U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 291917 
Storm Prediction Center ac 291915 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0215 PM CDT sun Mar 29 2015 

Valid 292000z - 301200z 

..there is a marginal risk of severe thunderstorms from the arklatex northeastward into the 
lower MS valley this evening... 

A few thunderstorms may produce severe hail this evening and tonight 
within an area extending from southeast Oklahoma and northeast 
Texas...eastward to the mid-south. 

No changes were made to the previous outlook. 

.Jewell.. 03/29/2015 

Previous discussion... /issued 1127 am CDT sun Mar 29 2015/ 

Recent water vapor loops indicate a midlevel shortwave trough from 
the upper MS valley to the Central Plains. This trough will continue 
tracking eastward toward the Appalachians while being overtaken by a 
disturbance amplifying from southern Manitoba. A front associated with 
these midlevel features will track eastward across portions the MS valley 
to the Ohio Valley and trail southwestward to the Southern Plains. 

..sern OK/northestern Texas eastward to the mid-south... 
The return of partially modified Gulf moisture ahead of the 
aforementioned front is underway across the Southern Plains...with 
50s-lower-60s surface dewpoints analyzed across much of southern/eastern Texas. 
Prefrontal surface slys will continue to maintain a steady influx of 
similar moisture toward the Red River of the south to the lower MS 
valley through the day. However...substantial capping aloft at the 
base of an eml sampled by the 12z oun and forward radiosonde observations will likely keep 
diurnal thunderstorm chances minimal despite the increase in 
convective instability. 

By this evening...the front will be intercepting the aforementioned 
modest return moisture across the region...favorably coincident with 
glancing DCVA/forcing for ascent attendant to the shortwave 
trough...to encourage thunderstorm development. Furthermore...with a 
strengthening nocturnal boundary-layer wind maximum augmenting 
front-preceding warm air advection along a low level jet /strongest across the lower MS 
valley/...isolated to scattered thunderstorms will likely develop 
in vicinity of the frontal zone in the 00z-04z period. This activity will 
likely be elevated above a nocturnally stabilizing planetary boundary layer layer and 
perhaps undercutting baroclinic zone. 

The latest forecast soundings suggest that 500-1000 j/kg of MUCAPE 
will be common across the area...which will support some hail 
potential given 25-40 knots of effective bulk shear yielding organized 
convective structures /possible supercells/. Given 700 mb-500 mb lapse rates 
around 7-8 c/km sampled by 12z forward/oun radiosonde observations...with similar values 
spreading eastward with time...normalized cape/updraft accelerations will 
be sufficiently robust -- in the presence of the aforementioned deep 
shear -- for isolated severe-hail potential this evening into tonight. 
This scenario is affirmed by the latest available 
convection-permitting model guidance...and warrants the upgrade to 
marginal-risk delineation. 

However...given the undercutting nature of the surface boundary...and 
the propensity for increasing cell interactions to eventually impede 
individual-cell inflow in this regime of boundary-parallel deep 
flow...a more substantial severe-thunderstorm risk is not expected to evolve. 

Mesoscale Discussion

acus11 kwns 290016 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 290016 

Mesoscale discussion 0156 
National Weather Service Storm Prediction Center Norman OK 
0716 PM CDT Sat Mar 28 2015 

Areas affected...central ND through extreme northern South Dakota 

Concerning...severe potential...watch unlikely 

Valid 290016z - 290145z 

Probability of watch issuance...5 percent 

Summary...thunderstorms should continue to pose a threat for a few 
strong to damaging wind gusts until around 02z from central ND through 
extreme north central South Dakota. Coverage of any severe events is expected to 
remain too sparse for a ww issuance. 

Discussion...line of high-based storms has intensified over central ND 
within zone of strong frontogenetic forcing accompanying a 
progressive shortwave trough. This activity is moving east at around 
50-55 knots. Bismarck 00z radiosonde observation indicates steep lapse rates between 
700-500 mb...but is convectively stable. However...a narrow zone of 
destabilization due to ascent within the frontogenetic zone will 
progress eastward into central ND. Fast momentum of the storms combined 
with strong evaporative cooling potential associated with steep 
lapse rates and dry air within the sub-cloud layer will continue to 
support strong...convectively-enhanced wind gusts next 1-2 hours 
followed by weakening as the boundary layer stabilizes. 

.Dial/Edwards.. 03/29/2015 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 45760208 47030163 48000133 48350069 47880014 45770046 
45390142 45760208