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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

FXUS64 KHGX 240458

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1158 PM CDT Tue Apr 23 2019

.AVIATION [06Z TAF Issuance]...

Mixed degradation across the area, but the general trend is
towards MVFR overnight, still with some potential for IFR around
sunrise in localized spots. Will be chances for showers from
mid/late morning on, but focus will be from later this afternoon
through tomorrow night as far as storms and heavier rain goes.
Will likely need much refining in coming cycles as storm-scale
factors that are hard to forecast at range will almost certainly
be in play here.


.PREV DISCUSSION /Issued 940 PM CDT Tue Apr 23 2019/...

Some light rain have been falling around Southeast Texas today associated
with weak disturbances moving across the area in the southwest flow
aloft. Anticipating a break in this activity tonight for a majority
of the area followed by a slight increase in rain chances during the
day tomorrow. Much better shower and thunderstorm chances are still
on track beginning early tomorrow evening across our western counties
and then spreading eastward during the remaining evening and overnight
hours across the remainder of the area as the upper low and associated
cold front move slowly eastward across the state. Dynamics are still
looking pretty good for possible strong/severe storms with this system.
The primary severe weather threat still looks like hail, strong winds
and lightning. Isolated tornadoes and locally heavy rainfall might
be possible too. While a majority of activity should be east of our
area by sunrise Thursday morning, the slow movement of the system might
allow for some daytime heating related redevelopment during the day
on Thursday. Everything should be off to our east Thursday evening
with high pressure beginning to build into the state. Looking at a
couple of coolish nights (Thursday night and Friday night) before
the high moves off to our east and onshore winds come back to the
area. While the end of the week and the weekend stay dry, lots of
sunshine will help to boost afternoon high temperatures into the mid
to possibly upper 80s. This forecast package has Monday dry followed
by low rain chances back to the area beginning Tuesday.  42

.NEAR TERM [Through Tonight]...

Surface analysis this evening has surface front from west central
Texas NE towards the Ozarks across Oklahoma. A few severe storms
were located along the boundary moving out of the Big Country
headed towards the DFW Metroplex. Outflow should re-enforce the
front and allow it to push farther south tonight into Wednesday
AM. Upper level trough over northern Mexico should push east
tomorrow across Texas. This should support a couple different
rounds of storms with heavy rainfall possible over the Brazos
Valley during the late afternoon/evening and then down along the
coast overnight. Squall line should move across the area overnight
but capping may limit the overall severe threat. SPC has a slight
risk over much of the area. Suspect the first round of storms towards
the Brazos Valley will have the higher severe potential given
weaker capping. Models hinting at a second increase in intensity
of storms overnight as the squall line pushes east of Houston
after midnight. There are still some timing differences in the WRF
runs as well as HRRR runs. The real question mark will be how much
the cap holds over SE Texas and if discrete cells can form which
will become severe. Otherwise there could be a mix of convective
modes and transition into more of heavy rainfall threat. Really
the mesoscale yet again will be giving us fits on how the severe
weather threat evolves tomorrow. Just now a really early look at
the 00Z WRF-ARW and the 00Z HRR extended range - both models hit
areas from near Brenham to Caldwell east to Huntsville/Crockett
with high QPF. This swath is quite a bit farther south and east
from where all the synoptic models place higher amounts of QPF. We
will have to watch to see if any of the other models from the 00Z
run show similar trends.


A fairly tight pressure gradient across the northern Gulf generated 
from a Mobile Bay High and lowering northwestern Texas pressures has 
maintained a moderate onshore wind. As the next storm system 
develops out west, the onshore pressure will remain tight enough to 
keep these regional Caution level winds in place through late 
tomorrow night. Other than some scattered showers and a rogue 
thunderstorm, local bay and Gulf weather will remain fairly benign 
through tomorrow night. As we approach the late Wednesday evening 
hours, the probabilities for rain and thunderstorms significantly 
increase going into the (overnight) early Thursday morning hours. 
Offshore winds behind a Thursday frontal passage will not be overly 
strong, briefly Caution level, at most. Sea state will remain 
elevated due to slightly higher period between Thursday morning's 
storms and post-frontal winds through Friday morning. High pressure 
settles in over the weekend and settles both winds and sea state out 
to tranquil. Weak onshore winds will return by Saturday afternoon.



College Station (CLL)  66  78  61  76  60 /  20  70  90  20   0 
Houston (IAH)          67  79  65  79  61 /  20  30  90  30   0 
Galveston (GLS)        70  75  68  77  67 /  10  20  90  50   0 



GM...SMALL CRAFT SHOULD EXERCISE CAUTION through Wednesday afternoon 
     for the following zones: Waters from Freeport to Matagorda 
     Ship Channel TX from 20 to 60 NM...Waters from High Island 
     to Freeport TX from 20 to 60 NM.



NEAR TERM...Overpeck