Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kfwd 211204 aaa 
afdfwd

Area forecast discussion...updated
National Weather Service Fort Worth Texas
704 am CDT Sat Sep 21 2019



Aviation...
/12 UTC taf cycle/

Concerns---ceiling trends. Low convective potential at Waco.

VFR to MVFR stratus with pockets of cigs at or below fl020 currently
blankets the I-35 corridor. After sunrise, confidence is high
that cigs will improve quickly and become all VFR by mid-
morning. Thereafter, broken stratocumulus at or above fl050 will prevail
through the afternoon with breezy south winds near 15 knots. Gusts
to 20 knots should be expected. A few showers may drift northward
in vicinity of Waco through the morning hours. For now, will only mention
vcsh in the Waco taf as chances for thunderstorms and rain are too low to include.

A few more showers/storms may attempt to drift eastward toward
the Bowie cornerpost late tonight into early Sunday morning, but
at this time I anticipate that most if not all convective cells
will remain north and west of the major airports. Another round
of MVFR stratus is anticipated on Sunday morning and i've included
a mention of this at d/fw...Arlington and Waco.

Bain

&&



Short term... /issued 350 am CDT Sat Sep 21 2019/

/this weekend/

Rain and thunderstorm chances continue this weekend across the
region as a very moist air mass remains in place. While overall
synoptic scale ascent is expected to remain modest, it will be
sufficient to produce showers and a few storms for parts of the
area.

Low level cloud cover continues to stream northward this morning
as 925mb vwp indicates southerly flow of around 25 to 30 knots. The
current location of the morning stratus---generally along the
I-35 corridor---likely highlights the region where showers and a
few isolated thunderstorms are most likely this morning and into
the early afternoon. However, it's quite possible that most
locations will remain rain/storm-free. Convection that is ongoing
across the south rolling plains will likely continue to scoot
northeastward this morning. The low level flow is expected to
slowly weaken and this should limit the potential for backbuilding
of convective cells southward toward North Texas. For now, i'll
advertise a 15 pop across the Big Country this morning and this
afternoon to account for the low probability of a few echoes
sneaking into parts of the forecast area. Any showers or
thunderstorms today will be efficient rain producers as
precipitable water values remain above 2" per GOES total precipitable water
product. This includes any showers or storms that may attempt to
lift northward into the Brazos Valley associated with a weak sea-
breeze front.

Otherwise, today (saturday) should be hot with high temperatures
in the mid 90s for most locations. The exception will be along the
immediate Red River where yesterday's rainfall may be enough to
keep temperatures from skyrocketing too far above 90 degrees.
Overnight into Sunday, our attention will turn to the northwest
where another cluster or complex of storms may emerge off of the
higher terrain to the west. Unlike Saturday morning's complex, the
upper synoptic forcing is a bit more definitive (a low amplitude
shortwave trough is forecast to move across the panhandles).
While I will increase pops to near 40% along the Red River, it
should be noted that confidence in a solid line of storms entering
North Texas early Sunday is low given that low level flow will be
weaker (around 20 knots at 850mb) and more veered compared to
Saturday am. If low level flow remains more backed and/or is
stronger than currently anticipated, there will be a greater risk
for rain/storms through the day on Sunday over a larger area of
North Texas.

If the latter scenario verifies (stronger/less veered llj), there
will be a heightened flood risk, especially along the Red
River...generally near and east of US Highway 281 where anomalously
wet antecedent conditions are in place. With low confidence in
the pop forecast, i'll forgo any flood/flash flood watches at this
time. Sunday afternoon temperatures will climb to above normal
values for most areas (outside of the red river) with highs in the
mid 90s. There will be a low potential for diurnal convection
across the Brazos Valley late in the afternoon on Sunday.
Temperatures of course will depend on the location of any outflow
boundaries and subsequent shower/storm activity.

Bain

&&

Long term... /issued 350 am CDT Sat Sep 21 2019/
/Monday through Friday/

Monday may be the autumnal equinox, but with subtropical ridging
attempting to re-establish itself, it will continue to feel like
Summer. But the atmosphere is beginning to concede that it is late
September, and the ridge axis will be displaced south of our
latitude, keeping the mid-latitude westerlies on our northern
doorstep. As a result, nocturnal convective activity that
originated deeper within this turbulent flow could be able to
impact areas north of the I-20 corridor Monday morning. The
associated surface front may be near (or within) our northwestern
zones on Monday, its definition and southward progress likely
determined by the extent of the convective activity. Redevelopment
of showers and thunderstorms may occur along this boundary Monday
afternoon as an unseasonably moist surface layer reaches above
normal peak temperatures. The proximity of the front and easterly/
northeasterly storm motion should keep the convective potential
confined to areas primarily along and north of the I-20 corridor
throughout the day on Monday, with greater inhibition to the
south.

A potent upper low will dig into the Desert Southwest on Tuesday,
gently shoving the summery ridge back into the southeast. This
will introduce active southwest flow above North Texas, which will
persist the remainder of the upcoming week, maintaining daily rain
chances. A powerful polar jet will set up across the northern tier
of states, fully cutting off the upstream low at our latitude. As
is typically the case with such a feature, guidance is literally
all over the map with its evolution. There is some agreement that
its residence time in the Desert Southwest will be fairly short,
but the timing of its ejection varies widely among operational
solutions and among individual ensemble members. Since its
eastward progress appears to be tied to the pull of the polar jet
to the north, the consensus reasonably favors a more northeasterly
track. This would limit the severe potential for North Texas and
reduce the likelihood of a refreshing autumn front, but it is
important to emphasize that there is considerable uncertainty in
both the timing and track of this storm system. Thursday or Friday
continue to be the most likely days for potential impacts in our
region, with unseasonably warm weather prevailing into the final
weekend of September.

25

&&

Preliminary point temps/pops...
Dallas-ft. Worth 94 75 92 75 91 / 20 10 10 10 30
Waco 96 73 96 72 93 / 30 10 10 0 10
Paris 88 71 89 71 86 / 10 10 10 30 40
Denton 93 75 91 73 90 / 20 10 20 20 30
McKinney 93 74 92 73 90 / 20 10 10 20 30
Dallas 94 76 92 76 91 / 20 10 10 10 20
Terrell 95 74 92 73 91 / 20 10 10 10 20
Corsicana 93 72 92 72 90 / 20 10 10 5 10
Temple 95 72 94 72 91 / 30 10 10 0 5
Mineral Wells 92 73 90 71 90 / 20 10 20 10 30

&&

Forward watches/warnings/advisories...
none.

National Weather Service Glossary of Abbreviations