Area Forecast Discussion

FXUS64 KHGX 180950
Area Forecast Discussion
National Weather Service Houston/Galveston TX
350 AM CST Sun Nov 18 2018
.NEAR TERM [Through Today]...
Surface analysis at 09Z has cold front through KACT to KJCT with 
temperatures dropping behind the front into the 50s/40s. There is 
also a thick post-frontal MVFR cloud deck evident on the RGB 
Nighttime Microphysics imagery from GOES 16. Radar is picking up 
on some showers off the Coastal Bend into Central Texas. Looking 
at 925mb/850mb analysis, this activity looks to be embedded within
a moisture axis. Looking at 300mb there is a jet streak moving 
across the Texas and Louisiana Gulf coast. It appears this feature
may not cause any enhancement in convection with it moving past 
the area and any large scale ascent will be over the Gulf. Short 
range high resolution models seem to be doing well to resolve 
these features and increase activity over areas west of I-45 later
this morning into the afternoon as the front pushes into the 
area. There could be some surface based thunderstorms ahead of the
front later this morning but more than likely the front will 
undercut any surface based activity leading to weaker elevated 
convection. Rain chances today then transition south along the 
coast and then off the coast this afternoon in line with the 
frontal timing.
The other forecast issue will be temperatures behind the front. 
Forecast shows a blend of HRRR/WRF/NAM models since they seem to 
be initializing the airmass the best. The front does seem to be 
moving faster than just a few hours ago which the HRRR runs have 
been depicting. This will put the front entering the forecast area
right around 12-13Z, Houston area 16-17Z and then coast 20-21Z. 
This means high temperatures will likely be achieved in the 
morning hours with falling temperatures through the afternoon.
.SHORT TERM [Monday Through Tuesday]...
Rain chances look to continue Monday and then end by Tuesday. The
southern branch of the jet moving across Mexico looks to remain 
active with another jet streak coming across Mexico into S Texas. 
With the front off the coast, a weak coastal trough may form which
could enhance rainfall over the area. Models seem to be backing 
off on QPF amounts and overall rainfall chances so we lowered the 
rain chances slightly during this time to match this trend. 
Rainfall amounts look to be around a half inch to an inch for the 
Sunday/Monday time frame.
Tuesday models are now bringing a second cold front into the area
as high pressure builds over the Plains on Tuesday. The net 
effect of this front is to bring in some cooler air and push the 
first front further into the Gulf of Mexico.
.LONG TERM [Wednesday Through Sunday]...
The GFS/ECMWF/Canadian have had some decent consistency going 
through the Thanksgiving holiday. That is still the case for 
Wednesday/Thursday but beyond that models are much more divergent 
in solutions than before. This is to be expected especially when 
systems in the Pacific are involved. Models are trending perhaps a
bit drier with rainfall for the Wednesday night coastal trough 
system. The coastal trough/low forms farther out in the Gulf since
the front is expected to be further in the Gulf. This means most 
of the rainfall will be just along the coast and well out in the 
Gulf. GFS is no longer bringing a warm sector airmass anywhere 
close to the coast. The ECMWF still has a more potent short wave 
trough coming across the area from the Rockies as this wave 
undercuts the ridge in the Pacific. We do lower rain chances 
inland but still keep some higher chances along the coast and in 
the coastal waters. The system does clear out so Thanksgiving day 
should be dry and cool. We also lower QPF amounts closer to a half
inch to an inch and really do not see where there could be 
isolated higher amounts.
The problem in the extended forecast for Friday through the 
weekend is that there is another trough that moves into Texas on 
Friday right on the heals of the Wednesday night system. The 
ECMWF/Canadian are much stronger but slower with the system than 
the GFS. GFS also has the system more in the central/southern 
Plains by 12Z Fri instead of southern Rockies like the ECMWF. That
makes a difference in where cyclongenesis occurs and location of 
precipitation. Forecast will add in some 20 PoPs for areas east 
of I-45 but think the higher chances will be NE of the area. 
Beyond that there is another shortwave that comes out of the 
Pacific NW for the Sat/Sun time frame that could bring another 
cold front into the area. Still some time to figure out those 
details but look for an active progressive pattern to continue.
A cold front continues to approach Southeast Texas late tonight. 
It will push through the land portions of our area through the day
today, but be slowed up by the weak coastal trough that is also 
developing. The front should push off the coast Monday morning 
before stalling out over the Gulf. Once this occurs, look for 
winds to become more northeasterly, as well as stronger. The 
increasing winds and seas, the need for a SCEC appears likely late
Monday into Tuesday. A brief small craft advisory is much less 
likely, but not impossible.
Winds should briefly lull on Wednesday, but are likely to pick up
again Wednesday night into Thursday. Though models are differing 
greatly on the specifics, there at least appears to be some 
general consensus about a coastal low developing in this time 
frame as the low exits the region. Along with this low, rain and 
thunderstorm chances will increase, and there are indications that
some storms will be strong enough to generate locally high winds 
and seas.
The E-NE winds will give tides a boost upward but the the 
departure should be 0.5-1.0 feet above normal and astronomical 
high tide isn't really that high so tide levels should remain 
under 2.5 feet.
College Station (CLL)  56  44  52  42  62 /  50  40  30  10   0 
Houston (IAH)          64  48  52  45  63 /  50  30  50  40  10 
Galveston (GLS)        67  56  58  52  62 /  40  40  60  50  10 
NEAR TERM...Overpeck
SHORT TERM...Overpeck
LONG TERM...Overpeck