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Area forecast discussion...updated 
National Weather Service Fort Worth Texas
646 am CDT Tuesday Mar 31 2015

Aviation...

Concerns...morning MVFR ceilings today and again on Wednesday.

Southerly low level flow continues to draw moisture northward as isolated
IFR ceilings and a large area of MVFR ceilings will spread across the
region. Kact went MVFR several hours ago and expect the dfw
metroplex to see some shortly. However...south winds veer
above the boundary layer with southwesterly flow at 20+ knots
between 1000 and 2000 feet...which may limit MVFR ceilings over kftw
and kafw this morning. It may take until late morning for ceilings to
improve at all affected terminals. VFR conditions will prevail
afterwards until late tonight when they return around 08z.

There is a small window that any terminal could experience IFR
ceilings around 800 feet...but it should not last more than two hours
in duration if it occurs. Flights headed through areas around ksps
and kadm will have IFR ceilings/visible through middle morning...ksps
currently 1/4sm fog v002 and kadm m1/4sm fog bkn001.

Winds will remain southerly at 10-16 knots through the forecast.
Could see gusts to 20 knots in the afternoon hours. 75

&&



Previous discussion... /issued 353 am CDT Tuesday Mar 31 2015/

00z upper air analysis showed a plume of steep middle-level lapse
rates in place over much of the Southern Plains...likely
associated with an elevated mixed layer (eml). Aside from steep
middle-level lapse rates...this eml also represents a fairly Stout
capping inversion in place over the region with regards to surface
based convective potential instability. Early morning surface
analysis showed that there was at least some modest moisture in
place below this eml cap...with dew points in middle 60s along the
Gulf Coast to the lower 60s across most of north and central
Texas. Water vapor satellite imagery showed a compact upper level
low pressure system over the Baja California peninsula...with upper level
ridging located due north of this feature...over the northern
Continental U.S. And Canadian rockies. Upper level troughing was located over
the northeastern Continental U.S. And just off the coast of the Pacific
northwest. This left the Southern Plains in weak west to northwest
flow aloft early this morning.

Today...with a Stout cap in place...expect that wherever early
morning stratus winds up...it will be slow to mix out this
morning. Expect clouds to eventually scatter out this
afternoon...leaving partly cloudy skies in place for most
locations. The cap should also ensure a dry forecast for most of
the County Warning Area today...with attention focusing just west of the County Warning Area as a
dryline organizes from Wichita Falls to near Abilene around 21z.
31/00z model guidance consistently advertises convection
initiation along the dryline at or around 00z/7pm this evening.
The flow aloft is generally out of the west-northwest as mentioned
above...so any convection that initiates along the dryline should
tend to move east into better low-level moisture...but also into
stronger capping associated with the eml. High resolution
convection allowing models also indicate convection initiation
along the dryline...but generally favor storms developing near
Abilene rather than near Wichita Falls which is what
global/coarser resolution models favor. Either way...there
appears to be a decent chance for isolated thunderstorms to
develop along the dryline west of the County Warning Area by late this
afternoon...moving east across western portions of the County Warning Area this
evening.

If storms are able to develop along the dryline...they will likely
be strong to severe with models advertising 1500 to 2000 j/kg of
surface based cape just east of the dryline late this afternoon.
The flow aloft is not overly strong however...and deep layer shear
is expected to be on the order of 25 to 30 kts...which is marginal
for a supercellular storm Mode. With the deep layer shear vector
and flow aloft oriented perpendicular to the dryline...the
initial storm Mode would likely be discrete...possibly growing
upscale into a multi-cell cluster or line a couple of hours after
initiation. Think that the lack of stronger upper level forcing
will limit the coverage of storms...so only went with a 20 pop
west of Interstate 35 this afternoon...and a 30 pop after sunset
taking into account the potential for upscale growth. It is
entirely possible that there will not be enough forcing along the
dryline to get convection initiated in the warm/moist sector to
the east...so also kept probability of precipitation low to account for uncertainty
regarding storms being able to develop and move into the County Warning Area. If
organized storms move into the County Warning Area...anticipate that large hail
and locally damaging wind gusts will be the primary hazards. Low-
level shear is expected to remain somewhat weak...so unless a
strong discrete supercell develops...think that the overall
tornado threat will be low this afternoon and this evening.

Wednesday...the Baja California upper trough/low is expected to move east off
the Mexican high terrain and over central Texas tomorrow
afternoon. Model guidance has been trending weaker and weaker with
this system as it moves over Texas on Wednesday...so overall
confidence in sufficient lift to support widespread rain showers
and thunderstorms over the region has diminished. The best forcing
for ascent associated with this upper trough is expected to move
over the far southeaster County Warning Area Wednesday afternoon. Went ahead and
kept probability of precipitation in the 30 to 40 percent range east of I-35 and south of
I-20 as a result...but dropped probability of precipitation into the 20 to 30 percent
range elsewhere. Overall the additional upper level cloud cover
out ahead of this system appears to diminish the potential for
strong surface heating...so chances are that the eml cap will
simply prevent thunderstorms for developing across most of the
County Warning Area. May see some elevated rain showers accompany the plume of
middle-upper level moisture associated with the upper trough...but
do not think any organized thunderstorm activity is likely near
the upper trough. The focus for thunderstorm activity on Wednesday
will likely be well north of the County Warning Area...centered over the Central
Plains where a cold front and stronger upper level forcing are
expected.

Thursday...for the most part on Thursday...upper level flow will
remain westerly with no obvious shortwave troughs upstream to
provide lift. This generally favors dry conditions across the
County Warning Area...and that may pan out. However...the cold front that moves
south through the Central Plains is expected to move across
Oklahoma Thursday...approaching the Red River by 00z/7pm Thursday
evening. To the south of this front...model guidance consistently
shows that a strong dryline will move east towards the Interstate
35 corridor. With persistent southerly flow from the preceding 48
hours...low-level moisture will be in place...albeit trapped under
a fairly strong inversion near the 825 mb level. This inversion is
the base of another eml that models indicate will advect over the
region Thursday afternoon. The combination of steep middle-level
lapse rates and low-level moisture has models advertising anywhere
from 2-3000 j/kg of surface based cape near the Interstate 35
corridor Thursday afternoon. The flow aloft is also expected to be
strong on Thursday...0-6 km bulk shear vectors forecast to be
anywhere from 40 to 50 kts out of the west...oriented
perpendicular to the dryline. While this combination of parameters
is highly favorable for supercell thunderstorms...the main
forecast challenge is determining whether storms are even possible
given the lack of upper level lift/support.

Convection allowing guidance does not extend out far enough to
resolve convection initiation chances along the dryline at this
time. Standard model/convection parameterized guidance all show
the dryline near the Interstate 35 corridor...and all fail to
generate precipitation Thursday afternoon/evening along the
dryline. While this seems like a fairly clear cut message...the
cap will be too strong for storms...these models are also
advertising a quick increase in middle-level relative humidity along
the dryline Thursday afternoon. This is likely due to persistent
lift...and possibly the models activating their shallow convection
schemes ahead of the dryline. Thought that the potential for
mesoscale lift along the dryline was sufficient to advertise at
least a small chance of thunderstorms along the Interstate 35
corridor Thursday afternoon and evening. If the cap is too
strong...we will likely just see some simple convection
attempts/orphaned anvil clouds along the dryline Thursday
afternoon. However wanted to at least advertise the chance for
storms along the dryline because if anything develops...it is very
likely to become severe quickly and be capable of producing very
large hail and damaging wind gusts. Will continue to keep a close
eye on thursday's dryline. Regardless of what happens with
thunderstorms on Thursday...critical fire weather conditions are
possible west of the dryline. These conditions are discussed in
more detail in the fire weather forecast.

This weekend...the Central Plains cold front is expected to move
south across the County Warning Area Thursday night into Friday morning. Because
this is the most stable time of day...chances are that the front
will move across the County Warning Area without any thunderstorm activity. If the
front were to speed up and meet the dryline Thursday evening...the
triple Point of dryline/cold front/warm sector would be a very
favorable initiation point for thunderstorm activity. At this time
it looks like the front will remain in Oklahoma until late
Thursday night/early Friday morning...after the near surface
environment is too stable for thunderstorm initiation.

Temperatures are expected to be much cooler behind the
front...with highs topping out in the middle to upper 60s Saturday
and Sunday across North Texas. Precipitation chances increase
quite a bit on Sunday as Gulf moisture surges north over the
front. Expect mostly rain shower activity with some embedded
thunderstorms as lapse rates aloft are expected to be near moist
adiabatic...or just barely unstable enough to support convective
updrafts.

Early next week...a warm front will move north across the region
Sunday evening...bringing US back into the warm sector by Monday
afternoon. We are expected to have steeper middle-level lapse rates
again with good quality low-level moisture in place. This general
combination yields a conditional thunderstorm threat across the
County Warning Area during the peak heating hours of the day for Monday through
Wednesday. It is too early to determine the likelihood of any
severe thunderstorm chances...however if there is sufficient lift
early next week...there will likely be an attendant risk of some
strong/organized thunderstorm activity. Temperatures will likely
be at or above normal Monday through Wednesday.

Cavanaugh



&&




Preliminary point temps/pops...
Dallas-ft. Worth, Texas 82 65 78 65 87 / 10 20 30 10 20
Waco, Texas 81 64 78 64 86 / 10 20 30 10 20
Paris, Texas 77 60 76 63 79 / 10 30 30 20 20
Denton, Texas 82 64 78 64 88 / 10 30 20 10 20
McKinney, Texas 80 62 78 64 83 / 10 30 30 10 20
Dallas, Texas 82 65 78 65 87 / 10 20 30 10 20
Terrell, Texas 79 62 78 64 83 / 10 20 30 20 20
Corsicana, Texas 79 63 77 64 82 / 10 20 40 20 10
Temple, Texas 81 64 78 64 85 / 10 20 40 10 10
Mineral Wells, Texas 85 62 80 63 93 / 20 30 20 10 10

&&

Forward watches/warnings/advisories...
none.

&&

$$

75/

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