Area forecast discussion
National Weather Service Fort Worth Texas
328 PM CDT sun may 19 2013
Discussion...
the dryline has reached a line from Wichita Falls to Graham to
Brownwood where it will likely stall before retreating west this
evening. The main forecast concern through this evening is
whether storms will initiate along the dryline and the amount of
coverage. As discussed in the morning update...most of the model
guidance is not initiating any convection in our region this
evening despite cin becoming almost negligible across the western
zones. However the RUC/hrrr/GFS have not wavered and one of the
hi-res wrfs at 12z has now joined the initiation Camp. The issue
at hand is likely that today/S strong winds and dry air aloft will
make it tough for an infant updraft to become established and
grow into a supercell without a shortwave to aid in lift. Right
now the best guess is that 1 to 3 storms will manage to develop
over the western County Warning Area by early evening...and will continue the
forecast of 20-30 probability of precipitation west of a line from Sherman to dfw to
Lampasas. Local objective analysis indicates cape values are from
2000-3000 j/kg over the County Warning Area and ample deep layer shear exists to
support very large hail and damaging winds. An isolated tornado
will be possible between 6 and 8 PM when low level wind shear
ramps up just before the surface airmass becomes too negatively
buoyant with loss of heating. Storms may hold together long enough
to affect locations farther to the east by middle-late
evening...especially north of I-20...but severe weather potential
will be diminishing. Otherwise a breezy and muggy night is in
store for the region.
The storm threat for Monday is looking greater across a larger
part of North Texas. The cin will be even weaker than today and
almost all of the models are indicating storm initiation in the
County Warning Area. The dryline will be roughly in the same location as it is
today. The GFS and NAM are most aggressive with height falls and
convection across the northwest County Warning Area...which raises confidence that this
area will likely see supercell storms and severe weather. Expect
several supercells to develop across the western zones...including
some isolated cells across the SW zones. Very high instability
and ample deep layer shear will support a threat of significant
severe weather including giant hail...damaging winds and a few
tornadoes. Low level wind shear gets stronger after 7pm with 0-3km
srh values above 300 m2/s2. Since there is less cin there is more
time for evening supercells to tap into this instability after
dark which is what is raising our concern for tornadoes. Have
bumped up probability of precipitation to 30-50 percent in the western zones...and
raised them for the central and northeast zones as well...as
supercells will head eastward and hold together longer.
On Tuesday a weak cold front will become draped across the County Warning Area
from roughly Paris to dfw to Eastland. High temperatures will be a little
cooler this day...but instability will still be very high
especially across the southern zones. All model guidance shows
strong upper level forcing over North Texas Tuesday afternoon as
the trough axis swings through the area. This will set the stage
for scattered to numerous showers and storms that will likely
develop along the front Tuesday afternoon and move east and
southeast into the nighttime hours. Since low level wind fields
relax a bit...these storms may tend to organize into a mesoscale convective system/squall
line over the central zones. Obviously a severe weather threat
will exist with this convective episode as well. Rainfall will
range from a trace in the northwest to 1.5 inches in the southeast zones.
Expect this convective episode to finally exhaust the atmosphere
and push the best moisture and instability southeast of the area
by Wednesday morning. Will keep Wednesday dry.
Weak ridging sets up over the area Wednesday and into next
weekend. Southeast winds will continue which will keep low temperatures
in the middle 60s to near 70...and highs in the middle 80s to near 90
each day. Convection is expected to occur over the High Plains
Thursday and Friday...and with a southeasterly flow in the lowest
800mb we will need to keep an eye on some of this activity making
a run at the County Warning Area during the overnight hours. Since there is a lack
of strong northwest flow aloft in the middle levels...believe
convection will dissipate before reaching most of the area...but
have inserted a slight chance in the northwest zones Thursday and Friday
nights. Will keep the remainder of the forecast dry.
Tr.92
&&
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 71 90 71 88 67 / 20 20 40 50 50
Waco, Texas 72 90 72 91 68 / 10 10 20 40 60
Paris, Texas 70 87 69 83 65 / 20 10 60 50 50
Denton, Texas 70 89 69 86 64 / 30 30 40 40 40
McKinney, Texas 70 89 70 85 65 / 20 20 40 50 50
Dallas, Texas 73 91 73 89 69 / 10 20 40 50 50
Terrell, Texas 70 89 71 87 68 / 10 10 30 50 60
Corsicana, Texas 71 89 72 88 69 / 5 10 20 40 60
Temple, Texas 71 90 72 92 69 / 5 10 20 40 60
Mineral Wells, Texas 70 94 68 88 65 / 20 30 30 40 40
&&
Forward watches/warnings/advisories...
none.
&&
$$
