August 2017: Looking Back at Harvey 1 Year Later

General Weather Discussions and Analysis
User avatar
DoctorMu
Posts: 1920
Joined: Sun Jun 28, 2015 10:58 am
Location: College Station
Contact:

Re: August 2017: Hemispheric Pattern Change/Eye On The Tropi

Post by DoctorMu » Tue Aug 01, 2017 8:16 pm

Area Forecast Discussion
National Weather Service Houston/Galveston TX
637 PM CDT Tue Aug 1 2017

.AVIATION...
First portion of the forecast looks generally on track, with VFR
conditions across the area and winds slowly coming down through
the evening. Big picture for the back half also appears good, but
uncertainty about the details - including the potential for
heavier rain - remains at this time.

As an upper disturbance swings into Southeast Texas, feel there`s
enough confidence to start bringing in TEMPOs for rain/storms at
the northern sites. The question comes closer to the coast, as
convergence in winds seen today over Colorado/Austin/Wharton
counties will set up and become the dominant feature for our
Houston and coastal TAF sites. While the blanket VCs seem
reasonable, whether the northern feature or the coastal feature
become dominant may impact the timing of when the best coverage of
storms is possible farther south by several hours. For now, both
scenarios seem plausible, so will punt on probs/tempos for this
cycle, and look for more clarity with the evening model runs.

It does seem likely that around 00Z, most of the rain will be
ending or at least moving east of the TAF sites. For most, this is
the end of period so I don`t explicitly forecast this at this time,
but does show up in the extended portion of the IAH TAF.

Luchs

&&

.PREV DISCUSSION... /ISSUED 358 PM CDT Tue Aug 1 2017/

DISCUSSION...
Gulf moisture nosing back into the region this afternoon had
allowed for a few showers to develop along and south/east of the
Highway 59 corridor, but most of the region has remained dry
today. However, recent dryness will quickly change to a relatively
wet pattern for Southeast Texas for early August as an
approaching disturbance from the Southern Plains reaches the
region later tonight into Wednesday.


Most shower activity is expected to dissipate with loss of
daytime heating this evening, but another round of rain will
approach the region from the north and northwest tonight into
early Wednesday morning as the upper level disturbance arrives.
Additionally, afternoon surface analysis shows several distinctive
surface convergence zones or boundaries located across the
northwest Gulf.
Height falls on the order of 2-4 decameters
tonight may result in enough of a surface reflection/trough to
draw one or both of these boundaries inland... but several
questions still exist on when, which one(s), or how far inland
they will travel but will need to monitor areas along and
south/east of Highway 59 based on consensus from 12Z guidance.

Convergence along these features should result in continued
shower development across the waters overnight with coverage
gradually spreading into the coastal counties along any one of
these boundaries. As the upper disturbance passes across the
region on Wednesday, additional showers and thunderstorms may
focus along whatever boundaries move inland. With forecast
soundings showing precipitable water values rising into the
2.2-2.4 inch range (near the 99th percentile for August), locally
heavy rain will be possible with any shower or thunderstorm that
develops tomorrow.
Luckily, recent July rainfall deficits of
anywhere from 1-3 inches below normal should help mitigate against
any widespread threat... but a splitting (albeit weak) 250-300 MB
jet over the region during the day should be enough to support
high rain rates
and this may result in minor flooding issues in
urbanized areas.

The main energy from the upper disturbance looks to clear the
region Wednesday night into Thursday morning with subsidence
behind this feature expected to result in a temporary decrease in
rain chances during the overnight hours. However, a secondary
shot of energy moving across the region during the day Thursday
should result in the development of another round of scattered
showers and thunderstorms into Thursday night before this energy
clears the region.


Northwest flow aloft will persist across the region through the
end of the work week and into the weekend, with rain chances
highest over the coastal waters at night and inland during the
day. Any smaller disturbance translating across the region during
this time in the flow aloft would certainly result in an
enhancement to coverage, but pinpointing any of those features (or
timing) at this point out is incredibly difficult. One such
disturbance may send a cold front into Texas by Friday, but with
the disturbance quickly pulling east across the Great Lakes the
front appears to lose too much of its upper level support to make
it into the region.
:cry: too good to have been true?

Temperatures over the next few days should remain near to below
seasonal normals due to rain and cloud cover, with highs in the
upper 80s to mid 90s and lows in the 70s to low 80s.

Huffman

User avatar
DoctorMu
Posts: 1920
Joined: Sun Jun 28, 2015 10:58 am
Location: College Station
Contact:

Re: August 2017: Hemispheric Pattern Change/Eye On The Tropi

Post by DoctorMu » Tue Aug 01, 2017 8:34 pm

The ensembles are holding to cooler and wetter conditions than normal until mid-August. Looking forward to a change in the usual script!

Image

Image

User avatar
Katdaddy
Global Moderator
Global Moderator
Posts: 2223
Joined: Thu Feb 04, 2010 8:18 am
Location: League City, Tx
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by Katdaddy » Wed Aug 02, 2017 4:13 am

Heavy rainfall is likely this afternoon and evening as GOM moisture moves inland and a a strong disturbance approaches from the NW. Rain and thunderstorm chances decrease slightly Thursday and Friday before another increase occurs for the weekend. Radar currently showing showers and a few thunderstorms moving toward the Upper TX Coast this morning.

The small non-tropical in the E GOM continues to move toward FL with only a 10% chance of development.
Attachments
Screen Shot 2017-08-02 at 5.12.11 AM.png
Screen Shot 2017-08-02 at 5.12.11 AM.png (35.15 KiB) Viewed 1603 times

User avatar
srainhoutx
Site Admin
Site Admin
Posts: 19081
Joined: Tue Feb 02, 2010 2:32 pm
Location: NW Houston FM 1960/SH 6
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by srainhoutx » Wed Aug 02, 2017 4:35 am

Complicated and complex unsettled weather pattern shaping up across Texas including the Upper Texas Coast as a rather strong upper air disturbance located over N Texas drops South in the N to NW flow aloft colliding with deep tropical moisture that has pooled overnight with PW's in the 2 to 2.4 inch range. No real focusing mechanism to offer clues as to which locales will see the heaviest rainfall potential, but a general 1 to 2 inches looks favorable area wide with the possibility of an isolated 3 to 5 inches possible today into this evening.

On Friday will need to ramp up rainfall potential again as a cold front advances South across Texas before stalling somewhere near or just inland from the Coast. The unsettled pattern continues throughout the coming weekend as additional upper air disturbances drop S in the N to NW flow aloft along the Eastern periphery of that Heat Ridge now anchored over the West Coast States.

The guidance is suggesting another strong disturbance dropping S into our Region on Monday, but we'll need to 'fine tune' our sensible weather forecast regarding early next week and beyond. Hopefully everyone across the Lone Star State that needs the rainfall will receive it. Let's just hope it's not too much.
Attachments
ecmwf-ens_z500a_namer_6.png
p168i(9).gif
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

Member: National Weather Association
Facebook.com/Weather Infinity
Twitter @WeatherInfinity

User avatar
srainhoutx
Site Admin
Site Admin
Posts: 19081
Joined: Tue Feb 02, 2010 2:32 pm
Location: NW Houston FM 1960/SH 6
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by srainhoutx » Wed Aug 02, 2017 5:53 am

08022017 mcd0614.gif
MESOSCALE PRECIPITATION DISCUSSION 0614
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
719 AM EDT WED AUG 02 2017

AREAS AFFECTED...SOUTHEAST TX...SOUTHWEST LA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 021118Z - 021645Z

SUMMARY...EXPECTED INCREASE IN ONSHORE BANDED CONVECTIVE CELLS
POSING RISK FOR FLASH FLOODING PARTICULARLY IN URBAN SETTINGS.

DISCUSSION...EXPERIMENTAL GOES-16 10.3UM IR DEPICTS A FEW NW-SE
SHALLOW CU BANDS WITH PERCOLATING TOPS THAT PRESENT THE SUGGESTION
THAT THE CAP HAS WEAKENED SUFFICIENTLY FOR FURTHER GROWTH AND
EXPANSION IN COVERAGE IN THE NEXT FEW HOURS.
RECENT SURFACE ANALYSIS ALSO SHOWS MODEST 1013 LOW OFF THE CENTRAL
TX COAST WITH SUBTLE BUT IMPORTANT SURFACE RIDGING ACROSS S
CENTRAL LA. THIS PROVIDES A EXCELLENT CORRIDOR FOR MOISTURE
ADVECTION AND LOCALIZED INCREASE IN ONSHORE FLOW FOCUSED ON THE
UPPER TX COAST.

CIRA LAYERED PW DOES SUGGEST THAT THE NARROW RELATIVELY DRY LAYER
SEEN IN 00Z SOUNDING FROM LCH HAS BEGUN TO MOISTEN WITH THE
APPROACH OF RETURN MID-UPPER LEVEL FLOW WITH 7-3H PWS SINKING
SOUTHWARD PINCHING OUT THE DRY ZONE NEAR/NORTH OF THE COAST.
ADDITIONALLY...SUB-8H FLOW IS QUITE MOIST AS WELL WITH LOW 60S
850MB TDS AND LOW 70S AT THE SURFACE. AS SUCH TPWS ARE JUST ABOVE
2.0" SUPPORTING WARM CLOUD/RAINFALL EFFICIENCY FOR THESE
DEVELOPING CELLS.

GOES-WV DOES SUGGEST SLOW SOUTHWARD DRIFT OF SHORTWAVE IN N TX
WILL AT LEAST PROVIDE GLANCING MID TO UPPER LEVEL
SUPPORT/EVACUATION FOR DEEPER ASCENT...WHILE ALSO PROVIDING SLOW
BUT EASTWARD CELL MOTIONS. WITH STRONGER LOW LEVEL SUPPORT
PROPAGATION VECTORS ARE LIKELY TO SUPPORT SOME BACKBUILDING WHILE
AT THE SAME TIME ALLOWING FOR CONCENTRATION OF THE ONSHORE
CORRIDOR TO FOCUS IN THE UPPER TX COAST. THIS MAY SUPPORT
ADDITIONAL ASCENT ON THE EASTERN SIDE WHERE FLOW/CELL MOTIONS
SUPPORT SLIGHT ANTICYCLONIC CONVERGENCE. RAP/HI-RES GUIDANCE ARE
FAIRLY AGGRESSIVE IN STRENGTH/RAINFALL EFFICIENCY WITH RATES UP TO
2-2.5"/HR POSSIBLE.

SOME LIMITING FACTORS...MAINLY THE OVERALL DRY PATTERN OVER THE
LAST FEW WEEKS HAS LEFT GROUND CONDITIONS MORE SUPPORTIVE OF
ABSORBING/WITHSTANDING THE MAGNITUDES OF UP TO 2.5"/HR AND TOTALS
IN THE 2-4" RANGE. OVERALL COVERAGE IS ALSO SUGGESTED BY GUIDANCE
TO BE LIMITED...EITHER WITH ONE CONSOLIDATING BAND OR MODERATELY
SCATTERED CONVECTIVE CORES...THINKING THE PRIOR IS MORE LIKELY AT
THIS TIME BUT THERE IS SOME LOWERED CONFIDENCE IN PRECISE
EVOLUTION.

ALL CONSIDERED THERE REMAINS SUFFICIENT ENVIRONMENTAL AND GUIDANCE
SUPPORT TO SUGGEST FLASH FLOODING IS POSSIBLE THROUGH THE EARLY
MORNING HOURS...PARTICULARLY IN URBAN/TRADITIONAL SLOW DRAINING
AREAS.

GALLINA

ATTN...WFO...HGX...LCH...
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

Member: National Weather Association
Facebook.com/Weather Infinity
Twitter @WeatherInfinity

User avatar
tireman4
Global Moderator
Global Moderator
Posts: 2554
Joined: Wed Feb 03, 2010 9:24 pm
Location: Humble, Texas
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by tireman4 » Wed Aug 02, 2017 6:57 am

000
FXUS64 KHGX 021131
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
631 AM CDT Wed Aug 2 2017

.DISCUSSION...

12Z Aviation...Will see convection really expand in coverage
across the area by mid-morning with heating. Already seeing
scattered showers and isolated TSRA across the coastal areas and
also seeing widespread SHRA approaching CLL from the NW. The
convection NW of CLL will continue to progress to the SE this
morning with a weak frontal zone. The most active time pd for
TSRA across IAH and HOU appears to be in the 16-21Z window. That
window may extend another hour or 2, not too confident on the
ending time. Will see SHRA and possible TSRA redevelop early
morning on Thursday, even across inland areas as another
disturbance moves across the area. 33

&&

.PREV DISCUSSION... /ISSUED 450 AM CDT Wed Aug 2 2017/

DISCUSSION...
A rather wet forecast is expected across much of SE TX today and
tonight. A plume of higher PWs (ranging from 2.1-2.4") has moved
in from the Gulf and settled over the region and will be helping
to fuel the development of widespread storms as a strong distur-
bance moves in from the N/NW. At this time, not seeing a favored
area for highest rains given the lack of a specific boundary but
the deeper moisture is generally over the eastern half of the FA.
Rainfall totals should average from 1 to 2 inches, with isolated
amounts of 3 to 5 inches possible. No flood/flash flood watch is
planned at present given the dry spell of late.

We should get a break late tonight but conditions do remain very
favorable for another round tomorrow afternoon with the approach
and passage of another disturbance. This wet pattern courtesy of
the persistent NNW flow aloft looks to stay in place through the
rest of the week as other disturbances move down off the Plains.
Rain chances could spike once again over the upcoming weekend as
a weak frontal boundary moves into the northern parts of the CWA.

However, long-range guidance is now hinting that the higher POPs
could be Mon with another strong short-wave. Temperatures should
remain at/just under normals given the clouds/rain wx these next
several days. 41

MARINE...
Light to moderate southeast winds will become light and variable
tonight and into Thursday as a cool front dissipates inland over
Southeast Texas. Low pressure will develop across West Texas on
Thursday and surface winds will veer to the south-southwest late
this week. A series of upper level disturbances will bring unsettled
weather to the coastal waters through next weekend. Winds and seas
will be higher in and near scattered showers and thunderstorms. The
pressure gradient will tighten over the weekend and slightly
stronger onshore winds will be possible on Saturday night into
Sunday. 33

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 86 74 89 75 94 / 70 40 30 20 40
Houston (IAH) 87 74 88 75 91 / 70 40 50 30 50
Galveston (GLS) 86 78 87 79 88 / 60 50 50 40 50

&&

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

$$

Discussion...41

User avatar
srainhoutx
Site Admin
Site Admin
Posts: 19081
Joined: Tue Feb 02, 2010 2:32 pm
Location: NW Houston FM 1960/SH 6
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by srainhoutx » Wed Aug 02, 2017 7:07 am

A quick look at the Tropics this morning suggest tropical waves continue to move off the West African Coast across the Atlantic and Caribbean, but current conditions are not that favorable for development due to African Dust and a bit of subsidence across the Main Development Region. The Convectively Couple Kelvin Wave we've been talking about is transitioning into the Western Atlantic Basin this morning and will continue to slowly move East across the Entire Atlantic Basin throughout the next couple of weeks. A rather robust area of Monsoonal Thunderstorms has emerged off of Africa this morning and MIMIC does suggest a bit of spin already associated with the tropical showers and storms. Some of the Ensemble Guidance suggest this disturbance may be worth monitoring as it traverses that Atlantic and arrives in the Caribbean Sea in about 7 or so days. Conditions may become more favorable for tropical development in the Western Caribbean in about 9 to 11 days, so my eye will be focused closely on that feature as it moves West.
The attachment 08022017 twc_mjoCCKW_vp200.png is no longer available
08022017 twc_mjoCCKW_vp200.png
Image
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

Member: National Weather Association
Facebook.com/Weather Infinity
Twitter @WeatherInfinity

User avatar
srainhoutx
Site Admin
Site Admin
Posts: 19081
Joined: Tue Feb 02, 2010 2:32 pm
Location: NW Houston FM 1960/SH 6
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by srainhoutx » Wed Aug 02, 2017 7:28 am

Michael Ventrice‏Verified account @MJVentrice · 16m16 minutes ago
Still seeing credible risks for tropical cyclone development over the western Main Development Region, and GoMEX (Bay of Campeche) in 1 week
Attachments
08022017 Mike Ventrice DGOglCdXYAEZN1K.jpg
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

Member: National Weather Association
Facebook.com/Weather Infinity
Twitter @WeatherInfinity

User avatar
srainhoutx
Site Admin
Site Admin
Posts: 19081
Joined: Tue Feb 02, 2010 2:32 pm
Location: NW Houston FM 1960/SH 6
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by srainhoutx » Wed Aug 02, 2017 8:21 am

Wednesday morning briefing from Jeff:

Unusually rare upper air pattern for early August will bring widespread rainfall to TX over the next several days.

Upper level ridge building into the NW US has carved out a large downstream trough across the central and eastern US. This pattern is resulting in unusually strong “cold” front for this time of year pushing into TX along with numerous disturbances moving southward down the plains and into the SE US. Old frontal zone from Sunday has washed out over the Gulf of Mexico allowing a tropical air mass to surge into the area this morning. Maximum influx of moisture has been aimed at areas east of a line from Palacios to Houston to Liberty where numerous showers and thunderstorms have developed. Leading edge of a slow moving complex of showers and thunderstorms extends from NC TX to WC LA and marks the southward advance of the lift associated with the short wave over NE TX. Expect moisture tongue to expand and spread inland over much of SE TX by late morning and with continued strong surface heating numerous showers and thunderstorms will be possible. Lift will also become maximized over the region by late morning to early afternoon and favorable position of a rare jet stream aloft for this time of year may even add a little divergence aloft.

Main concern will be slow cell motions and very moist air mass in place with PWS pushing 2.0 inches and forecasted to rise to near 2.3 inches this afternoon. This will support a heavy to excessive rainfall threat with the stronger cells with 2-4 inch per hour rainfall rates possible. Appears some sort of convergence boundary may attempt to set up across our central tier counties (roughly near I-10) by early afternoon, but I see little evidence of any such feature at this time. A more plausible potential is for outflow boundaries to move southward from NE TX and the seabreeze to move northward from the coast and collide along/near US 59 this afternoon.

Grounds are fairly dry from the recent dry spell and high heat of late. However potential for high short duration rainfall rates may lead to rapid street flooding in urban areas. The other threat will be cloud to ground lightning….and there has been several instances of persons be struck by lightning recently across the US. As a rule of thumb, one should remain in a safe location for 30 minutes after you last hear thunder.

Unsettled pattern will remain in place for the rest of the week and into the weekend as yet another frontal boundary approaches by Saturday. Tomorrow may end up being drier than currently forecast depending on how worked over the air mass is after today’s events. Another disturbance will approach on Friday and work with the seabreeze to produce additional storms and a slow moving frontal boundary will sink into the area this weekend keeping at least 40-60% chances going.

Combination of clouds and rainfall will help keep temperatures below normal for what is typically the hottest time of year for SE TX.
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

Member: National Weather Association
Facebook.com/Weather Infinity
Twitter @WeatherInfinity

User avatar
Texaspirate11
Posts: 1067
Joined: Tue Dec 31, 2013 12:24 am
Contact:

Re: August 2017: Unsettled WX/Eye On The Tropics

Post by Texaspirate11 » Wed Aug 02, 2017 10:15 am

srainhoutx wrote:Michael Ventrice‏Verified account @MJVentrice · 16m16 minutes ago
Still seeing credible risks for tropical cyclone development over the western Main Development Region, and GoMEX (Bay of Campeche) in 1 week
Love those squiggly lines that keep it out of Texas!
Just because you're disabled, you don't have to be a victim
Be Weather Aware & Prepared!
Barbara Jordan Winner in Media
Disability Integration Consultant

Post Reply