April 2023

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DoctorMu
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The Brazos County rain gradient could be 0.5 inches to nearly 3 inches. Crazy!

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Cpv17
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The FV3 and RGEM models look very interesting towards the end of their runs. Training setting up.
Stratton20
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00z gfs starting to hint at possible training setting up as well
Cromagnum
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I don't like those recent QPF models. Brazoria County gets shafted if that holds.
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srainhoutx
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Back in town until early Friday morning. Looking wet starting tomorrow into Saturday. Typical situation around these parts as a cold front stalls offshore and then a surface trough develops with embedded upper air disturbances ride across our Region. Almost time to monitor the short range meso guidance.
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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tireman4
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000
FXUS64 KHGX 041132
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
632 AM CDT Tue Apr 4 2023

...New AVIATION...

.SYNOPSIS...
Issued at 445 AM CDT Tue Apr 4 2023

The main focus for this forecast period is on the Wednesday to
Saturday timeframe. A cold front will make its way across
Southeast Texas, stalling over the Gulf waters, not too far off
the coast. This will provide multiple opportunities for showers
and storms late in the week. Here are some key things to remember:
- The main hazard of concern is locally heavy rainfall. A slight
risk (level 2 of 4) of excessive rain will be with us Wednesday,
primarily Wednesday night, through Thursday night. The highest
threat will be in low-lying, urban, and other poor drainage
locations.
- Total rainfall amounts of 3 to 6 inches are forecast, with
locally higher amounts in spots that see particularly heavy rain
or multiple rounds of heavy rain. How much of a problem this
causes at a given spot will be strongly dependent on the rate at
which this rain falls, rather than the total amount of rain.
- There will be a marginal risk (level 1 of 5) for severe weather
as the front moves into the area, with damaging winds the main
hazard and large hail a secondary concern.

&&

.SHORT TERM...
(Today through Wednesday Night)
Issued at 445 AM CDT Tue Apr 4 2023

A mid to upper level trough over the Four Counters/Rockies is
expected to fill NE on today. As it does, the trough will take on a
negative tilt with a warm front-dryline-cold front developing about
its surface low over the Central Plains/Middle Mississippi River
Valley. The southernmost portion of the dryline seems to slow/stall
over Central TX/Red River Valley during the day. Pair this with
widespread (-100) J/KG of SFC CIN from a robust subsidence inversion
and the chances of getting much in the way of rainfall looks slim.
HREF members depict some weakening in the cap during the late
afternoon/early evening over the northern fringes of our CWA, which
coincides with the arrival of shortwave energy aloft. If any air
parcels can overcome this cap, there will be plenty of ingredients
for them to tap into. PWs reach 1.5-1.6" during this time frame with
MLCAPE progged to be near 1800-2500 J/KG, SRH at 100-250 m2s2 and
a LLJ overhead nearing 30-40 knots. SPC currently has the
northern third of our CWA under a marginal risk of severe weather,
with strong winds and hail being the primary threat. Afternoon
highs should reach the 80s area wide, falling short of convective
temperatures in part to cloudy skies overhead.

A cold front associated with the aforementioned surface low/upper
trough should approach the Brazos Valley early Wednesday morning.
The 850 mb front appears to slow/stall near the northern portion of
our CWA while the surface front pushes offshore in the afternoon.
Showers and storms should accompany the front with cooler, drier air
filling in quickly thereafter to keep highs in the 70s. While this
may provide a brief lull in rain activity, a coastal trough should
develop offshore from the remnants of the front by Wednesday
evening. PWs near 1.6-1.7" and increasing shortwave energy should
work in tandem with this feature to put rain chances on the rise
into Thursday morning. Environmental soundings depict a deep warm
cloud layer in this environment with increasing precipitation
efficiency as the atmospheric column becomes saturated. WPC has our
area under a slight risk of excessive rainfall for Wednesday. Dry
soil conditions should limit the threat of heavy rainfall to
urban/low lying areas with poor drainage on Wednesday.

&&

.LONG TERM...
(Thursday through Monday)
Issued at 445 AM CDT Tue Apr 4 2023

The long term section begins as a continuation of the end of the
short term...a soggy mess. Like...wet cardboard lying in a muddy
puddle sort of soggy mess. I`ve got high PoPs from Thursday
morning right on into Saturday, particularly at the coast and over
the Gulf waters. Now, do I think it`s actually going to be raining
constantly that entire time? No, even by Southeast Texas
standards that would be a little ridiculous. But, there is high
confidence we will see plenty of intermittent showers and storms
through this whole window near a stalled front. Eventually, high
pressure will drop in strongly enough to shove the front/its
remains far enough offshore that rain chances will drop off from
north to south through the day Saturday and Saturday evening.

Let`s put a pin in this late week wet stretch and come back to
discuss this a little bit later. First, let`s finish off a quick
summary of the rest of the weekend and early part of next week. I
do this because it`s not going to take very long. Weak midlevel
ridging early Sunday morning will become well established into the
mid-week. At the surface, the pressure pattern looks pretty flat,
giving us pretty variable - but generally light winds for much of
the period. As a result, we should see generally fair weather with
the temperature trend a gradually increasing one. Expect dewpoints
to fluctuate diurnally but generally be on a slow climb. In the
afternoons I have some slight chances for diurnal showers/storms
as we`ll spend much of this time underneath northwest flow aloft,
which could help allow for a bit of instability. I`m not super
convinced that we`re there yet, but what`s a 15 percent rain
chance among friends? This spring and summer-like diurnal pattern
is going to have to emerge eventually, though.

Okay, with the rest of the long term out of the way, let`s go back
and take more of a look at Thursday to Saturday. If I could only
use one thing to talk about how late this week is going to go, I
would use the Euro ensemble Extreme Forecast Index for QPF. For
both 00Z Thursday to 00Z Friday (Wednesday night and Thursday)
and 00Z Friday to 00Z Saturday (Thursday night and Friday), there
is a large swath of an EFI greater than 0.5 indicating higher than
average rainfall likely. There is also a sizable stripe of EFI
greater than 0.8 around the stalled front, indicating that above
average rainfall is very likely, along with an increasing
potential for "extreme" rainfall (relative to the Euro`s
M-Climate) also seen in increasing values of the related "shift of
tails" contours.

Fortunately, though, I get to look at more than one thing, so I
can dig into this a little more. *Why* are we getting such a clear
signal for unusually high rainfall? From a very high level view,
we are getting into spring, and as the subtropical ridge becomes
more of a feature in our weather (even more so than it already was
this winter), cold fronts will be less able to cleanly clear
through the area, instead stalling out somewhere around here. It`s
getting warmer, and more humid, and with the stalled front to be a
persistent focus for storm initiation, we can squeeze out plenty
of rain. Or, more succinctly, it`s Stalled Front Szn. Tax
Day...Memorial Day...there`s a reason spring holidays around
Houston are infamous.

As for this stretch, specifically, we definitely have plenty of
moisture to work with. Both the NAEFS and EPS mean precipitable
water values are above the 90th and, at times, the 99th percentile
late this week in reaching the 1.5 to 1.8 inch range. Mean cloud-
layer flow will be close to front-parallel, increasing the
likelihood of training showers and storms. Helping us to reach
these high moisture levels is strong boundary layer inflow from
the Gulf here in the middle week, reaching 30ish knots at 850 mb.
However, this looks to drop off late in the week. As the 850 front
pushes a little closer to the coast, we actually see 850 winds
fall into the 10 to 20 knot range. This may mitigate rainfall
potential some - lesser Gulf inflow will keep the air over our
area from being able to "reload" its moisture supply as
effectively, limiting the length of time we can have those really
extreme moisture levels and potentially mitigating high-end
rainfall amounts.

By now, you`re probably shouting "Get on with it!" and so we will.
How much rain are we looking at here? In our rainfall forecast
worked out with WPC, we`ve got a widespread 3-6 inches for the
whole "stalled front" episode, with the highest amounts reserved
closest to wherever the front spends the most time stalled out. Of
course, localized areas could see even higher amounts should they
get a particularly heavy rainer or multiple rounds of solid rain.
Now, we have been pretty dry of late, so that will help mitigate
flood concerns. Additionally, rain rate will be important here. 6
inches is not so big a deal around here if it`s spread out
relatively evenly across three days. It is a much bigger problem
if those 6 inches happen in three hours. For the most part,
rainfall rates look more manageable, though again, we could easily
see more troublesome rain rates in localized spots. All in all,
the slight risk area - indicating a 15-40 percent chance of
exceeding flash flood guidance - in the Day 2 and 3 excessive rain
outlooks are appropriate. We have a concerning feature in a
stalled front, fueled by high levels of moisture and a setup that
supports training rainfall. But this is mitigated by relatively
dry antecedent conditions and weakening inflow, blunting the
emergence of higher threat levels.

&&

.AVIATION...
(12Z TAF Issuance)
Issued at 605 AM CDT Tue Apr 4 2023

MVFR CIGS will begin to scatter/lift this morning as gusty S/SE
winds develop across the region. VFR conditions resume this
afternoon while wind gusts approach 25 to 30 knots. MVFR CIGS
return during the late afternoon/early evening with breezy
conditions persisting overnight in advance of a cold front. The
front should reach KCLL/KUTS around 12z, bringing showers and
storms through Wednesday morning as it pushes south towards KIAH.

&&

.MARINE...
Issued at 445 AM CDT Tue Apr 4 2023

Light, patchy fog will remain a possibility into this morning,
though visibility restrictions look to be modest, in the 3-6 mile
range where fog occurs. Water temperatures have risen into the
lower to middle 70s, which is hampering the development of fog in
an airmass with dewpoints only in the lower 70s. Any fog that does
crop up should dissipate by mid-morning.

Moderate to strong onshore flow will persist into midweek, and a
Small Craft Advisory is in place later today and tonight on the
Gulf waters. Caution flags are up for the bays, which looks to see
slightly lower wind speeds. While this onshore flow will push
water levels above normal astronomical tides, water levels of only
2.5 to 3 feet above MLLW are expected over the next few tide
cycles. On area beaches the strong, persistent onshore flow will
continue to keep rip current risk high and beach patrols are
flying red flags for those rip currents.

A cold front is forecast to stall just off the coast on
Wednesday. Showers and isolated thunderstorms can be expected
along the front both as it moves in, and for several days after
its forward motion breaks down. Moderate northeast winds,
elevated seas and periods of showers and thunderstorms will
persist for the remainder of the week as series of upper level
disturbances pass over the remnant frontal zone.

&&

.CLIMATE...
Issued at 445 AM CDT Tue Apr 4 2023

A slew of daily records fell yesterday, with four of the five
first order climate sites tying or breaking their record high
minimum temperature. These locations were both the City of Houston
and Houston/Hobby, Galveston, and Palacios. College Station fell
only one degree below its record high min for the day.
Additionally, the City of Houston also tied its daily record
maximum temperature, reaching 87.

As onshore flow continues to keep a warm, humid airmass in place,
it`s more of the same today. Here`s a summary of the heat records
for today, along with our forecast in parentheses:

Site Min Temp Max Temp
---------------------------------------------------
City of Houston 72, 2001 (74) 88, 2017 (87)
Houston/Hobby 72, 2001 (74) 87, 1940 (85)
Galveston 72, 1929 (73) 82, 2011 (81)
College Station 73, 1923 (72) 98, 1893 (87)
Palacios 73, 2001 (74) 86, 1943 (82)

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 87 64 72 53 / 10 40 60 60
Houston (IAH) 87 71 79 58 / 10 10 60 80
Galveston (GLS) 81 72 76 64 / 0 0 70 70

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk through Wednesday morning for TXZ436>439.

GM...Small Craft Should Exercise Caution from noon CDT today through
late tonight for GMZ330-335.

Small Craft Should Exercise Caution until noon CDT today for
GMZ350-355-370-375.

Small Craft Advisory from noon today to 1 AM CDT Wednesday for
GMZ350-355.

Small Craft Advisory from noon today to 7 AM CDT Wednesday for
GMZ370-375.

&&

$$

SHORT TERM...03
LONG TERM....Luchs
AVIATION...03
MARINE...Luchs
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jasons2k
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Update from Jeff:

Widespread rainfall…some heavy likely Thursday and Friday.

A wet weather pattern will be developing over SE TX mid to late this week into early this weekend as a frontal system stalls over the area. Surface front will move across the area on Wednesday with scattered showers and thunderstorms. Overall rainfall amounts on Wednesday with the actual front look to be generally less than an inch. The front then stalls offshore over the northwest Gulf into Thursday and Friday and becomes a coastal surface trough. Flow above the surface will bring significant amounts of moisture into the area from both the Gulf of Mexico and the Pacific along with numerous disturbances in the southwest upper level flow. All these factors will combine to produce episodes of showers and thunderstorms from Wednesday night-Friday night. The stalling 850mb front may become a focus for showers and storms inland of the surface front and this boundary looks to slow and stall northwest of the US 59 corridor.

Rainfall Amounts:
Widespread rainfall totals of 3-6 inches will be possible from Wed-Sat with the majority of the rains falling on Thursday and Friday. Isolated higher totals will be possible given the saturated moisture profile. Rainfall rates look to be in the 1-2 inch per hour range which we can handle and hopefully well timed breaks in the activity will give a chance for urban ponding to drain off.

Hydro:
Grounds are dry from the recent dry spell and will be able to absorb at least much of the initial rainfall. Flooding in SE TX, especially in the urban areas, is strongly tied to the rainfall rate (how much rain falls in a period of time). Given the likely rounds and breaks in the rainfall through the period, think run-off will be on the lower side, however as grounds saturate over time run-off will increase even with rainfall rates of 1-2 inches per hour. Concern will be with any sustained training cells that could push higher rainfall in a smaller time window allowing greater run-off. This will be possible at times given the stalled boundaries over the area and the parallel flow along these boundaries.

Street flooding is the greatest concern at the moment along with rises on more rural creeks where extended rainfall tends to have the greatest influence…Little Cypress, Willow, Cypress, Spring, Clear, South Mayde, Bear, Langham. Depending on where the greatest rains fall over the course of the 2-3 days will determine where any potential flooding may develop.

Forecasted Rainfall (Wed-Sat):
C3EC4B18-2720-4DD1-8FB2-074735E05A14.jpeg

Jeff Lindner
Director Hydrologic Operations Division/Meteorologist
Harris County Flood Control District
9900 Northwest Freeway | Houston, Texas 77092
346-286-4000 (main) | 346-286-4165 (direct) | 281-924-2091 (cell)
jeff.lindner@hcfcd.org | Twitter: @jefflindner1
Stratton20
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12z NAM models coming in more aggressive with widespread heavy rain
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tireman4
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.AVIATION...
(18Z TAF Issuance)
Issued at 1223 PM CDT Tue Apr 4 2023

MVFR to VFR cigs (IFR for GLS) currently across SE TX taf sites
with S winds around 12-18 KTS with gusts of around 25-30 KTS.
MVFR to possibly IFR conditions are expected to return tonight
through Wed morning. Areas of SH/TS can be expected Wed morning as
a cold front passes through the region. There is some uncertainty
with the timing of this front, given that models are trending to
bring the front through later in the morning. The front is also
expected to slow down once it passes IAH area and eventually stall
near the coast, thus, some of the southern sites may experience
periods of SH/TS well through the end of the TAF period. Winds
will turn N once the front passes, but may remain VRB for sites
south of IAH. Will likely need to make a few more changes or AMDs
later today and tonight.

24
Cpv17
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We need to watch the middle of the month for some severe weather and more heavy rains/flooding threat.
Stratton20
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Interesting to see that the NAM models are much further north with the axis of heavy rain compared to other models, outlier right now, but something to watch
Cpv17
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Stratton20 wrote: Tue Apr 04, 2023 4:11 pm Interesting to see that the NAM models are much further north with the axis of heavy rain compared to other models, outlier right now, but something to watch
Some of the models have came in further NW today.
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DoctorMu
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Stratton20 wrote: Tue Apr 04, 2023 4:11 pm Interesting to see that the NAM models are much further north with the axis of heavy rain compared to other models, outlier right now, but something to watch
Yeah, NAM, CMC, Ensembles have "bailed" on the more south of Hwy 1*5 solution.

I'm going to need a bigger boat. :lol:
Stratton20
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DoctorMu 18z GFS continues the NW trend, we get about 5-6 inches , definitely gonna need a bigger boat for sure😂😂
Cpv17
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Stratton20 wrote: Tue Apr 04, 2023 5:46 pm DoctorMu 18z GFS continues the NW trend, we get about 5-6 inches , definitely gonna need a bigger boat for sure😂😂
I’m rooting for the Euro. Everyone gets a lot of rain.
Cromagnum
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I better get 2-3 inches minimum. If I get this less than 1 inch crap I'm going to lose my mind.
Cpv17
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Cromagnum wrote: Tue Apr 04, 2023 7:12 pm I better get 2-3 inches minimum. If I get this less than 1 inch crap I'm going to lose my mind.
The models today are trending for less rain for both me and you. Especially you.
Cromagnum
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Cpv17 wrote: Tue Apr 04, 2023 7:22 pm
Cromagnum wrote: Tue Apr 04, 2023 7:12 pm I better get 2-3 inches minimum. If I get this less than 1 inch crap I'm going to lose my mind.
The models today are trending for less rain for both me and you. Especially you.
Well hopefully it's more widespread. Since January, I've totaled about 1 inch.
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don
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WPC afternoon update. They are saying that a Moderate Risk is likely if the tend in the models continue.
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
439 PM EDT Tue Apr 04 2023

Day 3
Valid 12Z Thu Apr 06 2023 - 12Z Fri Apr 07 2023

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FROM SOUTHEAST
TEXAS TO WESTERN LOUISIANA...

...2030Z Update...

Thunderstorms ongoing along and to the north of a stalling cold
front along the Texas Gulf Coast overnight Wednesday/early
Thursday morning are forecast to continue throughout the day
Thursday given continuous moist onshore flow in the low levels
from the Gulf. This will promote the redevelopment of
thunderstorms and training storms over the Slight Risk area,
increasing the risk for higher rainfall totals. Anomalously high
precipitable water values 1-2+ standard deviations above the mean
will increase in areal coverage over the region given the
continuous onshore flow. This increasing moisture will support
additional heavy rainfall totals over the same general region of
southeast Texas/western Louisiana that saw heavy rainfall during
the day 2 period. The global ensemble guidance shows moderate
probabilities of areal average rainfall totals of around 2", with
the deterministic guidance hinting at the possibility of locally
higher totals into the 4-5" range. As noted overnight, an increase
in confidence in realizing these more significant totals over more
than just isolated locations in the hi-res guidance during the day
2 and/or day 3 period may likely require an upgrade to a Moderate
Risk for day 3 given increasingly wet antecedent conditions and
the additional excessive rainfall, likely during a relatively
continuous timeframe.
Cpv17
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I feel like this has potential to be a big bust for many of us. I’m seeing very sharp gradients of rainfall on just about every mesoscale model out there. It now looks like the heaviest rains will fall in the far western parts of our viewing area. At least on Thursday.
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