June 2020

[tireman4]

000
FXUS64 KHGX 231138
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
638 AM CDT Tue Jun 23 2020

.AVIATION...
An MCS is approaching SE TX from the north early this AM. Short
term guidance weakens this feature but radar trends seem to
suggest otherwise as this system is moving at a pretty good clip.
The atmosphere is primed for another active day and shra/tsra
could pop up at any time. Short range guidance is becoming in
better agreement that a slow moving boundary will serve as a focus
for additional shra/tsra tonight. High PW air and slow moving
storms could also yield heavy rain with reduced visibility at area
airports. Not enough confidence to TEMPO yet so will carry VCTS
for most of the TAF period. 43

&&

.PREV DISCUSSION... /ISSUED 427 AM CDT Tue Jun 23 2020/

SHORT TERM...(Today through Wednesday)

An MCS over North Texas will slide south this morning. Short term
guidance shows the system weakening as it moves south but the
residual MCV associated with the feature will likely produce
additional showers and storms across SE TX later today. Although
PW values have briefly fallen to around 1.60 inches, PW`s are
expected to recharge by later today and reach 2.00 inches by 18z.
Convective temps are between 86 and 88 degrees so convection
could really start at almost any time this morning. Low level
convergence gets maximized as the MCV approaches SE TX and the
best convergence is co-incident with the surge of deepest
moisture and a weakly splitting jet structure. There is potential
for some heavy rain late today into tonight. Will add locally
heavy rain to the wx grids. WPC has outlooked much of SE TX in
Slight Risk of excessive rainfall today and Wednesday. FFG
guidance is still reasonably high, with 3 hour FFG values between
2-3 inches south of US 59 and 3 to 5 inches to the north. At this
time, don`t think a Flash Flood Watch is warranted.

SPC has outlooked all of SE TX in a Marginal Risk for severe
storms as well if storms become better organized around the MCV.
The primary severe weather hazard will be strong damaging winds in
any of the stronger storms that develop. So much of the
convection today will be driven by meso-scale influences. Although
confidence is high that rain will develop today, confidence on
timing and placement is still somewhat uncertain. Since convection
is not expected to become widespread until this afternoon,
brought MaxT to around 90 today.

A weak cold front will slide into SE TX tonight and move very
slowly toward the coast and eventually stall near the coast and
become stationary. This feature will serve as another focus for
additional showers and storms. Again, some of the storms will
produce heavy rain with PW values exceeding 2.00 inches. Scattered
showers and thunderstorms will persist on Wednesday with high PW
air remaining in place coupled with low convective temperatures
and residual outflow boundaries. 850 mb temps cool a bit on
Wednesday and with morning convection possible, trimmed a few
degrees from MaxT. 43

LONG TERM [Wednesday Night through Tuesday]...

An active weather pattern will continue for the rest of the work
week as weaknesses move aloft and persistent onshore low level wind
flow continues to transport ample amounts of low level moisture,
yielding PWs of 2+ inches across Southeast TX. Unstable conditions
will carry on the chance of showers and thunderstorms all throughout
the rest of the week, which may result in some flooding issues for
some of the areas receiving daily heavy rainfall. Lower chances of
rain for this upcoming week.

The weather Wednesday night into Thursday will remain quite active
with the stalled frontal boundary in place along with moisture
convergence continuing well into early Thursday. With an already
unstable airmass in place, it will require very little for storms to
fire up quickly across portions of the CWA, especially along the
frontal boundary. Outflow boundaries from nearby storms could also
enhance ongoing activity and will make it difficult to pin point
when and where the strongest activity will be. Thus, kept PoPs
between 20 to 50% for most of Southeast Texas through early Thursday
morning. Chance of showers and thunderstorms further increase
Thursday throughout the day as a surge of moisture from the Gulf
moves into the local area (PWs increasing to around 2.2 inches) and
the boundary lifts northward. Thus, another day with heavy rainfall
can be expected over most of the CWA and could further increase the
risk of flooding for those areas already receiving good amounts of
rainfall these past few days.

For the weekend, Saharan dust moving westward from the Carribean may
give us a bit of a respite in the heavy rainfall, however, some
development is still forecast to occur. Another upper level trough
moving eastward across the Great Plains Saturday as well as onshore
flow continuing to provide sufficient low level moisture could be
enough for at least diurnal showers and thunderstorms to form. Area
of high pressure looks to build over TX early next week, which could
help keep PoPs on the lower end of the spectrum.

Cloud coverage and cooling from showers will give us a bit of
respite from very hot summer temperatures. Most days this week
should have high temperatures in the upper 80s to low 90s; these
will vary daily depending on when and where the activity develops.
Humid conditions will keep the lows, however, in the mid to upper
70s areawide. 24

MARINE...

High pressure over FL and low pressure over SW TX will maintain
onshore winds today. The gradient will tighten today and a SCEC
will probably be needed for this AM for seas offshore and for wind
and seas this afternoon. Wind/seas will be higher in and near
thunderstorms today through Wednesday. The pressure gradient
remains tight through the weekend as low pressure develops in the
lee of the Rockies. A SCEC will be needed over parts of the
coastal waters over the weekend. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 90 72 87 72 90 / 60 70 70 30 60
Houston (IAH) 91 74 86 74 90 / 60 90 80 50 80
Galveston (GLS) 90 78 85 79 88 / 50 90 70 40 70

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION from noon CDT today through
this evening for the following zones: Coastal waters from
Freeport to Matagorda Ship Channel TX out 20 NM...Coastal
waters from High Island to Freeport TX out 20 NM.

SMALL CRAFT SHOULD EXERCISE CAUTION through this evening for the
following zones: Waters from Freeport to Matagorda Ship
Channel TX from 20 to 60 NM...Waters from High Island to
Freeport TX from 20 to 60 NM.

&&

$$

Discussion...43
Aviation/Marine...43

[Cromagnum]

Geeze. If there is 7-8 inches of rain on already saturated ground in some areas...could get real cute around here.

[Kingwood36]

Stuff out west seems to be falling apart as we speak

[davidiowx]

That large blob off the TX coast is looking more interesting this morning.

[Belmer]

Could certainly get interesting this evening and overnight. NWS HGX has issued a FFW for our area:

...FLASH FLOOD WATCH IN EFFECT FROM 7 PM CDT THIS EVENING THROUGH
WEDNESDAY MORNING...

The National Weather Service in League City has issued a

* Flash Flood Watch for portions of south central Texas and
southeast Texas, including the following areas, in south central
Texas, Coastal Jackson and Inland Jackson. In southeast Texas,
Austin, Brazos, Burleson, Chambers, Coastal Brazoria, Coastal
Galveston, Coastal Harris, Coastal Matagorda, Colorado, Fort Bend,
Galveston Island and Bolivar Peninsula, Grimes, Houston, Inland
Brazoria, Inland Galveston, Inland Harris, Inland Matagorda,
Madison, Matagorda Islands, Montgomery, Northern Liberty, Polk,
San Jacinto, Southern Liberty, Trinity, Walker, Waller, Washington
and Wharton.

* From 7 PM CDT this evening through Wednesday morning

* A line of strong thunderstorms will develop over southeast Texas
this evening and slowly move eastward through Wednesday morning. A
combination between the slow moving nature of the thunderstorms,
back building/training of thunderstorms, and recent rainfall over
the area has led to an increasing threat of flash flooding.
Rainfall rates may reach one to three inches per hour or more at
times. There remains some uncertainty in the timing and location
of the line of strong thunderstorms. On average, two to four
inches of rain is expected through tomorrow morning with isolated
areas of six to eight inches possible.

* These storms with heavy rainfall may be capable of flooding
roadways. Low water crossings may flood becoming impassable and
dangerous. Small creeks and bayous may see minor rises.

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.

HGX FFW

hgx.png (11.18 KiB) Viewed 3392 times

[TexasBreeze]

Flood Watch in effect for all of SE TX 7pm tonight through Wednesday AM. More details above. Chances lowered to 40% rest of the day, but main focus is tonight. Gotta watch that blob offshore though for
chances of cutting off inflow or meeting up with this evening's action. Watch and see...

[Cpv17]

I’m not sure about the widespread 2-4” for everyone tonight. This setup could be one where one area just gets 10+” and the rest of us get very little. We’ll see.

[Stormlover2020]

Lol no it’s not, I’m looking at every model, the setup seems pretty good for 1-4 inches of rain looks pretty reasonable. This is a hard forecast better Hope rpm model is wrong

[txbear]

Seems like the gap between the coast and that blob over the gulf is slowly starting to fill in, coverage wise. Potentially cutting off the in-flow? Will be an interesting afternoon to see how things progress. Mesoscale models don't seem too worried about it, and still initiate some decent rains over the area.

[don]

Models show the blob moving off to the east/dissipating by the time the disturbance comes in tonight.I expect most areas to get at least 1 inch of rain.It looks like minor cyclogenesis starts to happen with tonight's disturbance as it enters southeast Texas and starts to slow down, a core rain event looks to be setting up.But with these setups its really hard to pinpoint exactly where the core rains will setup, often becoming a nowcasting situation.The system could ends up producing a pretty large swath of high QPF, or it could end up being a more localized concentrated area that end up with high QPF.

[Rip76]

Very Interesting indeed.

[djmike]

Core rain will probably set up over me in Beaumont. Seems we always get the Niagara falls here. ....but seriously, yes it could be anywhere and prob wont know till it’s actually happening. Its been nothing but sun and HOT here today. All i can think about is fuel for the fire....When do the rains start tonight? Early? Late? Morning?

[DoctorMu]

It will be hit and miss as the circulation and front move SE. More hit than miss.

Hope we get hit.

[don]

Kinda cool that the EURO Tropical ensembles are picking up on the cyclogenisis of the system. It looks like a low to mid level circulation develops and being so close to the gulf it taps into the moisture and behaves somewhat like an "inland depression". A similar system affected Louisiana back in August 2016.

[DoctorMu]

Kinda cool that the EURO Tropical ensembles are picking up on the cyclogenisis of the system. It looks like a low to mid level circulation develops and being so close to the gulf it taps into the moisture and behaves somewhat like an "inland depression". A similar system affected Louisiana back in August 2016.

Right. The center of circulation is drifting SE on Hwy 6 near Waco towards College Station. Development and movement of showers over the next 6 hours should be interesting.

[Waded]

Interesting here in eastern Harris County. Sky is this haze gray, but the sun is shining fiercely through it. Very hot and humid.

[Cpv17]

HRRR model seems to think the heaviest rains will be well south of Houston.

[MH5]

Latest from the WPC - notes that the latest HRRR runs might not have the best handle on the setup.

Mesoscale Precipitation Discussion 0371
NWS Weather Prediction Center College Park MD
625 PM EDT Tue Jun 23 2020

Areas affected...East-Central to Southeast TX...West-Central to
Northwest LA

Concerning...Heavy rainfall...Flash flooding likely

Valid 232225Z - 240425Z

SUMMARY...Showers and thunderstorms will tend to become more
numerous going through the evening and overnight hours. Very heavy
rainfall is expected locally from slow-moving and concentrated
bands/clusters of convection which will foster a growing threat
for flash flooding.

DISCUSSION...The latest GOES-16 visible satellite imagery shows a
very well-defined MCV moving slowly through east-central areas of
TX which is also driving a surface low along with an attendant
front. The airmass across the greater southeast TX coastal plain
and areas of western LA is moderate to strongly unstable with
MLCAPE values up around 2500 j/kg. This airmass ahead of the front
coupled with an uptick in low-level moisture convergence ahead of
the MCV-related forcing/dynamics is already fostering the
development and expansion of several clusters of relatively
slow-moving showers and thunderstorms, and especially just east of
the surface low center.

Over the next several hours, the slow-moving MCV is expected to
favor some locally focused clusters and bands of heavy rainfall as
showers and thunderstorms tend to develop and becoming more
closely aligned with the corridors of stronger low-level moisture
convergence and instability transport near the front and ahead of
the low center which will involve increasingly more areas of the
eastern and southeast TX coastal plain and also some adjacent
areas of west-central to northwest LA where some surface trough
activity is noted. Low-level inflow in itself is not expected to
be strong, but the vort energy and forcing along the front is
expected to be persistent with a gradual settling of the energy
down to the southeast with time. As this occurs, there will tend
to be more convective development farther south along the trailing
cold front.

The HRRR/HRRRx guidance is already a bit late with some of the
convective initiation/activity impacting areas of eastern TX, but
the experimental WoFS guidance does appear to have a reasonably
good handle of the current activity and does favor more
concentrated clusters/bands of convection evolving over the next
several hours.

The WoFS guidance supports some areal coverage amounts of 2 to 4
inches of rain going through late evening, with some ensemble
member output suggesting isolated 5 to 6 inch totals. Multiple
members of the 12Z/18Z HREF guidance suggest similar potential and
especially the NAM-conest prior to 06Z. Given the tropical nature
of the airmass with PWs approaching 2 inches, these heavier
rainfall totals are expected.

Given the set-up, areas of flash flooding will become increasingly
likely going through the evening and overnight time frame.

[Cromagnum]

What time are we talking about to kick all this off?

[MontgomeryCoWx]

Around 10-2 am it seems like