October 2017 - Halloween Forecast/Rain Chances

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Re: October 2017 - Halloween Forecast/Rain Chances

Postby Katdaddy » Tue Oct 31, 2017 5:34 am

A few showers over the NW GOM and along the coastal areas this morning as rain and thunderstorm chances increase thanks to a stalling cool front across SE TX. Expect showers and possibly a few thunderstorms for trick or treating this evening.

An portion of this morning’s Houston-Galveston Area Forecast Discussion regarding this evening:

It would be a good idea to be prepared for showers and storms while getting your Halloween activities out of the way earlier. Once done, settle in for some (potentially historic) TV at night.

Locally heavy rains will be possible later tonight near the stalled front. In addition, a few strong storms will be possible Wednesday if additional thunderstorms develop. The SPC has SE TX in a marginal risk area for severe thunderstorms. After some active weather days we will begin to dry out at the end of week.
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Re: October 2017 - Halloween Forecast/Rain Chances

Postby BlueJay » Tue Oct 31, 2017 6:27 am

Thunder on Halloween! Sounds scary.
Happy Halloween everyone!
Go Astros!
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Re: October 2017 - Halloween Forecast/Rain Chances

Postby tireman4 » Tue Oct 31, 2017 8:14 am

I believe his is alluding to the Astros in the World Series...



000
FXUS64 KHGX 311147
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
647 AM CDT Tue Oct 31 2017

.AVIATION...
Area will be seeing increasing SHRA/TSRA coverage today through
tomorrow morning with a weak frontal boundary in the vicinity.
Ceilings will be lowering to mainly MVFR levels. Anticipate
improving conditions tomorrow as the day progresses. 42
&&

.PREV DISCUSSION... /ISSUED 433 AM CDT Tue Oct 31 2017/

DISCUSSION...
Showers over the Gulf are hinting at wetter weather to come. The
character of this rain will initially be more showery and closer
to the coast, before transitioning to being more widespread and
tied to a cold front expected to stall over Southeast Texas
tonight. It would be a good idea to be prepared for showers and
storms while getting your Halloween activities out of the way
earlier. Once done, settle in for some (potentially historic) TV
at night.
While activity should generally be winding down
Wednesday, a marginal threat for severe weather exists as the
environment will become more supportive of stronger storms (should
any storms exist). Beyond Wednesday, some off-and-on potential
for showers will continue, but the trend will be towards drier
weather as we head towards the weekend. Along with this, we can
also look for a return of temperatures in the 80s.

NEAR TERM [Through Today]...

Regional observations show a cold front right on the doorstep of
Southeast Texas. Winds at Bryan/College Station and Caldwell have
gone light and northerly, but their dewpoints remain near 60
degrees at 3am. That said, the front should sag a little more
south through the morning, before stalling out and even retreating
back north a little this afternoon.

So far, the only rain over the region is mainly over the Gulf
waters, though a shower over Galveston has racked up just over
half an inch of rain. Any showers pushing onshore have so far have
largely fizzled beyond the immediate coast - GOES-16`s
precipitable water product shows just over an inch across the
area, verifying models soundings that show a column that is still
pretty dry. However, as the column moistens today, we should look
for greater shower activity over land. Expect a greater flourish
of showers and even some lightning towards mid-afternoon as HRRR
soundings show the column moistening rapidly in conjunction with
an increase in instability.

Temperatures today should have a pretty decent gradient. Just on
the cool side of the front for most of the day, temperatures in
the far north will likely fail to reach 70 degrees. However, near
the coast, temperatures in the upper half of the 70s can be
expected in locations that don`t become rain cooled.

SHORT TERM [Tonight Through Thursday]...

At some point tonight, the atmosphere should become more
saturated, with more widespread rain tied more to convergence
along the stalled front. Midlevel heights look to drop slightly -
enough to give us a "skinny CAPE" profile that can be associated
with heavy rainfall. On the plus side, strong winds aloft should
make individual cell motion relatively speedy, so no one cell is
likely to drop a ton of rain over any one spot. Also, even though
instability looks to rise, it only does so modestly, which will
likely limit updraft strength. On the downside, the mean steering
wind looks to be fairly front- parallel, meaning that training of
cells can occur as long as onshore flow from the Gulf continues
to fuel development along the front.

So rather than getting downpour from one particular storm, rains
may add up over time. It`s hard to pinpoint a specific time for
this to occur right now, but examination of multi-model soundings
seem to suggest a window between the late evening and sunrise
Wednesday for this setup to occur. Another source of uncertainty
is location. The heaviest rains should occur along and near the
stalled frontal feature. In the current forecast, this would be
along a line roughly parallel to the coast, but over the
relatively rural area between the Houston metro and College
Station. However, any change in the push of the front would impact
where this focus area occurs.

There seems to be pretty good agreement among the models for a
rainfall max near the front. However, there`s a pretty decent
spread in how much rain falls. The GFS is driest of the major
deterministic models, with rain totals around an inch. The Euro is
in the 2-3 inch range, while the NAM and GEM push towards 4
inches. We are beginning to come into the range of the CAM suite
of guidance, as well. The TTU WRF is also relatively dry with
totals peaking around 2-3 inches, and its ensemble showing less
than a 10 percent change of exceeding 3 inches. On the wet end,
though, the NCAR ensemble shows a 50-70 percent chance of
exceeding three inches near the front, and a 10-30 percent chance
of exceeding 6 inches. Those numbers may sound low, but a 1 in 3
chance of getting more than 6 inches of rainfall is a fairly
significant potential.

Ultimately, think the placement of the front, relatively modest
amount of instability, and quick cell motion will keep things from
getting too out of control. The GFS is probably a little too
optimistic, but something in the middle of the envelope seen by
the Euro and TTU-WRF seems entirely reasonable. But, the setup of
having a stalled front over Southeast Texas, inflow from the Gulf,
and potential for training makes me leery of writing off at least
locally heavier rainfall entirely. So, after coordination with
WPC, a marginal risk for excessive rainfall exists in the area.
If there are indications through the day that things are
overperforming and trending towards the higher end of the
guidance, the severity of that threat will have to be stepped up.

On Wednesday, we should generally be looking for things to be
winding down. As winds become more unidirectionally southwesterly,
look for the column aloft to dry up and become capped. However,
before things are totally shut off, this setup will create some
potential for severe weather. MLCAPEs will begin to approach 2000
j/kg, with deep layer shear remaining above 30 kts. With DCAPE
approaching 1000 j/kg and a fair amount of shear and curvature in
the lowest km, there will be a nonzero potential for damaging wind
gusts and even a quick tornado should any storms manage to get
going. That "should any storms manage to get going" will be the
operative phrase, though. Because of that, we are also in a
marginal risk area for severe weather in SPC`s Day 2 outlook.

Potential for rain comes down on Thursday - but with an upper
trough moving along the Red River Valley though and with continued
inflow from the Gulf, we may see some isolated updrafts to
overcome the cap. There`s a decent amount of instability to tap
into if the cap can be overcome, so thunderstorms are a
conditional risk. However, whether anything can overcome the cap
is a very big question here.

LONG TERM [Thursday Night Through Tuesday]...

Ridging aloft will begin to develop over the Rio Grande Valley or
northeastern Mexico through the weekend, which should trend our
weather towards the dry side. With onshore winds at low levels and
a location towards the fringe of the ridge, can`t totally rule out
some rain, but there`s enough confidence to put in a dry forecast
for this weekend and early next week. With the midlevel high
building heights over Southeast Texas, we can also look for
temperatures to trend towards above normal values, currently
forecast to be in the lower 80s. Another front looks to approach
the area later next week, but there is significant differences in
the guidance at this time, and is fortunately for this forecaster
beyond the scope of this forecast.

MARINE...

Increasing onshore winds and building seas can be expected into
the middle of this week under a tightening pressure gradient.
Caution flags are anticipated, and advisories might be needed.
Look for rising shower and thunderstorm chances through Wednesday.
Lighter onshore winds and lower seas will develop toward the end
of the week and will persist into the upcoming weekend. 42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 68 58 76 66 87 / 60 80 40 10 10
Houston (IAH) 75 68 79 69 86 / 70 90 80 20 30
Galveston (GLS) 77 73 79 74 82 / 50 60 80 30 30

&&

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

$$

25/42
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Re: October 2017 - Halloween Forecast/Rain Chances

Postby unome » Tue Oct 31, 2017 3:40 pm

poor kiddos - hope this doesn't ruin their trick-or-treating

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Re: October 2017 - Halloween Forecast/Rain Chances

Postby DoctorMu » Tue Oct 31, 2017 3:44 pm

Things have begun to saturate up and down trop column. Light rains erupting and beginning more stead.

WAs hoping it would hold off until trick or treating has concluded in the BCS area...but then we've been pretty dry since Harvey.

Intermittent Showers are the operative phrase.

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Re: October 2017 - Halloween Forecast/Rain Chances

Postby DoctorMu » Tue Oct 31, 2017 3:46 pm

Trick and Treat:

PREV DISCUSSION... /ISSUED 1121 AM CDT Tue Oct 31 2017/
UPDATE...
This shift wishes it had better weather news for all of
those across southeastern Texas that want to spend time outdoors
this All Hallow`s Eve. High to likely chances for periods of rain
and isolated thunderstorms from this afternoon on through
Wednesday afternoon hours.
So, the question has been answered as
to precipitation occurrence but question marks still linger for
the amounts of rain we will receive through tomorrow. Of
course...when looking over the model du jour menu there are a
couple of solutions that peg 3 to 4 inch storm total rain amounts
over the coastal regions. These solutions develop a surface
low/trough off to the southwest and provide better mid-level
inflow into this current lower level boundary currently positioned
roughly from a Matagorda Bay to city of Houston to south of a
Lake Livingston line. Tale of two regions across the CWA this
morning...lower 60s north of boundary and lower 70s south of
stalled front. The focus is there...as is the moisture (1.6
pwats)...so it is just a matter of time before we will begin to
experience inland convective development. This forecast update has
an areal average 1 to 2 inches falling between this afternoon and
late Wednesday...locally 3 to 4 inches in the vicinity of the
front is certainly not out of the question. As the earlier shift
mentioned...there is a 30-40% chance of counties south and west of
metro to pick up 3 inches or greater by the end of the day.


Tomorrow remains unsettled...high chance for showers/storms earlier
in the day and...if you split the CWA with a southwest-to-northeast
orientated line...the higher TSRA chances would reside east of that
line. Progged sounding (indices) not showing anything super impressive
within the resident environment that would suggest severe but there
is enough instability for any cell to briefly exhibit strong draft
structure. 31

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 68 56 76 66 87 / 50 80 30 10 10
Houston (IAH) 75 65 79 69 86 / 70 80 80 30 30
Galveston (GLS) 76 69 79 74 82 / 50 50 70 30 30
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Re: October 2017 - Halloween Forecast/Rain Chances

Postby BlueJay » Tue Oct 31, 2017 4:19 pm

We are getting a nice shower now. Hmmm. I also hope that the kids aren't rained out.
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Re: October 2017 - Halloween Forecast/Rain Chances

Postby BlueJay » Tue Oct 31, 2017 8:03 pm

It's raining.
It's pouring.
I think our little trick or treaters have been thwarted.

On to November 2017.
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Re: October 2017 - Halloween Forecast/Rain Chances

Postby tireman4 » Wed Nov 01, 2017 11:03 am

00
FXUS64 KHGX 011511
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1011 AM CDT Wed Nov 1 2017

.DISCUSSION...
Surface analysis has stalled frontal boundary basically from
Victoria to Tomball to Lufkin this morning. Temperatures south of
the front are in the low 70s with temperatures north of the front
in the 50s/60s. Front should dissipate today and with cloud cover
gradually decreasing, high temperatures still look on track for
the upper 70s. Main forecast update was to adjust rain chances for
ongoing trends. Radar shows some shower and thunderstorm activity
along the coast but all of this activity is moving east. Latest
model trends with the HRRR support this so look for drying
conditions the rest of the day.

Overpeck

&&

.PREV DISCUSSION... /ISSUED 651 AM CDT Wed Nov 1 2017/

AVIATION...
The NE to SW oriented line of SHRA/TSRA will continue moving eastward
and out of the HOU-LBX-GLS area TAF sites over the next several hours.
Low ceilings will begin to slowly improve after sunrise, and TAF sites
are anticipated to become mostly VFR later this morning or this afternoon.
S to SSW winds will be increasing to 10 to 15 knots, and some locations
could see some gusts around 20 knots this afternoon. The S to SSW winds
are expected to be around 8-10 knots overnight, and this should help
to keep the potential for significant fog development on the low side.
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