482
FXUS64 KHGX 140922
AFDHGX
Area Forecast Discussion
National Weather Service Houston/Galveston TX
422 AM CDT Sun May 14 2023
...New SHORT TERM, LONG TERM, MARINE, HYDROLOGY...
.SHORT TERM...
(Today through Monday Night)
Issued at 415 AM CDT Sun May 14 2023
The Flood Watch has been expanded northeastward based on the latest
radar trends and high-resolution model guidance, more on that in the
Hydrology section towards the bottom of the AFD. A corridor of 1.8"-
2.0" PW values (90th percentile: ~1.74") will remain steady over
Southeast TX throughout the day. Offshore this morning, an embedded
shortwave trough will continue to drift northward throughout the day
and act as the lifting mechanism for the sufficient moisture in
place. This is already evident with the widespread rainfall going on
near Matagorda Bay early this morning. Some models indicate that
this may evolve into a mid level low with a subsequent surface low
developing as it pushes inland late this morning. As of ~330am CDT,
radar reflectivity reflects some slight spin to it offshore, so it
definitely appears that it'll make a run at a surface low
developing.
A 25-30 kt LLJ looks to develop west of I-45 this morning as well
and in combination with sufficient instability (1000-1500 J/kg
CAPE), there will be favorable support for the development of
showers/thunderstorms. Long story short, widespread rainfall is
expected to continue into the afternoon hours across Southeast TX,
but especially for areas along and west of I-45. The trends from the
HRRR have been fairly consistent showing a swath of 3-6" of
additional rainfall today across portions of Southeast TX where
training occurs. Isolated higher totals will be possible. We'll have
to monitor rainfall rates as well, we've already seen rates of 2-
3+"/hr yesterday and will likely see this today as well. As a result
of all of that, WPC has increased the excessive rainfall outlook to
a moderate (level 3 out of 4) for most of Southeast TX.
Rainfall begins to taper off going into the late afternoon/evening
hours as we lose the favorable dynamic forcing. As far as
temperatures go, with widespread rainfall and overcast cloud cover
prevailing today we won't get too warm. Expect high temperatures to
top out in the upper 70s to low 80s. Going into Monday, a 588-590
dam mid level high slides in overhead from the east, so cloud cover
will break up enough to raise temperatures into the mid to upper
80s. Some locations further east could even reach the 90°F mark. A
weak cold front still looks to approach us late Monday night, but
will be washing out as it does so. The main impacts we'll get from
this front is persistent chances of showers/storms going into the
overnight hours and at least a brief break from the onshore flow. As
a result, most locations may see temperatures in the upper 60s on
Monday night.
Happy Mother's Day to all of the moms out there! We really wish we
could have better weather for y'all today, but it's going to be a
wet one with localized flooding possible. Please be sure to have
multiple ways of receiving any potential flood warnings today, check
roadway conditions before you venture out, and if you see any water
on roadways...turn around, don't drown.
Batiste
&&
.LONG TERM...
(Tuesday through Saturday)
Issued at 415 AM CDT Sun May 14 2023
The pattern changes to a more seasonal during the long term period.
Upper ridging weakens and shifts eastward on Tuesday as a weak
cool front attempts to cross the region during the day. Latest
trends continue to bring a weaker front, so it might washes out
before reaching the coast. Given some PV anomalies aloft and high
low level moisture, showers and thunderstorms will be possible as
the "front" approaches the area. Depending on the location of the
"front" and any other boundary (-ies), rain/storm chances will
continue on Wednesday. The best chances will fall in the aftn with
peak heating. Upper ridge builds in to our west by mid-week,
increasing NW flow aloft and subsidence to our area. Therefore,
lower precipitation chances are possible through Friday. A
deepening upper low will develop over the Great Lakes later this
week, dragging a cold front southward into the Southern Plains and
Southeastern CONUS this weekend. This FROPA is progged tt bring
rain and storms chances by Saturday. Behind the front, a strong
ridge of high pressure builds in over the Plains, bringing drier
conditions into the upcoming week.
JM
&&
.AVIATION...
(06Z TAF Issuance)
Issued at 1138 PM CDT Sat May 13 2023
Mostly VFR across the area, though MVFR ceilings will be mixed in,
especially near convection. Periods of shra/tstms anticipated
into around 10-12z along the I-45 terminals, possibly followed by
a brief lull, then additional precip development after 16z with
heating and additional surges of moisture rolling in from the
Gulf. Visibility restrictions and wind variability will be common
in/near the heavier rain. Otherwise, a mix of MVFR/VFR in the
morning gradually lifting in the mid-late morning hours. Though
there is some uncertainty, expect precip to wind down near the
coast ~20z and well inland 0-2z. 47
&&
.MARINE...
Issued at 415 AM CDT Sun May 14 2023
Scattered to numerous showers and thunderstorms will continue to
increase in coverage today as different disturbances move through
the region. Light to moderate southeast winds will persist today
with seas around 5 to 6 ft. Strong gusty winds, heavy rain and
frequent lightning can be expected with the strongest storms. In
general, caution flag continues through early this evening, with
winds approaching advisory levels at times. Daily chances for
isolated showers and thunderstorms will continue this week. Light
and variable winds are possible on Tuesday as a weak front attempts
to make its way offshore. However, onshore winds will prevail
through most of the week.
JM
&&
.HYDROLOGY...
Issued at 415 AM CDT Sun May 14 2023
The Flood Watch (goes through 7pm CDT Sunday) has been expanded
further northeastward and now includes Harris, Montgomery, Grimes,
Waller, Austin, Fort Bend, Galveston, and Brazoria Counties in
addition to those that were in the initial watch. This is based on
both radar trends along with the persistent QPF trends in high-
resolution model guidance. Over the past several hourly runs, the
HRRR has depicted a swath of 3-6" of additional rainfall over
portions of Southeast TX along the I-45 corridor. Excessive rainfall
has already occurred on Saturday with western Montgomery County
receiving an estimated 4-6" of rain. Montgomery County OEM reported
that multiple roadways are not passable in the western portion of
the county as a result. Soils are fairly saturated, so the
additional rainfall that is expected today will quickly runoff and
could lead to additional localized street flooding and flooding in
low-lying/vulnerable areas.
There are multiple river flood warnings out mainly in Jackson and
Lavaca Counties along the Lavaca/Navidad rivers as some sites have
crested into minor and even moderate flood stage. Rainfall continues
to fall in this area this morning, so we will have to monitor QPF
trends causing additional rises along area rivers, creeks, and
bayous. This includes monitoring bayous and creeks in and around
Harris County as well as there are indications that some may reach
top of bank if the HRRR QPF forecast verifies.
Batiste
&&
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 79 68 84 67 / 70 30 30 20
Houston (IAH) 81 70 88 69 / 70 20 20 20
Galveston (GLS) 80 74 83 73 / 40 20 20 10
&&
.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flood Watch through this evening for TXZ198-199-210>213-226-227-
235>238-313-335>338-436>438.
High Rip Current Risk through this evening for TXZ436>439.
GM...Small Craft Should Exercise Caution through this evening for
GMZ330-335-350-355-370-375.
&&
$$
SHORT TERM...Batiste
LONG TERM....JM
AVIATION...Cady
MARINE...JM
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
436 AM EDT Sun May 14 2023
Day 1
Valid 12Z Sun May 14 2023 - 12Z Mon May 15 2023
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST TEXAS...
...Texas...
The Slight risk was trimmed back even more across TX with this
issuance, however a relatively narrow Slight risk remains across
portions of southeast TX. Observational trends at 08z show a well
defined vort max offshore the TX coast, with this feature expected
to move inland today and likely help focus a flash flood risk.
There remains some question as to the strength of this feature as
it moves northward across east TX, and thus also the degree of
convective organization. Recent observational trends seem to
suggest this feature is pretty well defined, and recent HRRR runs
have generally been trending upwards with QPF. The environment is
supportive of efficient rainfall, with high PWS, sufficient
instability and wind profiles supportive of some backbuilding of
cells on their southern flank. So these observational and HRRR
trends are a bit concerning, and after discussion internally and
with HGX, we made a late call to upgrade a portion of this area to
a Moderate risk. Overall there is pretty good agreement on the
axis amongst HREF members, recent HRRR runs and the Gem Reg, so
not much uncertainty there. The uncertainly deals more with the
magnitude of the event. Whether cells stay disorganized and
generally transient in nature, or if they grow deeper, become more
organized and then show some backbuilding characteristics. We are
leaning towards the latter scenario, hence the MDT risk upgrade,
and some locally significant flash flooding could evolve from a
setup like this.
...OK/KS into the Mid MS Valley...
A Slight risk was introduced across portions of northeast KS into
central/northern MO and southwest IL. An interesting setup here,
with what is pretty much a backdoor cold front dropping south
southwest into the region through the day. Meanwhile weak vort
centers lifting northward in the deep layer southerly flow should
interact with this front and help organize convective development.
One piece of energy is the remnant MCV currently over the TX
Panhandle (as of 08z) and the other is the strung out pieces of
vorticity streaming north out of TX and OK. Convection should
break out this afternoon within the Slight risk area, with some
merging of cells possible as south to north moving cells move into
the frontal axis. Most of the KS and MO portion of the Slight risk
has below average soil saturation and streamflows, so FFG is high.
Thus flash flooding here may tend to be more isolated in nature
for the afternoon/evening hours. However there is a decent signal
for potential continued training convection overnight over
portions of northeast KS into adjacent areas of MO. In fact the
00z HREF shows 5"+ neighborhood probabilities of over 30%, and 3
hour FFG exceedance probabilities get over 30% as well. This type
of nocturnal convection that is being depicted by several of the
models tends to be very efficient warm rain driven. Confidence is
only average, but the ingredients do appear to be there for a more
focused flash flood threat by tonight. Over the eastern edge of
the Slight risk FFG is lower, and 3 hr FFG exceedance
probabilities in the HREF are actually over 50% from far eastern
MO into southern IL. So scattered FFG exceedance seems pretty
likely here, which should translate into at least some flood
impacts within any more susceptible basins/urban areas.
The Slight risk area aligned well with the overlap in convergence
and the highest PW anomalies (approaching mid May max values). It
is also aligned with the highest HREF probabilities and a Slight
risk area depicted by our GEFS based CSU machine learning ERO. So
all in all seems to be pretty good agreement on this area
experiencing some flash flood risk today/tonight.
This Slight risk is surrounded by a broader Marginal risk.
Ingredients do support a localized heavy rainfall threat across
much of OK/KS into portions of the MS valley not in the Slight
risk. The Slight risk was placed where the best organized threat
appears to be, but the risk of localized flash flooding exists
with the Marginal risk as well...just expected to be more isolated
in nature.
Chenard
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt