Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 201130
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
630 AM CDT Sat Jul 20 2019

.AVIATION [12Z TAF Issuance]...

Sporadic MVFR conditions have been observed so far at CLL, UTS,
and CXO - this is expected to continue through sunrise and briefly
into the morning before joining the rest of the area in VFR.
Slightly better chances of isolated showers today, with onshore
winds increasing to around 10 knots. For now only have a short
VCSH mention at IAH - rain chances look better, but not THAT much
better. We may see more widespread MVFR towards dawn tomorrow, but
mostly stick with persistence for now. Keep an eye on that in
coming forecast issuances.


&&

.PREV DISCUSSION /Issued 406 AM CDT Sat Jul 20 2019/...

.DISCUSSION...

- Moisture should increase today and Sunday with an inverted
  trough moving into the area this weekend. This will cause an
  increase in shower and thunderstorm activity especially for
  Sunday.
- Upper level ridge should build over the Rockies Monday and
  Tuesday with a trough over the Great Lakes. This allows for a
  front to move into the area Tuesday with higher chances of
  showers and thunderstorms.
- Drier air should move into the the area behind the front
  Wednesday into Thursday which should decrease rain chances.




.SHORT TERM [Today and Tonight]...

Ridging continues to dominate the region, though we are a bit
more towards the fringe of that ridging now. This should provide
at least a slightly better opportunity for isolated showers and
possibly a thunderstorm to crop up, mostly off the convergence
provided by the seabreeze boundary. GOES-East still shows
precipitable water values in the 1.3-1.5 inch range, but deeper
moisture lurks offshore, and may move in enough to provide a more
plentiful source of moisture for diurnal convection. Of course,
with the diurnal pattern continuing to command weather trends,
potential should fall off pretty rapidly after sunset.

With the persistent onshore flow, dewpoints will remain elevated,
as will the temperature floor in anomalously high overnight lows.
Like the last couple days, suspect we`ll slide safely below
record values, but expect that both this morning and overnight
tonight that we`ll be closer to record warm minimum values than
normal minimum values. On the flip side, temperatures this
afternoon will be hot, but high temps do not look as anomalously
warm as the low temps do. Look for pretty stable temperature
trends, with highs around 90 right at the coast, rising into the
mid 90s deeper inland. Similarly, expect maximum heat indices to
be around or above 100 degrees, but we`re not looking for any
widespread 105+ readings today. The plus to this is that
conditions will be no more severe than they have been in recent
days. The drawback is that heat stress is cumulative, and with
such warm nights, you can find yourself in trouble more rapidly
without time to recover in air-conditioned spaces.

Luchs


.LONG TERM [Sunday Through Saturday]...
Inverted trough along the northern Gulf should push into the area
on Sunday increasing thunderstorm chances. There will also be a
surge of higher moisture to further support the need for higher
thunderstorm chances. the 00Z Tx Tech WRF has more scattered
activity than the other WRF model runs, but all point to scattered
activity from Houston eastward into east Texas. It will be quite
possible for a few of these storms to drop some locally heavy
rainfall, gusty winds and lightning.

A trough over the Pacific NW today should move across the
northern Plains and into the Midwest/Great Lakes by late Monday.
Upper level ridge should develop over the Rockies in response to
this developing trough. Northerly flow aloft will support a front
pushing into the area Tuesday into Wednesday. By in large, model
data has become fairly consistent with this pattern developing so
there is overall growing confidence in a front pushing off the
coast Tuesday night.

We did bump up thunderstorm chances along the front to 60-70
percent mainly on Tuesday when the front moves through the area
slowly. We will need to watch for locally heavy rainfall as
precipitable water values climb to 2 to 2.2 inches ahead of the
front but storms should be moving fast enough with no training
that the flood potential looks rather low. Also antecedent
conditions have been dry for the most part so the general 1 inch
rainfall amounts should not cause any problems. Even isolated
higher amounts should not cause any flooding issues.

Ridge/trough pattern over the US should continue through the week
so with the weakness in the ridge, it looks like we could have a
wet pattern set up. However it looks like from Wednesday through
at least Friday much drier air will be in place. In fact the 00Z
NAEFS show precipitable water values under 1 inch for 12Z Thursday
and this correlates to 0.5 to 1 percent of climo or close to a
record minimum for PWAT for this time of year. The front also
pushes a little further into the Gulf than previous runs which
also indicates that drier/cooler air will be in place behind the
front. Not only that, but the 00Z NAEFS has 850mb temperatures at
or near climo minimums for this time of year. All that to say, the
airmass behind the front is anomalously cooler and drier than
climo norms.

It looks like now we might not see a return flow event until
Friday into Saturday when precipitable water values climb back
above 1.5 inches. So we will include some increased rain chances
for the end of the week but confidence still pretty low now that
there will be more dry air behind the front.

Overpeck


.MARINE...

Typical summertime conditions continue on the waters through the
weekend and into early next week, with generally light to moderate
onshore flow. Similarly, seas are expected to be 3 feet or less.
The next significant change will be likely to come Tuesday into
Wednesday as a cold front looks like it will manage to bring a
increased showers and storms, and also briefly shift winds to
northeasterly. Onshore flow is expected to return before the week
ends.

At the coast, the persistent light to moderate onshore flow
should support moderate rip current strength as reported by beach
patrols, and boost tides above astronomical norms. Despite coming
in higher, winds are unlikely to be strong enough for water levels
to reach critical thresholds along the coast.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  96  76  96  76  96 /   0   0  10   0  20
Houston (IAH)          94  78  92  77  94 /  30  10  40   0  30
Galveston (GLS)        90  82  88  81  88 /  10  20  20  20  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...None.
GM...None.

&&

$$

SHORT TERM...Luchs
LONG TERM...Overpeck
AVIATION...Luchs
MARINE...Luchs


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