Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 241115
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
615 AM CDT Fri Mar 24 2017

.AVIATION...
Decent cap will preclude thunderstorm chances until this
afternoon. Until then, strong warm air advection and a tight
pressure gradient will lead to very breezy southerly winds through
the morning. Isolated to scattered showers will develop under the
cap by late morning to early afternoon from KCLL eastward/
southeastward. The latest high resolution model data continues to
show best thunderstorm chances will be ahead of the dry
line/surface trough during the mid afternoon period in the north
and late afternoon to early evening period in the south and toward
the coast. Best chances will be from metro Houston northward.
Still looking at the slight chance of a strong thunderstorm
especially for KCXO, KUTS, and KCLL.

After these showers and storms dissipate later this evening, some
of the model data was bringing at least a slight chance of a
shower ahead of the actual cold front Saturday morning. Showed
this possibility in the KIAH outlook period.

40

&&

.PREV DISCUSSION... /ISSUED 420 AM CDT Fri Mar 24 2017/

DISCUSSION...
A cloudy, warm and breezy start across SE TX this morning. Was on
the fence on how to handle the the strong winds early this morning
but will issue a Wind Advisory for the western third of SE TX. The
winds will drop off around sunrise only to increase again later
this morning and aftn. The advisory may need to be expanded
eastward to include Harris and Montgomery counties later this
morning. 00z 850 mb analysis shows 50 knots and the KHGX VWP is
showing 40-45 kts at 5000 ft and 30 knots at 1000 feet.

850 mb 00z analysis shows strong high pressure over the SE U.S.
with a deep area of low pressure over western Nebraska and a
trough of low pressure extending S-SW across the southern Rockies
with another trough extending across the Big Bend region. Moisture
looked very scarce at 00z and it will be interesting to see how
much increase in moisture will occur by 12z. At 300 mb, a deep low
was noted across southern Uta with a trough extending south into
northern Mexico. A weak ridge was noted over eastern Texas. Sfc
analysis shows a deep low over eastern CO with a dry line
extending south across the TX panhandle and a cold front trailing
across central New Mexico. A very tight pressure gradient was
noted across East Texas with almost a 10 mb difference across East
Texas.

The dry line will approach the region by mid afternoon and should
trigger shra/tsra. Models are in good agreement with jet dynamics
and SE TX will lie in a splitting jet and will also lie in
departing 90 kt RRQ. The better dynamics favor the northern zones
late this afternoon and this evening. There is plenty of shear
available with this system but CAPE values remain modest generally
between 800-1600 J/KG. Helicity values were a bit higher over the
northern zones with values exceeding 200 m2/s2. SPC has outlooked
areas north of I-10 and for the most part this seem reasonable.
Feel the greater threat is still further north and have added
severe to the weather grids for areas north of a Brenham to
Livingston line for this afternoon and evening. There is capping
further south and it is still a bit unclear where/when and if the
cap will break. There could be a sharp cut off with the
precipitation as the dry line approaches this aftn.

The sfc low over Colorado will move NE tonight and Saturday and as
it does, it will drag a cold front across SE TX early Saturday.
The Hi Res ARW and NMM both develop some showers along the front
so will carry PoPs near the coast for Saturday morning. It should
dry out quickly behind the front and a mild and dry Saturday is
expected. Clear skies will persist Saturday night with patchy fog
developing late. Sunday will remain warm with some increase in
clouds late in the day. An upper level low will move across the
southern plains Sunday night and Monday and the tail end of the
system will clip SE TX. Moisture levels not looking too impressive
but there might be enough to squeeze out a few showers. SPC has
placed the extreme north in Marginal Risk on Sunday night. Despite
low moisture levels, jet dynamics look pretty good with SE TX in a
110 kt LFQ.

Another upper level low will move across North Texas on Wednesday.
PW values increase to between 1.65 and 1.85 inches. Jet dynamics
again look very favorable so more active weather possible Wed and
Wed night. SPC outlooked much of East/Southeast TX on Wed/Wed
night. Could also be getting some locally heavy rain with the mid
week system. 43

MARINE...
A tight pressure gradient was helping to provide for strong onshore
winds early this morning. As a dry line moves into Southeast Texas
later today, expect that the onshore winds will slowly diminish and
probably below advisory criteria by this afternoon. However,
confidence in the model solution is low and will keep the advisory
up through the afternoon for now. After a brief period, the pressure
gradient will again tighten and help provide for stronger onshore
winds later tonight. These will in turn diminish once more as another
storm system moves across the Plains over the weekend. Onshore
southerly flow is expected through at least the first half of the
upcoming week.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      79  57  81  58  86 /  80  30  10  10  10
Houston (IAH)              81  66  83  61  85 /  50  60  10  10  10
Galveston (GLS)            79  71  80  69  81 /  20  50  20  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Wind Advisory until 4 PM CDT this afternoon for the following
     zones: Austin...Brazoria...Brazos...Burleson...Colorado...
     Fort Bend...Jackson...Matagorda...Waller...Washington...
     Wharton.

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

     Small Craft Advisory until 10 PM CDT this evening for the
     following zones: Coastal waters from Freeport to the
     Matagorda Ship Channel out 20 NM...Coastal waters from High
     Island to Freeport out 20 NM...Waters from Freeport to the
     Matagorda Ship Channel from 20 to 60 NM...Waters from High
     Island to Freeport from 20 to 60 NM.

&&

$$

Discussion...43
Aviation/Marine...40


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