-6 inches. Could see a few locations go a little higher than that….especially up to the north closer to the HPC bullseye of 6-7 inches over NE TX. Will need to watch the trends of the next 24-36 hours closely and if the heavier rains look to focus more southward a Flash Flood Watch may be required.

[wxman57]

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.

[srainhoutx]

The 12Z Euro and UKMet are in fairly good agreement suggesting a prolonged heavy rainfall event beginning Thursday as the U/L slowly creeps E from the 4 Corners Region into New Mexico. A potent short wave disturbance develops S of the upper low in Old Mexico as a shallow frontal pulls up stationary just N and W of the Houston Metro Area. On Friday night/Saturday morning a surface low is depicted near Corpus and begins to move NE along the stalled boundary. The fly in the ointment remains the evolution of that secondary short wave upper air disturbance moving into Central Texas on Saturday. The QPF output suggests 3-4 inch amounts with up to 10+ inches near the ARKLATX area as mentioned by the HPC. The SPC has issued a Slight Risk for severe storms for tomorrow afternoon and evening for parts of Central Texas and points NE into Arkansas. Again, hail and damaging winds are the primary thread, but an isolated tornado or two cannot be ruled out. As the U/L finally ejects NE from the Texas Panhandle on Sunday, the stalled frontal boundary will retreat N easing the heavy rainfall event Sunday afternoon/evening, if guidance is correct. I suspect Flood Watches will be required for parts of Central/NE/SE and E Texas sometime tomorrow or Friday and likely extended into the weekend before all is said and done. We will see.

[Andrew]

Some pics from the 12z runs:


Euro:

f72 (1).gif

Gfs:

gfs_namer_081_500_vort_ht.gif

gfs_namer_129_precip_ptot.gif

Cmc:

f84.gif

[jasons2k]

Already getting some decent showers here - and it's only Wednesday!

[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.