Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/05/21
Area Forecast Discussion
National Weather Service Houston/Galveston TX
615 PM CDT Sat Sep 4 2021
A few showers south area TAF sites will diminish with the loss of
heating leaving skies generally clear overnight. There could be
some patchy fog at the usual spots (CXO,LBX and SGR) but it
should be brief and patchy. The first half of Sunday looks good
with generally VFR conds but a weak disturbance approaching from
the NE could bring some late afternoon shra/tsra over northern TAF
sites by 21z. Confidence is low but added a VCTS for KCXO,KUTS
and KCLL for Sunday afternoon. Will assess at 06z if a VCTS is
needed at KIAH and KHOU. 43
.PREV DISCUSSION... /ISSUED 254 PM CDT Sat Sep 4 2021/
Much of this week looks fairly quintessential late summer in
Southeast Texas, complete with hot, humid weather and some chances
for showers and thunderstorms. A weak front may drift into the
area from the north early next week, providing a focus for showers
and storms, but not much in the way of "cold" (or even "cooler")
behind it. Finally, we`ll have to keep an eye on the Gulf as a
feature of interest, Invest 91L, has some potential for tropical
development as it makes its way north across the waters.
SHORT TERM [Sunday Through Sunday Night]...
Sea breeze is starting to push inland and a few showers in our
southwestern counties are starting to sprout. Higher PWAT air still
remains along our eastern counties and continues to push east into
LCH`s area. Backed off slightly on PoPs for this afternoon as AMDAR
soundings shows a stout 850mb cap across our CWA that daytime
surface temps might not get warm enough to break it, despite
reaching the mid-90s this afternoon. Any convection that continues
to form should dissipate shortly after sunset with the loss of
Overnight, clear skies and light winds will enhance radiational
cooling and some patchy fog may form across our rural and low-lying
inland areas. Our usual summer pattern of isolated coastal showers
are possible overnight through early tomorrow morning as well.
Throughout the day tomorrow, with high pressure overhead and weak
synoptic flow, much of our rain chances will be mesoscale driven and
diurnally driven with daytime heating, seabreeze collisions, and
other boundary collisions. A front will be pushing south through TX
and some precip and forcing mechanisms ahead of this FROPA could
reach our northern counties by late afternoon and early evening.
Therefore, rain chances will be slightly higher overnight for our
northern counties at 20-30%.
Regarding temperatures, overnight lows will still reach the mid to
upper 70s for our inland areas and near 80 along the coast. High
temperatures should peak in the upper 90s tomorrow and flirt with
100 for some isolated areas. Heat index values should still reach
the triple digits, but remain below heat advisory criteria.
LONG TERM [Monday Through Saturday]...
Monday opens with an upper ridge dominating the Western US, and a
trough north of the Great Lakes that just happens to string a
tendril of lowered heights and vorticity down into Northeast
Texas. At the surface, that trough supports a low pressure center
just south of Hudson Bay, trailing a cold front across the eastern
US, and also into Northeast Texas. There is not likely to be a lot
to this front, but it will at least make a decent focus for
convection on Monday afternoon across the area as the front and
upper trough drift down into the area.
That drift looks to be far enough south that we could see some
drier air filter into the northern part of the forecast area,
which largely eliminates precip chance through the end of the
week with precipitable water progged to fall to around an inch.
Still keep chances near the coast at least through the midweek, as
moisture may pool there even as the front and trough dissipate. Of
course, the modestly drier air will easily overcome what (if any)
cold advection comes with this new airmass, and forecast highs
continue to be in the middle to upper 90s well inland, and in the
lower to middle 90s closer to the coast. This only sticks with us
as a ridge comes to command the region later in the week, likely
choking off any rain chances even more and keeping the summer-like
temperatures fully in place.
And then there`s the matter of one other little thing in the long
term...and that`s the tropics. More on this in the tropical
section, but with the bulk of the deterministic and ensemble
guidance favoring no tropical cyclones tracking into our area, the
forecast reflects that. Ensemble spread is still fairly wide, and
we`re speculating about a feature that has yet to even develop, so
things are subject to change - potentially dramatically - based on
the evolution of Invest 91L.
Light to moderate winds are expected through the first half of
the week, with a general diurnal land breeze/seabreeze pattern and
seas 3 feet or less. Rain chances will be relatively low over the
weekend underneath high pressure, then increase modestly next
week as deep tropical moisture from the Gulf pushes into the area.
Mariners should closely monitor the forecasts from local NWS
offices and the National Hurricane Center regarding potential
tropical cyclone development in the Gulf of Mexico towards the
middle of next week.
While a major hurricane, Larry, spins in the open Atlantic,
locally we also need to pay attention to Invest 91L currently over
the Yucatan Peninsula. Conditions will not be conducive to
development as it emerges over water and drifts northward through
Monday or so. However, conditions should gradually become more
conducive for tropical development after that. At the very least,
we`ll have a solid chunk of moisture heading north across the Gulf
As far as track of any potential TC goes, model guidance favors a
path more towards the north or even northeast Gulf coast, rather
than the northwest. The 12Z model cycle saw a bit more
consolidation towards that solution, particularly among the
deterministic models. This likely is occurring because of center
development on the northeast corner of the broad trough lifting
northward. But in the ensembles, there are members (particularly
in the Euro ensemble) that still show a surface low that heads
towards Texas. If the low doesn`t coalesce in the spot that the
current consensus has it happening, we could see things swing
pretty dramatically. Is this likely? Perhaps not - if forced to
put down some money, I`d go along with the bulk of the guidance.
Something we`ll want to watch as things evolve next week, though
not necessarily with a ton of stress right now. As always, it`s a
good reminder that we are near the peak of hurricane season, and
whether this becomes a threat to our area or not, preparation is
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 76 97 76 94 74 / 0 20 30 40 10
Houston (IAH) 77 97 77 96 76 / 0 20 30 50 20
Galveston (GLS) 82 92 81 91 80 / 0 20 30 40 40