fxus64 kfwd 201208 aaa 

Area forecast discussion...updated 
National Weather Service Fort Worth Texas 
608 am CST Wed Feb 20 2019 

/12z tafs/ 

Ceilings near fl010 early, then VFR. West winds today, but no 
significant crosswind issues. South flow tonight and Thursday. 

Guidance has overestimated the dry advection and resulting stratus 
erosion. But with drying west winds near the top of the frontal 
inversion, the persistent cloud deck should eventually scatter 
this morning. The back edge in western North Texas is making slow 
progress eastward, and extrapolation of the current rate of 
erosion puts the clearing line into the I-35 corridor after the 
15z amendments. VFR will prevail thereafter, but a stream of 
cirrus off the Pacific is already spreading across the region. 
These wisps will steadily thicken today, the river of cirrus 
remaining overhead tonight. 

West winds will remain under 15kts and pose no significant 
crosswind threat. Wind speeds will diminish late in the afternoon, 
and light southeast flow will be in place by nightfall. Deepening 
Lee troughing will increase the southerly winds on Thursday. This 
will surge low clouds back into central and East Texas, but MVFR 
ceilings won't return to any of our terminals until Thursday 



Short term... /issued 432 am CST Wed Feb 20 2019/ 
/today and tonight/ 

Westerly winds have ensued in the wake of tuesday's inclement 
weather, but the dank surface layer has been slow to dry. 
Nonetheless, a T/TD spread (albeit small) should preclude any 
additional drizzle or ground fog. A blanket of stratus remains 
trapped within a persistent frontal inversion, but the back edge 
is slowly approaching our western boundary. Drying 850mb flow has 
already invaded and will thin the cloud deck from the top, but it 
will still be well after daybreak before the clearing line reaches 
the I-35 corridor. The peaks of sun may be short-lived as Pacific 
moisture streams into Texas from the southwest. These high clouds 
will steadily grow denser over the course of the day, but dry, 
downslope winds should still allow the entire County Warning Area to top 50f for 
the first time since last Friday. 

As Lee troughing re-establishes itself on the High Plains, 
southeasterly winds will return to much of North Texas tonight. 
However, central and East Texas may feel the tug of a coastal low 
in the western Gulf, resulting in a more easterly direction to 
the surface flow early Thursday morning. This would recycle some 
of the cool air from the departing postfrontal high while our 
western zones experience warm advection. The result will be rather 
uniform low temperatures across the region, in the mid 30s to 
lower 40s. 



Long term... /issued 432 am CST Wed Feb 20 2019/ 
/Thursday through next Tuesday/ 

A progressive mid-upper level weather pattern will occur late 
this week into the first half of this coming weekend. It's been 
quite a while since we've had severe weather around these parts, 
but we saw yesterday that, despite winter-like temperatures at the 
surface, some hail was observed. This happens when you get 
significant forcing, resulting in steepening mid-level lapse rates 
aloft and substantial instability over the top of cool-cold and 
stable low-levels. A similar scenario will likely unfold as we 
progress through the day Thursday. Southerly flow within the 
900mb-750mb layer is expected to increase quickly between 20-35 
knots and combine with increasing pressure advection (vertical 
motion) within this layer through the day. This transformation 
will occur above a cool and stable surface air mass where morning 
temperatures in the 30s-lower 40s are expected to only warm into 
the lower-mid 50s, as this warm advection is not realized below 
the lingering and shallow frontal inversion. These processes will 
be in response to an impressive lead shortwave disturbance exiting 
downstream of a strengthening storm system over northern Mexico 
and the Desert Southwest. 

Areas south of I-30 and east of I-35 with see rapid development 
of scattered showers and thunderstorms on the western edge of the 
best moisture advection above the frontal inversion. In addition 
to the aforementioned lift and upglide across this area, mid level 
lapse rates will steepen on the order of 6.5-7.5 deg c/km with 
MUCAPE (not surface-based) over 500 j/kg. This may not seem like 
much, but when combined with impressive kinematics, including 
deep layer bulk shear of 70-80 knots, stronger storms with hail 
and frequent lightning are a good bet. To be honest, it would not 
surprise ME from mid-morning Thursday into the early-mid afternoon 
hours for a few marginally severe storms with hail to quarter 
size or even slightly larger if everything comes together as 
advertised by the model output regarding our elevated environment 
and winds aloft across our far eastern counties. At this time, 
however, it does appear the better concentration of thunderstorms 
will be just to our east across far East Texas into Louisiana and 
the lower Mississippi Valley. 

A brief lull in convective activity will likely occur later 
Thursday afternoon and continuing through midnight Friday morning. 
The reprieve will be short-lived however as increasing warm 
advection and isentropic ascent return in earnest in advance of 
our slow-moving and vigorous storm system lifting east across the 
deserts of Arizona, New Mexico, and northern Mexico. Though 
Friday will be similar in some aspects to Thursday with regard to 
storms being mostly elevated, some warm advection may be realized 
late in the day across our far southeast counties. As such, there 
is the potential for strong surface-based storms in these areas 
with SBCAPE values approaching 1000 j/kg and steep lapse rates 
aloft in excess of 7 deg c/km, resulting in total MUCAPE values 
approaching 1500 j/kg. This will likely be the beginning of our 
concerns for the threat of severe storms, with at least a marginal 
severe weather threat extending northward to areas along and east 
of I-35/35w Friday night into Saturday morning as we continue 
seeing impressive, southwesterly deep layer shear in excess of 60 
knots along with the increasing instability. 

The one big unknown factor in advance of our vigorous mid-level 
trough and associated surface dryline will be how much preceding 
warm sector convective activity occurs and how it affects (or 
corrupts) the thermodynamic environment. Regardless, there will at 
least be a threat for damaging winds and large hail, to go along 
with locally heavy rainfall and minor flood concerns across 
eastern parts of the region. Another possible mitigating factor 
for a higher-end severe weather event is everything coming 
together during the nocturnal hours Friday night into Saturday 
morning, except possibly our far eastern counties where the 
surface dryline doesn't exit until midday or early afternoon 
Saturday. Otherwise, the storm threat will end rapidly west of 
I-35 by late Saturday morning and by mid-afternoon in the east as 
the system lifts northeast away from the region and a cold front 
overtakes the surface dryline. I'm still concerned with the gusty 
west or west-northwest winds of 20-30 mph that will enter areas 
west of I-35 in the wake of the dryline. Combined with low 
humidity and mild temperatures, there's the potential for elevated 
fire weather concerns west of I-35/35w Saturday afternoon. 
However, it does appear low level cold advection may arrive sooner 
than what was anticipated 24 hours ago. That, combined with off 
and on days of at least light rainfall, should keep fire weather 
concerns from getting out of hand. 

North and central Texas finally will see a much-needed, relative 
break from any threat of winter or strong-severe weather Sunday 
and beyond, though low rain chances will return early next week. 
Breezy north winds and temperatures falling into the 30s and 40s 
will make for a cool start to Sunday, but winds will slack off by 
Sunday afternoon with the arrival of a broad surface high. 
Plentiful sunshine will allow temperatures to warm back into the 
upper 50s along the Red River to the lower-mid 60s elsewhere. Mild 
conditions will continue Monday and Tuesday in advance of the 
next cold front. Highs generally in the 60s are expected along 
with low chances for a few light showers across the southeast half 
of the County Warning Area. 



Preliminary point temps/pops... 
Dallas-ft. Worth 55 39 53 46 59 / 0 0 10 40 70 
Waco 59 38 55 48 63 / 0 0 20 50 70 
Paris 51 36 52 43 58 / 0 0 20 40 70 
Denton 54 36 53 44 58 / 0 0 10 30 60 
McKinney 53 35 52 45 59 / 0 0 10 40 70 
Dallas 55 41 54 48 60 / 0 0 10 40 70 
Terrell 55 38 54 46 62 / 0 0 20 40 70 
Corsicana 57 41 54 47 63 / 0 0 30 50 70 
Temple 60 39 56 48 64 / 0 5 20 50 70 
Mineral Wells 57 37 56 43 59 / 0 0 5 30 60 


Forward watches/warnings/advisories... 

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