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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

FXUS64 KHGX 162028

Area Forecast Discussion
National Weather Service Houston/Galveston TX
328 PM CDT Thu May 16 2019

.NEAR TERM [Through Tonight]...

A thin cumulus field has spread from west to east across SE TX this 
afternoon as seen via visible satellite imagery. Radar imagery is 
continuing to show showers firing up along the sea breeze, mostly 
west of I-45 and south of I-10 at this hour. Where the cu appears 
the thickest on visible satellite imagery, over Wharton County, 
thunderstorms have started to develop. These cells have not been 
fast movers, and are nearly stationary, focusing and redeveloping on 
the sea breeze as it slowly creeps further inland. Moderate 
northwesterly upper level winds are at fault, providing 
resistance against the inland progression of the seabreeze. 
Anticipate most of the convection to diminish near sunset this 
evening, with the loss of daytime heating.

Tonight, low temperatures will bottom our in the low 60s across our 
NE zones to the mid 70s along the coast. Patchy fog also looks to be 
possible once again tonight, with light winds, low level moisture, 
and narrowing dewpoint depressions to 1 to 3 degrees. Surface winds 
will be a touch stronger tonight between 3-7 knots, depending on the 
location, so not as confident that we will see widespread patchy fog 
tonight. Some of the short term guidance, such as the TT WRF, NMM, 
and ARW are also picking up on some light showers developing over 
our far western zones early Friday morning between 09-12Z. 

.SHORT TERM [Friday Through Saturday Night]...

Upper level ridging dampens as heights lower over New Mexico and W 
TX Friday. Moisture values will be slightly more saturated by 
tomorrow afternoon, with precipitable water values (PWs) increasing 
to 1.2 to 1.4 inches area wide. Look for a similar set up tomorrow 
as today, with the sea breeze likely remaining the main focus for 
development of shower and thunderstorm activity. Additionally, 
convective temperatures again tomorrow will hold in the low 80s area 
wide. A general consensus of short term guidance shows more 
widespread development of showers and thunderstorms further inland, 
which makes sense given weaker flow aloft, out ahead of our next 
storm system. 

By Saturday morning, PWs surge up to over 1.5 inches, ranging from 
1.6 to 1.8 inches by the afternoon and evening hours. Global 
guidance such as the Canadian and ECMWF look to kick of the 
precipitation out ahead of the main line as early as 21Z Saturday, 
with the main line of convection reaching our northern zones closer 
to 00Z Sunday. Upper level jet dynamics still do not look overly 
favorable late Saturday into Sunday, with the 90 knot jet streak 
centered over N TX, and the best diffluence situated north of SE TX. 
One change worthy of mentioning by the global guidance is the 
increase in the frontogenesis fields in the mid levels starting 
00Z Sunday. Both the NAM12 and GFS show stronger signals of 
frontogenesis across our northern counties, essentially north of 
I-10, Saturday night and into Sunday morning. The 850mb low level 
jet also looks stronger in the latest model runs, holding on to 
30 knots of southerly flow out ahead of the approaching storm 
system. In general, it still appears as though instability will be
better off the further inland the storms develop, with moderate 
capping holding tight at 700 mb closer to the coast. All for all, 
run to run trends show this storm system being rather progressive,
and as a result, pushed our higher PoPs further east by Sunday 
morning, as SE TX falls on the subsident side of the trough axis by
15Z Sunday.

.LONG TERM [Sunday Through Thursday]...

High temperatures Sunday and Monday are still looking warm, in 
the mid to upper 80s. Temperatures will not cool down too much 
overnight, with low temperatures forecast to fall into the mid 70s
area wide. Next week's storm system looks to arrive in SE TX late
Tuesday. The latest runs show the ECMWF and Canadian as the 
faster model solutions when compared to the GFS with the overall 
progression of this system. Plenty of time to work out the details
with this system, but it does appear as though showers and 
thunderstorms will be possible across much of SE TX, late Tuesday 
into Wednesday.


.AVIATION [18Z TAF Issuance]...

VFR conditions expected into the overnight hours. Exception would
be in/near any isolated to scattered showers or tstms that 
develop along the seabreeze this afternoon. Patchy fog is a slight
possibility late tonight, with KCLL probably being the more 
favorable TAF site to see this. Look for some brief MVFR ceilings
to develop a couple hours after sunrise along with spotty shra 
developing with continued daytime heating. 47



Light to moderate onshore winds should persist into Friday morning. 
Winds and seas begin increasing later in the day and continue to do 
so into Saturday night as the pressure gradient tightens. Caution 
and/or Small Craft Advisory flags are a good possibility during that 
timeframe. Winds & seas will slightly diminish Sunday and Sunday 
night, but the gradient tightens once again on Monday and breezy 
conditions and elevated seas should persist into the middle parts of 
next week.

Ongoing elevated tides will likely get worse in the coming days. 
Guidance suggests water levels topping out between 3.4-3.8 feet MLLW 
around high tide each day beginning Saturday morning and continuing 
at each high tide into early next week. Coastal Flood Advisories 
appear to be a decent bet at this point. At these levels there could 
be impacts at the Highway 87/124 intersection on Bolivar, Blue Water 
Highway and Surfside. In Galveston, wave run up may approach the 
Seawall at some locations. Rip current risk will also increase. 47



College Station (CLL)  67  85  71  85  70 /  10  20  20  80  80 
Houston (IAH)          68  85  73  85  72 /  10  30  20  40  70 
Galveston (GLS)        74  81  75  82  75 /  10  20  10  20  70