Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Houston/Galveston Texas
1049 PM CDT Thursday Jul 31 2014
been a busy night with lots of rain and one damage report. Radar
estimates in the Polk/San Jacinto/Liberty show widespread rainfall
totals of 2 inches with isolated amounts of 4 to 6.5 inches.
Cold front has stalled around a Hearne to Tyler line with the
storms having moved off the boundary reinforcing the cold pool
with the outflow from the frontal boundary storms colliding with
the seabreeze and focus the rains across the north. The storms
have continued to push very slowly south and 2 inch precipitable water at gls
streaming into the cluster in east Harris-Liberty County. Have
concerns that redevelopment is going to occur after midnight along
the front as it gets a nudge later tonight and pushed the front
down toward the coast by 15-18z Friday.
Have adjusted probability of precipitation based the hrrr/RUC of late which have done a
good job and show this redevelopment scenario...generally raised
in the central and east...and continued the heavy rain threat.
Temperatures look on track to cool into the lower 70s north in the
wake of the front.
Previous discussion... /issued 652 PM CDT Thursday Jul 31 2014/
see aviation for 0z taf issuance.
showers and thunderstorms are now into College Station and
forecasted to continue to push to the southeast this evening. High
res models have struggled initializing as all but the rap missed
this afternoons precipitation near ksgr/ klbx. Because of the above have
leaned towards rap with evolution of showers and thunderstorms.
Most likely this line will move into kiah and khou in the next two
hours before starting to weaken. Looks like most taf sites will
see thunder with klbx and kgls still in question on whether
current convection will make it or not. Global models then begin
to differ on how the front will progress tomorrow morning. The GFS
plunges the drier air farther to the south while the NAM holds the
drier air up just around kiah tomorrow. If the NAM is right rain
could linger around near and south of kiah tomorrow. If the GFS
is right the precipitation will be confined more near the coast. Future
taf packages will work to narrow down when and where the front
will stall. Either way behind the font precipitation looks to come to an
Previous discussion... /issued 627 PM CDT Thursday Jul 31 2014/
heavy rain threat looks to be rapidly taking shape over the
northern 1/3 of the area. Areas from Caldwell to College Station
to Madisonville have ongoing thunderstorm that moved off the
frontal boundary and generally moving at 15-20 knots to the southeast.
Seabreeze and outflow boundary from storms in the metropolitan marching
inland and the collision area looks to favor something 20 miles either
side of a line from Brenham to Navasota to Cut and Shoot to
Livingston. Have done a quick update to add locally heavy rainfall
and raised probability of precipitation for this corridor. Precipitable water 2+ inches pooled in there
and a boundary collision look to favor at least a few hours of
heavy rain. Storm motions should slow and some backbuilding may
occur...latest satellite precipitation estimate statement highlighting this threat as well.
Previous discussion... /issued 325 PM CDT Thursday Jul 31 2014/
a northwesterly flow aloft will help push a cold front into southeast Texas
tonight and Friday morning...and then off the coast late Friday.
Leaned heavily on the 12z nam12 although a model consensus agreed
with the NAM output. The main forecast challenge for tonight
through Friday is thunderstorm coverage.
Weak shortwave troughs moving through the flow aloft may help
generate thunderstorms ahead of the cold front. The seabreeze has
helped generate thunderstorms to the southwest of metropolitan Houston.
Expect these will be fairly scattered this evening. Overnight
should see more widespread coverage ahead of the front as it sinks
into the forecast area. There may be a break in the coverage later
Friday morning before redevelopment Friday afternoon. The front
should work its way along the coast by Friday night. That said...
the models have backed off of the rainfall potential...especially
on Friday. Model soundings have the best precipitable water/S of about 2 inches
tonight and early Friday. The nambufr forecast soundings show that
the best chances for isolated strong storms will be late this
afternoon and early evening.
The front will move back inland and the subtropical ridge will try
and build back over the area next week. This will lead to a warmer
and more humid trend during the first half of the week.
light to occasionally moderate onshore winds will continue through
tonight. A weak cold front will approach the coast on Friday...
probably stall and meander back and forth near the coastline
through the weekend. This boundary should serve as a focus for
periods of showers and thunderstorms. Light and variable winds
should persist with low seas... except in and near storms. An
onshore flow is expected to return to the area with winds and seas
remaining below caution levels. 47
Previous discussion... /issued 1209 PM CDT Thursday Jul 31 2014/
not too many changes to ongoing taf package...mainly to push back
tempos a few hours. Frontal boundary making slow progress toward
southeast Texas. Sat imagery does show some breaks in clouds ahead of it
which should allow some destabilization in advance. GOES precipitable water
estimates 2-2.3" precipitable waters across the area. Do anticipate increased scattered
activity to develop across north half of southeast Texas this afternoon...then
sagging southward toward 1-10 & metropolitan areas during the evening and
nighttime hours. Several models showing further
enhancement/redevelopment between 1-7am CDT south of a Columbus-
Livingston line so kept vcts's going overnight at least until
trends & increased confidence can be established. Considering
deeper available moisture...rainfall could be locally heavy at
times. Probably see a break after sunrise...followed by possible
more scattered activity during the afternoon depending where the boundary
becomes situated and if we can get some instability.
Otherwise...VFR outside of convection. 47
Preliminary point temps/pops...
College Station (cll) 73 89 71 90 71 / 30 20 10 20 10
Houston (iah) 75 90 73 90 73 / 60 40 30 20 10
Galveston (gls) 80 87 79 89 79 / 40 30 30 20 20