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July 2018: Weekend/Early Next Week Rain Chances

General Weather Discussions and Analysis

Re: July 2018 4th Of July Outlook

Postby wxman57 » Fri Jun 29, 2018 1:13 pm

This morning's European run is much lower with precip on the 4th, only 1/4 inch across Houston. Closer to the GFS, which has about an inch of rain.
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Re: July 2018 4th Of July Outlook

Postby srainhoutx » Fri Jun 29, 2018 2:29 pm

Next week appears to bring a change in the Upper Air Pattern as the Upper Ridge weakens enough to allow our 4th of July inverted trough to pass and then additional Easterly waves to march beneath the Upper Ridge far enough to our North to allow for almost daily rain chances to end the upcoming short Holiday Work Week into next weekend. Another area of disturbed weather associated with an Easterly Wave approaches next Thursday/Friday increasing PW's again to the 2.3 range possibly bringing additional unsettled weather to our Region. I see some of the longer range Ensembles are suggesting the Upper Heat Ridge may breakdown further as we near the second full week of July.
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Re: July 2018 4th Of July Outlook

Postby DoctorMu » Fri Jun 29, 2018 2:32 pm

srainhoutx wrote:Friday morning briefing from Jeff regarding the 4th of July:

Typical summer weather in place over the region with hot and mostly dry conditions with an isolated 20% chance of an afternoon thunderstorm…this will continue for the next couple of days.

Changes appear on the horizon as we start the 4th of July week as vorticity over the SE US begins to dig SSW around the building of a large upper level high pressure system that will bring dangerous heat to the Midwest and NE US this weekend into early next week. Easterly mid and upper level flow will begin to develop along the US Gulf coast early next week on the southern side of the large high pressure cell over the Midwest to NE US. Active weather over the NE Gulf of Mexico is forecasted to begin to shift westward and arrive into SE TX by late Tuesday into Wednesday. This feature will likely consists of an upper level trough and a surge of tropical moisture. Confidence is starting to increase that the period from late Tuesday into Thursday of next week will feature active showers and thunderstorms and some of these storms may contain very heavy rainfall.

Note: the much talked about Saharan Dust will be starting to arrive across SE TX today and encompass the entire area on Saturday into Sunday. Most of this dust is elevated well above the surface…above 5,000 ft, but at times some of the particles can drift to the surface and cause some breathing irritations. Such outbreaks of dust have occurred in past summers resulting in a hazy look to the sky over the area for a few days.


The dust has definitely arrived. I'd be OK if the temp. was lowered, but not such luck,


GFS has a little less rain around the 4th, but we appear to stay underneath the Midwest ridge for another week with a series of retrograde impulses drifting westward over us and south/underneath that ridge. So potentially a week of on and off scattered showers.

We'll see. After 25 years+ in Texas the promise of summer rain in CLL meets with well-worn skepticism. Canadian, ICON, Ensemble also show chances of rain all along the Gulf cast from Florida to Texas from July 4-11, fwiw.

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Re: July 2018 4th Of July Outlook

Postby srainhoutx » Sat Jun 30, 2018 9:26 am

Saturday morning briefing from Jeff:

Confidence continues to increase that rain chances will begin to rise on Tuesday and peak on Wednesday over the region.

An upper level trough will be developing over the NE Gulf of Mexico over the next few days under the southern flank of a very upper level high pressure cell over the Midwest and NE US. Tropical moisture with PWS of 2.0-2.5 inches will become entrained within this trough and both the moisture and the trough will begin to move westward this weekend into early next week. Global forecast models continue to indicate that moisture will begin to increase over SE TX on Tuesday and peak on Wednesday with expected PWS of 2.2-2.5 inches on July 4th. Rain chances will begin to increase Tuesday afternoon from the east and peak on Wednesday with the trough overhead or just to our west.

High moisture levels look to support very heavy rainfall during the period from late on July 3rd through July 4th. Convective trigger temperatures on the 4th will cool into the mid 80’s suggesting little to no heating will be required to produce showers and thunderstorms. The air mass becomes nearly saturated by late on the 3rd and into the 4th with rainfall production in showers and thunderstorms maximized. At this time, it is unclear when and where the greatest rains may occur. The models have been bouncing around within an area from Houston to Lufkin to Lake Charles to offshore the last few days. Based on the incoming air mass and extremely moist conditions high short duration rainfall rates of 2-3 inches in an hour will be possible on the 4th.

Overall 48 hour storm totals (3rd and 4th) will likely averaged 1-3 inches over the area with isolated totals of 5-6 inches in any areas of slow storm motions or cell training.

Residents are encouraged to continue to monitor forecasts for the middle of next week as rainfall amounts, timing and locations will likely change over the next few days.
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Re: July 2018 4th Of July Outlook

Postby srainhoutx » Sat Jun 30, 2018 4:43 pm

July begins as June ends with hot and dry weather the theme until Tuesday when the upper air pattern changes and rain returns to our sensible weather forecast for the remainder of the first full week of July.

Unfortunately there is a chance for showers and storms on the 4th of July, so have alternate plans ready for that cookout and possibly the area fireworks displays scheduled for Wednesday evening. The GFS is a bit quicker in moving the inverted trough currently seen in the NE Gulf of Mexico through the SE Texas Region possibly bringing the rain to an end before the fireworks displays start. On the other hand, the ECMWF is much slower and actually stronger with its 700/850/500mb vorticity lingering into Wednesday. The latest afternoon Updated 7 Day QPF charts suggest a general 1 to 3 inch amounts with isolated higher total of 4 to near 6 inches possible. The inverted trough passes leaving Thursday a bit drier, but short lived as the next Easterly Wave arrives moving from East to West beneath the Upper Ridge far enough to our North to bring additional rain chances. Rain chance could linger into next weekend as the Upper Ridge remains somewhat displaced far enough North.

A word of caution is probably needed in the coming week expected sensible weather forecast. It appears that there is enough volatility in the very high PW's near 2.5 inches which is in the 90th percentile for our area this time of year that mesoscale features will determine the final rainfall totals. The ECMWF has stayed the course of the last 4 days insisting a stronger vorticity at multiple levels may influence where the heaviest rain may fall. Areas from Lake Charles/Beaumont/Lufkin to Houston have repeatedly been the high precipitation target zones with several runs showing some locations receiving 7 to 10 inches. We'll continue to monitor throughout the rest of the weekend and into early next week, so check back daily and we'll do our best to provide the latest data for the busy 4th of July Holiday. Stay Tuned!
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Re: July 2018 4th Of July Outlook

Postby DoctorMu » Sun Jul 01, 2018 12:08 pm

Forecast is generally on track. Trough moves through on the 4th and 5th. Canadian is a little more aggressive about rainfall amounts than GFS (which has backtracked) or ensemble. ICON has a steeper grade with the coast inundated. Weakness persists under the ridge from the 4th to 11th with potential disturbances passing through and isolated/scattered showers.

Ridge may slide southward into Death Ridge position after the 12th per GFS. Ensemble not as sure. Hopefully not.
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Re: July 2018 4th Of July Outlook

Postby DoctorMu » Sun Jul 01, 2018 12:19 pm

Holiday rain even seems more modest at the moment. Canadian is still more aggressive than Euro or GFS. (FWIW, Canadian had a better handle on the last rain event). Movement of the ridge in the long-term seems less certain than yesterday.

Good news about the dust - it's beginning to clear away from the area. Yesterday was incredibly hazy, but didn't keep the temps down!

In the meantime, stay cool!

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1033 AM CDT Sun Jul 1 2018

.DISCUSSION...
Upper air analysis shows a strong ridge of high pressure over SE
TX. At 850 mb, a weak area of low pressure was noted over SE New
Mexico with a weak trough extending across the Big bend. Another
area of low pressure was noted over southern Alabama and it`s
this feature that will be heading west early next week and bring
SE TX some much needed rain. 12z soundings support high
temperatures in the mid and upper 90`s today. Moisture profiles
look very dry so not expecting any rain today. Previous forecast
has things covered nicely and other than tweaking some hourly
grids to match observations, no other changes were required.

The Galveston Beach Patrol has indicated that strong rip currents
remain an issue. A Rip Current Statement has been reissued for area
beaches through this evening. 43

&&

.CLIMATE...
June has come to a close and it was another very warm month.
Houston and Hou Hobby had their 6th warmest average June
temperature while Galveston had its 5th warmest June on record.
It was the monthly average low temperature that helped fuel the
warm monthly average. The average June low temperature was the
warmest on record for Houston, third warmest at Galveston, fourth
warmest at Hobby and fifth warmest at College Station. Looking
further back, the average temperature for the months of may and
June are now the warmest on record for Galveston and the 2nd
warmest on record for the city of Houston. A Public Information
Station with June climate information will be issued later today.
43


&&

.PREV DISCUSSION... /ISSUED 642 AM CDT Sun Jul 1 2018/

AVIATION...

Early morning MVFR ceilings at CLL will scatter and lift by mid-
morning, making way for mostly clear skies at all airports today.
A tight surface pressure gradient returns, allowing for some gusty
southerly winds from 17Z-01Z. Southerly winds today will cause
the sea breeze to arrive about an hour earlier at most TAF sites.
Rain chances remain negligible.

22

PREV DISCUSSION... /ISSUED 359 AM CDT Sun Jul 1 2018/

NEAR TERM [Through Today/Tonight]...

Temperatures will reach the mid to upper 90s as the upper level
ridge maintains its influence over our weather in Southeast Texas.
Dew points will once again peak in the mid 70s, bringing maximum
apparent temperatures of 103-107. Will monitor hourly trends
throughout the day to determine whether heat advisory criteria will
be met. Should dew points mix out as they have done the past several
days, we will likely fall just short of criteria.

Otherwise, the morning low level clouds will scatter out to mostly
clear skies this afternoon with occasionally gusty winds. As the
surface low pressure system over the Panhandles remains fairly
stationary, the surface pressure gradient will increase during the
afternoon, leading to wind gusts near 10-15 mph. Although rain
chances remain near zero, today will begin a gradual moistening of
the air mass as the African dust moves northeastward out of our
area. Precipitable water values increase from 1.1" this morning to
1.5" late tonight. According to NASA`s Global Modeling and
Assimilation Office, Galveston reached its peak particulate matter
content yesterday and today will be the peak for Houston. Expect
poor visibility at times and limit outside exposure for sensitive
groups.

22

LONG TERM [Monday Through Sunday]...

Upper air analysis at 500mb for 00Z shows lower heights over
Tallahassee FL at 588dm where models have been forecasting an
inverted trough to develop. Water vapor imagery also shows several
weak areas of vorticity trying to organize near this low. Upper
level ridge had taken shape over the Mid-Atlantic with a weaker
ridge over the NW Gulf. So going forward through the holiday week,
thunderstorm chances still exist for Independence Day.

So what has changed since last few model runs for Wednesday?
- Timing of the rainfall has changed. GFS/NAM and now to some
degree the ECMWF, have all shown thunderstorm activity starting
more Tuesday night/Wednesday morning and ending Wednesday night.
The Canadian is still slower and the ECMWF makes a nice
compromise between all solutions. Forecast leaned more the ECMWF
for timing of the thunderstorm activity. This also means that
firework shows may have a small chance of happening although
crowds may have to deal with wet conditions.
- Rainfall amounts have changed which is to be expected. GFS seems
to be on the same page as the last few runs with a general 1-2
inches. ECMWF has come in line with the GFS amounts and may have
backed off on the 4-6 inch amounts forecasted over E TX. But it
could very well bring that back depending upon now the inverted
trough evolves.

What are we still confident in for the forecast Wednesday?
- Still confident in the inverted trough coming over SE Texas
providing lift.
- Still confident in high precipitable water airmass moving into
the area (2-2.4 inches of PW).
- Confident in scattered to numerous thunderstorms caused by these
conditions - PoPs now 60-70%.
- Growing confidence in timing mentioned above.

What we do not have confidence in for the Wednesday forecast?
- Rainfall amounts - overall think 1-2 inches looks reasonable but
really unsure of any isolated higher amounts. There most likely
will be a few spots with 3-4 inches of rain. There is that
potential.
- Flooding impacts - not seeing really heavy rainfall to cause
flooding other than the typical street/urban flood situations.
But we have little confidence in the isolated higher amounts
which could cause impacts.
- Location of highest rainfall amounts - again models have been
not only all over the place with rainfall amounts but also where
those amounts occur.
- Strength of the inverted trough. Models have been showing
variability in how much vorticity develops with the trough.
With the trough still developing, suspect models are having a
hard time resolving/initializing the feature leading to
different forecasts for rainfall.

Thursday through next Sunday we will need to monitor how the
upper level pattern evolves because this will determine whether we
remain in a wet pattern. The upper level ridge over the Mid-
Atlantic expands and strengths through the middle of the U.S.
through the end of the week. Another inverted trough could reach
the area by Friday/Saturday but models are having more timing
issues with this system. The ridge slides back over the Rockies
for the weekend and a broad weakness in the flow develops from the
Great Lakes down the the Gulf Coast. This may hold up any troughs
riding underneath the ridge. For now the forecast will keep some
type of rain chances going with higher moisture lingering and the
lower upper level heights in place.

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Re: July 2018 4th Of July Outlook

Postby DoctorMu » Sun Jul 01, 2018 12:32 pm

Naturally, we should be skeptical of a bullseye (96 hour accumulation) exactly over NW Harris Co., but keep in mind there *could* be LOCALIZED heavy rain with the trough, but no reliable way to precisely predict where that might occur. The max amount of 4 - 4.5 in may be reasonable. Be prepared just in case.

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Re: July 2018 4th Of July Outlook

Postby srainhoutx » Sun Jul 01, 2018 2:53 pm

Not seeing much of a change regarding the sensible weather for Wednesday (July 4th into the end of next weekend. HGX has leaned on the slower ECMWF/Canadian solution as the steering flow is much weaker than the fast GFS solution suggests. It still appears High PW's around 2.35 inches, a fully saturated column and low convective temperature will set the stage for scattered to numerous showers/storms. The European and Canadian models hint at domes or pockets of very heavy rainfall, so still think 1 to 3 inches of rain for Wednesday looks reasonable with isolated higher amounts possible.

A brief respite from the rain may be possible on Thursday, but with the weakness in the upper ridge still present and no capping, heat of the showers/storms are possible. A second inverted trough arrives Friday again increasing the chance of widespread showers/storms and a 3rd Easterly wave arrives next Sunday keeping an active weather pattern ahead for the next 7 days.
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Re: July 2018 4th Of July Outlook

Postby jasons » Sun Jul 01, 2018 9:23 pm

My high today was 99F.
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