MCS Potential Houston and Gulf Coast Thursday

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MCS Potential Houston and Gulf Coast Thursday

Post by LarryCosgrove » Mon Mar 24, 2014 10:02 am

There appears to be emerging model agreement (two runs ECMWF and latest GFS) for the potential of a large MCS Thursday into Friday. GGEM and 12z ECMWF versions may tell us something. Inflow is good, some separation from the cold front passing through the Midwest at that time. Key feature: subtropical jet stream that runs from central equatorial Pacific Ocean into the Gulf Coast. That wind field could carry the impulse to start off concentrated thunderstorms in C/S TX on Thursday afternoon.

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Re: MCS Potential Houston and Gulf Coast Thursday

Post by LarryCosgrove » Mon Mar 24, 2014 4:27 pm

FWIW, both 12z ECMWF and 18z GFS schemes are similar with the formation of an MCS west of Houston around 18z on Thursday.

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Re: MCS Potential Houston and Gulf Coast Thursday

Post by BlueJay » Mon Mar 24, 2014 4:55 pm

Although we do need the rain an Allison type of rain may not be what we had in mind. Please keep us informed about this upcoming MCS possibility. Thanks!

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Re: MCS Potential Houston and Gulf Coast Thursday

Post by srainhoutx » Mon Mar 24, 2014 8:46 pm

The early meso guidance is suggesting storms firing across Central Texas where they need the rain. The WRF and HIRES NAM have a rather impressive jet streak across the Southern half of Texas near the Wednesday evening time frame extending into early Thursday.
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Re: MCS Potential Houston and Gulf Coast Thursday

Post by srainhoutx » Tue Mar 25, 2014 8:17 am

The Morning QPF discussion is keying in on SE Texas and Southern Louisiana in the Day 2-3 time frame. Since areas N of I-10 have been dry, the rainfall will be appreciated to wash down all of the pollen.

DAYS 2-3

...SOUTHERN PLAINS TO LOWER MS VALLEY...

A DEVELOPING RETURN FLOW WILL TRANSPORT HIGHER MOISTURE CONTENT
AIR INTO THE SOUTHERN PLAINS ON DAY 2...WITH SHOWERS AND STORMS
DEVELOPING IN TX/OK AS POCKETS OF LOW LEVEL CONVERGENCE DEVELOP
AHEAD OF THE 700 MB WAVE. THE WAVE CONTINUES INTO THE LOWER MS
VALLEY ON DAY 3...WHICH ALLOWS THE LOW LEVEL INFLOW TO
INCREASE...TRANSPORTING MOISTURE AND INSTABILITY ONSHORE FROM THE
GULF OF MEXICO INTO SOUTHEAST TEXAS AND LOWER MS VALLEY. UPPER
DIVERGENCE/LOWER CONVERGENCE MAXIMA IN THE VICINITY OF THE HIGHEST
POOL OF AVAILABLE PRECIPITABLE WATER SUGGESTS MODERATE TO HEAVY
SHOWERS/STORMS DEVELOP IN SOUTHEAST TX AND MOVE ACROSS SOUTHERN
LA.
MANUAL PROGS BLENDED THE 12-00Z ECMWF/00Z CANADIAN GLOBAL/00Z
UKMET QPF. SEVERAL GEFS/ECMWF ENSEMBLE MEMBERS KEEP THE HEAVIER
QPF OVER THE GULF OF MEXICO...WHICH WILL HAVE OT BE MONITORED. FOR
NOW THE ECMWF/UKMET 300 MB DIVERGENCE MAXIMA STREAM ONSHORE...SO
THESE SOLUTIONS WERE USED.


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Re: MCS Potential Houston and Gulf Coast Thursday

Post by jasons2k » Tue Mar 25, 2014 8:19 am

Good. It's been awhile since we had a good old-fashioned MCS rain down upon us.

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Re: MCS Potential Houston and Gulf Coast Thursday

Post by srainhoutx » Tue Mar 25, 2014 10:00 am

The 12Z WRF/NMM and GFS as well as the 09Z SPC SREF mean are suggesting that the potential of a possible MCS may develop near SE Texas and shift E Thursday evening into Southern Louisiana. If the trends continue, I will not be surprised to see the SPC place portions of E Texas and Western Louisiana in a Slight Risk for severe storms with their updated Outlooks.
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Re: MCS Potential Houston and Gulf Coast Thursday

Post by srainhoutx » Tue Mar 25, 2014 11:01 am

Morning Update from Jeff:

Progressive upper flow will bring a couple of fast moving storm systems to the area this week.

Weak cold front has pushed into the Gulf waters overnight with weak (5-10mph) northerly winds in progress over the area extending southward into deep south TX. Dewpoints have fallen into the 30’s and 40’s areawide so the air mass is fairly dry at the surface. Aloft SW flow is pumping high level Pacific moisture into the region…a sign of what may be to come if central Pacific water temperatures continue their impressive upward swing…a potentially strong El Nino event (more on that in the next few weeks).

First disturbance will approach the Rio Grande this evening and spread lift across the area overnight into Wednesday. Strong SE winds will begin to pump low level moisture back into the region as low pressure forms over the southern high plains. Think models may be slightly aggressive in their returning of low level moisture and while impressive mid and upper level moisture will be in place on Wednesday not sure how much rainfall will actually “reach” the ground with a dry surface layer having to be overcome first. Think this will eventually happen by early to mid afternoon, but this may cut down on overall amounts and duration of the rainfall.

Warm front moves northward late Wednesday as the next and stronger system digs into the SW US and takes aim at the state. Impressive 50kt low level jet develops Wednesday night with moisture surging northward out of the Gulf. Dewpoints rise into the mid to upper 60’s while at the same time a strong sub-tropical jet streak carves into the coastal bend region placing SE TX in favorable lift by Thursday morning. Mid level warm layer does attempt to advect eastward from northern MX, but this appears to be breakable with the expected lift and warm air advection pattern in place over SE TX Thursday morning. 0-6km shear values are progged in the 40-50kt range over the region, but instability is only modest in the 500-1500 J/kg range. Appears storms will develop in moisture axis ahead of a dryline feature over our western counties mid morning Thursday if capping can be overcome…which thus far this spring season has been hard to do. If storms do develop favorable dynamics, shear, and modest instability will support a strong to severe threat across SE TX Thursday midday into the afternoon hours. Would like to see some of the meso models resolving of this event to get a better feel of how it might play out. Recent guidance performance has been too aggressive on rain chances over the area with the meso models handling the past few events better.

Sub-tropical ridge axis attempts to build into the area from the SW over the weekend which will result in clearing skies and significantly warmer temperatures. Glancing blow from a cold front late Friday may help to temper the temperature rise some if the front actually pushes through the area.

Marine:
Conditions will greatly deteriorate over the next 24 hours as very strong SE to S winds develop across the western Gulf and coastal bays. North winds currently with become east this afternoon and SE early Wednesday and rapidly increase from 5-10mph today to over 20mph on Wednesday. Long fetch and intensity of the winds will build Gulf swells to 7-11 ft by Wednesday afternoon and 3-5 feet in the bays. Aircraft yesterday indicated an oil slick extending from roughly the Texas City Dike 12 miles southeast into the open Gulf of Mexico off the eastern tip of Galveston Island. After noon today the wind direction will becoming increasingly onshore and begin to move this slick toward the Gulf facing beaches. Strong SE winds on Wednesday will be more favorable for advancement of the oil toward the coast both on the Gulf facing beaches and within Galveston Bay. In addition to the increasing winds and seas, favorable ESE to SE winds will push greater amounts of water toward the coast and elevate tide levels especially on the Gulf facing beaches where swell run-up will trap water on the beaches. Expect tides to run 1.0-2.0 above predicted levels by Wednesday evening which will push water levels well up the beaches and potentially flood tidal marsh areas that thus far have been dry due to the north winds. Even though dewpoints will rise over nearshore water temperatures, think the sea fog threat is low given the strong winds mixing the low levels. Showers and thunderstorms late Wednesday and again on Thursday could produce locally higher and varying winds and chaotic sea states along with heavy rainfall and lightning.
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Re: MCS Potential Houston and Gulf Coast Thursday

Post by LarryCosgrove » Tue Mar 25, 2014 12:07 pm

The 12z models are in, and every one shows strong potential for an MCS formation just north and west of Houston on Thursday afternoon, with risks for heavy rain and severe weather in SE TX by evening and lasting into Thursday night (eventually moving along the Gulf Coast, largely below Interstate 10, through Friday.

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Re: MCS Potential Houston and Gulf Coast Thursday

Post by srainhoutx » Tue Mar 25, 2014 7:50 pm

Watching the rather impressive jet streak nearing California behind the lead upper low. As HGX mentions this places portions of our area in a left front quadrant. I suspect the Texarkana to Shreveport area could see the biggest threat for a tornado. Damaging winds and hail N of I-10 continues do raise an eyebrow. Transitional patterns are a bit worrisome for 'finer details' even at this range.

THURSDAY THE CHANCE OF RAIN WILL CONTINUE DUE TO AN APPROACHING
DRY LINE. GLOBAL MODELS CONTINUE TO DEVELOP A HEAVY QPF REGION
OVER SOUTHEAST TEXAS THURSDAY EVENING. THURSDAY EVENING MODELS
ARE IN PRETTY GOOD AGREEMENT WITH MOVING SOUTHEAST TEXAS INTO THE
LFQ OF THE SUBTROPICAL JET. AT THE SAME TIME ANOTHER SHORTWAVE
WILL MOVE THROUGH THE TEXAS PANHANDLE HELPING TO FURTHER COOL THE
600 - 300MB REGION. GFS AND NAM SOUNDINGS BOTH SHOW LAPSE RATES
APPROACHING 8 C/KM. CAPE VALUES ALSO ARE IN THE 1500 TO 2000 J/KG
RANGE. BECAUSE OF THE FACTORS ABOVE SPC HAS PUT SOUTHEAST TEXAS
INTO SEE TEXT. STRONG STORMS WILL BE POSSIBLE IF THIS SETS UP AND
WE WILL HAVE TO CONTINUE TO WATCH THIS IN THE NEXT COUPLE OF MODEL
RUNS.

The attachment 03252014 15Z SREF_prob_sigtor_3__f057.gif is no longer available
03252014 15Z SREF_prob_supercomp_6__f045.gif
03252014 15Z SREF_prob_cbsigsvr_20000__f057.gif
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