Area Forecast Discussion
Issued by NWS Houston/Galveston, TX
FXUS64 KHGX 252034
Area Forecast Discussion
National Weather Service Houston/Galveston TX
334 PM CDT MON JUL 25 2016
Though it was dry most of the morning, showers and storms began
breaking out in earnest around 17Z across much of the area. Where
rain hasn`t fallen, temperatures have risen up into the mid-90s
and a few heat indices have pushed towards 105 degrees. Most of
the convection has been relatively minor, but some storms have
been fairly efficient rainfall producers. This is most significant
along the Gulf Coast, which has seen a small handful of slow
moving storms drop a radar-estimated 2-3 inches in coastal
portions of Brazoria, Galveston, and Chambers counties.
Rest of today and tonight...
As the lead vort max traverses the area, we should expect more of
the same this afternoon and evening. And, given the longevity of
convection yesterday, some storms may linger longer into the
night. On the plus side, the NAM finally gave up the ghost of
parking an MCS-like structure over the Houston metro all night,
and joins the rest of the guidance in winding activity down
tonight. Indeed, it now swings to being among the drier of the
models tonight. Ultimately, with the loss of insolation and
potential for a brief period of anticyclonic vorticity advection
behind the lead shortwave, would expect activity to mostly end
except over the waters. While cloudiness and rain blunt
temperatures this afternoon, it should keep temps from dropping
much farther than previous nights.
Tomorrow, focus turns towards the upper trough that`s
worked its way across the Gulf and will finally approach the area.
Have actually trimmed PoPs down for tomorrow, as now even the
wetter guidance has trended downwards. This seems reasonable, as
it appears both from water vapor imagery trends and in the models`
height fields that the base of the trough may only glance by to
our south. This creates a scenario in which the rainfall shield
passes over the waters of the Gulf, leaving the land drier. On one
extreme as seen in the Euro, convection is still able to break out
across the area. Some guidance enhances convection along the
seabreeze, but showers are harder to come by elsewhere. On the dry
end, like the NSSL WRF ensemble and Texas Tech WRF, even seabreeze
convection is a bit harder to come by. Still, even the drier
guidance keeps precipitable water above 2 inches and so am not
buying into a very dry scenario. Maybe wouldn`t expect quite the
same production as this afternoon, but will count on at least a
fair amount of convection breaking out Tuesday. As one might
expect, temperatures in such a scenario will be near or below
normal. But, it`s worth noting that these temperatures will be too
low if a drier, less cloudy result does occur.
While confidence in precip potential has decreased for tomorrow,
still expect a decent slug of moisture off the Gulf just on the
backside of the inverted trough to set up a scenario to help keep
rain chances in the picture for Wednesday. Additionally, it
appears that some of the vorticity from the trough may get drawn
into a passing trough to the north, which would mitigate the
impacts of anticyclonic vorticity advection that might normally be
seen in this scenario. In fact, the PoPs in some locations are
higher on Wednesday than on Tuesday, though this is partly a
function of uncertainty, and being more confident in drawing a
sharper scenario for the nearer timeframe. So, while it wouldn`t
be fair to expect Wednesday to match today`s convective activity,
it seems plausible that it should at least meet, and potentially
even exceed Tuesday. And thus, temperatures should also end up in
a similar spot as well.
Thursday and on into the weekend...
The story for the rest of the week will focus on a gradual
rebuilding of the midlevel ridge from the east, with the major
uncertainty being how long weakness in 500 heights will carry on
over our area, split between the ridges to the east and west. The
guidance does seem to be coming to terms on a middle ground
between the Euro`s and GFS` extremes, in which Thursday may see
a day which, though less productive than the first half of the
week, still resembles the pattern in which coverage is fairly
widespread. After that, it appears we take on the look of a more
typical diurnal pattern with the best potential near
seabreeze/landbreeze convergence zones. For what its worth, the
Euro still clings to being a bit more wet, while the Canadian and
the GFS keep things restricted a bit more to the seabreeze area.
Temperature trends seem a bit more certain, as high temperatures
should rise modestly into the weekend as convective coverage
wanes. However, temperatures are not likely to match past days
even under the warmest of circumstances.
A deep pocket of moisture will linger over the coastal waters for
the remainder of Monday and through the early evening on Tuesday.
Scattered shower and thunderstorm coverage will slowly taper off on
Wednesday as we begin to dry out towards the weekend. Winds will
pick up early Tuesday afternoon, as some thermally induced mixing
with our low level jet brings 10-15 kt winds down to the surface and
over the coastal waters. A lighter wind regime holds out for the
remainder of the week and into the weekend.
Seas of 1 to 3 feet will be the norm through the weekend. Tide
levels one half to one foot above normal can be expected as well.
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 76 92 75 93 76 / 30 60 30 50 20
Houston (IAH) 77 91 77 92 78 / 40 60 30 60 20
Galveston (GLS) 79 88 81 89 83 / 50 70 30 60 30