U.S. Severe Weather Forecast (Previsión convectiva)

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Storm Prediction Center ac 231630 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1130 am CDT sun Apr 23 2017 


Valid 231630z - 241200z 


..there is a slight risk of severe thunderstorms over 
western/central Georgia... 


..there is a slight risk of severe thunderstorms over South 
Carolina... 


..there is a marginal risk of severe thunderstorms from northern 
Florida into Georgia and South Carolina... 


... 
Areas of strong-severe thunderstorms are expected over the southeast 
today and overnight. The main threats appear to be damaging gusts 
over parts of western/central Georgia and central South Carolina 
this afternoon, followed by potential for a few tornadoes and 
isolated wind damage overnight in parts of South Carolina. 


..Georgia and South Carolina... 
Satellite imagery indicates an upper low has formed over western 
Tennessee, and this feature is forecast to move southeastward 
reaching the Alabama/Georgia border by the end of the period. A 
band of stronger mid/upper level winds curving cyclonically around 
the southern periphery of the circulation is expected to spread 
across parts of Georgia and northern Florida into tonight. 


At the surface, a low over extreme northwest Georgia will move 
mainly eastward along a quasi-stationary front extending across 
east-central Georgia to the central South Carolina coast. The low 
is forecast to reach east-central Georgia this evening and cross 
into South Carolina by 24/12z. A cold front trailing southward from 
the low will progress eastward to the Atlantic coast from Georgia to 
northeast Florida by the end of the period. The frontal boundaries 
are expected to focus the stronger thunderstorm activity through 
tonight. 


Initial storm development is expected along the advancing cold front 
by early afternoon from west central Georgia into the Florida 
Panhandle as it moves into an axis of slightly greater moisture. 
Although mid-level lapse rates are generally weak, visible satellite 
imagery indicates stronger diabatic heating will occur in the warm 
sector where fewer clouds are present. This will enhance low-level 
lapse rates and contribute to modest destabilization with MLCAPE of 
500-1000 j/kg this afternoon. With some cam guidance indicating 
development of qlcs structures along/slightly ahead of the front, 
stronger cells within the line segments will have potential to 
produce damaging downbursts as they move through the focused 
moisture/instability axis. See mesoscale discussion 550 for more 
detailed information. 


Other storms are expected to develop over parts of central/southern 
South Carolina this afternoon near the aforementioned east-west 
front. The lack of clouds south of the boundary is promoting a 
strong differential heating zone where attendant mesoscale 
circulations will support storm potential this afternoon. Isolated 
severe storms will be possible as vertical shear increases over the 
area, especially along and immediately north of the boundary where 
backed surface flow will enhance low-level shear. 


The severe threat over South Carolina is expected to increase 
somewhat tonight as a south-southeasterly low-level jet strengthens 
in response to the approaching upper low. This will result in 
increasing moisture advection from the Atlantic and be associated 
with stronger low-level shear with an attendant risk for supercells 
to develop. Low local levels and moderate-strong srh indicate 
potential for a few tornadoes to occur with any persistent discrete 
supercells that develop. 


..northern/central Utah... 
Isolated weak thunderstorms may develop this afternoon and evening 
in association with an upper short wave trough that will move 
eastward across the Great Basin. Column moisture/total precipitable 
water values are quite minimal /approximately 0.25 inch/ which will 
limit the coverage and intensity of any convection. However, a dry 
sub-cloud layer will enhance evaporative cooling and promote 
Transfer of stronger mid-level horizontal momentum to the surface, 
suggesting potential for convectively-enhanced surface wind gusts. 
Given the aforementioned limiting factors, we will maintain a 
sub-severe outlook at this time over the area. 


.Weiss/Cook.. 04/23/2017 


$$ 

Mesoscale Discussion


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acus11 kwns 231602 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 231602 
gaz000-flz000-alz000-231800- 


Mesoscale discussion 0550 
National Weather Service Storm Prediction Center Norman OK 
1102 am CDT sun Apr 23 2017 


Areas affected...portions of western/central Georgia...far southeastern 
Alabama...and a small part of the Florida Panhandle 


Concerning...severe potential...watch possible 


Valid 231602z - 231800z 


Probability of watch issuance...40 percent 


Summary...thunderstorms should strengthen along a cold front by 
early afternoon, posing mainly a strong to locally damaging wind 
threat. Watch issuance is possible. 


Discussion...as of 16z, a surface low was located over far 
northeastern Alabama/northwestern Georgia. A cold front extends southward from 
this low generally along the Alabama/Georgia border into far southeastern Alabama 
and the western Florida Panhandle, moving eastward with time. Visible 
satellite imagery shows partly to mostly sunny skies ahead of the 
front across parts of west-central Georgia into the central Florida Panhandle. 
A narrow corridor of greater low-level moisture was analyzed along a 
line from Atlanta to Macon to Albany GA, continuing southward to 
Tallahassee Florida and vicinity. A residual pocket of somewhat lower 
Theta-E air was located across central Georgia into northern Florida per 
latest surface observations. 


As large-scale ascent associated with a mid-level low over western 
Tennessee overtakes the surface cold front, an increase in convective 
coverage is expected along the length of the front over the next 
several hours. Mid-level lapse rates remain generally poor across 
this region per various 12z soundings and should remain so through 
the afternoon per rap forecast soundings. Even with some diurnal 
heating ahead of the front coincident with the narrow corridor of 
greater low-level moisture, these poor mid-level lapse rates will 
likely act to limit the amount of instability that can develop ahead 
of the front. Most short-term guidance suggests MLCAPE should range 
between 250-750 j/kg. Mid-level winds are forecast to strengthen 
slightly, although only modest veering with height will likely limit 
effective bulk shear values to 30-35 kt. 


Multicells and line segments along the front should pose an isolated 
threat for strong to locally damaging winds through the afternoon, 
with perhaps marginally severe hail in a transient supercell 
structure also possible. The eastward extent of this isolated threat 
will likely be limited by the previously mentioned pocket of 
slightly drier low-level air across central Georgia/northern Florida. Radar 
trends will be monitored for an increase in convective 
coverage/intensity that may necessitate watch issuance. 


.Gleason/Weiss.. 04/23/2017 


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


Attention...WFO...ffc...tae... 


Latitude...Lon 33258455 33428414 33398360 33098332 32768321 32058330 
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