Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Fort Worth Texas
1120 PM CDT Wednesday Oct 1 2014
an upper level trough currently making steady eastward progress
across the Great Basin is still slated to bring an active round of
convective weather to North Texas Thursday afternoon and
evening. A cold front will accompany this system...with the front
pushing across the Dallas-Fort Worth metroplex terminals 00-02z
Thursday evening and then the Waco area 02-04z.
For the overnight hours...30kt southerly low level jet winds
should bring another layer of stratus overhead during the morning
hours Thursday. We will continue indicating MVFR ceilings beginning at
09z at kact then 11z in the metroplex. Otherwise...isolated
elevated convection should remain northwest of area taf sites.
Surface heating and boundary layer mixing will lead to improving
conditions late Thursday morning...with the return of VFR by
midday. Thursday afternoon...moisture and instability ahead of
the front will be sufficient for thunderstorm development as lift
from the upper trough overspreads the region. Activity will likely
be scattered in nature in the metroplex and also in the Waco area
late afternoon and early evening. We will indicate thunderstorms in the vicinity at the
Dallas-Fort Worth area airports beginning at 22z and Waco at 23z.
Storms should then solidify into a squall line just east of area
taf sites as the system encounters deeper moisture. Northwest
winds near 15 knots and VFR conditions will follow the passage of the
scattered showers and storms that developed just west of the
region on a weak dry line late this afternoon should continue to
decrease in coverage as they move northeast. However...increasing
large scale lift from the approaching western U.S. Trough may
sustain a few storms during the late evening and overnight hours.
Therefore...we will keep some 20 probability of precipitation in the northwest zones
through the night.
A fairly strong early fall cold front will continue to move south
across the Central High plains tonight. Temperatures north of the front
were in the upper 30s and lower 40s in many locations. The front
should continue surging south across the High Plains with slower
movement expected father east. Therefore...the front will change
orientation a bit and this will delay frontal passage across North Texas
until Thursday afternoon/evening. It still appears the best
rain/storm chances will be along and east of I-35 Thursday
afternoon and evening so we will make no changes to 2nd and 3rd
period probability of precipitation at this time.
The current forecast is in good shape so no update is needed at
Previous discussion... /issued 346 PM CDT Wednesday Oct 1 2014/
afternoon satellite imagery shows an extensive cumulus field across the
eastern half of Texas this afternoon indicative of ample low level
moisture being pulled northward ahead of an approaching upper
trough. This shortwave trough can be seen on water vapor imagery
digging into the southwest U.S. And it will continue eastward
overnight. In the immediate short term...our primary concern will
be potential for convective development across the far western
counties this evening. There is a thin band of cumulus that has
developed along a diffuse dryline across west-central Texas.
Temperatures have climbed into the middle and upper 90s across this
region and inhibition is weakening. It is hard to tell whether
there is any additional forcing for ascent being provided to the
area from the approaching trough as Texas currently appears to be
between systems. What is clear though is that forcing will begin
to increase later tonight as the upper trough gets closer...so any
activity that does develop might be able to sustain itself for a
while. Went ahead and kept some 20 probability of precipitation across the far western
counties to account for this.
By tomorrow morning the western U.S. Trough will be approaching
the Southern Plains. A surface low will be located across
northwest Oklahoma and will quickly be moving to the northeast
while a cold front begins to surge southward. The guidance has
continued to support a slower arrival of the upper trough but
appears to be consolidated around a midday to middle afternoon
timeframe. This would be favorable for more widespread convection
along the cold front as temperatures are likely to warm into the
middle 90s across parts of North Texas...especially along and east of
I-35. The tricky part for the 8 million or so people who live in
North Texas and desperately want rain is exactly where the
thunderstorms initiate along the cold front. High resolution
guidance is very well clustered with initiation occurring between
3 and 5 PM Thursday afternoon. The variance comes with a couple
of models showing thunderstorms developing from Dallas eastward
and others indicating that they will develop farther west. This
forecast will favor a slightly farther west development based on
the strong forcing coming in along the front during peak heating
which should help weaken the cap quickly. Our current forecast
will indicate thunderstorms developing in the middle afternoon along
a line from near Gainesville southwest to Decatur and Weatherford.
Initial activity will primarily remain north of I-20 but should
quickly expand southward as the front moves east. All of this
means that the western half of the metroplex and areas west of there
could miss out on the more significant rainfall. Areas along and
east of I-35 will have much better chances for rainfall. The front
will continue east through the evening with showers and
thunderstorms affecting primarily the eastern half of the County Warning Area
through midnight before quickly coming to an end with frontal passage.
Concerning severe weather potential...with the upper forcing
coming in coincident with peak heating...an area of moderate
instability will have developed along and ahead of the cold front.
Deep layer shear of around 45 kts will be more than sufficient
with instability around 2500 j/kg to support severe convection.
Wind profiles become veered rather early in the event which is typical
of frontal type convection...and this is likely to limit the
overall tornado threat. The exception may be areas south of
Interstate 20 where capping will be a little stronger and a discrete
supercell or two may develop along or ahead of the cold front.
Again...while wind profiles dont appear to be favorable...discrete
supercells can quickly modify the local environment...so the potential
needs to be monitored. The most likely severe threat will be large
hail and damaging winds from squall line convection across the
eastern half of the County Warning Area.
Thunderstorms will come to an end Thursday night as the front
clears North Texas. It wont be considerably colder behind the
front but it will be much drier. Dewpoints will fall into the 30s
by late Friday with temperatures in the upper 70s and lower 80s.
The coolest morning will be Saturday when the surface high is
centered across the region. Temperatures will drop into the 40s
and lower 50s with significant topographical effects due to near calm
winds. The forecast will remain dry into next week although
moisture will work back into the area by Monday and temperatures
will warm back into the middle and upper 80s.
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 75 95 61 83 53 / 10 60 20 0 0
Waco, Texas 74 94 58 85 52 / 5 30 40 5 0
Paris, Texas 72 92 57 77 48 / 10 50 60 0 0
Denton, Texas 73 94 57 81 47 / 10 60 10 0 0
McKinney, Texas 73 94 58 80 46 / 10 70 30 0 0
Dallas, Texas 75 95 61 82 54 / 5 60 30 0 0
Terrell, Texas 74 93 60 80 50 / 5 40 50 0 0
Corsicana, Texas 74 93 60 83 52 / 5 30 60 5 0
Temple, Texas 73 92 61 85 52 / 5 20 50 5 0
Mineral Wells, Texas 72 92 56 80 49 / 10 30 5 0 0