Scientific Forecaster Discussion
fxus64 kfwd 261810
Area forecast discussion
National Weather Service Fort Worth Texas
1210 PM CST sun Feb 26 2017
Clouds have moved in this morning bringing all metroplex sites and
Waco to MVFR conditions. Moisture will continue to stream in today
bringing with it a chance of showers late this afternoon. Latest
short-term guidance suggest the possibility of a line of storms
developing west of the dfw metroplex taf sites and moving to the
northeast along the approaching cold front. Have opted not to
include this in the taf given its relatively new in the models but
this will need to be watched the next couple of model runs and
may need to be added to the metroplex sites if there is more run
to run model consistency.
Winds behind the front will primarily be out of the east/southeast.
Behind the cold front, expect ceilings to drop below 1000 feet
with drizzle reducing visibility to around 2sm. Conditions will
begin to improve Monday morning with the return of MVFR conditions
and southerly winds around 12 kts.
For Waco, have kept showers beginning around 21z as moisture and
instability increase this afternoon. Ceilings will also dip down in
the IFR category late tonight into Monday morning with visibility
reductions due to drizzle.
The impulse responsible for the less-than-optimal flying
conditions will move off to the northeast and conditions should
improve late Monday morning.
Previous discussion... /issued 330 am CST sun Feb 26 2017/
this morning's cool, tranquil weather won't last long;
substantial changes are on the way which will bring several
forecast challenges over the next few days. Low-level moisture
will begin returning to the region this morning with dewpoints
climbing back into the 50s this afternoon accompanied by a swath
of low stratus. This will be due to strengthening wind fields in
the 925-850mb layer in advance of a deepening trough across the
southwestern US. Strong warm advection will be the result and it
will be capable of producing scattered showers this afternoon
mostly along and east of I-35. Late this afternoon and evening,
lapse rates will begin steepening due to mid-level cooling
associated with an approaching shortwave. Thunderstorms will be
capable of developing within the axis of strong warm advection
mostly across the southeast half of the forecast area after about
4-5pm. While MUCAPES should be less than 1000 j/kg, strong
effective shear will allow for rotating updrafts in elevated
thunderstorms this evening and tonight, thus storms may pose a
threat for borderline severe hail. The main area we'll be
monitoring will be roughly southeast of a Canton to Killeen line.
Any storms should be shifting east out of our forecast area after
Late this evening, the aforementioned shortwave trough will drag a
weak front into North Texas. Most guidance has this front sinking as
far south as I-20 before it stalls. The GFS continues to be the
exception keeping this boundary north of the Red River. Have
sided with ECMWF, NAM, tt WRF, and other high-res guidance that
brings the front farther south. Models generally disagree
regarding the convective potential along the front itself as it
stalls across North Texas. Have kept low pops and sided with most of
the drier high-res guidance given that isentropic ascent will be
decreasing with weakening low-level wind fields as well as some
weak subsidence aloft with the departing shortwave. Immediately
along and behind the front, some drizzle and very low clouds will
prevail through late tonight and into early Monday.
The stalled front will lift back north on Monday morning with
moisture continuing to increase to it's south. A dryline will take
shape across the western portion of the forecast area Monday
afternoon with a potent warm sector to the east. If storms are
able to develop east of the dryline Monday afternoon, they could
certainly become strong given the buoyancy shear parameters.
However, most guidance is keeping a fairly Stout cap in place
Monday afternoon. Without much in the way of dynamic forcing and
the strongest warm advection displaced to the northwest, there may
not be sufficient lift to overcome the cap on Monday. Have left
low pops roughly east of I-35 with the highest storm chances
across the far eastern portions of the area.
Tuesday continues to be of more concern as stronger forcing should
actually be available in the form of a deepening shortwave
sweeping across the plains states. The warm sector airmass from
Monday will still be in place across roughly the eastern 2/3rds
of the forecast area east of a well-defined dryline. Very steep
mid-level lapse rates in excess of 8 c/km will overspread this
airmass resulting in MUCAPE values around 2000 j/kg. There is
still some question as to if the forcing will arrive early enough
in the day to generate storms along the dryline during the
afternoon hours, or if it will remain too far west. If scattered
storms are able to develop Tuesday afternoon or evening in the
vicinity of the dryline, they will be capable of producing very
large hail given the environmental characteristics. If not, the
main chance for storms will not arrive until a cold front moves
through late Tuesday night and early Wednesday morning.
The cold front on Wednesday morning will effectively end the rain
chances for the remainder of next week as it brings in much cooler
and drier air. Temperatures should return to near seasonal normals
to begin the month of March. Some near- or sub-freezing lows will
be possible across rural areas of North Texas on Thursday morning.
By late Friday and Saturday, a deep trough is expected to be
digging very far south through northern Mexico which will bring
chances for widespread rain to parts of south Texas over the weekend.
If this trough takes the track that guidance is currently
advertising, we'll remain mostly dry with only low chances for
showers mostly across central Texas over the weekend; we would
remain cut off from the better moisture and the stronger forcing.
Preliminary point temps/pops...
Dallas-ft. Worth 65 56 78 62 83 / 20 30 30 5 30
Waco 65 58 79 61 81 / 40 30 30 10 30
Paris 62 50 70 59 77 / 40 60 40 10 30
Denton 65 53 77 59 81 / 20 20 20 5 30
McKinney 64 54 74 60 78 / 30 30 30 10 30
Dallas 65 57 77 63 82 / 30 30 30 10 30
Terrell 63 56 74 62 79 / 40 50 30 10 40
Corsicana 64 59 77 63 81 / 50 50 40 10 40
Temple 63 58 79 61 82 / 50 30 30 10 30
Mineral Wells 70 52 79 55 83 / 10 20 10 5 20