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2018 Rain Thread

Hollywood

By Hollywood
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South Austin
South Austin

I'd keep playing.  I don't think the heavy stuff is gonna come down for quite a while.

RamjetFDO
RamjetFDO

Sorry ... just had to read it in this voice:  

NorthLoop
NorthLoop

That's called dusk

phdhorn

phdhorn 6224

Posted
Posted
3 hours ago, Hate said:

It’s going to be very wet this weekend...like your mom.

I know you live in/near Houston, so the rain will maybe linger on into early Sat afternoon, but most of it will be gone by Sat morning.  

ATX will actually have a decent weekend, Sat clearing, Sunday sunny and 51° or so. The rain thing is really just Friday.

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Hate

Hate 20122

Posted
Posted

Here is the latest update from Jeff Lindner, the chief meteorologist for the Harris County Flood

District:

 

A significant storm system will bring high impacts to SE TX Friday and Saturday

 

Widespread heavy rainfall and flooding increasingly likely

 

A strong storm system currently off the CA coast will move offshore today and into the SW US/NW MX tonight into Thursday and then arrive into TX on Friday into Saturday. Surface high pressure is starting to move eastward this morning and winds will return to the SE later today and begin to advect moisture into the area. Clouds will rapidly increase from west to east late today and tonight and expect mostly cloudy conditions on Thursday. A weak short wave will eject out of the trough and across TX on Thursday and this feature combined with deepening moisture levels will likely result in streamer showers from the coastal bend NNE across C TX and into our western counties by the afternoon hours.

 

Friday-Saturday midday:

 

Significant weather event increasingly likely.

 

Strong trough will begin to move into TX with both a surface cold front and surface low pressure system arriving across SE TX Friday evening. Moisture levels are still forecast to rise to near record or even exceed record levels by Friday evening with the advancement of two source streams over the area from the deep southern Gulf and the eastern Pacific. PWS are forecasted to rise to near 2.0 inches which for early December is near the maximum values. In fact a review of Lake Charles historic PW plots indicates that the highest early December value ever record was 1.98 inches and for Corpus Christi 2.07 inches. The maximum moving average for Lake Charles for this time of year is around 1.8 inches and the 90% average is 1.35 inches…to put is simply there is going to be excessive amounts of moisture in place that is fairly uncommon during this time of the year.

 

In additional to the deep tropical moisture profile, a slow moving SW to NE oriented frontal slope which will be nearly perpendicular to the upper level winds from the SW will be crossing the area and a surface low pressure system will likely form somewhere in/near SE TX. A low level jet of 45-55kts will develop from the TX coast bend into SE TX Friday afternoon and support both strong moisture and temperature advection across the region. Low level inflow will become maximized early Saturday morning over the region with the formation of the surface low. Upper level divergence will increase with the trough progressing into SW TX late Friday helping vent convective elements. All of these ingredients point toward a widespread heavy rainfall event.

 

Rainfall Amounts:

 

Widespread rainfall amounts of 3-5 inches are likely with significantly higher totals of 6-9 inches under sustained training bands. While it is still uncertain where the heaviest rains will fall, some of the latest global model guidance and the longer term short range guidance is starting to favor area along and N of US 59 for the heaviest axis of rainfall. Interestingly the CMC model has been fairly consistent in its axis of very heavy rainfall from about I-10 NNE toward the Lake Livingston area, while the GFS continues to favor areas just north of our area. For consistency, the GFS continues to produce a point rainfall for IAH of over 3.0 inches for this event.

 

Hydro:

 

Grounds are fairly wet over the region given both the time of year and recent rains in October with KBDI values of 0-200 across much of the eastern half of TX and 6-hr flash flood guidance values of 4.5 inches for Harris County. Since the area has already experienced an early season killing freeze, most vegetation is dead or dormant which is leading to little to no soil evaporation. Given the expected widespread nature of the rainfall totals, significant rises on area rivers, creeks, and bayous is becoming likely with this event and some locations may reach or exceed flood stage. Additionally, high rainfall rates with convective elements support local street flooding conditions in urban areas.

 

I want to be clear that rainfall of these amounts this time of year will have a significantly different response on area watersheds than during the warm season months…a more run-off will be generated.

 

Decision Support:

 

Timing: Friday afternoon-midday Saturday

Rainfall Totals: 3-5 widespread, 6-9 isolated

Location: heaviest rainfall likely will focus along and N of I-10, but this remains in flux

Confidence: event confidence is high, location is heaviest rainfall remains low to moderate.

 

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Hate

Hate 20122

Posted
Posted

Here is the latest from Jeff Lindner for those of us in SE Texas:

Powerful storm system will bring high impact weather to TX starting later today

Flash Flood Watch has been issued from noon Friday until noon Saturday for all SE TX counties

Flash Flooding of streets along with significant rises on area bayous, creeks, and rivers to flood levels is possible.

Powerful upper level storm system moving into S CA and NW MX this morning will track generally eastward and into TX over the next 48 hours. SW flow aloft is already spreading clouds across the area with currently best moisture return focused across SC/C TX where scattered showers have already developed. Activity will increase today from the coastal bend northward along the I-35 corridor where favorable moisture transport overlaps with short wave energy aloft. Some of this activity will likely affect our far western and southwestern counties this later this morning into the afternoon hours.

Friday-Saturday:

Excessive rainfall event likely Friday afternoon-Saturday morning resulting in flooding.

A surface cold front currently moving southward is now expected to reach our NW counties around College Station early Friday and then slowly move across SE TX during the day. This front will act as a strong lifting feature to promote widespread showers and thunderstorms within a very favorably moist air mass. In fact models continue to suggest near record/record moisture levels will be in place by Friday afternoon with PWS of 1.8-2.0 inches over much of the area. Forecast soundings show little instability, but loaded with plentiful moisture form the surface into the upper levels indicating convection will be very effective at heavy rainfall production. Unfortunately it appears the slow moving surface front will be nearing the US 59 corridor around the time that maximum parameters for heavy rainfall focus over SE TX. This includes a very strong 45-55kt low level jet which will transport copious moisture into the frontals slope. Additionally, winds aloft become increasing divergent helping to aid lift and vent near surface lift. Add in a slow moving surface boundary and a nearly “tropical air mass” and you pretty much have everything needed for excessive rainfall rates.

Rainfall Amounts:

Widespread rainfall amounts of 3-6 inches appear likely over nearly all of the area with isolated totals of 8-10 inches. It is still somewhat uncertain where those higher isolated totals may occur, but areas along and NW of US 59 may have a slightly greater risk than areas S of US 59. Much of the higher totals will tend to focus closely with the surface front and where it slows at times as it crosses the region. In addition to the overall totals, high hourly rainfall rates of 2-3 inches per hour will be possible which will lead to rapid urban flooding of street systems.

Hydro:

Forecasted rainfall amounts and the widespread nature of the rainfall pattern strongly support significant rises on area watersheds. Think most basins can handle 6 hour totals of 3-4 inches, but anything greater than about 4 inches in 6 hours is going to likely be cause for concern. Creek, bayou, and river flooding will be possible especially in the San Jacinto, Trinity, and Brazos basins. For Harris County, all of the creeks and bayous will likely see significant rises and exceeding of flood stage levels is possible on some of the watersheds depending on exactly where the heaviest rains fall. Greatest concern at the moment is for the watersheds over the northern half of Harris County, but think all watersheds have about equal chances of seeing significant rises and possible flooding. Usual common flooding locations on Little Cypress Creek and lower South Mayde Creek will likely experience flooding. Some structure flooding will be possible if watersheds exceed their banks or intense rainfall rates overwhelm street systems.

Decision Support

Timing: Friday morning College Station area, mid to late afternoon Houston area through Saturday morning

Amounts: 3-6 inches widespread isolated 8-10 inches

Watersheds: flooding of creeks, bayous, and rivers is possible Street Flooding: high threat for street flooding

Severe: a few storms late Friday night may become severe near the coast with a tornado threat.

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phdhorn

phdhorn 6224

Posted
Posted (edited)

Models now kinda sorta backing off to 1"-3" for stuff west of IH-35.  Still the bullseye is the swath between Austin and the coast - up to 6" (yeah yeah har har) in spots around there.  SE of us in the LaGrange/El Campo/Victoria areas, watchyerasses.

Still, Flash Flood Watch issued for our area, pretty much the eastern half of Texas.

The Big Kahuna part of the storm is expected to push through about midnight here.  Up to then, scattered heavy rain but not everyone.  Once that big part of the system moves through, clearing in ATX by noon and chilly 2 days.

More tomorrow when the radar is actually useful.

 

Edited by phdhorn
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