April 2017 - MS 150 Forecast This Weekend

[Katdaddy]

A 40% chance of scattered showers and thunderstorms this afternoon across SE TX. Some strong storms may be possible over the far SW counties near Victoria as a storm complex pushes across STX today.

[srainhoutx]

Noticing a bit of agitation at several levels via GOES 16 Visible imagery suggesting the MCV located near Beeville moving ENE may fire off a round of storms near the Victoria Crossroads later this morning and possibly extend East in the afternoon hours with some daytime heating.

[srainhoutx]

Monday morning briefing from Jeff:

Couple areas of thunderstorms approaching SE TX this morning

1) One well defined area extends from NW LA to SC OK and is sagging southward on a SSW moving outflow boundary perpendicular to the morning SSW low level jet over N TX
2) A weakening area of thunderstorms over SC TX into S TX which developed from a trough axis out of NE MX overnight. Current mid level vortex is located over Frio and Medina Counties and drifting ENE.

Main questions for today center around thunderstorm activity to our NNE and SW and how these areas will impact SE TX later today. Air mass is certainly moist with dewpoints in the upper 60’s and lower 70’s across the area and with a few hours of sun this morning the air mass will become increasingly unstable. Hard to find any defined outflow boundary approaching from the SW, but suspect there is something down there that will move into the Matagorda Bay area by late morning. NE TX activity will continue to build SW today into an increasingly unstable air mass. What is interesting is the general lack of much short range high resolution guidance support for showers and thunderstorms over SE TX in what would seem to be a fairly primed air mass. Models seem to have a good idea of current convective trends, but generally weaken and dissipate the coastal bend activity while slowly allowing the NE TX activity to approach by this evening.

Not overly confident that models have a good handle on how things may unfold today with an inland moving seabreeze boundary and potential outflow boundaries approaching from both the SW and NNE. Morning capping should erode with surface heating and boundaries should help to add a surface focus and trigger. Will cap rain chances at 50% for the area and not expecting any severe weather, but slow moving heavy rainfall will be possible as storm motions look to be less than 10-15mph this afternoon.

Short range models are a little more robust on Tuesday with the SC TX trough axis laying across the coastal plains, but much of this will depend on how exactly things unfold today into tonight. If there is more widespread development than currently expected today, then the air mass will need time to recover on Tuesday.

[jasons2k]

Fly, meet ointment:

The complex to the west just spit out an outflow boundary that is about to race across Harris County.

[DoctorMu]

That is one big, complicated Meso mess. Awesome wall cloud in Bryan.

Hope the power holds. I'm submitting a proposal for work...

[CrashTestDummy]

100% chance of some REALLY heavy rain in Pearland right now. Wow!

[Ptarmigan]

What is Quais?

[jasons2k]

Raining here again, pretty hard too. Radar may be busy overnight...

[Katdaddy]

Very heavy rains falling across Brazoria and Galveston Counties early this morning.

The National Weather Service in League City has issued a

* Flood Advisory for Minor Flooding in Poor Drainage Areas for...West central Galveston County in southeastern Texas...Northeastern Brazoria County in southeastern Texas...

* Until 400 AM CDT.

* At 104 AM CDT, Doppler radar and automated rain gauges indicated heavy rain due to thunderstorms. This will cause minor flooding. Overflowing poor drainage areas will result in minor flooding in the advisory area. Up to two inches of rain have already fallen.

* Some locations that will experience flooding include...
Southwestern League City, southwestern Friendswood, Alvin, eastern Angleton, Santa Fe, Hitchcock, Danbury, Iowa Colony, Hillcrest, Liverpool, Bonney and Chocolate Bayou.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Be especially cautious at night when it is harder to recognize the dangers of flooding.

Excessive runoff from heavy rainfall will cause flooding of small creeks and streams, country roads, farmland, and other low lying spots.

[Katdaddy]

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

The National Weather Service in League City has issued a

* Flash Flood Warning for...
Central Brazoria County in southeastern Texas...

* Until 400 AM CDT.

* At 159 AM CDT, Doppler radar indicated thunderstorms producing
heavy rain across the warned area. Up to 5 inches of rain have
fallen. Flash flooding is expected to begin shortly.

* Some locations that will experience flooding include...
Danbury.

The thunderstorms generating the rainfall are slow moving.
Additional rainfall amounts of 2 to 4 are possible in the warned
area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don`t drown when encountering flooded roads. Most flood
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the
dangers of flooding.

Please report flooding to your local law enforcement agency when you
can do so safely.

[srainhoutx]

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.

[Katdaddy]

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

[Katdaddy]

...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.

[Katdaddy]

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.

[tireman4]

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.
&&

$$

[srainhoutx]

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.

[srainhoutx]

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.

[Cromagnum]

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.

[tireman4]

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.

Huffman

[Katdaddy]

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.