Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 251559
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
959 AM CST Sun Feb 25 2018

.UPDATE...
Two features are at play across SE TX this morning. A mid-level
short wave currently situated just north of I-10 stretching from
Austin to Polk county, is aiding in overall coverage of showers
and thunderstorms. Mid to upper level southwesterlies will help
to advect this feature to the northeast through the late morning
hours, eventually sliding into W LA by early afternoon. Ahead of
this feature, ample lift and moisture are allowing for the best
shower and thunderstorm coverage. Rain rates beneath stronger
storms have ranged between 0.5-1" in a half hour. As this system
shifts further east where the soil is more saturated due to
previous rainfall, runoff and localized flooding could be
possible. Behind this feature, subsidence has helped to yield
further convective development.

The second feature to account for this morning is the stationary
front positioned further south of the shortwave. As of 9 am, this
boundary was located just south of highway 59. South of the this
boundary dewpoints are in the low 70s, while to the north of this
feature dewpoints are in the 50s. A very saturated air mass is in
place over SE TX with precipitable water values ranging between
1.5-1.8 inches. The best instability is situated north of the
front, where MU CAPE values range between 1000-1500 J/kg.
Although, low level lapse rates are not super impressive according
to forecast soundings, ranging between 4.5-5.0 deg C/km.

Overall, the forecast is in pretty good shape and no major
changes were needed. Tweaked PoPs a bit to account for recent
trends in radar imagery as well as short term guidance. Expect
precipitation to continue north of I-10 through the afternoon
hours as the shortwave lifts northeast of the region. The chance
for development of precip further south along the frontal
boundary early this afternoon will also be possible, as the front
slowly slides to the north.

Hathaway

&&

.PREV DISCUSSION... /ISSUED 409 AM CST Sun Feb 25 2018/

DISCUSSION...
At 4am...frontal boundary was situated from roughly Columbus to
north Houston to Moss Hill. Model guidance suggests it`ll sag
into the coastal counties toward sunrise, slowly meander back to
around I-10 later today, then receive a push offshore later
tonight. We did see a round of shra/tstms flare up ahead of the
boundary and produce a quick 0.5-1.5" of rainfall. Thankfully the
convection has been moving, but the strongest cells dropped
around 1/2" in 5 minutes at some some the HCFCD gages. Radar
trends have shown a break in the activity, but hires short term
guidance indicates the potential for some additional development
to the west and southwest possibly training over the same
locations. (FWIW their performance, while ok, has been hit/miss
so confidence is not particularly high in the finer details).

Increasing southerly flow over the frontal boundary should aid
with precip expanding further inland later this morning and
afternoon. Though always worth watching trends and for any
embedded elevated convection, think the vast majority of this will
be more of a steady type light/moderate rain with totals adding
up to 0.5-1.25" by the end of the day. Precip will taper off from
nw to se this evening followed by a rain-free Monday (inland,
anyway).

The front will head back north as a warm front Tuesday and bring
the typical fog, dz, -ra that occurs with these. We may even see
some embedded tstms should any disturbances in the sw flow aloft
move overhead later in the day. The next front is still penciled
in for late Wed night. Unless the H5 ridge offshore becomes a
little more suppressed, would expect the associated line of
shra/tstms along the boundary to be weakening as it makes its way
toward the coast and offshore. High pressure in its wake should
yield decent wx into Saturday before rain chances return Sunday.
47

MARINE...
Per obs/webcams, we are starting to see some redevelopment of the
sea fog over the bays/nearshore waters this morning as the strong
onshore winds decrease a bit (with the passage of the upper level
jet/disturbance to the NE). May have to re-issue the Marine Dense
Fog Advisory sooner than later if these trends continue.

Otherwise models are still indicating that the stalled cold front
over central parts SE TX will be getting a secondary push of cool
dry air tonight and we could see a brief wind shift over the bays
and nearshore waters by Mon morning. At this time...not expecting
this boundary to make it too far offshore as onshore winds resume
Tue. Conditions for sea fog will become more favorable once again
early Tue on into Weds. Extended guidance still going with a pass-
age of a strong cold front into the Gulf for Thurs. 41

AVIATION...
Scattered TSRA coverage winding down a bit at present as the dist-
urbance that moved across the cold front pushes further E/NE. The
forecast for the rest of the day should remain messy as the front
lingers over the central/coastal portions of SE TX and additional
disturbances try to move up from the SW. A mix of MVFR/VFR likely
for the northern TAF sites this afternoon with mostly MVFR/IFR at
the rest. GLS may prove to be the most problematic today with sea
fog redeveloping in between systems. 41

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      62  51  70  56  73 /  80  20  10  10  60
Houston (IAH)              68  55  73  59  76 /  80  60  10  10  50
Galveston (GLS)            70  60  68  63  72 /  60  40  10  10  40

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 6 PM CST this evening
     for the following zones: Waters from Freeport to the
     Matagorda Ship Channel from 20 to 60 NM...Waters from High
     Island to Freeport from 20 to 60 NM.

&&

$$

Discussion...08



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