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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

FXUS64 KHGX 182041

Area Forecast Discussion
National Weather Service Houston/Galveston TX
341 PM CDT Tue Jun 18 2019

.SHORT TERM [Tonight Through Wednesday]...
Surface high pressure over the region has kept skies partially 
cloudy, breezes light and allowed most interior ambient temperatures 
to warm into the lower 90s at 3 PM. Feedback from this has been 
drier mid level air more efficiently mixing to the surface and 
lowering dew points into the upper 60s to lower 70s. This has 
maintained upper 90 to near 100 F heat indices. A sea breeze 
boundary is beginning to lift off the coast. Thus, there are low end 
probabilities of late afternoon into early evening southern third 
CWA isolated showers/storm that may develop along or behind the sea 
breeze boundary. Also, higher moisture behind the breeze will also 
briefly spike heat indices to around or above 106 F.

Quiet overnight with a decent chance for low clouds to develop past 
midnight over the west central forecast area. A shortwave trough 
passage across the Central Plains tomorrow afternoon will likely 
spark north to northeastern Texas convection. Outflow from this 
activity entering an unstable and humid mid-day northern county air 
mass will increase late day into evening shower and storm chances 
primarily north of a Brenham to Huntsville to Livingston line. 31


A fast moving short wave will move across East Texas Wednesday
night. The short wave will bring a chance of showers and
thunderstorms to mainly the northern third of the region. Mid
level forcing and jet dynamics are not too impressive so it'll
probably be just a glancing blow. Upper level ridging will try
amplify over the western Gulf and 500 heights build to around 590
dm which isn't all that impressive, but temperatures at 850 mb
increase rather significantly. The warmer 850 mb temps translate
to surface temperatures in the upper 90's to around 100 degrees.
Fcst soundings show some mid level dry air which should mix to the
surface so not expecting precip and sfc dew points should also mix
out in the afternoon. Heat index values should remain below 108 
degrees over most of the area but have some concern that dew pts 
could shoot up in the wake of the sea breeze during the late
afternoon. Will need to watch trends but a Heat Advisory might be
needed for Thursday afternoon for areas along and east of I-69.
850 mb temperatures cool on Friday as 850 winds back from the
southwest to the south. 

The zonal flow aloft will transition to the southwest as an upper
level trough moves toward the great basin. A series of upper level
disturbances embedded in the upper flow will traverse the region
over the weekend into early next week. Models diverge with the
strength of an upper level ridge over the Gulf of Mexico but the
strength of the upper high will determine whether the short wave 
energy will move up the Texas coast or be shunted further west 
and move over West/Central Texas. Will maintain slight 
chance/chance PoPs for now and hope that the global models will 
become in better agreement. For now, just split the difference 
between the wetter ECMWF and the drier GFS. 43


A couple of quiet days over the maritime until the onshore pressure 
gradient tightens up late Thursday into Friday. Southwest to south 
winds will generally remain at Caution levels from Thursday through 
Saturday with brief jumps to Advisory criteria. Very low western 
Texas pressures in relation to high eastern Gulf pressure will create 
a tight enough onshore gradient to produce more persistent Advisory 
level winds on Sunday through Monday. Current 2 to 3 foot Gulf seas 
will lift to average 4 to 6 feet by the weekend...topping out in the 
6 to 8 foot range across the western Gulf early next week. Of 
course, early next week's strong onshore fetch will introduce 
greater than 3 foot high tide nearshore sea heights increasing the 
coastal run up threat. The rip current will also likely restrengthen 
to Advisory levels by Sunday. 31


College Station (CLL)      76  96  78  98  78 /  10  10  10   0   0 
Houston (IAH)              79  95  79  97  80 /  10  10   0  10   0 
Galveston (GLS)            82  89  83  90  83 /  10  10   0   0   0