December 2018: Mid Week Rain/Christmas Outlook

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Katdaddy
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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by Katdaddy » Thu Dec 06, 2018 8:57 pm

Time to be weather aware across the Houston-Galveston areas as the atmosphere loads up with high-end moisture for this time of year which is more like August along with a slow moving cold front and developing low pressure. A Flash Flood Watch for all of SE TX and SW LA with a marginal risk area of severe weather across S, S Central, and SE TX. Widespread 3-6” rains with some locally higher amounts. Street flooding will be the main concern so remember “Turn around don’t drown”. The Upper TX Coast may likely be in the warm sector with severe weather becoming an additional threat while inland areas see widespread heavy rains.

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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by srainhoutx » Fri Dec 07, 2018 3:55 am

Concern increasing as the Weather Prediction Center further expands the Moderate Risk for Excessive Rainfall.
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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by DoctorMu » Fri Dec 07, 2018 4:05 am

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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by Katdaddy » Fri Dec 07, 2018 5:42 am

Rain beginning to increase across inland areas this morning with a Flash Flood Watch in effect for all of SE TX. Widespread 2-5” totals with isolated total of 8-10” expected through Saturday morning. Continue to monitor the weather throughout the day.
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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by srainhoutx » Fri Dec 07, 2018 7:10 am

NWS SPC‏Verified account @NWSSPC · 1m1 minute ago

7:00am CST #SPC Day1 Outlook Marginal Risk: across the texas coastal plain http://go.usa.gov/YWq5

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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by snowman65 » Fri Dec 07, 2018 7:24 am

what a difference a year makes. potential 5" of rain could fall today, and this same date a year ago we got 5" of pure snowfall....

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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by unome » Fri Dec 07, 2018 7:47 am


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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by tireman4 » Fri Dec 07, 2018 8:01 am

000
FXUS64 KHGX 071233
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
633 AM CST Fri Dec 7 2018

.DISCUSSION...12Z AVIATION...

Passing scattered showers are currently affecting areas north of
I-10, mostly affecting KCLL/KUTS/KCXO during the night and early
morning hours resulting in brief periods of IFR/LIFR conditions
for these locations. SHRA/VCTS will continue to increase and spread
southward during the morning and afternoon hours. The potential
for +RA and TSRA will increase further this evening through
Saturday morning across all TAF sites ahead of a cold front. This
will result in periods of MVFR to LIFR mainly during later half of
the TAF period. Also, winds will increase tonight and overnight
to 10-15 KTS with gusts up to 25-30 KTS.

&&

.PREV DISCUSSION... /ISSUED 402 AM CST Fri Dec 7 2018/

DISCUSSION...
Flash Flood Watch for heavy rain event across the region this
afternoon through early Saturday morning.

Cold front has made it down to an San Antonio to Giddings to
College Station to Lufkin line at 3 am. It should creep slowly
southward through 3 pm possibly setting up around a Groveton to
Navasota to Columbus line. All the ingredients still in place with
this forecast. A slow moving cold front with a very vigorous upper
level low pressure system. Strong to very strong isentropic
upglide and highly sheared environment with precipitable water off
the chart for this time of year (max or at least 3rd dev). Getting
lightning already this morning in the frontogenic zone near CLL
and going into the afternoon/night as the incredibly strong
coupled jet sets up expect to see more widespread thunderstorms.
The lead short wave should push through the region this afternoon
and give the area a good wetting. Main event comes tonight with
the upper jet couplet and will see a broad swath of heavy
showers/thunderstorms with heavy rain and worsening flooding after
the ground saturates. Heavy rainfall is the main issue many times
over with this set up and still expecting widespread 2 to 5 inch
amounts and isolated 8 to 10 inches. Much of the guidance is
showing the greater amounts just to the north of the Houston
Metro. Still very concerned that any faster progression of the
frontal boundary would put the Metro under the gun for the axis of
the heaviest rainfall. Of course the some of the CAMs do bullseye
the Metro and have kept a second axis of higher QPF in the grids
to account for this very likelihood. The system should push
through the western counties with rain tapering off 6-9 am
Saturday and central (including the Metro) 8-10 am and then the
eastern counties 10 am-noon. May still have some lingering light
rain/showers into mid afternoon but if so very light. Wrap around
clouds and the deformation zone to the north will likely keep the
cloud cover going well into Saturday night.

Severe threat for the coastal counties and marine waters remains
an issue with the likelihood that the warm sector mixing in will
have some SB CAPE to work with and given the very strong LLJ and
ML wind profile (01-km SRH 130-170) can`t rule out an isolated
tornado or damaging wind gust in the 2 pm to midnight window then
shifting southeast out entirely over the Gulf waters.

Saturday night and beyond...moderate north/northwesterly winds
with dry air spreading over the region and cool weather to prevail
for a few. Monday the profiles look like we could see an abrupt
drop in dewpoints as we warm up in the afternoon (lowered the RH
to the mid 30s). Chilly nights and cool days on tap Sunday through
Tuesday. May see another brief freeze Monday and Tuesday mornings
in the northeast. High pressure finally slides away to the east
Tuesday afternoon and the southeasterly flow returns with a
noticeable warming trend and moisture return. Next upper trough
moving out of the Rockies will ramp up winds Wednesday and the
area has a chance of showers or thunderstorms mainly late
Wednesday/early Thursday and trended the forecast toward the ECMWF
solution with a drier frontal passage late Thursday.
45

MARINE...

SE winds are expected to increase and shift W-NW late this afternoon
and continue through Saturday morning as a cold front approaches the
local waters. Exercise Caution flags continue in effect for the
outer waters and will go into effect this afternoon for the
nearshore waters. A Small Craft Advisory has been issued for all of
the waters from 7 PM CST this evening through Sunday evening/night.
Exercise Caution flags will go into effect this evening for the
bays. Expect periods of showers and thunderstorms Friday through
Saturday, with heavy rainfall possible Friday night through Saturday
morning. The front is forecast to move across the waters by Saturday
morning, maintaining strong/gusty northerly winds and elevated seas
through at least Sunday night. Tides are currently slightly above
normal, which could combine with some wave run up and result in some
minor flooding particularly across the locations of Galveston Bay
Friday night through Saturday. 24

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 58 46 50 39 50 / 100 100 20 0 0
Houston (IAH) 69 52 54 42 52 / 100 100 40 0 0
Galveston (GLS) 67 57 59 45 52 / 90 100 70 0 0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flash Flood Watch from noon CST today through Saturday morning
for the following zones: Austin...Brazoria Islands...
Brazos...Burleson...Chambers...Coastal Brazoria...Coastal
Galveston...Coastal Harris...Coastal Jackson...Coastal
Matagorda...Colorado...Fort Bend...Galveston Island and
Bolivar Peninsula...Grimes...Houston...Inland Brazoria...
Inland Galveston...Inland Harris...Inland Jackson...Inland
Matagorda...Madison...Matagorda Islands...Montgomery...
Northern Liberty...Polk...San Jacinto...Southern Liberty...
Trinity...Walker...Waller...Washington...Wharton.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION from this evening through
Sunday morning for the following zones: Galveston Bay...
Matagorda Bay.

Small Craft Advisory from 7 PM this evening to 7 PM CST Sunday
for the following zones: Coastal waters from Freeport to
Matagorda Ship Channel TX out 20 NM...Coastal waters from
High Island to Freeport TX out 20 NM.

SMALL CRAFT SHOULD EXERCISE CAUTION from 3 PM CST this afternoon
through this evening for the following zones: Coastal
waters from Freeport to Matagorda Ship Channel TX out 20
NM...Coastal waters from High Island to Freeport TX out 20
NM.

Small Craft Advisory from 7 PM this evening to 11 PM CST Sunday
for the following zones: Waters from Freeport to Matagorda
Ship Channel TX from 20 to 60 NM...Waters from High Island
to Freeport TX from 20 to 60 NM.

SMALL CRAFT SHOULD EXERCISE CAUTION through this evening for the
following zones: Waters from Freeport to Matagorda Ship
Channel TX from 20 to 60 NM...Waters from High Island to
Freeport TX from 20 to 60 NM.

&&

$$

Discussion...45
Aviation/Marine...24

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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by tireman4 » Fri Dec 07, 2018 8:39 am

Jeff Lindner update...
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Re: December 2018: Friday/Saturday Heavy Rainfall Potential

Post by srainhoutx » Fri Dec 07, 2018 8:43 am

Friday morning weather briefing from Jeff:

Heavy rainfall event for SE TX today into early Saturday

Flash Flood Watch will be in effect from noon today until noon Saturday.

Rises on area creeks, bayous, and rivers likely.

Powerful upper level storm system moving into TX today will result in impactful weather across much of the state with ice and snow across the NW portions of the state to heavy rainfall and flooding over the central and eastern parts of the state and some risk of severe thunderstorms near the coast and Galveston Bay later this afternoon. Moisture has significantly increased over the region as expected and will continue to increase as a strong 45-55kt low level jet brings a tropical air mass into the region from the deep southern Gulf. PWS will continue to climb today peaking around 2.0 inches this evening and overnight which is near maximum record levels for this time of year. Record PW max for CRP in early December is 2.07 inches so we are certainly in that ballpark and will be running 2-3 SD above normal…in other words we will be seeing summertime moisture interacting with the stronger dynamics of a wintertime storm system.

Surface cold front is slowly making progress into SE TX this morning and is along a line from near Lake Livingston to near Navasota to south of San Antonio and moving southeast slowly. This front is acting as a surface lifting feature and helping to develop scattered showers and a few thunderstorms over the northern half of the region this morning. Short wave ejects out of the trough to the west will increase lift over the top of this slow moving surface front today and will result in an increase of rainfall coverage. Surface front may make it down toward the US 59 corridor by this evening, but 925mb and 850mb front will remain stalled out over the central and northern sections of SE TX. Combination of these features, and significant incoming lift from the main storm system will result in widespread development of corridors of thunderstorms and heavy rainfall. Favorable Gulf inflow into these features support a period for sustained training rainfall from mid to late afternoon into the overnight hours.

Rainfall Amounts:

There has been no significant change in the forecasted rainfall amounts with a widespread 3-6 inches likely for much of the region with isolated totals of 8-10 inches possible. Shorter term guidance is favoring areas along a line from about Columbus to Conroe to Lake Livingston for some of those higher isolated totals, but much of this will depend on where the surface, 925,850mb fronts slow or stall and where any sustained training develops. Overall there has not been much change in the rainfall reasoning for the last few days. This will be a widespread event with much of SE, E and C TX seeing 3-5 inches of rainfall. Latest WPC update has expanded the moderate risk of excessive rainfall and flooding to include all of SE TX and much of eastern TX.

Hydro:

Forecasted rainfall amounts will certainly lead to rapid rises on area watersheds including creeks, bayous, and rivers. Most concern is for the Trinity, San Jacinto, Brazos, Navasota, San Bernard, and Colorado basins and the Harris County bayous and creeks across the northern, northwestern, and northeastern parts of the county (Cypress, Willow, Little Cypress, Cedar, West and East Forks of the San Jacinto, South Mayde, Langham, Bear). It is likely that heavy rainfall will impact all of the Harris County system and cannot rule out flooding on any of the watersheds especially if those isolated higher totals are realized. Think Brays, White Oak, and Buffalo can likely handle at least 6 inches of rainfall before any concerns…but some of their tributaries (Brickhouse Gully, Willow Waterhole, Keegans Bayou) could have problems with lesser amounts. Think most creeks and bayous can handle about 4.5-5.0 inches in 6 hours…with any higher totals likely resulting in more serious concerns for overbank flooding potential. If higher hourly rainfall rates materialize over the urban areas…2-3 inches per hour…significant street flooding and ponding would be likely.

Lake Conroe:

Lake Conroe is currently near normal pool elevation and currently not releasing any water.

Addicks/Barker:

Both reservoirs and currently empty with normal gate settings in place. Floodgates will be closed today. Forecasted rainfall amounts of both reservoirs bring pools to levels that may impact minor recreational roads and facilities. Should rainfall of near 10 inches fall across the reservoirs impacts to the major roads (HWY 6, Eldridge Pkwy, Westheimer Pkwy) would be possible.
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