Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 260903
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
403 AM CDT Wed Apr 26 2017

.DISCUSSION...
Regional radar mosaic early this morning shows dry conditions in
place across Southeast Texas, with a few light showers occurring
across West and Northwest Texas in the vicinity of a southeastward
moving cold front. 05Z/12 AM CDT surface analysis showed this
cold front stretching from near Jal, NM east towards Wichita Falls
and northeast towards Tulsa, OK, with an attendant
dryline/surface trough located roughly from Throckmorton to
Dryden. As a shortwave trough swings across Oklahoma towards the
Great Lakes today and tonight, it will send this frontal system
into Southeast Texas.

Veering surface winds ahead of the front (southerly 10-15 MPH
this morning becoming southwest late morning/early afternoon) will
promote continued warm air advection ahead of the front as well
as encourage cloud cover to scatter. This will allow high
temperatures in many locations to range from the mid 80s to
possibly even the low 90s. This may be the first 90 degree day for
the Houston metro as well as a record high temperature day for
Galveston (current record is 84 set in 2011), but these
temperatures are largely contingent on when winds shift and skies
begin to clear. More information about first, average, and last
observed 90 degree days for Houston are included in the climate
section below. Current timing for the cold front brings it into
the Brazos Valley early this afternoon (12-2 PM) and into the
Houston Metro late afternoon/early evening (4-6 PM) before
clearing the region and the coastal waters later this evening
(8-10 PM).

Evening upper air observations from around Texas and Louisiana
revealed an elevated mixed layer/cap in place across most of the
region, with 700 MB temperatures ranging from 10-12 degrees C
across most of Texas. The evolution of this cap today will play a
crucial role in rain chances for the region as well as the
potential for thunderstorm development this afternoon along the
cold front. For this morning, warm air advection should promote
the development of a few showers beneath the cap across Southeast
Texas and the adjacent waters. Forecast soundings from Lufkin do
show a weakening of the cap later this afternoon (after 21Z/4 PM),
likely as a result of some mid-level cooling associated with the
shortwave troughs passage across the Southern Plains. If the cap
is able to weaken, isolated to possibly scattered thunderstorms
may be able to develop along the cold front with best chances
remaining along and east of a Madisonville to Huntsville to Winnie
line given the anticipated trends with the cap. Environmental
conditions in these areas would support a strong to possibly
severe thunderstorm (if thunderstorms were to develop), with mid-
level lapse rates around 7-8 C/km enhancing updraft intensity
enough to promote large hail or possibly gusty winds. Rain chances
will quickly end from west to east this evening behind the cold
front.

Weak surface high pressure is expected to build into the region
behind the front tonight, with clear skies and cold air advection
allowing overnight low temperatures ranging from the upper 40s
across the Piney Woods to mid 50s around the Houston metro and low
60s along the coast. Quasizonal flow aloft as Texas sits at the
base of a broad longwave trough and moisture briefly being pushed
offshore behind today`s front will promote dry conditions across
the region on Thursday. After a cool start Thursday morning,
temperatures will rebound into the upper 70s to mid 80s with
onshore flow resuming in the afternoon as the surface high slides
east.

The upper pattern transitions to more of a southwest flow aloft on
Friday as energy from the northern Pacific enters the base of the
upper longwave trough. In response to the approach of this
feature, surface troughing over the Southern Plains will deepen
and increase southerly flow across the region on Friday with
breezy to windy conditions expected across the region. This
increasing southerly flow will also give the region another shot
at 90 degree temperatures, so even if 90 is not reached today...
parts of the region will have another chance on Friday.

Breezy to windy conditions will persist again on Saturday as the
upper disturbance becomes a closed low near the Four Corners,
resulting in additional deepening of the surface low/trough across
the Southern Plains. While Saturday will not be a washout, warm
air advection will promote a few showers Saturday morning with
possibly a few thunderstorms by the afternoon with diurnal
heating. As the closed low near the Four Corners is expected to
lift across the Southern Plains, it will send a cold front into
Southeast Texas late Saturday night into Sunday morning with
scattered to numerous showers and thunderstorms developing along
the front. Veering wind profiles ahead of the front may provide
enough shear for storm organization, with a strengthening low
level jet encouraging precipitable water values to possibly rise
above 1.8 inches. This shear and moisture, combined with
sufficient instability and lift from the upper level system, may
also result in strong to severe thunderstorms developing during
this time.

Expect the cold front and any associated storms to clear the
region Sunday afternoon with dry conditions expected Monday and
Tuesday in the wake of the front. The next upper level system may
approach the region by the middle of next week, bringing another
round of rain. However, poor agreement amongst medium range
guidance precludes speculation on when this rain will return for
now.

Huffman

&&

.MARINE...
Moderate to occasionally strong onshore winds will persist this
morning and will maintain the SCA for all waters through 15z. Tide
levels continue to increase and may briefly reach 3 feet around
high tide (5 AM). There may be some minor coastal flooding along
the Bolivar but impacts should be short lived and minimal. The
winds will briefly decrease this afternoon as a cold front nears
the coast. The front should cross the coastal waters this evening.
SCEC/SCA conds possible in the wake of the front.

Onshore winds resume on Thursday as high pressure moves off to
the east. Winds/seas increase to near advisory criteria Friday
evening and will persist into early Sunday. Will need to keep an
eye on elevated water levels and risk of rip currents going into
the weekend. Tide levels could potentially exceed 3.5 feet near
high tide early Saturday morning. Another cold front will cross
the coastal waters early Sunday morning with strong offshore winds
developing in the wake of the front on Sunday. 43

&&

.CLIMATE...
Below are the earliest, average, and latest observations for the
first 90 degree days for the City of Houston.

Houston           Date (Year)
Earliest First    February 20 (1986)
Average First     May 7
Latest First      June 15 (1897)

Huffman

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      86  51  84  67  90 /  20   0   0  10  10
Houston (IAH)              89  56  84  69  90 /  20  10   0  10  10
Galveston (GLS)            84  64  78  74  82 /  10  10   0  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...Small Craft Advisory until 10 AM CDT this morning 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...Galveston Bay...Matagorda
     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.

&&

$$

Discussion...14
Aviation/Marine...43


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