Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0744 am CDT Friday Mar 28 2014


Valid 281300z - 291200z


..there is a slight risk of severe thunderstorms portions central Texas to
middle-south region and Gulf Coast states...


...
Downstream from large northestern Pacific cyclone...progressive/quasi-zonal
flow will persist across Continental U.S.. shortwave trough associated with
convection over MO/Iowa yesterday is moving east-northeastward across upper Great
Lakes at this time...and will continue to weaken as it accelerates eastward over
southern ont...southern Quebec and New England. Meanwhile...shortwave troughs
now over Black Hills and southern High Plains are separate but moving
nearly in step with each other. By 00z...these perturbations should
reach fsd-Oma and dfw-vct corridors...respectively. Southern-stream
trough should eject northeastward across Tennessee Valley region by daybreak
tomorrow morning...as initially weak/intermediary trough amplifies
over Ozarks. Moisture-channel imagery also indicates precursory
shortwave trough has developed in association with -- and probably
resulting from -- persistent/disorganized mesoscale convective system over la/MS/al. This
feature should track eastward across central-eastern Gulf coastal plain and
Georgia through remainder period.


At surface...frontal zone associated with departing northern-stream trough
has stalled across southwestern Arkansas...southeastern OK...N-central Texas between
metroplex and Red River and northwest Texas...to weak surface cyclone centered
between abi-sps-cds. As middle-upper level wave moves over central
Texas...cold front will move southward over that region while surface low
migrates east-southeastward to E-central/southeast Texas. Overnight...low should
shift/redevelop east-northeastward over northern MS...deepening and reaching
middle-eastern Tennessee by 12z. At that time...cold front should extend southwestward
through western Alabama..sern MS...southeastern la and northwestern Gulf.
Dryline...currently analyzed from northern coahuila northeastward across bwd
area...should mix eastward by middle-late afternoon to I-35/US-77 corridor before
being overtaken from north-S by cold front.


..central Texas to middle-south region and Gulf Coast states...
Broad...messy and somewhat conditional severe threat is evident over
this region. Big 15%/slight area actually is aggregated from three
somewhat distinct threats that overlap spatially...


1. Lower Delta to southern Alabama and Florida Panhandle today --
ongoing/persistent mesoscale convective system over this region is expected to translate
slowly eastward...offering risk of sporadic damaging downdrafts...mainly
from outflow driven by precipitation loading in small bows. Hail threat
appears marginal and tied to any sustained supercell structures...given
weak ambient lapse rates. Tornado potential from any
embedded/transient supercells cannot be ruled out but is very
dependent on mesoscale-Beta to storm-scale effects.


2. S Texas to arklatex and mid-south...morning through evening --
scattered...initially elevated thunderstorms have developed between sjt-mwl
in regime of low-level warm air advection and moisture transport above strong
inversion layer evident in 12z forward/drt radiosonde observations. This or more likely
subsequent/afternoon convection near dryline should move eastward into
diabatically destabilizing air mass. Timing...duration...coverage
and evolution of convection across this area remains very uncertain.
As such...probabilities in this area are adjusted little from prior
outlook.


Very steep midlevel lapse rates are likely...such that maximum
cloud-layer Li of -13 to -16 and 2000-3000 j/kg MLCAPES are possible
even with reduction in surface dew points due to boundary-layer mixing.
That mixing will produce inverted-v thermodynamic profiles suitable
for damaging gusts as well as for maintenance to surface of large hail
generated aloft. Forecast soundings indicate supercell-supportive
low-middle level wind profiles...and presence of large cape aloft in
ideal hail-generation zones. As such...significant/damaging hail is
quite possible from any sustained/discrete storms. Activity may
undergo cold-pool-driven aggregation into one or more bands or arcs
moving east-northeastward to eastward over this area with damaging winds and large
hail possible.


3. MS Delta Region tonight --
another round of thunderstorms may develop in vicinity of surface cold front...offering
damaging winds and isolated hail. Any such activity would move eastward
over air mass that...by then...should have recovered sufficiently
from current mesoscale convective system activity to support renewed severe potential.
Meanwhile deep shear and large-scale ascent each will be enhanced by
approach of shortwave trough...amidst surface dew points middle-60s f.


.Edwards/Smith.. 03/28/2014