Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Fort Worth Texas
1156 PM CDT Sat may 23 2015

Aviation...
concerns...periods of convection through the taf period.

A mesoscale convective vortex /mesoscale convective vortex/ southwest of kact at 05z...
will continue to move north northeast overnight...bringing
numerous showers and thunderstorms near the I-35 corridor through
daybreak. Thus have kept tafs generally MVFR with tempo
thunderstorm through 10z....and thunderstorms in the vicinity through 14z. Timing of
thunderstorms during the day tomorrow is difficult...some have
placed vcsh in through most of the day but left out thunderstorms
for now. An improvement to VFR ceilings may occur for a few hours
during the late afternoon into the evening...before ceilings fall
back to MVFR by 04z.




58

&&




Previous discussion... /issued 330 PM CDT Sat may 23 2015/
scattered showers and thunderstorms are developing across the
region as upper level forcing for ascent and increasing divergence
aloft begin to spread into the area in advance of an upper trough
axis. Local objective convective parameters are now indicating
inhibition is near 0 over all but the western and northwestern
zones as warm/moist advection brings temperatures up into the low
to middle 80s despite widespread cloud cover. Dewpoints have also
climbed into the lower 70s and precipitable water is likely now
pushing 2 inches...which is unseasonably high. All of these
parameters including undirectional shear profiles with winds
increasing to 30-40kt in the low levels...continue to suggest that
a heavy rain event will occur somewhere in the region during the
next 24 hours.

The warm/moist advection pattern will continue into the evening
hours...with convective inhibition decreasing across the northwest
zones where we are most concerned for the threat of severe
weather and possibly tornadoes this evening. Instability fields
are actually a little higher than what was forecast for this
afternoon with values now pushing 2000 j/kg south of I-20. The
best low level shear should remain north and west of the dfw
metroplex...where any discrete cells in this area may try to
rotate and produce tornadoes. Elsewhere...severe weather risk is
lower due to widespread/messy storm coverage...but strong winds
would be the primary threat.

The first round of convection has already developed and these
scattered showers and storms will continue to stream north across
the area late this afternoon into the evening. Locally heavy
rainfall is possible...but this activity should move quick enough
to mitigate flash flooding. Additional thunderstorms will develop
across West Texas late this afternoon...and track northeastward
into the western County Warning Area later this evening and tonight. But most
importantly...a line of storms...or mesoscale convective system...has developed in
western Oklahoma and is moving southeast into northwest Texas. A
strong cold pool has formed with this mesoscale convective system which is causing its
slow southeastward motion. On its current track...it should reach
the northwest zones around 9 PM. This mesoscale convective system will likely be the primary
feature that focuses the heavy rainfall tonight as cells will
train or backbuild along and just ahead of it. We still expect
widespread rainfall amounts of 2-4 inches across the northwest
zones. As the nighttime progresses...the mesoscale convective system and the convection
moving in from the west should form a solid north-south band of
rain/storms that moves gradually eastward through the area late
tonight and into Sunday. Rainfall across the central and eastern
County Warning Area will generally range from 1 to 3 inches...with the 2-3 inch
totals more likely north of I-20 than south. Some low severe
weather threat will exist overnight with this line as it moves
east...but the time of day and storm Mode suggests just a very
marginal wind threat.

The line of rain/storms will likely push out of the eastern zones
Sunday afternoon...but due to continued strong forcing across
western areas...additional scattered showers and storms may
develop Sunday afternoon and evening west of I-35. Some sunshine
may occur out west...which would increase instability and the
severe weather threat...but this potential is highly conditional
on how worked over the atmosphere is after the main round of rain.
Will keep probability of precipitation in the low chance category.

On Monday...yet another shortwave trough will move through Texas
and bring another round of rain and storms. However...we expect a
much more unstable airmass to be in place ahead of this
system...and the likely result would be a mesoscale convective system/squall line that
develops across the northern Hill Country early in the afternoon
and moves east-northeast into across mainly the southeastern half
of the County Warning Area. The main threat with this round would be damaging
winds and another 1-3 inches of rainfall...again mainly southeast
of a Paris to dfw to Comanche line. This part of the forecast may
still be in flux...as Sunday/S round of rain/storms may impact the
favorable zone for where Monday/S activity to develop and track.

More sunshine is expected on Tuesday as a weak/broad upper trough
remains over the region. Model guidance is unanimous in
developing an extremely unstable airmass with surface based cape
in excess of 5000 j/kg over the area. A dry line should organize
near the western County Warning Area...which would be a focus for isolated storms
to develop. While deep layer shear is weak...if the forecasted
amount of instability verifies...it would certainly be enough for
supercell structures and severe weather. Also given a slow
movement of any storm that develops...the localized heavy
rainfall and flooding threat is assured. We will be watching the
Tuesday time period with interest...even though probability of precipitation are only
20-30 percent.

Continued moderation of temperatures will occur through the week with
more afternoon sunshine Wednesday through Friday. Instability is
forecast to remain high...but not as bad as on Tuesday. Forcing
and deep layer shear will be very weak...and therefore only
expect a slight chance of unorganized afternoon and early evening
convection.

Chances of rain increase again on Friday and Saturday as the next
strong upper level trough moves into the region with a possible
cold front. Additional heavy rainfall and flooding will be
possible with this system....but it is too early to get into the
details now.

Tr.92




&&



Preliminary point temps/pops...
Dallas-ft. Worth, Texas 68 76 68 81 66 / 100 80 30 60 50
Waco, Texas 70 78 69 81 67 / 100 80 30 80 50
Paris, Texas 68 74 67 79 65 / 90 90 50 60 60
Denton, Texas 67 76 66 80 66 / 100 80 30 50 50
McKinney, Texas 67 75 67 79 66 / 100 90 40 50 50
Dallas, Texas 68 76 68 81 66 / 100 80 30 60 50
Terrell, Texas 69 74 69 80 67 / 100 80 40 70 50
Corsicana, Texas 70 76 70 80 67 / 100 80 40 80 60
Temple, Texas 70 79 69 81 67 / 100 70 30 80 50
Mineral Wells, Texas 66 79 67 81 64 / 100 70 20 50 40

&&

Forward watches/warnings/advisories...
Flash Flood Watch through Sunday evening for txz091>095-100>107-
115>123-129>135-141>148-156>162-174-175.



&&

$$

58/58

National Weather Service Glossary of Abbreviations