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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Tuesday
• 
• High: 91 °
• Low: 75 °
• Chance of a Thunderstorm

• Wednesday
• 
• High: 90 °
• Low: 73 °
• Chance of T-Storms

• Thursday
• 
• High: 91 °
• Low: 73 °
• Chance of Rain

• Friday
• 
• High: 91 °
• Low: 72 °
• Mostly Cloudy

• Saturday
• 
• High: 91 °
• Low: 70 °
• Mostly Cloudy

Area forecast discussion 
National Weather Service Houston/Galveston Texas 
1024 am CDT Tuesday may 21 2013 


Discussion... 
the main problem of the day continues to be the timing and 
possibility of thunderstorms...mainly over the northern counties 
this afternoon and evening. There was a special sounding conducted 
by Texas a&m which still showed a cap at around 900 mb. The high 
res model arw and nmm differed a bit on the timing...but both 
indicate that the storms should begin to affect locations along 
and north of a line from College Station to Crockett during the 
early and middle evening. Will try and time the events after the 12z 
models come in. For now the current forecast for today is on track 
and an update is not anticipated. 


40 


&& 


Previous discussion... /issued 626 am CDT Tuesday may 21 2013/ 


Discussion... 
see 12z aviation discussion. 


Aviation... 
MVFR ceilings continue to mix out this morning and forecast soundings show 
conds mixing out to VFR between 15-16z. A few showers are skirting 
the northwest edge of the County Warning Area and added a vcsh for kcll for mainly 
this morning. Models are in good agrement with convection firing 
over North Texas late this afternoon and moving southeast toward the northern 
taf sites by 00z. Will tempo thunder for kcll and kuts this 
evening. Confidence shrinks for southern taf sites as the 
convection pushes south. Hi res models remain quite bullish on 
probability of precipitation bu none of the hi res models have initiailized well so will 
carry thunderstorms in the vicinity/vcsh for kiah...khou and ksgr overnight. 43 


Previous discussion... /issued 355 am CDT Tuesday may 21 2013/ 


Discussion... 
warm and humid early morning across the region the continued 
southerly flow. Upper trough over the Great Plains and extending 
down toward El Paso this morning. Very strong cap in place this 
morning with a few bits of light rain and drizzle showing up on 
radar and out the window...mainly over the southern areas. The 
upper trough will slowly shift east with short wave over Arizona/nm this 
morning tracking east through the afternoon then east-northeast. This feature 
should combine with the strong middle/upper level flow to 
dramatically increase lift after 3 PM and around the cll-dkr areas 
peaking after 7 PM. Model soundings are favorable for strong to 
severe thunderstorms. Frontal boundary pushes east with rain 
cooled air and expecting showers and thunderstorms to expand 
rapidly in coverage building south into Austin area then moving 
eastward. Very unstable 3000-4000 j/kg atmosphere to west of the 
southeast Texas will be the initiation zone but should be reaching the cll 
area around 6 PM with instability decreasing. Expect severe threat 
of mainly hail and damaging winds between around 5 PM through 
midnight for the northern areas with the arrival of short wave and the 
associated cold front. Tornado threat looks low but can't rule out 
short lived spin ups but will probably be confined to areas north 
of Brenham to Groveton line (greatest ehi 2.0+ from Madisonville 
to Crockett but out ahead of cap eroding). Do have some concerns 
with the strong cooling aloft that the severe threat could need 
extending beyond 06z and expanding to the coastal areas. Texas 
tech WRF and some of the high res arw/nmm models indicating 
possibly squall line/Bow developing and moving through Houston and 
to Galveston between midnight and 2 am. Diminishing instability 
and return of cap should limit that outcome. So as for the 
forecast have raised rain chances for areas generally north of 
I-10 this afternoon and overnight. Boundary pushes to near the 
coast and slows and will raise the rain chances for Wednesday in 
the south with the cap eroding in the afternoon and cape of 
1800-2500 returning and slow/erratic storm motions...may have some 
brief heavy downpours given the light steering winds and counter 
to sea breeze flow aloft. 


Upper ridge expands up out of Mexico Thursday through Sunday with 
the 500 ridge centered over southeast Texas Saturday an Sunday. This should 
lead to warmer temperatures returning and have gone above guidance 
for the afternoon Friday-sun timeframe temperatures. Rain chances 
fall off and moist southeast flow resumes. Also of interest looks 
to be a tropical wave moving out of the Caribbean and possibly 
impacting southeast Texas and western Gulf Monday and Tuesday next week. 


On a technical note...surface observation and lightning data 
outage 04-07z appears to be corrected. 


Marine... 
moderate to occasionally strong onshore winds will persist into this 
evening before beginning to diminish Wednesday and Thursday. Light 
to moderate onshore winds will prevail through next weekend as 
surface high pressure ridges into the northern Gulf Coast. Will 
maintain an scec for today for the Gulf waters. Tide levels will 
remain slightly elevated today and return to normal levels 
Wednesday. 43 


&& 


Preliminary point temps/pops... 
College Station (cll) 91 73 89 72 91 / 30 40 20 10 10 
Houston (iah) 91 73 88 72 90 / 20 50 30 10 20 
Galveston (gls) 80 75 81 75 81 / 10 30 30 10 20 


&& 


Hgx watches/warnings/advisories... 
Texas...none. 
GM...small craft should exercise caution until 4 PM CDT this 
afternoon for the following zones: waters from Freeport to 
the Matagorda Ship Channel 20 nm to 60 nm...waters from 
Freeport to the Matagorda Ship Channel out 20 nm...waters 
from High Island to Freeport 20 to 60 nm. 


&& 


$$ 


Discussion...40 
aviation/marine...41