April 2017 - MS 150 Forecast This Weekend

General Weather Discussions and Analysis

Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby srainhoutx » Tue Apr 18, 2017 3:50 am

That pesky MCV continues to fire off showers and storms early this morning with some locations in Brazoria County receiving 7 inches of rainfall. Additional rounds of storms are developing to the West of Metro Houston where multiple cold pool boundaries seem to have set up. Will need to monitor for additional thunderstorm development throughout the morning as additional upper air disturbances rippling out of Mexico head our way during the day.

I continue to see the possibility of unsettled weather across our Region as a potent Convectively Coupled Kelvin Wave combined with a rather impressive MJO Pulse continue as we head toward the end of April and begin May.

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
428 AM EDT TUE APR 18 2017

...VALID 12Z TUE APR 18 2017 - 12Z WED APR 19 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL


MID TO UPPER TX COAST

A MARGINAL EXCESSIVE RAINFALL RISK AREA WAS MAINTAINED ALONG THE
MID TO UPPER TX COAST FOR THE UPCOMING DAY 1 PERIOD AHEAD OF SLOW
MOVING MID TO UPPER LEVEL VORTS EXPECTED TO IMPACT THE TX GULF
COAST. CONFIDENCE ON THE EXACT HANDLING OF THESE VORTS IS LOW AS
IS THE RESULTANT CONVECTIVE EVOLUTION. WITH PW VALUES REMAINING
ABOVE AVERAGE FROM PERSISTENT SOUTHERLY LOW LEVEL FLOW OFF THE
WESTERN GULF AND THE SLOW MOVEMENT OF THE MID TO UPPER LEVEL
VORTS---LOCALLY HEAVY TO EXCESSIVE RAINFALL AMOUNTS ARE POSSIBLE.
WHILE THE LATEST MODELS DIFFER ON MANY OF THE SHORTER TERM
DETAILS--THERE IS A CLEAR MODEL SIGNAL FOR THE HEAVY TO LOCALLY
EXCESSIVE AMOUNTS ACROSS THIS AREA.
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Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby Katdaddy » Tue Apr 18, 2017 5:25 am

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Houston/Galveston TX
508 AM CDT TUE APR 18 2017

The National Weather Service in League City has issued a

* Flash Flood Warning for...
Northwestern Galveston County in southeastern Texas...
East central Brazoria County in southeastern Texas...

* Until 800 AM CDT.

* At 503 AM CDT, Doppler radar and automated rain gauges indicated
thunderstorms producing heavy rain across the warned area.
Rainfall amounts of 2 to 5 inches with isolated amounts of 6 to 9
inches of rain have fallen. Storms will be slow moving or nearly
stationary and capable of 2 to 3 inch per hour rainfall rates.
Flash flooding is on going and expected to develop over a larger
area.

* Some locations that will experience flooding include...
Danbury, Santa Fe, Liverpool, Dickinson, Texas City, Alvin,
northeastern Angleton, La Marque, Hitchcock, Hillcrest, Bonney,
San Leon, Bacliff, Chocolate Bayou and Rosharon.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Be especially cautious at night when it is harder to recognize the
dangers of flooding
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Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby Katdaddy » Tue Apr 18, 2017 5:38 am

...FLASH FLOOD WATCH IN EFFECT THROUGH THIS AFTERNOON...

The National Weather Service in Houston/Galveston has issued a

* Flash Flood Watch for portions of Southeast Texas and
southeast Texas...including the following counties...in
Southeast Texas...Jackson. In southeast Texas...Austin...
Brazoria...Chambers...Colorado...Fort Bend...Galveston...
Harris...Liberty...Matagorda...Waller and Wharton.

* Through this afternoon

* Overnight showers and thunderstorms are expected to persist
through much of the day today. Upper level disturbances and
favorable winds aloft in this warm moist and unstable airmass
will aid in storm development this afternoon. Rainfall amounts
of 2 to 3 inches will be possible in the watch area with the
potential for higher isolated amounts of 4 to 6 inches. These
higher rainfall amounts could lead to flash flooding.

* Flash flooding will be possible from any storms that produce
heavy rainfall. This includes water rapidly rising in roads
with poor drainage, rising waters on area creeks, bayous and
rivers due to runoff. Flood waters could damage bridges over
streams impeding travel. Flooding could impact homes in low
lying areas. Flooding will likely be at night in which
visibility will be restricted. Do not drive into any water at
night.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Flash Flood Watch means that conditions may develop that lead
to flash flooding. Flash flooding is a very dangerous situation.

You should monitor later forecasts and be prepared to take action
should Flash Flood Warnings be issued.
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Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby Katdaddy » Tue Apr 18, 2017 5:51 am

Yesterday evening's MCV re-ignited again across the Upper TX Coast early this morning resulting in very heavy rains and flash flooding. Radar estimates up to 9" of rain have fallen since midnight in Central Brazoria County at Danbury with several homes flooded. A Flash Flood Warning has been issued for NW Galveston and E Central Brazoria Counties until 8AM. In addition a Flash Flood Watch has been issued for the Upper TX Coast including the Houston-Galveston areas through this afternoon as additional very heavy rains continue with very slow storm motion. I would not be surprised to see some areas of Brazoria and Galveston Counties pick up 12-15" if training continues through the late morning along with additional development across Matagorda and Wharton Counties that will progress NE into the same areas being hit currently with flash flooding. Remember "turn around, don't drown" should you encounter high water this morning through this afternoon.
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Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby tireman4 » Tue Apr 18, 2017 7:50 am

000
FXUS64 KHGX 180926
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
426 AM CDT Tue Apr 18 2017

.DISCUSSION...

Flash Flood Watch has been issued for the southern half of SE TX
for this morning through this afternoon.

MCVs over SE TX this morning are producing quite a bit of rain...
with the highest amounts across Brazoria/North Galveston counties
thus far. Radar estimating up to to 9 inches (since midnight) for
locations near Danbury (in Brazoria county). Short-range guidance
keeping this unsettled weather pattern over the CWFA through most
of the rest of the day. Other incoming perturbations (per WV sat-
ellite loops), daytime heating and the proximity of the upper low
itself all lending itself to keeping high POPS across SE TX today.
Jet dynamics aloft also hinting at the continuation of this back-
building pattern of storms.

Despite the weakening upper low over the area, we could see scat-
tered activity on Weds. Lingering boundaries, the seabreeze along
with daytime heating will all be contributing factors. As the up-
per ridge begins to build in from the west, we should see quieter
weather by Thurs/Fri. Looking further ahead, models are remaining
in decent agreement with the cold front on Sat. The upper low de-
epning over the Central Plains will help to drag this boundary a-
cross the state as it moves off to the northeast. Will be looking
for widely scattered/scattered activity with FROPA at this time.
Cooler/drier weather on tap for the rest of the weekend into the
start of next week. 41

&&

.AVIATION...
Messy conditions across the area terminals mainly VFR but patchy IFR
CIGS/VISBY due to proximity of TSRA/+TSRA. Series of slow
moving/meandering upper disturbances should combine with rich Gulf
moisture to keep scattered to numerous showers and thunderstorms
going across the region and at least in the vicinity of the TAF
sites. Areas from ARM-SGR-HOU-GLS probably the most under the gun
through 21z as vorts put the squeeze on the atmosphere. Tonight
should see a diminishing trend in storms with the loss of heating
but vorts remain close by or overhead. So VCSH at a minimum will
probably remain in the area terminals.

45
&&

.MARINE...
South to southeast flow of 10 to 15 knots today should be the norm
outside of the storms today and tonight. The southerly flow
continues through Friday before a Pacific cold front arrives
Saturday. Winds in the wake of the front will likely reach SCEC
conditions and may even reach SCA for 6-12 hours.
45
&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 76 65 82 68 84 / 70 20 20 10 10
Houston (IAH) 77 66 81 68 84 / 70 40 30 10 20
Galveston (GLS) 77 70 78 72 79 / 70 30 20 10 10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$
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Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby srainhoutx » Tue Apr 18, 2017 7:58 am

7:38 AM Tuesday morning Update from Jeff:

Excessive rainfall occurring over Brazoria and Galveston Counties where 6-12 inches of rain has fallen overnight leading to significant roadway and some structure flooding.

Band of excessive rainfall has is being overtaken by an eastward moving line of thunderstorms which will help to end the excessive rainfall threat across areas that have been hard hit this morning. As the previous e-mail stated, there were two options of convective evolution this morning and the first option of the storms anchoring near the coast and progressing offshore has been generally been verifying. Eastward moving line of thunderstorms will progress across Galveston County and into the bay and offshore helping the stabilize the local air mass.

However main mid level vortex that is shearing out across SE TX still lingers overhead producing general large scale lift across a very moist air mass. Recent radar images show new development trying to occur near Victoria and suspect with only modest daytime heating and numerous low level outflow boundaries across the area additional storms will develop late morning into the afternoon hours.

Storm motions will be very slow at 10mph or less and with high moisture levels high short duration rainfall rates will be possible. Nearly the entire area is at risk for additional development later today with those areas seeing breaks in the overcast most likely.
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Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby srainhoutx » Tue Apr 18, 2017 9:07 am

Worrisome to see back building of storms near Matagorda Bay and the Victoria Crossroads Area. It appears via surface analysis the Mesoscale Convective Vortex is situated near Matagorda Bay and meandering, at best toward the East, in a very weak steering flow. Cloud tops continue to cool near Victoria and along the Coastal tier of Counties suggesting additional rounds of heavy rainfall rates nearing 2+ inches per hour may be possible.

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Re: April 2017 - Quais Zonal Pattern Active WX Week

Postby Cromagnum » Tue Apr 18, 2017 12:00 pm

Was any of this even hinted at in the predictions? I don't recall anything more than seeing casual mentions of 40-50% chances of some rain showers and occasional rumbles of thunder.
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Re: April 2017 - Quasi Zonal Pattern Active WX Week

Postby tireman4 » Tue Apr 18, 2017 1:07 pm

000
FXUS64 KHGX 181736
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1236 PM CDT Tue Apr 18 2017

.AVIATION...
Still looking for periods of SHRA/TSRA at TAF sites this afternoon and
on through at least tomorrow morning as the storm system continues
to meander across the area. Mostly MVFR ceilings are anticipated outside
the activity with possible IFR ceilings/visibilities in/around the
storms. This is a messy and low confidence forecast as models continue
to give different model solutions. Many amendments will likely be needed.
42
&&

.PREV DISCUSSION... /ISSUED 1131 AM CDT Tue Apr 18 2017/

UPDATE...
Areas of light to moderate rain continue to move across the
southern half of Southeast Texas this morning, with more intense
convective activity associated with a mesoscale convective vortex
(MCV) located along the Upper Texas Coast. This MCV appears to be
located around Matagorda Bay, where associated surface troughs/
outflow boundaries have served as focusing mechanisms for
thunderstorms over the coastal waters. Subsidence behind the
offshore activity has done a fairly good job of limiting the
intensity of inland showers and thunderstorms so far, but
beginning to see additional development where visible satellite
has shown breaks or clearing in cloud cover. Through early
afternoon, think most areas will see a break in overall rainfall
intensity. However, morning soundings from Corpus Christi and Lake
Charles as well as CIRA layer precipitable water estimates all
show at least 1.4-1.5 inch precipitable water values across the
region.

After a brief break, mid-afternoon heating may contribute enough
to destabilization for isolated to scattered thunderstorms to
again produce rain rates close to 2 inches an hour (given the
PWATs in place now). With weak shear/flow aloft, storm motions
will continue to be very slow and this will allow rain totals to
pile up should more robust convection develop... but the weak flow
will help limit overall ascent so that is some good news in terms
of thunderstorm development. Due to the 8-10 inches of rain parts
of Brazoria and Galveston Counties received overnight as well as
a favorable environment persisting for heavy rain, have made no
changes to the ongoing flash flood watch.

What is interesting to note is that some guidance (RAP/ HRRR/
TTU- WRF/ ARW/ NMM) show the development of another inflow band
associated with the MCV close to the Interstate 45 corridor later
this afternoon (essentially Houston to Galveston). This guidance
indicates another 1-3 inches of rainfall would be possible within
the line if it sets up... and that`s the big question right now as
the movement of the MCV may be affected by how much a small
vorticity maxima also located near Matagorda Bay pivots northeast
as well as how much stabilization/suppression the ongoing activity
over the coastal waters will provide. Again higher totals than
this are certainly possible if the line sets up.

Essentially, a brief break in rainfall intensity is expected
through early afternoon, but considerable uncertainty still exists
over the next 6-12 hours in how the MCV/heavy rainfall threat
will evolve.

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Re: April 2017 - Quasi Zonal Pattern Active WX Week

Postby Katdaddy » Wed Apr 19, 2017 5:50 am

Radar shows scattered showers and thunderstorms offshore of the Upper TX Coast and a along the immediate coast this morning A few small showers and an isolated thunderstorm have developed over inland areas of SE TX during the last hour. With the moist unstable airmass in place; isolated heavy downpours capable of dumping several inches of rain in a short period will be possible across SE TX today.
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