Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 270315
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1015 PM CDT Sun Mar 26 2017

.UPDATE...
A disturbance rotating down into the base of the passing southern
Plains shortwave trough this evening...along with the eastern push
of the north central Texas dry line...the two most likely elements
that initiated the string of supercells passing across FWD`s CWA
this evening. We have been monitoring the southern flank...or
those two supercells now traveling across Hill and Coryell Counties
(just west of Waco)...on either side of I-35. Although cloud tops
haven`t cooled much in the past few hours...they haven`t really
warmed much either. Southeastern propagating gust fronts from
these storms may reach the far northern reaches of the CWA shortly
after midnight so have slightly raised POPS in thsoe counties. A
30-40 kt low level jet streaming across the extreme the northeastern
forecast area has placed slight to low end chances in for these
counties to be clipped by pre-sunrise scattered storms. Two
factors may play a role in keeping eastern and southern CWA rain
convective chances in place for Monday`s forecast. One may be the
passing of a northeastern Texas low level boundary as the upper
trough axis reaches the MS River Valley...providing just enough
convergence within a moist and weakly-caped (near 80 F) air mass.
The second could be the lifting of a sea breeze boundary off the
coast that may prove to provide enough mid to late afternoon lift
to allow for scattered southeastern county storms. 31


&&

.PREV DISCUSSION... /ISSUED 612 PM CDT Sun Mar 26 2017/

AVIATION...
18z TAF fcst trends still look to be on track and won`t be
changing much for the 00z package. MVFR cigs should fill in thru
the evening hours and persist until mid/late morning Monday before
lifting. We`ll keep an eye on northern parts of se Tx late this
evening and overnight to make sure tail end of convection
currently initiating across n Tx stays up there as the vast
majority of guidance suggests. May still see a few remnant
showers pass nearby CLL & UTS later tonight. 47

PREV DISCUSSION... /ISSUED 412 PM CDT Sun Mar 26 2017/
An upper level disturbance is continuing to move west just north
of the Texas Panhandle this afternoon. As this shortwave continues
to propagate westward overnight and into Monday, there will be a
slight chance for showers and isolated thunderstorms for the
northern zones of our CWA in the early morning hours. This chance
for precipitation will sink easterly through the late morning. The
NAM and GFS forecast soundings show a decent cap at 850mb, that
hangs tight throughout the day Monday. Therefore, not expecting
too much in the means of convection for Monday, but still cannot
rule out the chance for showers and an isolate thunderstorm. By
late Monday evening, the likeliness for showers will diminish, and
the overnight hours should be dry.

The surface pressure gradient begins to tighten on Tuesday between
18-06Z, as the next upper level disturbances begins to slide in from
the west. Model guidance shows positive vorticity being advected
into the far inland region, beginning early Wednesday morning around
06Z, and continues to stream in a channel of positive vorticity
through 00Z Friday. A few disturbances embedded within this band of
vorticity, will result in an extended period of precipitation
Wednesday and throughout the day Thursday. Beginning Wednesday
morning, high temperatures in the mid 80s should well surpass
convection temperatures in the upper 70s/ lower 80s. Forecast
soundings during this time period also pick up on higher values of
precipitable waters, ranging between 1.25-1.75 inches. The
capping inversion should also erode by late morning, allowing for
deep convective initiation to occur by early afternoon. The storm
relative helicity values between the surface and up to one
kilometer increase Wednesday morning and into the early afternoon,
from 230-300m^2/s^2. CAPE values will also range between
2500-3500J/kg Wednesday afternoon and into the evening, therefore
slightly concern about the chance for some low level rotation in
developing storms. Forecast soundings are also indicating the
possibility of hail formation, as the CAPE values will be large,
and wet bulb zero heights will fall below 10,000ft.

On Thursday, the trough slings through the region, and heights begin
to rise behind it. Conditions for convection improve Thursday, as
the forecast soundings have CAPE and SRH values diminishing, and a
low level cap holds tight throughout the day. Expecting the chance
for showers and thunderstorms to linger, and slowly dissipate by
late Thursday evening.

High temperatures will remain in the lower 80s Thursday and increase
by a degree or two come Friday. Drier conditions with lower
precipitable water values move in Friday morning and will hold tight
through Saturday morning. Saturday afternoon, another upper level
feature moves into north Texas, and will bring in the next best
chance for precipitation.

Hathaway

MARINE...
Winds coming back up as expected with increasing gradient and
development of LLJ to the west. Winds in the 20-60nm waters into
SCEC conditions and could bump up and stay in SCA...evening shift
will need to keep an eye on trends there. Building seas through
Wednesday. Seas of 6-8 feet should common by Wednesday morning in
the offshore waters. Slowly lowering after the main trough axis
comes through Wednesday night/Thursday and winds pivot around with
the frontal passage. CAA is weak and don`t expect strong winds in
the wake of the front. 45

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      66  83  67  85  68 /  20  20  10  10  20
Houston (IAH)              67  85  68  85  71 /  10  30  10  10  10
Galveston (GLS)            70  83  70  82  73 /  10  20  10  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 4 AM CDT Monday for
     the following zones: 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...31



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