Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 201138
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
638 AM CDT Thu Jul 20 2017

.AVIATION...
Isolated SHRA/TRSA this morning near the coast and possibly inland later
this morning and this afternoon. However, not confident enough on inland
activity to mention in the TAFs at this time. Light winds this morning
becoming S to SE at 4 to 7 knots this afternoon. A majority of the
area will remain VFR today.  42
&&

.PREV DISCUSSION... /ISSUED 346 AM CDT Thu Jul 20 2017/

DISCUSSION...

Another day with heat indices that are undesirably close to the
heat advisory threshold. Though again widespread heat indices
reaching 108 is still probably not going to happen (isolated
locations may very briefly brush that level), we are still in a
situation with above normal heat, and so even greater attention
than usual need be paid to heat stressors.

This level of heat looks to continue into the first half of the
weekend until we back off ever so slightly with the new week. But
I wouldn`t exactly call it welcome relief - just a slight retreat
back towards the normal summer situation. Also worth mentioning -
even if/when the afternoon heat backs off a little, we still look
to remain fairly humid overnight, which will keep overnight lows a
few degrees above normal. This is important, as it will make
recovery overnight difficult for those that do not have access to
air conditioning.

NEAR TERM [Through Today]...

Believe it or not, the heat index forecast managed to fall a bit
short on Wednesday, generally reaching "only" the 100-105 range
rather than 103-108. But, isolated spots which likely did not see
dewpoints mix out as much as the surrounding area for whatever
reason did reach up to around 108 degrees for a very brief period
in the afternoon.

As a result, will likely take a similar approach to the forecast
today, shading a bit towards the hot end of the range, knowing
that localized spots able to maximize temperature against dewpoint
will push their max heat index above 105. This approach yields a
range of 102-107 for max heat index, which seems reasonable. This
brings us close to heat advisory levels again, but still a bit
shy. That said, even normal summer heat in Southeast Texas can be
hazardous without adaptation, so even non-advisory, above normal
heat does require some extra attention to heat stress,
particularly if you are uncommonly sensitive to heat-related
illness.

Otherwise, we`ll continue to find ourselves towards the fringe of
a midlevel ridge centered around the Kansas/Oklahoma border, with
bits of vorticity dancing around that edge. Like the past couple
days, we should see continued isolated to scattered shower and
storm development, with the best potential coming near the
seabreeze boundary, with some shift to isolated cells farther
inland. The strongest cells will be very efficient rain producers,
so an inch or so could still be picked up in an hour, but most
will likely see considerably less. I can only hope that this time
I will not be sharply (and rudely) snapped awake by a very close
lightning strike and power flash after only a couple hours of
being asleep.

SHORT TERM [Tonight Through Saturday]...

Into the first half of the weekend, look for the upper ridge to
drift slowly eastward towards the midsouth and slowly weaken,
while a weak upper low pinched off from a northern stream trough
drifts westward along the northern Gulf coast.

As you might expect, high temperatures look to come down slightly
from Friday to Saturday, and with the ridge weakening and upper
disturbance moving in, rain chances Saturday should be modestly
higher following another relatively dry Friday. Still, we`re not
looking for any dramatic changes in the situation, particularly
west of I-45, which will be farther from the influences of the
upper low.

LONG TERM [Saturday Night Through Thursday]...

Sunday looks to continue the idea of some more shower and storm
development, especially in the eastern third/half of the area, but
aloft, the upper low will be getting sheared apart - caught
between the older weakening ridge and a new ridge building in from
the east behind the low. The impact of this looks to be felt more
in the first half of the work week as rain chances come back
down and imply more isolated development nearer the coast. Now,
though the isobars on my workstation imply that the old and new
ridge weakly connect across Texas, the wind barbs imply a more
nuanced situation, where Southeast Texas remains in a bit of a
dead spot on the fringes of two separate ridges. Not only this,
but wind flow in the lower half of the atmosphere doesn`t imply
real strong capping - because of this, I chose to hang onto some
slight chance PoPs. Additionally, I didn`t really get into
rebounding temperatures strongly, only keeping them around or
slightly above normal.

MARINE...

Light to moderate onshore winds will continue through the
end of the week. Increasing winds and building seas can
be expected over the weekend in response to a tightening
pressure gradient. Caution flags might be needed. 42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      98  76  98  76  96 /  10  10  10  10  20
Houston (IAH)              97  78  95  78  93 /  20  10  20  10  30
Galveston (GLS)            90  81  90  82  89 /  20  20  20  20  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...25
Aviation/Marine...42



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