September 2017 - Rain Chances/End Of Month Cold Front

General Weather Discussions and Analysis

Re: September 2017 - Rain Chances & Typical Late Summer WX

Postby Electric Lizard » Thu Sep 21, 2017 8:13 pm

Does anyone have a QPF for next week's frontal passage? The combination of a slow, early season cold front moving through a very high PW air mass bothers me. I've seen this movie before...
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Re: September 2017 - Rain Chances & Typical Late Summer WX

Postby Ptarmigan » Thu Sep 21, 2017 9:31 pm

Electric Lizard wrote:Does anyone have a QPF for next week's frontal passage? The combination of a slow, early season cold front moving through a very high PW air mass bothers me. I've seen this movie before...


NWS Houston Area Forecast Discussion
http://forecast.weather.gov/product.php ... glossary=1

Code: Select all
000
FXUS64 KHGX 212032
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
332 PM CDT Thu Sep 21 2017

.DISCUSSION...
Scattered to numerous slow moving showers and thunderstorms continue
across Southeast Texas this afternoon as a disturbance moves eastward
across the area. The slow moving activity and precipitable water values
above 2 inches have brought locally heavy rainfall to the area resulting
in several advisories/warnings. At one point, a Harris County Flood
Warning System rain gage (Cypress Creek at Huffmeister) had rainfall
rates of 0.48 inches in 5 minutes and 0.80 inches in 10 minutes. Expect
decreasing coverage/intensity late this afternoon through early this
evening. The area remains on the southern fringes of ridging both at
the surface and aloft, and enough heating should allow for some mainly
daytime shower and thunderstorm development over the next several days.
But compared to today, expect to see much less coverage for the end
of the week and over the weekend with lower precipitable water values.
Still looking at an eventual increase in rain chances next week as
mid/upper level ridging edges eastward and a western U.S. trough gradually
works its way toward the east. Will be carrying higher rain chances
as we head on into the middle to end of the week when the trough and
associated slow moving cold front begin to work their way toward our
area. Will need to keep a close eye on model trends over the next several
days as some have precipitable water values approaching a very high
2.50 inches under the persistent onshore flow ahead of the slow moving
boundary. This potential heavy rain event is still many days away,
and a lot can change with the models. Obviously, our area does not
need to see another significant rainfall event as the Harvey recovery
continues.  42
&&
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Re: September 2017 - Rain Chances & Typical Late Summer WX

Postby Katdaddy » Fri Sep 22, 2017 4:26 am

Fall 2017 has officially arrived but Summer conditions will continue. Only a slight chance of scattered showers and thunderstorms through the weekend.
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Re: September 2017 - Rain Chances & Typical Late Summer WX

Postby srainhoutx » Fri Sep 22, 2017 5:34 am

Regarding rainfall amounts or if we may see heavy rainfall across SE Texas as the cold front arrives, there is a lot of uncertainty as we typically expect 7 days out. The GFS is more aggressive with higher rainfall totals as it is the slowest in pushing the 850mb cold front through SE Texas versus the faster and drier ECMWF. We will be monitoring over the weekend into early next week for better agreement before mentioning a potential heavy rainfall event, particularly after what we went through with Harvey just about a month ago. The morning Updated Quantitative Precipitation Forecast for the next 7 Days suggests the heavy rainfall will be to our West over the Edwards Plateau, Permian Basin and the Central Texas Regions.
Attachments
09222017 09Z 7 Day QPF p168i.gif
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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Re: September 2017 - Rain Chances & Typical Late Summer WX

Postby tireman4 » Fri Sep 22, 2017 8:29 am

000
FXUS64 KHGX 221126
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
626 AM CDT Fri Sep 22 2017

.AVIATION...
Have had to hit this morning`s fog a little bit harder north of
Houston as CXO has crashed to VLIFR for visibility. CLL and UTS
have shaded a little more to low stratus, dropping to LIFR on
ceilings, and only MVFR/VFR vis. Farther south, am trying to be a
bit more optimistic, holding at VFR. Despite not seeing it in the
obs yet, kept the MVFR TEMPO at SGR given visibility at
surrounding sites. Similar story at LBX - its ob has been missing
for a couple hours now, but given its propensity to fog up, will
leave in the fog TEMPO.

Expect improvement back to VFR mid to late morning as mixing
deepens. Short range models aren`t enamored of rain chances today,
and satellite/obs show the best moisture plume to our south.
Despite this we still have a decent environment, albeit less
impressive than past days, and so will leave afternoon VCSH in
place for isolated to scattered showers today. Overnight, expect
conditions to be generally similar to tonight`s conditions.

Luchs

&&

.PREV DISCUSSION... /ISSUED 405 AM CDT Fri Sep 22 2017/

DISCUSSION...
So the calendar says its fall and we all know that means
absolutely nothing in SE Texas. It is still humid as a sauna and
morning temperatures are in the 70s with areas of fog. At least we
did not have any record high minimum temperatures yesterday.
After yesterday`s isolated heavy rainfall fall and flash flooding,
today should be on the dry side comparatively speaking. Axis of
higher moisture seen in GOES 16 derived precipitable water imagery
has become oriented over the western portions of the area and
into central Texas. Upper level pattern remains rather amplified
with a large long wave trough west of the Rockies, ridging through
the central U.S. and then weak troughing over the Carolinas and
SE U.S. With the moisture axis moved west and perhaps a bit more
sinking motion from the ridge, best rain chances today will be
from Bay City to Columbus westward. There still could be some
isolated showers across SE Texas but far less coverage than
yesterday.

The weekend forecast remains rather unchanged with mainly 20/30
PoPs each day. The upper level pattern remains amplified with the
trough over the Rockies but the ridge completely breaks down with
the trough over the Carolinas retrograding towards the Mississippi
River Valley. Moisture also increases Sunday into Monday so expect
slightly higher rain chances each of those days, but coverage
still looks isolated to widely scattered for showers and
thunderstorms.

On Monday the upper level trough begins to transition east with
one piece of vorticity moving NE towards the northern Plains by
Tuesday night. Forecast models still have another upper level low
back over the Great Basin/Four Corners region by Wednesday. This
is also when a cold front pushes into north Texas with the
Canadian model faster with the front, GFS slower and ECMWF
somewhere between the two. The pattern becomes more supportive of
a cold frontal passage for the end of next week as a trough
develops over the plains with northernly flow aloft. Surface cold
front should push into the area late next Thursday into Friday.
Both the GFS and Canadian show quite a bit of rainfall during this
period with the ECMWF quite dry. Forecast will remain
conservative with 40 percent rain chances but would not be
surprised if the models continue to depict heavy rainfall with the
front. GFS is bringing precipitable water values of 2.3 to 2.5
inches into the area late Thursday into Friday just as the front
arrives. Given the circumstances of Harvey, I really don`t want to
forecast heavy rainfall with this front, but this will be a
pattern to watch in the coming days. GFS in particular has right
entrance region of jet over SE Texas along with a slow moving
850mb front that could support a deformation zone. Heavy rainfall
would be possible until next Saturday when the 850mb front pushes
through and trough axis swings east. On the other end of the
spectrum, the ECMWF is very dry and has a much stronger ridge
aloft that develops as the front pushes through with drier air
behind it. Again this is all out on days 7 through 9 of the
forecast so a lot will change especially with a transitional
upper level pattern. We just need to be diligent to keep up with
those changes in the models and not bite off on any one model run
at this time.

Overpeck

MARINE...
Near caution winds over parts of the Gulf waters are expected to
diminish slightly to more light to moderate onshore winds. These
winds are expected to persist into the middle of next week until a
front approaches the area. Scattered showers, with a few
thunderstorms, can be expected daily. Winds and waves will be
higher in the vicinity of any thunderstorms. The best chance for
storms over the waters will likely come in the very late night and
morning hours. Tides have been consistently running a few inches
to half a foot above norm, and this should be expected to continue
into the weekend, perhaps increasing a little more if wind
directions and speeds align more favorably.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 91 72 91 72 91 / 20 10 20 10 20
Houston (IAH) 90 73 91 73 89 / 20 10 20 10 30
Galveston (GLS) 89 79 88 79 88 / 20 10 20 10 30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Dense Fog Advisory until 9 AM CDT this morning for the following
zones: Austin...Brazos...Burleson...Colorado...Grimes...
Houston...Madison...Montgomery...Polk...San Jacinto...
Trinity...Walker...Waller...Washington.

GM...NONE.
&&

$$

Discussion...39
Aviation/Marine...25
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Re: September 2017 - Rain Chances & Typical Late Summer WX

Postby srainhoutx » Fri Sep 22, 2017 2:17 pm

The afternoon Updated Quantitative Precipitation Forecast for our neighbors to the West is looking worrisome. If the 7 day rainfall forecast verifies, some locations could exceed 15 inches of very heavy rainfall mainly West of an Austin to Corpus Christi line.
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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Re: September 2017 - Rain Chances/End Of Month Cold Front

Postby Katdaddy » Mon Sep 25, 2017 4:21 am

20-30% chance of scattered showers and few thunderstorms through the week. A backdoor cool front still looks to arrive Friday afternoon resulting in drier and cooler temps for next weekend.
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Re: September 2017 - Rain Chances/End Of Month Cold Front

Postby tireman4 » Mon Sep 25, 2017 7:36 am

000
FXUS64 KHGX 251106
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
606 AM CDT Mon Sep 25 2017

.AVIATION...
Satellite and obs show some patchy fog developing north and west
of Houston. Though it looks fairly dense in a few spots, expect
the TAF sites to stay MVFR at worst. Any of those MVFR spots
should rapidly improve to VFR, with another bout of isolated to
scattered showers (and maybe a storm) this afternoon with SE
winds to near 10 knots. Going into tonight, there`s still no
expectation of change from the persistent pattern, with winds
backing off and skies clearing. Looking for fog again overnight,
with the most impact for the usual suspects like CXO.

&&

.PREV DISCUSSION... /ISSUED 353 AM CDT Mon Sep 25 2017/

DISCUSSION...
Looking at 08Z observations and available GOES 16 satellite data,
low clouds and fog appear less than the last couple of mornings.
There is still plenty of time for fog to develop through the
morning hours and expect there to be more patchy fog to develop
across SE Texas. Today`s forecast is setting up much like the last
couple of days. There may be enough moisture to support a few
showers and thunderstorms with day time heating. Aloft 500mb
heights have dropped a few decameters with the weak upper low over
the northern Gulf coast. Given neutral vertical motion in the
atmosphere, diurnal heating and any sea breeze boundary should be
enough for storm initiation so will keep 20/30 PoPs in the
forecast for today.

Tuesday into Wednesday upper level riding should expand with
maybe a few vorticity maximums rotating through the flow from an
upper level low over the Desert SW. While 500mb heights rise
slightly so does overall atmospheric moisture. Again with daytime
heating look for 20 to 30 PoPs to continue through Thursday.
Overall models are not highlighting any one day for higher rain
chances.

Thursday night into Friday while upper level ridging remains over
Texas, a deep trough develops over the Great Lakes. This gives
support for a cold front to push through the area later on Friday.
The front still looks like a strong backdoor front with NE flow,
but models are showing it pushing through later on Friday instead
of earlier like previous forecast data had shown. Still there is
good confidence that the front will push through but the effects
may not be felt until the weekend.

Conditions behind the front Saturday and Sunday do look to be
more fall like with high temperatures in the low/mid 80s and low
temperatures in the low/mid 60s. Surface dewpoints in the 50s
behind the front will feel refreshing compared the the air you can
wear 70 dewpoints. Relative humidity each afternoon could reach
below 40 percent for the weekend.

Overpeck

MARINE...
Light to moderate southeasterly winds can be expected into the
midweek, before backing easterly as pressures along the coast dip
slightly. Late in the week a cold front will cause winds to further
back to the northeast. A push of drier, slightly cooler air is
likely to increase winds and seas into the weekend. In the coming
days, the persistent onshore flow will cause tides to run several
inches above astronomical levels.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 89 72 91 73 90 / 10 10 20 20 20
Houston (IAH) 88 73 89 73 90 / 20 10 20 10 20
Galveston (GLS) 87 80 87 79 87 / 30 10 20 10 20

&&

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

$$

Discussion...39
Aviation/Marine...25
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Re: September 2017 - Rain Chances/End Of Month Cold Front

Postby DoctorMu » Mon Sep 25, 2017 10:58 pm

The cool snap this weekend will only last a few days. Enjoy while you can

PREV DISCUSSION... /ISSUED 312 PM CDT Mon Sep 25 2017/

DISCUSSION...
Precip coverage remains sparse this afternoon but a little more
heating should continue to trigger some additional showers through
7 PM. Showers are expected to wane quickly after sunset. Tuesday
through Thursday look about the same each day fcst soundings
supporting high temperatures near 90 degrees and convective temps
in the middle to upper 80s. The pattern favors weak disturbances
embedded in a SW flow aloft to remain west of SE TX through the
end of the week. As the trough deepens out west, weak upper level
ridging will try to develop over East Texas. This feature will
likely impart some subsidence over SE TX so rain chances will
likely remain on the low side through the end of the week.
Moisture levels will exceed 2 inches on Thursday so despite the
subsidence, rain chances may be a bit higher along the wind shift
Thursday.

The front will not usher in cooler and drier air right away. Winds
will become NNE on Thursday but the drier air will only slowly
filter into SE TX on Friday and Saturday.
The upper ridge dampens
out a bit as weak 500 mb s/wv moves across the southern plains on
Saturday and heights will fall a little bit. Cooler 850 mb temps
over the weekend will translate into cooler sfc temps and the
drier air with sfc dew pts in the 50`s will allow for cooler
overnight low temps over the weekend. Next weekend is looking good
with dry conds and high temps in the mid 80`s and low temps in the
60`s. Both the GFS and ECMWF develop a strong 500 mb ridge over
OK/AR by the first week of Oct. Drier and warmer weather expected
for the first few days of October.
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Re: September 2017 - Rain Chances/End Of Month Cold Front

Postby Katdaddy » Tue Sep 26, 2017 4:51 am

Only a slight chance of scattered showers and thunderstorms across SE TX through the rest of week ahead of Friday’s cool front.
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