Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Angelo Texas
304 PM CDT Thursday Apr 17 2014

Short term...
(tonight and friday)

A weak cold front is moving into the Big Country, and will slowly
move through all of west central Texas overnight. A few light
showers will be possible this afernoon and tonight, and I have kept
pops in the slight chance category across all of the area. The front
will result in slightly cooler temperatures and a wind shift to the
north. I lowered temperatures slightly, but abundant cloud cover
overnight should help to keep temperatures up somewhat. Isolated
showers will still be possible Friday morning, but any precipitation
should end by late morning/early afternoon. Highs on Friday were a
bit tricky and will be dependent on cloud cover. The coolest
readings will be acoss the Big Country and Heartland where cloud
cover will persist into the afternoon, with the warmest readings
across the Interstate 10 corridor.


Long term...
(friday night through thursday)

The primary forecast concern in the long-term is the potential for
showers and thunderstorms this weekend, possibly lingering into

The synoptic pattern will be characterized by shortwave ridging over
the Southern Plains, with bookend shortwave troughs located to the
east and west. As the western trough approaches, large scale ascent
will increase across the region. Showers are expected to develop
over far West Texas late Friday, spreading slowly eastward Friday night
into Saturday. I trimmed back the pops for Friday night, basically
keeping the precipitation potential confined to Crockett County
through sunrise. However, this activity is expected to move into the
Big Country and Concho Valley during the day. Cape profiles look
rather thin, suggesting relatively weak updrafts typically
associated with your garden variety thunderstorms. Temperatures
during this time will generally range from the mid/upper 50s to the
mid 70s.

Warmer temperatures are expected on Sunday with highs in the upper
70s to lower 80s. Mid-level lapse rates will steepen as we move into
Sunday, becoming nearly adiabatic between 750 mb and 550 mb. GFS and
NAM bufr soundings indicate SBCAPE values increasing to around 2000
j/kg by Sunday afternoon with a 0-6km bulk shear magnitude of 40-50
kts. However, mid-level winds look relatively weak and are resulting
in an ugly hodograph. There is some potential for severe convection
during the Sunday afternoon/evening period, so this will be
mentioned in the hazardous weather outlook.

This precipitation is expected to end Sunday night as the primary
trough axis passes to the east. A weak surface boundary will move
south into west central Texas Monday night but is expected to stall
before eventually washing out, having little affect on temperatures
and moisture. In fact, temperatures are expected to warm into the
mid/upper 80s Monday afternoon. This boundary may, however, serve
as a focus for isolated diurnal convection Monday afternoon. I did
maintain the area of 20% pops, but I trimmed it down to the
southeast corner of the County Warning Area.

Generally dry weather is expected on Tuesday with temperatures
warming into the lower 90s. West to southwest flow aloft will induce
Lee cyclogenesis, promoting gusty south winds by mid-week. This may
also set the stage for the dryline to move away from the higher
terrain, propagating east into the County Warning Area during the day and sloshing
back to the west overnight. Whether or not the dryline is able to
support convection remains to be seen. Shear/instability parameters
look good, but the southwest winds aloft will aid in the development
of an elevated mixed layer which tends to cap off surface based
convection. However, with the approaching trough, the large scale
forcing may be sufficient to offset the warming aloft. I did not
include pops for Wednesday or Thursday, but we'll have to monitor
the model trends as this system evolves.



Preliminary point temps/pops...
Abilene 52 74 57 77 60 / 20 10 10 20 50
San Angelo 54 78 58 78 60 / 20 10 10 30 40
Junction 56 78 58 78 60 / 20 10 10 20 30


Sjt watches/warnings/advisories...