U.S. Severe Weather Forecast (Convective Outlook)

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Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0233 PM CDT Thursday Apr 17 2014 


Valid 172000z - 181200z 


..no severe thunderstorm areas forecast... 


... 
a strong storm or two remain possible this afternoon across a 
portion of central and South Florida...with the risk for hail and 
wind gusts near severe limits. 


... 
Aside from trimming thunder/severe probability lines to reflect 
current and anticipated trends...the overall forecast/reasoning 
remains valid. A stronger storm or two still could produce 
local/marginally severe hail or wind over parts of central/S 
Florida...mainly over the next 1-2 hours. Elsewhere...lightning may 
spread across the Gulf Coast region overnight as a more widespread 
cluster of storms crosses the Gulf of Mexico...and a few strikes 
will be possible later this afternoon/evening over parts of northern 
California/southeastern Oregon/southwestern Idaho/northwestern Nevada as an upper system approaches from 
the eastern Pacific. 


.Goss.. 04/17/2014 


Previous discussion... /issued 1056 am CDT Thursday Apr 17 2014/ 


..South Florida... 
Visible satellite imagery indicates cumulus congestus swelling over 
South Florida commensurate with diurnally bolstered planetary boundary layer 
circulations. The greatest agitation to the cumulus field is noted over 
the southern tip of the peninsula...where surface observations indicate 
temperatures in the lower 80s amidst lower 70s dewpoints. This 
yields 2000-3000 j/kg of SBCAPE...aided by steep middle-level lapse 
rates sampled by the 12z mfl radiosonde observation depicting an 500 mb temperature around 
-12c. This thermodynamic environment is representative of much of 
the South Florida peninsula...where an increasing influx of maritime 
tropical air has occurred during the past 24 hours owing to veering 
of Post-frontal flow. Farther north...such air mass modification has 
been less prominent yielding a decline of buoyancy with northward extent 
across Florida -- especially along and north of a Tampa-Melbourne line. 


Convection will continue to deepen through the day as static 
stability diurnally lowers and Sea/Lake breeze circulations 
intensify. With Miami vwp sampling modest 0-6-km bulk shear -- 
I.E. Around 20-25 knots -- multicell clusters with a few instances of 
marginally severe hail/wind will be possible. The greatest 
concentration of this activity is expected to occur west of the East 
Coast metropolitan areas...as mesoscale convergence is favored in vicinity of the West 
Coast by background low-level elys and convection regenerates toward 
7.0-7.5-c/km surface-3-km lapse rates over the interior. However...with 
relatively weak low/mid-level flow in place...convection may be 
rather disorganized -- reducing the overall severe coverage and 
precluding the need for slight-risk designation. 


... 
A middle-level trough currently crossing the central/Southern Plains will 
continue to gain amplitude as it progresses eastward...with leading 
moisture transport/warm advection focusing showers and non-severe 
thunderstorms along the Gulf Coast and vicinity. The potential for 
isolated storms may also extend northward into the arklamiss region within 
a plume of elevated buoyancy preceding the trough. Additionally...a 
few storms may occur across parts of the Sierra Nevada mountains to 
the Great Basin...as DCVA preceding a shortwave trough currently 
approaching the Pacific northwest coast intercepts steep tropospheric lapse 
rates and modest middle-level moisture downstream. 






Mesoscale Discussion


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Mesoscale discussion 0363 
National Weather Service Storm Prediction Center Norman OK 
0325 PM CDT Wednesday Apr 16 2014 


Areas affected...east central Minnesota/northwestern WI 


Concerning...heavy snow 


Valid 162025z - 170030z 


Summary...heavy snow -- locally exceeding an inch per hour -- will 
continue over the next several hours. 


Discussion...latest WV imagery shows a strong cyclonic circulation 
center crossing the sux /Sioux City Iowa/ vicinity at this time...moving 
eastward/east-northeastward with time. An associated surface low is analyzed just to 
the NE -- over far southwestern Minnesota...with a warm front extending eastward across 
southern Minnesota into central WI. A zone of strong qg ascent -- in advance of 
the upper system and north of the surface warm front -- is spreading 
gradually eastward across the upper MS valley area...and is supporting an 
arcing band of moderate to heavy snowfall from southwestern and central Minnesota 
northeastward into northwestern WI per latest radar loop. 


As the upper system and associated surface low advance into the 
evening hours...the band of heavy snow is prognosticated to 
persist...shifting gradually from west central Minnesota into northwestern WI and then 
later into western Upper Michigan. Snowfall rates locally in excess of an 
inch per hour are expected for several hours...particularly across 
the northwestern WI vicinity late this afternoon into this evening. 


.Goss.. 04/16/2014 


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


Attention...WFO...dlh...mpx... 


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