July 2021

[don]

Area Forecast Discussion
National Weather Service Houston/Galveston TX
248 PM CDT Wed Jul 7 2021

...FLASH FLOOD WATCH REMAINS IN EFFECT FOR COASTAL AREAS THROUGH
FRIDAY MORNING...

.SHORT TERM [Tonight Through Thursday Night]...

A broad upper level low over South Texas and a weak surface low in
roughly the same area of South Texas and a weak coastal trough of
low pressure will focus periods of showers and thunderstorms near
the middle and upper Texas coast through Thursday night. SE TX has
received a bit of a lull this afternoon and that is allowing some of
the heavier rain over Jackson and Matagorda counties to drain.
However, continued heating this afternoon should spawn scattered
shra/tsra by late afternoon into this evening. Am expecting rainfall
to increase in coverage later tonight along the coast as the sfc low
slowly deepens and the inflow on the east side of this feature
increases and both surface and speed convergence increase. Am
expecting rainfall to increase along the coast by 06z with locally
heavy rain possible along the coast and just inland. Will let the
current Flash Flood Watch run as configured but if heavy rain pushes
a bit further inland, will need to expand the Watch to include
inland portions of the coastal counties and possibly include Wharton
county. Forecast soundings show PW values between 2.20 and 2.40
inches and jet dynamics look very favorable with a weak splitting
jet over SE TX.

Not a lot of change for the rest of Thursday into Thursday Night as
the upper level and surface feature remain nearly stationary. Low
level directional and speed convergence will remain strong and upper
level winds remain favorable. PW values remain between 2.20 and 2.50
inches so the potential for heavy rain will persist. One additional
concern for Thursday night into early Friday is some extra level
upper level support with a departing 45 knot speed max placing SE TX
in the favored RRQ. This feature should help to enhance rainfall
over the SE half of the region. Some of the CAMs are suggesting some
rather heavy rainfall totals between 06-12z Friday.

[djmike]

MX Mexico

[Stratton20]

DjMike ah gotcha, I see that circulation as well, pretty interesting

[Cpv17]

After just now looking at the 18z HRRR, I believe Wharton County should be added to the FFW and possibly Fort Bend and Brazoria as well.

[jasons2k]

This is interesting:

https://www.tdlr.texas.gov/weather/summary.htm

http://southtexasweathermodification.com/

[Stratton20]

Im in katy, any chance we get added to the flash flood watch? Looks like the 18z hrrr brings some heavy totals into my area

[Rip76]

This is interesting:

https://www.tdlr.texas.gov/weather/summary.htm

http://southtexasweathermodification.com/

That is very interesting

[Cpv17]

Im in katy, any chance we get added to the flash flood watch? Looks like the 18z hrrr brings some heavy totals into my area

Well part of Katy is in Fort Bend County so maybe. Harris County is close so I wouldn’t completely rule it out.

[Andrew]

Interesting to see such different solutions from the GFS and ECMWF on Thursday night/Friday morning. The GFS has a weak surface trough drift more northeast, along the coast while the ECMWF tries to push everything further west. The GFS also has a low-level vort max rotate in from the gulf which could provide additional lift across the region. If the GFS solution comes to fruition a MCS could develop along the coast Friday morning. The HRRR is picking up on it some too but remains further south near Matagorda Bay. Something to watch for tomorrow night.

[Stratton20]

CPV17 I am on the fort bend side of katy

[Stratton20]

Andrew also interesting to note that the 18z GFS has the low pressure (1007mb) just offshore by Corpus, I dont want to jump to conclusions, but if that's the case would it be possible gor the low to develop into maybe a depression? Just curious

[Cpv17]

These warm-core lows produce our biggest flooding events so this is definitely something to watch out for. They can sometimes produce rain rates of 5+“ per hour. Things look interesting down here in Wharton County as early as tonight.

[Stratton20]

Cpv17 if we get any pf those potential 5+ hourly rainfall rates, we could be in some serious trouble potentially

[Cpv17]

18z GFS is still sticking to its guns. Lots of rain south and sw of Houston.

[Stratton20]

Heres what I think is going to happen in terms of rainfall in houston, most will probably get 1-3 inches overall, but someone somewhere is most definitely going to see way more than that, I always take the placement of the heaviest rainfall totals by the models with a huge grain of salt, we have seen time after time again that these low pressure systems can give us some big surprises

[Andrew]

Andrew also interesting to note that the 18z GFS has the low pressure (1007mb) just offshore by Corpus, I dont want to jump to conclusions, but if that's the case would it be possible gor the low to develop into maybe a depression? Just curious

Low-level shear is strong across the western gulf and if this low tracks into the gulf at all it won't be there long enough for any development, anyways. Tropical development is not expected.

[Stratton20]

Andre ah gotcha, at this point it doesnt really matter though, flooding has already been a huge problem

[Cpv17]

Andre ah gotcha, at this point it doesnt really matter though, flooding has already been a huge problem

Yeah even if it doesn’t develop it can still produce flooding.

[Andrew]

Andre ah gotcha, at this point it doesnt really matter though, flooding has already been a huge problem

For sure. I think those along the coast are definitely most at threat but most of the region has seen a lot of rain over the last 30 days so the ground is pretty saturated. Just something to continue to monitor. Luckily, as it stands right now, I think the Houston metro region looks okay. Luckily after Friday the rest of the weekend looks a little drier.

[Stratton20]

For me in katy at least the 10 day forecast only has one dry day and thats sunday, rest of the weak after that features 40-50% chance of storms, does not really seem like we can break this wet pattern for an extended period