September 2017 - Rain Chances/End Of Month Cold Front

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Electric Lizard
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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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Ptarmigan
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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

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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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Katdaddy
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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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srainhoutx
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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.
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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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tireman4
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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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srainhoutx
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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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Katdaddy
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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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tireman4
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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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DoctorMu
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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.
43
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Katdaddy
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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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Screen Shot 2017-09-26 at 5.33.07 AM.png
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Katdaddy
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Another partly cloudy warm SE TX weather day with isolated to scattered showers and a few thunderstorms while heavy rains remain over S and Central TX. A cool front still expected to drift across SE TX at the end of the week.
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Screen Shot 2017-09-27 at 5.18.55 AM.png
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DoctorMu
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It will be a welcome relief to get the dew point below 70°. The wind is light this time of the year in CLL...so the stuffiness can drag on into the fall.

A chance of rain in CLL Friday night as most of the rain continues to remain west. A short respite during the weekend with drier and slightly cooler air. Before a bounce back Monday in PW/DP. We may not see something that resembles a Fall cold front until about the 10th of October.


PREV DISCUSSION... /ISSUED 248 PM CDT Wed Sep 27 2017/

DISCUSSION...
Radar imagery shows a few showers in Jackson, Wharton, and Matagorda
counties this afternoon, currently over the pocket of higher
moisture as seen on the GOES-16 satellite imagery. Not expecting
much in terms of coverage tonight, but kept widely scattered
showers and thunderstorms in the forecast to continue into the
early evening. Short term guidance such as the HRRR and RAP are
hinting at some isolated shower development in the eastern zones
of the forecast area early Thursday morning. By Thursday
afternoon, PW values increase to 2.00-2.20 inches, so moisture
will be in surplus. Additionally, diurnal heating and lift
provided from both the seabreeze and stationary/ "cool" front as
it sags southward into the region, will provide a better chance
scattered shower and thunderstorm development Thursday. Kept
precip in the forecast for Friday as well, with less coverage in
comparison to Thursday. High temperatures for the rest of the
week will be in the upper 80s to lower 90s, with lows in the mid
60s to upper 70s along the coast.

Besides the possibility of a few isolated lingering showers late
Friday into early Saturday, not expecting much in terms of precip
through the weekend. Weak upper level ridging attempts to build in
behind the frontal boundary. More seasonable weather can be
anticipated Saturday and Sunday with lower dew points, as drier
air ushers in behind the weak front. Temperatures will also be a
tad cooler and closer to normal for this time of year.

With the rise in PWs ranging from 1.40 to 1.70 inches beginning
Monday, a more summer-like pattern will return to the forecast.
Winds will shift back to out of the southeast with the start of the
new week, and as a result carrying scattered showers and
thunderstorms associated with diurnal/seabreeze activity.
Conditions look to dry out by mid-next week as both the ECMWF and
GFS begin to build in an upper level ridge over the region. This
area of high pressure will enhance subsidence (sinking air), so
therefore holding PoPs at 30% or lower through the remainder of
the week. High temperatures will rise into the mid to upper 80s,
with lows falling into the upper 60s inland to upper 70s closer to
the water.

Hathaway
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tireman4
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000
FXUS64 KHGX 281141
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
641 AM CDT Thu Sep 28 2017

.AVIATION...
VFR early this morning with plenty of mid/high level clouds, especially
out west. Daytime heating should get SHRA/TSRA to develop this afternoon
across SE TX. Activity should weaken this evening with models indicating
some stuff hanging around and/or redeveloping overnight. Winds N to
NE today (5 to 10 knots) becoming N tonight (under 5 knots inland and
5 to 10 knots at the coast). 42
&&

.PREV DISCUSSION... /ISSUED 346 AM CDT Thu Sep 28 2017/

DISCUSSION...
Showers and storms should be more numerous today than the past
couple of days with ample moisture and a few features to support
upward motion in spite of a building upper ridge over the region.
That potential should wind down for the weekend, with drier and
slightly cooler (mainly at night) weather expected. By next week, we
should return to a pattern more akin to the summertime than the
fall, with corresponding daily shower and thunderstorms chances
and temperatures warmer than seasonal averages.

NEAR TERM [Through Today]...
The radar shows a few areas of interest late tonight - the first
is another fairly large mass of rain in Rio Grande Valley and
border region. Though the coldest IR cloud tops are around -88C,
the strongest storms also are further on the Mexican side of the
border, and thus intensity in Texas appears to be less than in
previous nights. Still, some showers appear close to our western
border. To the north of our coverage area, some light showers
(perhaps not even hitting the ground) are present near or just
north of the sagging cold/quasistationary front. Finally, to the
east, a localized area of surface convergence is kicking off
showers near our eastern border - though most are dissipating
before reaching our easternmost counties, an occasional shower
may be dropping a small amount of rain before falling apart.

All three of these features may play a role through the day today
along with any seabreeze feature drifting inland. Precipitable
water at or exceeding two inches in the GOES-16 TPW product, which
is bolstered by continued levels of moisture in the guidance.
Between this, scattered to numerous showers and storms should
erupt this afternoon. Model soundings suggest 500-1000 j/kg of
MLCAPE, in a skinny distribution through a fairly warm and
saturated column. Such a profile suggests potential for locally
heavy rainfall, though the lack of any shear to speak of will
limit updraft longevity and should keep rain totals from getting
too out of hand (key word here being `should`). DCAPE values look
pretty decent, and there`s an inverted-V looking feature in the
lowest portion of the atmosphere as well - this could imply some
gusty winds in the strongest cells, but again with such a weak
wind profile, it seems unlikely that we`d manage any damaging
gusts.

SHORT TERM [Tonight Through Friday]...
As northeasterly flow becomes established overnight, we should
begin to see the first influences of drier, post-frontal air in
the HTP (Houston-Trinity- Polk counties). Without a real solid
push behind the front, and triggering features that aren`t
diurnally driven, I do keep some PoPs in the west through the
night and into Friday morning, though the loss of instability
through heating and no cooling aloft, don`t expect things to be
very vigorous. Expect the eastern bulk of the area to stay dry and
potentially even a couple degrees cooler, while some potential for
showers and storms will linger in the westernmost portion of the
area where PW values continue to exceed 1.75 inches and could
even remain near 2 inches.

LONG TERM [Friday Night Through Wednesday]...
The post-frontal regime really begins to assert itself Friday
night and Saturday, with lows dropping into the lower 60s well
inland (still staying in the lower 70s along the water). Weather
should remain dry through the weekend. However, winds should be
veering from northeasterly to more easterly later Sunday, and
signals the end of the brief reign of more seasonable conditions.
Look for humidity and temperatures (especially at night) to nudge
slowly upwards into the new week.

Easterly to southeasterly winds, increasing in strength thanks to
potential developing low pressure around the Yucatan, will surge
moisture back into the area early next week. PW could even rise to
2.25 inches if the GFS were correct. Perhaps unsurprisingly, the
GFS (and the Canadian, for that matter) is very gung ho on rain
in the first half of the week. The Euro has a similar pattern, but
is not quite as aggressive with the rain. Additionally, GEFS
plumes show the operational GFS is significantly wetter than the
ensemble mean, and only one ensemble member is within a quarter
inch of the op run at IAH - Bush Intercontinental. So, though the
GFS influence on blends push PoPs way, way up in the long range,
I chose to step things down, and go with values in the 30-40
percent range to signal a little better shot than usual for rain.
These probabilities can always be tuned in the coming days if more
confidence in widespread rain emerges. For now, I will shade more
towards the Euro and the ensembles.

MARINE...
Light east winds early this morning will become more east to
northeast and gradually strengthen through Friday night and
Saturday as a weak frontal boundary moves off the coast. Caution
flags might be needed. Winds and seas should come down a little
Saturday night and Sunday. A tightening pressure gradient is
expected to bring strengthening east winds and building seas to
the area next week, and caution flags might be needed once again.
This prolonged easterly flow may cause some minor coastal flooding
issues in the mid to late week time period. 42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 87 71 85 66 88 / 50 30 20 10 10
Houston (IAH) 88 73 88 68 87 / 40 30 10 10 10
Galveston (GLS) 87 78 87 76 85 / 30 20 10 10 10

&&

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

$$

25/42
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