Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Fort Worth Texas
710 PM CDT Monday Aug 3 2015
No significant concerns...continued VFR. Persistence forecast
with generally southeasterly winds and passing middle/high clouds.
A weak impulse grazing the Red River valley is resulting in some
high-based showers...but at best...only sprinkles will be able to
penetrate the deep dry sub-cloud layer. More widespread and
vigorous convection is ongoing across West Texas...but once
again...this activity will find an increasingly less favorable
environment as it drifts eastward. Showers may encroach on western
portions of North Texas late tonight and Tuesday morning...but
precipitation is unlikely at any taf sites.
A seasonally weak surface pressure gradient will yield light
winds overnight that will have a tendency to vary in direction.
More organized boundary layer flow will ensue Tuesday morning...
but the resulting southerly surface winds will remain generally
Previous discussion... /issued 311 PM CDT Monday Aug 3 2015/
water vapor loop today shows an upper level low moving through
Utah and into Wyoming. Forcing ahead of this feature will kick off
scattered showers and storms on the Front Range of the Rocky
Mountains southward into the Texas Panhandle this afternoon and
evening. The upper level steering flow will bring this activity
east and southeastward toward the region late tonight. This
convection will weaken as it approaches North Texas due to very
limited moisture and instability in the critical 700mb to 900mb
layer. However...the airmass will remain fairly saturated above
700mb with some meager amounts of instability. This means a few
elevated weak showers could sustain themselves long enough to
affect the northwest zones late tonight and the northern zones
during the day Tuesday. Due to the weak nature of the convection
and the dry air in the low levels...measurable rainfall will be
difficult to achieve and have kept probability of precipitation at 10 percent...even
though the radar should have a more promising presentation.
The upper level low will move east through the central US during
the next couple of days. The southern end of this system should
provide just enough forcing for some isolated convection
Wednesday afternoon and evening across the Red River counties and
the northeast zones where we will maintain 20 probability of precipitation. The airmass
over North Texas on Wednesday will actually feature quite a bit of
instability and very little to no cin in many areas. With northwest
flow continuing over the region on the eastern fringe of the upper
level high...it is certainly a pattern that can result in
unforecasted convection. Have shown 10 probability of precipitation down to I-20 Wednesday
afternoon and evening...as stray pop-up convection will be
possible in this airmass. If there is better forcing farther south
than models suggest...it will result in much higher coverage.
Aside from the Wednesday afternoon potential there is another
very slight chance over the northeast zones late Friday as a weak
front approaches from the northeast and stalls across the Red
River valley. Right now...just the GFS bring this front into the
County Warning Area...so will keep probability of precipitation out of the worded forecast.
Otherwise the main story this week and into next week will be the
heat. The upper level high will spend most of this week to the
west of our area...but the aforementioned upper low that tracks
across the plains will have the effect of turning the low level
winds to a more westerly direction. This will drag a blob of very
warm air just above the surface from West Texas into our area. So
high temperatures will be climbing through midweek with temperatures near
100 for most North Texas locations by Thursday even though the
high does not build in over our area until the weekend.
Temperatures this weekend and into next week look like they will
range from 99 to 104 across the County Warning Area. Furthermore...the consensus
of model sources suggest that afternoon dewpoints will be a degree
or two higher than what we saw during the last couple of
weeks. This would result in peak heat indices in the 103 to 109
range...and necessitate heat advisories for a good portion of the
County Warning Area beginning perhaps as early as Wednesday and persisting into
the weekend. It is too early to issue any advisories now...but we
will be looking at this potential over the next couple of days.
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 79 99 80 100 80 / 5 5 5 10 5
Waco, Texas 76 100 78 100 78 / 0 0 0 5 0
Paris, Texas 74 97 76 99 76 / 0 10 5 20 20
Denton, Texas 75 98 78 100 77 / 5 10 5 10 10
McKinney, Texas 75 97 78 99 79 / 5 10 5 10 10
Dallas, Texas 80 100 81 101 81 / 5 5 5 10 5
Terrell, Texas 75 99 77 99 77 / 0 5 5 10 10
Corsicana, Texas 76 100 77 100 77 / 0 0 0 5 5
Temple, Texas 74 100 75 100 75 / 0 0 0 5 0
Mineral Wells, Texas 74 97 76 99 76 / 10 10 5 5 5