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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

                            
000
FXUS64 KHGX 211726
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1226 PM CDT Sun Jul 21 2019

.AVIATION...
Higher PW air is working westward across the CWA this afternoon. 
Convective temperatures from 12z soundings were around 90 degrees 
so would expect shra/tsra to increase in coverage this afternoon. 
Convective temps a bit warmer at KCLL so not sure how far west 
convection will eventually go. Fcst soundings show an inverted V 
signature so a few of the stronger storms could produce brief 
gusty winds. Convection should end this evening with the loss of 
heating. VFR conditions expected areawide through this evening 
except in and near storms. Just like the past couple of nights, a
brief window of MVFR/IFR ceilings will be possible at KCLL between
11-15z. Another burst of convection is expected early Monday as a
weak disturbance rotates into the area from the east and PW 
values increase to around 2.20 inches. 43

&&

.PREV DISCUSSION... /ISSUED 1032 AM CDT Sun Jul 21 2019/ 

UPDATE...
Eastern Texas is on the western periphery of a 2-plus inch pwat 
moisture ridge whose southwest-to-northeast axis is orientated 
from the northern Gulf into Appalachia. A broad weakness in the 
height field over the northern Gulf has slowly meandered west
towards us. The general westward movement of this area of disturbed
weather hugging the central Gulf coast will introduce primarily 
eastern CWA afternoon showers and isolated thunderstorms. Surface 
analysis depicts a weak boundary positioned between Galveston Bay 
and the Sabine River Valley that is laying within upper 70 dew 
point air. Thus, it will likely not take much more heating (low 90
F convective temperatures) to flare up inland convective activity.
Modest afternoon PoPs reside in and around the Galveston Bay region
that include Houston and surrounding metro. The main threat with
any strong storm will be greater than 40 mph wind gusts in
association with downdrafts. 31

PREV DISCUSSION /Issued 354 AM CDT Sun Jul 21 2019/...

DISCUSSION...
- Scattered showers and thunderstorms possible to start the week.
- Front still on track to push through slowly on Tuesday. Still
  holding onto 60-70 PoPs for Tuesday.
- Much drier airmass behind the front Wednesday through the end of
  the week.
- Low temperatures Thursday morning in the 60s.

SHORT TERM [Today and Tonight]...

Persistent onshore flow continues to hold overnight low 
temperatures closer to record warm values rather than a more 
typical number, but otherwise we continue to be entrenched in the 
usual July pattern for this area. Radar shows very early morning 
showers are beginning to crop up over the Gulf, moving towards 
shore. Some of these may manage to scrape coastal communities, 
dropping light amounts of rain in a very brief period. 

Rain and thunderstorm potential will be better this afternoon 
with more time to accumulate solar heating, also bringing us to 
very familiar highs around 90 near the coast, and rising into the 
middle 90s well inland. I expect most showers and storms should be
concentrated in the southeastern part of the area this afternoon.
This is closer to the better upper support provided by an 
inverted trough currently over the Gulf near Louisiana. This is 
also where precipitable water values of 1.5 to 1.8 inches are 
pooling, providing the deepest moisture. Meanwhile, a drier pocket
of low PW air from the interior of Texas is pushing towards the 
coast, and should provide a limit to potential generally west of 
I-45, and away from the coast. In this drier pocket, precipitable 
water values dip to just above 1 inch.

As one might expect while in this fairly typical summer setup, 
look for showers and thunderstorms to collapse pretty quickly 
around sunset, and for clouds to scatter out as the high cirrus 
above us dissipates. But, as we push towards dawn, we'll again 
look for marine stratus to develop over much of the area after 
midnight, towards daybreak. Luchs

LONG TERM [Monday Through Sunday]...

Overall looking at the 00Z guidance there is not a lot of change 
to the forecast. We are still looking for the short wave trough 
now over the northern Rockies to move into the Plains and Midwest 
by Monday. This allows for the upper level ridge to take shape 
over the 4 Corners region. Northerly flow aloft helps bring a 
front into Texas late Monday into Tuesday. Front pushes off the 
coast Tuesday night so bulk of the rain chances are Tuesday and 
Tuesday night. There will still be the threat for a few pockets of
higher rainfall amounts but generally looking at a half inch to 
an inch of rain during this time. Precipitable water values are 
still on track to reach 2 to 2.2 inches but given northerly upper 
level flow there should be enough of a storm motion to limit any 
kind of flash flood threat.

Wednesday through the end of the week looks drier. NAEFS still 
showing much lower than normal 850mb temps by 12Z Thursday with 
much drier air as well with PWAT close to climo minimums. Surface 
pressures Wednesday into Thursday across the plains are also near 
the 99th percentile for high pressure. These signals all point to 
the front pushing well into the Gulf. With this in mind, we did 
adjust temperatures a degree or two lower for Thursday morning and
also have dewpoints getting into the low 60s and upper 50s with 
mixing. Return flow may not happen until Friday into Saturday with
more of an increase in PoPs on Saturday. Overpeck

MARINE...

The usual summer pattern continues, and is expected to extend 
into early next week. Onshore flow, lighter during the day and 
more moderate overnight, will remain the rule, with seas holding 
around 3 feet or less on the Gulf. Daily scattered showers and 
storms should be expected, beginning in the very late night hours 
well offshore, and shifting towards land through mid-day. 
Persistent onshore flow should boost water levels above expected 
astronomical values, but is not strong enough to cause any notable
coastal flooding concerns.

Change is expected on Tuesday, with a cold approaching the 
waters, eventually veering winds around to northeasterly Tuesday 
night or Wednesday. Rain chances will be greater as the front 
moves in, but conditions should turn much drier for the bulk of 
the second half of the week. These conditions will persist until 
onshore flow returns late in the week. Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      96  77  97  75  90 /   0  10  20  30  50 
Houston (IAH)              94  77  95  77  89 /  40  10  40  30  60 
Galveston (GLS)            89  82  91  79  87 /  20  30  40  40  70 

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...31
Aviation/Marine...43