Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS64 KFWD 280229
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
929 PM CDT Mon Mar 27 2017

.UPDATE...
A stalled frontal boundary is draped through Central TX this 
evening and is beginning to slowly lift northward as a warm front.
Rich moisture on the southern side of the front, illustrated by 
the upper 60s dewpoints roughly from Lampasas to Palestine, will 
accompany the front's northward advance. The very light winds in 
vicinity of the front combined with minimal dewpoint depressions 
suggests that the development of at least some patchy fog will be 
possible across Central TX beginning after ~3am. Have introduced a
a fog mention to the forecast but am not expecting any fog that 
develops to be particularly dense or long-lived. Otherwise, have 
increased temperatures slightly across Central TX where dewpoints 
will remain in the mid to upper 60s overnight. Temperatures should
be nearly steady in the upper 60s in these areas.

We will continue to assess the potential for strong/severe storms
tomorrow as new data arrives. Most high-res guidance is not 
particularly enthused regarding convective potential along the 
northward-moving warm front as a fairly stout cap should be in 
place. A couple rounds of storms developing along the dryline west
of the forecast area late in the afternoon and evening will 
continue to be the main concern as this activity will transition 
into North and Central TX later tomorrow evening through Wednesday
morning.

-Stalley

&&

.AVIATION...
/ISSUED 724 PM CDT Mon Mar 27 2017/
East winds 5 to 10 knots will gradually come around to the 
southeast Tuesday as a warm front lifts northward. VFR conditions 
will prevail through most of the overnight hours, before moisture 
spreads northward bringing in MVFR ceilings into the Metroplex by 
12z. Ceilings should continue to lower into the IFR category by 
15z. Some drizzle/light rain is possible from 15z through 21z. As 
the warm front lifts north to near the Red River, ceilings should 
improve to MVFR but isolated to scattered showers and 
thunderstorms will possible late afternoon through the evening.

At Waco...MVFR ceilings are expected to spread north into the 
area around 06z and lower to IFR around 10z with drizzle and fog 
possible. Some LIFR conditions are possible between 12 and 16z. 
Expect conditions to improve to MVFR by 18z as the warm front 
through the region. Ceilings should improve to VFR after 21z. 
There is a low chance of thunderstorms during the afternoon but 
the chances are not high enough to include in the Waco TAF at this
time. 

58


&&



.PREV DISCUSSION... /ISSUED 422 PM CDT Mon Mar 27 2017/
Active weather will continue over the next week
as the flow generally remains quite progressive. As a result, 
there will be numerous opportunities for showers and thunderstorms. 
While rainfall will be welcomed, it's likely that severe
weather will likely accompany some of the better rain chances.

Surface analysis and radar imagery this afternoon indicated that 
the cold front that has swept through the area was located across
parts of Central and East TX at this time. It also extended back
towards the west towards the Permian Basin. Further upstream, the
next trough is sliding eastward across Southern California. As 
this feature rapidly translates eastward, it should induce lee- 
side pressure falls and allow the cold front to lift back towards 
the north and we are already seeing some semblance of this per 
KGRK radar imagery and surface observations across Central TX. The
position of this feature will be paramount to severe weather 
chances across North and Central TX late Tuesday afternoon. We 
will visit this more in detail later. 

For tonight, expect generally warm temperatures as low level
moisture quickly streams northward. With not a large amount of
colder air to the north, I expect that lee-side pressure falls
should be efficient at lifting warm and moist air towards the Red
River. The implied isentropic upglide may be enough to spark a few
isolated showers down across Central TX and I've kept some low
PoPs through midnight. Through the early morning hours, I've 
carried a dry forecast, but trends in hi-res output will need to 
be monitored for potential showers and a storm or two. I've kept 
the forecast dry mainly due to the generally shallow nature of the
moisture return at least initially. Later in the morning hours, 
however, the low level wind field will intensify which will 
support a greater magnitude of theta-e advection, especially 
across western zones. Right now, the threat for strong to severe 
thunderstorms during the morning hours looks low, but we will have
to monitor closely for a potential hail threat.

For Tuesday, breezy, warm and humid conditions are expected as
a very stout upper trough arrives from the west. 100 meter height
falls will overspread the southern TX panhandle and a dryline 
will start to sharpen out west. The approach of the upper trough 
should further drive lee-side cyclogenesis and help to accelerate 
the warm front to the north. The location of this boundary will 
likely play a role in the behavior of any deep moist convection in
its vicinity. Most guidance pulls this warm front near the Red 
River by around 21 UTC, with the TTU WRF being the lone slow 
outlier. The 3km NAM is quite aggressive and lifts the boundary 
very far to the north into southern Oklahoma. That being said, I 
have highest confidence in the general model consensus and the 3km
NAM given the front's current behavior mentioned above. One 
possibility for a slower warm frontal passage across the area 
would be if convection were to develop across the Ozarks and 
reinforce the cooler airmass to the north. Most if not all 
guidance indicates WAA showers will be probable across the area 
tomorrow morning into tomorrow afternoon. The synoptic background,
however, will be characterized by either neutral to subsident 
motion. This would generally support generally shallow convection 
with little to no severe weather threat through at least the early
afternoon hours. With that being said, we will have to keep tabs 
on the position of the front, as well as the behavior of any 
shallow convection as this activity could morph into severe storm 
clusters should it tap into any of the surface based instability. 
In addition, if these storm clusters interact with the likely SRH-
rich warm frontal boundary, a tornado risk may develop. This 
scenario bears watching, but current thinking is that the better 
probability for more widespread severe convection will not occur 
until later in the day.

Later in the day on Tuesday, forecast soundings indicate that the
cap will begin to weaken, especially across western zones where
large scale ascent coupled with mixing should help to erode any 
afternoon inhibition. The dryline will most likely remain out 
across the western zones, so it's likely that activity will be a
bit further west than it was on Sunday. As a result, I've kept 
the highest rain chances along and northwest of a Comanche to Fort
Worth to Gainesville line. Further east closer towards the I-35 
corridor, streamer showers will likely continue through the 
afternoon. The cap does weaken here as well, but it's unknown as 
to whether or not this convection will become robust and breach 
the cap. If it does, this convection closer to the I-35 corridor 
will also have the potential to become severe during the afternoon
hours.

Severe hazards on Tuesday afternoon---The main risks will be 
large hail and damaging winds. There will be a threat for 
tornadoes, especially for surface based supercells that come 
within close proximity of the warm front. Heavy rain will also be 
a threat, especially for areas that received heavy rainfall on 
Sunday evening. 

Tuesday evening into Wednesday morning will continue to be active
as the main trough finally encroaches from the west. Strong DPVA
coupled with impressive height falls will overspread the entire
region and as a result, a line of showers and storms is expected
to erupt. With ample instability and deep layer shear in place,
numerous strong to severe thunderstorms are expected. Given the
magnitude of forcing, it's likely that activity will congeal into
a squall line and this is handled well by most short/hi-resolution
numerical guidance. 

Severe hazards on Tuesday night into Wednesday---The main hazards
with the squall line will be damaging straight-line winds and 
perhaps some large hail. There will be a risk for an embedded 
tornado or two as well. The line should march from west to east 
through all of North and Central TX, before exiting sometime 
Wednesday morning or afternoon. 

Wednesday afternoon could prove to also be another active day
depending on the amount of recovery in the wake of the morning
MCS. Climatologically speaking, airmass recovery across North and
Central TX behind the MCS is a function of MCS longevity/motion. A
slower MCS would more than likely limit the amount of recovery in
the afternoon, while a swifter MCS would allow for a greater 
potential for airmass recovery. At this time, it's unknown as to 
whether or not the airmass will recover in time for potentially a 
second round, as some hi-res guidance (3km NAM) indicates. If the 
3km NAM is to verify, there will be the potential for severe 
storms (likely supercells) capable of large hail, damaging winds 
and perhaps a few tornadoes. In addition, steep lapse rates 
beneath the upper low that is expected to swing southeastward 
would result in a hail threat even with seemingly weak convection
along the Red River.

Thursday and Friday should be relatively quiet with additional
rain chances returning on Saturday. The active pattern will 
continue through the latter half of the weekend and into next
week. While a little early to tell, there could be a risk for
strong to severe thunderstorms during this time as well. 

24-Bain



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    60  80  65  76  56 /   5  30  70  60  10 
Waco                64  82  65  78  57 /  10  20  60  60   5 
Paris               53  74  63  70  56 /   5  30  50  80  40 
Denton              55  76  63  75  55 /   5  40  70  50  10 
McKinney            54  76  63  73  56 /   5  30  70  60  10 
Dallas              61  81  66  76  58 /   5  30  70  60  10 
Terrell             60  82  66  74  56 /   5  20  60  70  20 
Corsicana           63  83  66  76  58 /  10  20  50  70  10 
Temple              67  84  63  78  56 /  20  20  60  60   5 
Mineral Wells       55  77  57  79  51 /   5  40  70  20   5 

&&

National Weather Service Glossary of Abbreviations