Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 181121

Area Forecast Discussion
National Weather Service Houston/Galveston TX
621 AM CDT Wed Oct 18 2017

VFR conds expected through 06z with high pressure continuing to
ridge into the region from the northeast. Light NE winds will
gradually become east and slowly strengthen this afternoon. Could
get some patchy ground fog toward sunrise Thursday. A surge of
deeper moisture should produce some increase in clouds Thursday
morning. 43


.PREV DISCUSSION... /ISSUED 400 AM CDT Wed Oct 18 2017/

Pleasant and dry weather is expected to continue across the
region today as surface ridging extends from the Mid-Atlantic
states into Texas with highs in the low to mid 80s. Early morning
water vapor imagery shows a shortwave trough near the Arizona/New
Mexico border and as this disturbance lifts towards the Southern
Plains tonight, deepening lee surface troughing over the High
Plains will result in increasing easterly winds across the coastal
waters. This will draw deeper Gulf moisture over the northern and
central Gulf towards the Texas Coastal Bend, with isolated to
scattered showers spreading across the Upper Texas coastal waters
tonight and into the extreme western/southwestern counties
tomorrow. Lows Thursday morning are expected to be about 10
degrees warmer than what the region experiences this morning with
lows in the mid 50s to upper 60s. Near surface saturation may
result in patchy fog development early to mid morning Thursday,
but any fog is expected to lift with increased daytime mixing.
Expect highs on Thursday to again top out in the low to mid 80s.

Continued moisture advection will allow for scattered to numerous
showers and thunderstorms to spread inland by Friday as forecast
precipitable water values rise into the 1.6-1.8 inch range and the
aforementioned shortwave trough lifts across North Texas. Despite
main mid and upper support remaining north of the region on
Friday, expect greatest coverage closer to the Upper Texas
coast/south of Highway 59 where deeper moisture will reside. Wind
profiles are not unidirectional, indicating a low potential for
training showers and storms, and support storm motions around or
above 20 MPH, which should support storms moving across the region
fairly quickly. However, saturating forecast soundings, high
atmospheric moisture content, and mid-level instability as the
shortwave trough lifts north of the region raise concerns for
brief periods of heavy rainfall during the day on Friday. Rain and
cloud cover on Friday should keep high temperatures in the lower

By Saturday, another upper trough begins to approach the Southern
Plains from the Pacific Northwest. As an associated 60-70 knot
jet streak noses across the region during the day and mid-level
lapse rates steepen into the 6.5-7 C/km range with the trough`s
approach, scattered showers and thunderstorms will again blossom
across the region on Saturday. Shear remains borderline for
promoting thunderstorm organization (0-6 km shear around 20-25
knots), but may see a strong multicellular thunderstorm or two
during the day on Saturday. The potential for strong to possibly
severe thunderstorms looks to increase on Sunday as the upper
trough digs across Texas, increasing shear and instability across
the region as it sends a cold front into Southeast Texas during
the day.

Similar to 24 hours ago, medium range deterministic guidance has
maintained almost no consistency regarding the evolution of this
upper trough once it reaches Texas on Sunday. The GFS now develops
a closed low at the base of the upper trough, while the European
keeps the trough open as it moves across the state. The main
differences between this closed low solution and the open wave are
that how quickly the cold front moves across the region and when
rain chances end. The closed low would result in a slower frontal
passage with rain chances lingering into Monday for at least part
of the region with the open wave providing quick movement of the
front with rain chances ending by Sunday night. Given the
continued signal in the GFS ensemble guidance for at least some
closed low to develop near the state, have continued low rain
chances for the northeastern/extreme eastern counties of Southeast
Texas into Monday as this upper trough or closed low exits the

Drier and cooler weather is expected to settle into the region
behind the cold front by the middle of next week with temperatures
near to slightly below seasonal normals. Currently advertising
highs in the upper 70s to near 80 with lows in the mid 50s to mid


High pressure over the eastern U.S. and lower pressures over the
southern Gulf of Mexico will produce an easterly flow across the
coastal waters today. The gradient begins to tighten tonight and
winds will increase. A moderate to occasionally strong onshore flow
will persist through Saturday and a SCEC may be required over parts
of the coastal waters. The persistent onshore flow will produce
elevated tides and tide levels are currently progged to exceed 3.0
feet Thursday morning and could exceed 3.5 feet on Friday. A cold
front will cross the coastal waters on Sunday afternoon and a
moderate to strong offshore flow will develop Sunday night and
persist into the first half of next week. 43

RH values will fall to below 35 percent north of a Columbus to
Conroe to Livingston line this afternoon but east winds will remain
generally light. Moisture levels begin to increase tonight and
increase significantly late Thursday and Friday as onshore winds
strengthen. Rain chances will increase on Friday and should remain
high through the weekend. 43


College Station (CLL)      83  58  85  63  83 /   0   0  10  10  40
Houston (IAH)              83  62  85  67  81 /   0   0   0  20  60
Galveston (GLS)            82  71  84  73  81 /  10  10  10  30  60




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