Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 192016
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
316 PM CDT Tue Sep 19 2017

.DISCUSSION...
More typical late summer weather in Southeast Texas for the next
several days. Several very subtle features will impact the forecast
into early next week. This makes the forecasting process intriguing,
but the impacts appear to be mostly limited to temperature changes
of a few degrees and just how scattered the scattered showers and
storms will be. Based on how how these subtleties play out, things
like preferred days for more numerous showers may shift a bit in the
coming days. However, the broad concept of typical late summer
weather seems clear. Of course, "typical" does not always mean "no
hazards". The strongest of each day`s storms can be capable of some
gusty winds and/or locally heavy rainfall. This is the type of setup
in which one gauge might see 4 inches of rain, while another gauge
nearby sees about a third of an inch.


.NEAR TERM [Through Tonight]...

A subtle, but readily apparent shortwave ridge is beginning to exit
Southeast Texas per analysis and water vapor imagery. Its impact on
today`s convection has been similarly apparent, with considerably
fewer showers and storms so far today. However, it appears the next
weak shortwave trough will begin to approach the region, and is
attended by an uptick in convective activity to our west. This may
mean a little more activity for the late afternoon until we lose
heating this evening, but we still look unlikely to match
yesterday`s activity. Temperatures today have been a little higher
than forecast as convection so far has been even more limited than
already expected. But with thoughts that clouds may tick up in the
next few hours and our lows look to be governed at least in part by
the high dewpoint floor, don`t think it will have a very significant
effect outside of these first few hours of the forecast.


.SHORT TERM [Wednesday Through Thursday Night]...

By Wednesday, a new shortwave trough will be crossing the area,
which should provide some upward boost to that day`s convection.
Now, that said, this doesn`t seem to appear in all of the guidance,
which ranges from virtually dry (NAM) to decently wet. It`s worth
noting that guidance does seem to step precipitable water values
down a little from the two inch numbers we`ve seen of late, and
there may be some timing issues - a slightly faster shortwave may
put us just on the subsident side of the trough by late afternoon.
This could hamper convective development as well.

Probably don`t want to get too terribly wrapped up in the details as
the difference in impacts isn`t huge. What there does seem a clearer
signal of in the guidance is that a coastal boundary looks to be the
primary focus for convection, and we still have enough moisture to
produce locally heavy rainfall. The NCAR WRF ensemble shows a fair
to strong signal for some locally heavy rain along the coast. The
strongest signal looks to lie just east of our area closer to the
TX/LA border, but there`s surely some potential for cells dropping a
quick few inches here.

For Thursday, cyclonic flow aloft looks to stay in place, and give
us stable or slightly falling midlevel heights over the area again
on Thursday. This would bolster the idea the previous shift had that
Thursday could see one more day of relatively higher coverage in
showers and storms. This may be somewhat subject to change as the
broad eastern US ridge will be starting to amplify, and could see a
scenario in which we actually are drier on Thursday. However, given
the relative consistency in seeing a developing upper low on the
Gulf Coast in the models, will hold onto the idea of a wetter
Thursday.

.LONG TERM [Friday Through Tuesday]...

Guidance continues to show a trend to an amplifying west trough/east
ridge pattern, but also with an upper low developing along the
northern Gulf Coast. Farther to the east, Jose and Maria continue to
have a tricky interaction - this dance of tropical cyclones won`t be
directly impacting our weather, but I do wonder how it may impact
the aforementioned upper low, as our precip chances this weekend
into early next week may be influenced by just how far west it gets
before being drawn back up into the northern stream westerlies.
Because of this, I try to work in broad strokes on the PoPs with
less variation than I might normally. In general, go a little lower
Friday and Saturday, and a bump up for the rest of the weekend into
early next week. This is not a significant difference from the
previous shift, which had similar trends. As far as temps go, I
don`t see heights going low enough to really imply a big shift in
temperatures, but do get a couple degrees cooler on highs as we head
deeper into the weekend.

It`s beyond the scope of the forecast, but models diverge
significantly later next week as a cold front drags into Texas and
potentially towards the area. There is precious little agreement in
the models outside of the existence of a front, however, so details
on this will have to be sussed out in the coming week.

&&

.AVIATION [18Z TAF Issuance]...

Scattered showers and possibly a few thunderstorms are forecast this
afternoon at most terminals, with the greatest thunderstorm
potential generally north of KIAH. Showers and storms should
diminish after sunset. Another round of fog/low stratus is likely
overnight tonight and will probably be pretty similar to last
night/this morning. KCXO will likely be the hardest hit with LIFR
conditions likely in the early morning hours. Other sites, if
impacted, should mostly remain in the MVFR to IFR range. Greatest
likelihood of fog/stratus overnight should again be generally north
of KIAH with conditions improving steadily at all terminals after
sunrise. Another round of showers and thunderstorms is expected
during the day tomorrow and into tomorrow evening.

11

&&

.MARINE...

Light to moderate onshore flow, seas around 2 to 4 feet, and periods
of showers and thunderstorms are expected along the Upper Texas
Coast through the forecast period.

11

&&

.CLIMATE...

As noted in social media posts last night, an annual record
rainfall was set yesterday for Bush Intercontinental Airport. The
record is (for now) 71.30 inches, besting the previous record of
71.19 inches set in 2001. It`s probably little surprise that the
old record belonged to the year of Alison.

An important note - this record is for IAH only, not for the City
of Houston, though the airport is the city`s current official
site. So far, 2017 is in third place among annual precip totals
for the city. We are currently 1.08 inches behind the second place
year of 1919, and 1.56 inches behind the record year of 1900. With
104 days of rainfall yet to record, there are very few scenarios
in which this record will not fall by the end of the year.

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  76  91  76  92  72 /  20  20  10  30  10
Houston (IAH)          77  90  77  89  73 /  20  50  20  40  10
Galveston (GLS)        81  86  80  87  78 /  20  30  20  30  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

NEAR TERM...Luchs
SHORT TERM...Luchs
LONG TERM...Luchs
AVIATION...11
MARINE...11
CLIMATE...Luchs



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