U.S. Severe Weather Forecast (Konvektivudsigt)

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Day Three

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Storm Prediction Center ac 271232 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0632 am CST Mon Feb 27 2017 


Valid 271300z - 281200z 


..there is a marginal risk of severe thunderstorms today from parts 
of the lower Mississippi Valley to northeast Texas...and tonight 
into Missouri.... 


... 
Isolated strong to severe storms will be possible today from parts 
of the lower Mississippi Valley to northeast Texas, and tonight into 
Missouri. 


... 
Gradual amplification of the pattern is ongoing across the 
contiguous U.S. As a midlevel trough moves inland from the Pacific 
coast to the Great Basin, and a relatively Flat Ridge persists over 
the southeast states. A broad belt of west-southwesterly flow 
between the two will support Lee cyclogenesis across the Central 
High plains, as well as northward moisture return across la and from 
East Texas toward MO by tonight. 


..la and southern MS today... 
Smaller-scale perturbations within the flow are now crossing the mid 
MS valley and the Red River valley of TX/OK. Clusters of 
slightly-elevated thunderstorms are ongoing in a warm advection 
regime from The Ark-la-tex to the lower MS valley. Additional 
convection will likely continue to develop along the 
convection-reinforced warm front from northern la to southern MS 
through the afternoon. Some of these storm clusters will pose a 
marginal risk of damaging winds/hail given potentially moderate 
buoyancy (mlcape of 1000-1500 j/kg) and effective bulk shear near 50 
kt. 


..north and northeast Texas today... 
More isolated storm development will be possible across north and 
northeast Texas along the warm front today. Other than weak low-level 
convergence and warm advection, the focus for storm development 
becomes unclear after about midday as the speed Max over the Red 
River begins to move away from the area. If storms develop today, 
as suggested by a few operational and experimental hrrr runs this 
morning, the storm environment will favor supercells capable of 
producing large hail/damaging winds, and perhaps a tornado. Still, 
storm coverage is still very much in question, so will only add low 
severe probabilities to north and northeast Texas in this update. 


..MO area tonight... 
Later this evening and overnight, a southwesterly low-level jet will 
strengthen from eastern OK to the mid MS valley. Moisture transport 
will contribute to destabilization and the potential for some 
slightly-elevated convection across MO. Some of this activity could 
produce isolated large hail. 


.Thompson/Kerr.. 02/27/2017 


$$ 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 262358 
txz000-270200- 


Mesoscale discussion 0215 
National Weather Service Storm Prediction Center Norman OK 
0558 PM CST sun Feb 26 2017 


Areas affected...parts of central Texas 


Concerning...severe potential...watch unlikely 


Valid 262358z - 270200z 


Probability of watch issuance...5 percent 


Summary...developing thunderstorms near the Austin/San Antonio Metro 
may pose a very isolated risk for hail, gusty winds, and perhaps 
even a brief tornado over the next several hours. Watch issuance is 
not expected at this time. 


Discussion...visible satellite loops from the past few hours have 
shown an area of weak low-level confluence and agitated cumulus 
field over central Texas. Better low-level moisture (surface dewpoints 
in the lower to mid 60s) has developed northward from south Texas and 
the western Gulf through the day, and steep mid-level lapse rates 
present on the 12z drt sounding have advanced eastward over central 
Texas. With some diurnal heating, MLCAPE of 500-1000 j/kg is presently 
located across the discussion area, decreasing with northward extent 
due to more limited moisture. 


Large-scale forcing for ascent is also increasing across central Texas 
with the approach of a low-amplitude shortwave trough from the west. 
Strong westerly to southwesterly mid-level winds attendant to this 
trough are contributing to 50-55 kt of effective bulk shear, which 
is more than sufficient for supercell structures. Indeed, several 
low-topped supercells have been observed per the kewx radar between 
Austin and San Antonio over the past hour or two. Main limiting 
factor that has suppressed more robust thunderstorm development so 
far has been pronounced mid-level capping centered between 850-700 
mb. Even so, with continued low-level moistening and mid-level 
cooling forecast to occur over the next several hours, these 
developing thunderstorms may eventually breach the cap and pose a 
very isolated risk for hail approaching severe levels, strong/gusty 
winds, and perhaps even a brief tornado given effective srh of 
200-250 m2/s2 across central Texas. 


.Gleason/Edwards.. 02/26/2017 


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


Attention...WFO...hgx...fwd...ewx... 


Latitude...Lon 29559826 30869757 30839720 30589689 29859680 29409737 
29359814 29559826