Area Forecast Discussion


701 
FXUS64 KHGX 212144
AFDHGX
Area Forecast Discussion
National Weather Service Houston/Galveston TX
344 PM CST Wed Feb 21 2018
.DISCUSSION...
A rainy, dreary day across Southeast Texas, but fortunately the
heaviest rains have been isolated, sporadic, and ultimately
not enough to manifest in any flooding issues. Look for rain
chances to wax and wane through the week, but never truly go away
as an active weather pattern continues. The next more significant
shot for rain looks to come this weekend with another cold front,
but at this time the focus for the heaviest rain again looks to
be to our northeast.
.NEAR TERM [Through Tonight]...
Rain showers are copious across Southeast Texas this afternoon,
with isolated cells of heavier brief downpours embedded within
generally lighter rain. This pattern is readily apparent in
satellite, radar, and in the sound of rain falling on our roof.
This pattern of rain should generally continue tonight, though
gradually winding down even more in intensity. The heaviest
showers will continue to be in the vicinity of the front, which
should drift down towards the coast overnight. There is one
potential wrench in these plans. Farther west is another cluster
of showers and storms - the models are pretty unanimous in the
bulk of this cluster being yanked far to our north, while the
southern end withers. Given the direction of mid-level flow and
general lack of progged associated vorticity, this seems
reasonable. However, I'm a bit nervous looking at the water vapor
imagery showing pretty solid flow right into the back of a bit of
a leaf structure. Along with that, the HRRR surface wind field
does hint at an outside shot of an MCV feature developing. If this
occurs, all bets are off on that southern precip withering and
maybe even the hard northeast course of the main bulk.
Temp-wise, we should see cooler air continue to reign far inland,
which has already been in place most of the day. As the front
droops coastward, the warmer coastal areas should also start to
cool off. However, with the front ultimately stalling out as
onshore low level flow cuts it off from any baroclinic push...it
might not get quite as cold as you'd think given how much
temperature spread existed across the front at its peak.
.SHORT TERM [Thursday Through Friday Night]...
Shower and thunderstorm potential continues through the short 
term as the front stays mostly around the coast Thursday, and 
lifts back north Friday. Meanwhile, little vort maxes/subtle 
shortwaves are progged to stream through the upper flow, which 
will likely modulate when and where the best chances for rain are.
These subtle features are likely to be very difficult to time, 
even at this relatively short time range. Tried to highlight where
the best support for vertical motion would be by enhancing PoPs
a little where the model consensus seems to peg the best chances,
but generally keep broad swaths across the area so as not to
overstep the bounds of uncertainty with these features.
The location of the front will also play havoc with temperatures,
as the temperature gradient seen today continues (to a lesser
magnitude) even into tomorrow's high temperatures, before the
retreat northward results in a warmer day on Friday. Without any
real significant cold advection beyond the shallow surface layer
that will be displaced by the retreating front, Friday should get
pretty warm, particularly in that little band that is closer to
the coast, but far enough inland to escape from any marine
influence.
.LONG TERM [Saturday Through Wednesday]...
If you're looking for any real change in the forecast for the long
term, well...keep on looking, as the active pattern continues.
Indeed, with another upper trough and surface low rolling through
the Central/Southern Plains, it will mean the arrival of the next
cold front. The timing at this point looks to be a bit faster
Saturday night, and will bring a pretty decent shot at showers and
some thunderstorms. Not expecting quite as much moisture with this
front, as progged precipitable water values are clustered around
1.5 inches, but it's still fairly juicy. Like today's front, and
really, most of the recent fronts, the best potential for heavier
rainfall is likely to be northeast of our area - the upper trough
and its associated surface low get ripped off to the Western Great
Lakes, and we don't see much push of cold air to sustain the cold
front this far south. This should also mean cooler air for the
first half of next week, but nothing particularly brutal, or even
all that winter-like for that matter.
One thing we will want to keep an eye on is if/where the front
stalls out. The GFS leaves a very sharp surface trough over the
Gulf where the front stalls. Now, as explicitly modeled, it's far
enough offshore that any rain generated there falls way out over
the Gulf, and really winds become northeasterly enough that it may
give us a brief period of dryness. But...if the front stalls out
around the coast instead, it would likely make for a considerably
wetter period.
&&
.AVIATION [18Z TAF Issuance]...
Cold front bisects the southern areas of SETX...IAH has north
winds and temperatures down to 58 while HOU in the warm sector
with gusty south winds and 75 degrees. Front slowing and should
crawl southward into HOU this hour and LBX by 21z. GLS may only
get winds to relax and become more variable as it may never move
through GLS tonight. Areas along and north of the front will have
IFR-LIFR ceilings with a mix of light rain and showers...closer to
the frontal interface MVFR ceilings becoming IFR and showers with
isolated thunderstorm. South of the front MVFR to VFR with sea fog
off the coast. As winds relax tonight and LLJ weakens expecting
the ceilings to lower area wide and sea fog to move into the GLS
Bay area cratering GLS 09z and could reach HOU by 15-18z THU. 
Over-running precip mainly -RA/-DZ probably redeveloping THU 
morning/afternoon as SW LLJ veers to the S and strengthens well 
inland boosting the upglide. 45
&&
.MARINE...
Winds have increased dramatically along the immediate coast and over 
the bays just prior to the cold front. Have hoisted a SCEC for 
Galveston Bay through 8 pm with the approach of the s/w over the 
Hill Country. This should help to nudge the front out into the 
coastal waters where it stalls. Fog south of the boundary tonight so 
will keep a Marine Dense Fog Advisory going in the nearshore waters. 
The front lifts back north Thursday morning and could see dense fog 
moving back into Galveston Bay area around 6 am and most likely by 
around 10 am. Moist onshore flow strengthens Friday which should 
maintain the threat of fog through Sunday morning until the passage 
of a Pacific cold front. 
45
&&
.HYDROLOGY...
Rain over the widespread area has been light enough that area
rivers and streams should react favorably. CREST Streamflow via
FLASH indicates that there may be some small rises in parts of
Harris County. A tour of channel status among the Harris County
bayou gauges indicates that some have risen a bit, but all are
safely within their banks. We also are watching where heavier
rains are falling to our north/northeast, but even there, rain is
not expected to result in sufficient rises downstream in our area
to warrant any worry. We are continuing to monitor rainfall and
gauge status in coordination with our neighbors, the West Gulf
RFC, and WPC.
&&
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)  42  57  53  76  64 /  60  70  70  50  40 
Houston (IAH)          55  71  62  80  67 /  70  50  50  30  30 
Galveston (GLS)        62  71  64  74  65 /  70  50  30  20  30 
&&
.HGX WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Dense Fog Advisory until 6 AM CST Thursday for the following 
     zones: Coastal waters from Freeport to the Matagorda Ship 
     Channel out 20 NM...Coastal waters from High Island to 
     Freeport out 20 NM.
     SMALL CRAFT SHOULD EXERCISE CAUTION until 8 PM CST this evening 
     for the following zones: Galveston Bay...Waters from 
     Freeport to the Matagorda Ship Channel from 20 to 60 
     NM...Waters from High Island to Freeport from 20 to 60 NM.
&&
$$
NEAR TERM...Luchs
SHORT TERM...Luchs
LONG TERM...Luchs
AVIATION...45
MARINE...45
HYDROLOGY...Luchs