Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kfwd 190436 

Area forecast discussion
National Weather Service Fort Worth Texas
1136 PM CDT Wed Sep 18 2019

/06z tafs/

As tropical depression Imelda continues its slow northwestward
movement across southeast Texas, rich tropical moisture will aid
in the development of low-end MVFR to high-end IFR ceilings across
all taf sites after 10-11z. Several airports east of the taf sites
are already reporting ceilings ranging from fl007 to fl025, and
expect a westward expansion to continue in the coming hours. Opted
to push back the arrival of stratus to 10-11z based on the latest
high res guidance.

Ceilings across the metroplex will likely struggle to lift to VFR
and will remain closer to high-end MVFR near fl025 through the
remainder of the day. For Waco, it is possible ceilings may lift
to near or above fl035 as drier air on the western side of the low
aids in scattering the stratus by the afternoon hours.

As far as precipitation affecting the taf sites on Thursday, the
greatest potential remains during the afternoon and evening hours
as Imelda moves inland. Similar to previous days, will maintain a
mention of vcsh from 19-01z and will allow future issuances to
address the potential for shra/tsra.

Sref guidance indicates another round of stratus early Friday
morning, with a greater potential across the metroplex terminals
as low-level moisture edges northward. Cams also develop scattered
showers/storms during this time period, but confidence in timing
is too low to mention in the dfw taf.



Short term... /issued 459 PM CDT Wed Sep 18 2019/
/this afternoon through Thursday afternoon/

Imelda will continue to move slowly northward through the next 24
hours and the remnant low pressure swirl should be near Palestine
by sunrise and Canton by sunset Thursday. While this might sound
promising for rain at face value, the issue is that the main core
of the system will become detached from the low level circulation
tonight and tomorrow, leading to the bulk of the dynamics for lift
in two favored areas - neither in our County Warning Area. The first favored area
will be well east of the surface low center where favorable
moisture flux off of the Gulf combines with strong dynamics for
lift as the mid level vorticity center gets grabbed by the
westerlies and heads northeast. The second favored area will be a
region of strong low level convergence to the southwest and south
of the low center where northerly flow will meet the prevailing
southeasterly Gulf trade winds and act as an effective frontal
boundary. This "tail" of the system may impact our region Thursday
night, but tonight and tomorrow it will be much too far south.

All of that said, have lowered pops and quantitative precipitation forecast for this afternoon
and tonight for most of the region, with the exception of the
Palestine area where the surface low center will arrive late
tonight. The surface low center will likely be cut off from any
rich flux of Gulf moisture/instability, and thus will primarily
be a swirl of light to moderate rain. During the day on Thursday
extensive cloud cover around the low center will keep temperatures
cool, and thus also limit day time heating for vigorous
convection to its northwest. Instead just expect some weak
showers and perhaps an isolated storm, with best chances closest
to the low center and just a slight chance to the west. Do not
expect convection to be intense enough to lead to a flooding
threat through Thursday, especially with very dry soils helping to
absorb rainfall.

Low temperatures tonight will be cool and in the lower 70s for
most areas, with some upper 60s in the west. High temps on
Thursday will be modulated by cloud cover and only reach the lower
80s in the southeast zones near the low center to near 90 across
the western and northern zones where more sunshine will occur.
It's not the cold front we were all hoping for by this time, but
we'll take what we can get.



Long term... /issued 459 PM CDT Wed Sep 18 2019/
/Thursday night through next week/

The remnants of Imelda will lift northward across the
northeastern portion of the forecast area Thursday night and
Friday as an upper level tough advances eastward from California
to The Rockies. The strongest convection and heaviest rain
associated with the system may actually remain just east of the
region across East Texas and Louisiana where a deep Gulf moisture
fetch should remain in place. However, an eastward-training band
of rain along the system's southern flank could pose at least a
low-end concern for flooding for areas east of I-35 where 2+ inch
pwats will persist. Likely pops will subsequently continue across
the eastern third of the region with a gradual northward shift in
placement Thursday night through Friday. Though locally heavy
rainfall with totals of 2 to 4 inches will be possible in some
areas, the recent dry spell precludes the need for a Flood Watch
at this time.

The system will accelerate north then northeast Friday night and
Saturday as it encounters stronger steering winds. The potential
for a lingering band or two of showers warrants at least slight
chance pops across the eastern half of the region for Saturday.
Otherwise, mostly dry conditions with seasonable temperatures can
be expected over the weekend.

Meanwhile, the previously mentioned upper trough will weaken and
become positively tilted while lifting northeast across the
plains on Saturday. The trough will be accompanied by a cold
front, but because of the overall lack of energy associated with
the system, the front will likely stall late Saturday prior to
reaching North Texas. It is still possible that outflow
associated with any convection along the front will reach the
northwest counties, so low pops will continue along the Red River
for Saturday night/Sunday.

Shortwave ridging will develop overhead by Monday, bringing about a
warm and precipitation-free forecast for the start of next week.
An upper low will approach the area from the west on Tuesday, but
models diverge significantly on its evolution thereafter. The
operational GFS progresses the low steadily eastward, bringing
scattered showers and thunderstorms back into the forecast for the
second half of next week. However, its ensemble members are all
over the place, and the European model (ecmwf) actually keeps the system well west
of the region through day 10. Will therefore play it conservatively
and wait for better model consistency before committing to any one
solution for the extended portion of the forecast.



Preliminary point temps/pops...
Dallas-ft. Worth 72 87 73 90 74 / 10 40 50 60 20
Waco 70 87 74 92 73 / 10 50 50 40 10
Paris 72 87 70 82 71 / 20 50 70 80 30
Denton 71 87 71 90 73 / 10 40 50 60 20
McKinney 72 87 71 87 73 / 20 40 60 70 20
Dallas 73 87 74 90 75 / 20 50 60 60 20
Terrell 73 84 73 89 73 / 20 50 60 70 20
Corsicana 71 82 72 87 72 / 30 60 60 60 10
Temple 71 88 74 92 73 / 10 50 50 40 10
Mineral Wells 69 88 69 90 71 / 10 30 30 50 10


Forward watches/warnings/advisories...

National Weather Service Glossary of Abbreviations