Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Houston/Galveston Texas
618 am CDT Wednesday Aug 20 2014
see 12z aviation discussion.
high precipitable water values will surge into southeast Texas today with values reaching
2.00 inches. Convective temperatures are in the lower 90s so feel
rain showers/thunderstorms and rain will once again redevelop with a bit of heating. Leaned
a bit toward a rap/hrrr blend for precipitation coverage and the nam12
for winds. Convection should wane quickly tonight with the loss of
heating. The pressure gradient is rather tight so it'll be breezy
at times. MVFR fog possible early this morning and again Thursday
Previous discussion... /issued 405 am CDT Wednesday Aug 20 2014/
low light satellite showing mostly cirrus hanging around tonight
with breaks appearing across the area. 250 mb hand analysis for 0z
today shows southeast Texas again in diffluent flow thanks to
anticyclonic flow to our southwest in Mexico along with a weak
shear axis just to the east of southeast Texas. At 500 mb a
shortwave was analyzed that is forecasted to shear out and move
into the Dallas/ Fort Worth area this afternoon. Current precipitable water
values are around 1.40" inland with precipitable waters near 2.00" over the
waters (according to GOES sounder).
Another tricky forecast this afternoon as many models showing
conflicting data. In general... models do agree on bringing the
2.00"+ precipitable water air into the area this afternoon and weak positive vorticity advection moving
over this afternoon. GFS forecast soundings aren't extremely
supportive for rain. Precipitable waters for kcll are 1.87" with a k index of
30. The NAM forecast soundings on the other hand do support rain.
For kcll the NAM is forecasting a 1.99" precipitable water with a k index of 37.
Ironically the GFS precipitation field shows more rain than the NAM. The
Omega fields for the NAM do show lift moving into the central
zones around noon and moving inland this afternoon. The GFS only
shows very weak lift at best. High res models for the most part
show coverage starting around noon in the coastal counties and
then push it northward this afternoon. The disagreement is in the
placement. Given the current upper level maps... upper level
lift... and moisture it looks that most of the area will see a
chance of rain today. The lowest chances towards Jackson County
where there are slightly warmer 850 temperatures (more capping).
Have also raised probability of precipitation for today given incoming high moisture
values... weak upper level diffluence... and wedge of positive vorticity advection moving
On Thursday models quickly begin to build ridging into the area
from the East. Heights on Thursday afternoon rise to 594 dm.
Forecast soundings at this time also develop a cap and bring lower
precipitable water air into the area (1.40" - 1.60"). This will bring an end to
the rain chances on Thursday. The ridge remains in close enough
proximity to the area through Saturday to keep rain chances out of
the forecast. By Sunday the ridge may drift far enough north to
allow a return to afternoon showers and thunderstorms to the area.
Definitely by the start of the next work week this looks possible.
a tight pressure gradient will produce moderate onshore winds
through Thursday night. High pressure building into the area from
the east will weaken the gradient and winds will diminish toward the
end of the week. Light onshore winds will persist through the first
half of next week. 43
Preliminary point temps/pops...
College Station (cll) 96 77 98 77 98 / 50 10 10 10 0
Houston (iah) 96 78 96 77 98 / 50 10 10 10 10
Galveston (gls) 92 84 92 83 92 / 40 20 10 10 10
Texas...heat advisory until 7 PM CDT this evening for the following