U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 171940 
Storm Prediction Center ac 171938 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0138 PM CST sun Feb 17 2019 

Valid 172000z - 181200z 

..no severe thunderstorm areas forecast... 

isolated thunderstorms will continue over portions of the southeast, 
Tennessee Valley, and Appalachians today. 

..20z update... 
Some adjustments have been made to the northern extent of the 
general thunderstorm area across MS/TN/KY into the central 
Appalachians to account for current convective trends. Across the 
southeast, thunderstorms will likely remain confined to the cool 
side of surface front. With only weak elevated instability expected, 
severe potential continues to appear too low to include any 
probabilities across this region. 

.Gleason.. 02/17/2019 

Previous discussion... /issued 1030 am CST sun Feb 17 2019/ 

..Tennessee Valley/southeast states... 
Showers and occasional thunderstorms are expected today along an 
advancing cold front. Relatively warm mid-level temperatures and a 
displacement of the stronger lift to the north will result in poor 
lapse rates and minimal instability overall. While 
deep-layer/low-level shear will be strong, and semi-organized 
convection may evolve particularly across al, severe potential is 
still expected to be considerably limited by the marginal 
thermodynamic environment. 

..northern/central California coast... 
In relation to a south/southeastward-digging shortwave trough, some 
shallow convection is likely but updrafts reaching temperatures 
needed for lightning production will be sparse. Thus, lightning 
coverage is expected to be less than 10 percent. 


Mesoscale Discussion

acus11 kwns 170646 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 170646 

Mesoscale discussion 0106 
National Weather Service Storm Prediction Center Norman OK 
1246 am CST sun Feb 17 2019 

Areas affected...central into eastern Iowa 

Concerning...heavy snow 

Valid 170646z - 171045z 

Summary...heavy snow, with up to 1 inch/hr snowfall rates, is 
expected to continue for a few more hours. 

Discussion...a mid-level shortwave trough continues to impinge on 
the discussion area, with strong divergence noted at 300 mb 
associated with the left-exit region of a pronounced jet streak. As 
such, adequate upper-level support for ascent remains in place to 
encourage the lifting of saturated parcels through a deep dendritic 
growth layer (-12 to -17 c), where heavy snow will remain possible, 
including at least brief occasions of 1 in/hr snowfall accumulation 

As sunrise approaches, the intensity of the primary band of snow is 
expected to wane, with much lower snowfall rates expected per latest 
high-resolution model guidance. 

.Squitieri.. 02/17/2019 

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


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