U.S. Severe Weather Forecast (Previsão Convectiva)

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Storm Prediction Center ac 231959 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0259 PM CDT Thu Mar 23 2017 


Valid 232000z - 241200z 


..there is a slight risk of severe thunderstorms this afternoon and 
evening over parts of the High Plains... 


..there is a marginal risk of severe thunderstorms from parts of 
Minnesota/Iowa southward into Texas... 


..there is a marginal risk of severe thunderstorms over central and 
South Florida... 


... 
Strong to severe thunderstorms are expected from parts of the 
central and Southern Plains to the mid Missouri Valley late this 
afternoon into tonight, offering hail and damaging gusts. 
Thunderstorms with a marginal risk for severe wind and hail remain 
possible this afternoon into the early evening across parts of 
central and southern Florida. 


..western Texas to western Kansas and NE... 
The previous forecast issued for these areas remains valid into 
tonight, with no changes needed. 


..central and South Florida... 
No changes are needed for the marginal severe risk area across 
central and South Florida as storms continue to develop and spread to the 
west/southwest within a moderately unstable environment. The 
general thunderstorm area has been expanded a little north across 
west-central Florida (to the north and northeast of tampa), where an area 
of showers with sporadic thunderstorm development will persist 
through the late afternoon, advancing to the west/southwest. 


..southeast ND... 
The general thunderstorm area has been expanded a little to the 
north, given a recent lightning strike or two in this area, within a 
regime of low-level warm advection near the northeast extent of a 
surface boundary. 


.Peters.. 03/23/2017 


Previous discussion... /issued 1125 am CDT Thu Mar 23 2017/ 


A large upper trough is moving eastward across the western states 
today. Upper-level height falls and associated large-scale forcing 
for ascent will spread into the High Plains this afternoon, helping 
to initiate scattered thunderstorms. Activity will likely form along 
the dryline over western Kansas and the western Texas Panhandle, but also 
in a region of stronger low level warm advection and lift across 
western and central NE. This scenario will result in a 
several-hour-long period of risk of severe storms capable of large 
hail and damaging winds in these areas. 


... 
The primary forecast problem today is the limited low-level moisture 
and capping inversion in place. 12z models suggest that storms will 
develop in the 4-6pm window as stronger forcing impinges on the 
dryline. Forecast soundings suggest this activity will be mainly 
high-based. This will promote strong downdraft winds and 
occasionally intense updrafts capable of large hail. Present 
indications are that storms will not progress very far eastward this 
evening before beginning to weaken due to the onset of diurnal 
cooling. 


..northwest KS/NE... 
Forcing for convection will be more subtle over NE this afternoon 
and evening. However, this area will be in proximity to the surface 
warm front and weak cyclogenesis, where stronger low level vertical 
shear is forecast. Storm Mode will likely be more 
discrete-supercell in this area, with the potential for an isolated 
storm or two capable of very large hail or significant wind gusts. 
Low-level moisture will be limited, which should preclude a more 
substantial tornado threat. 


... 
Few changes have been made to the marginal risk for this region. 
Strong daytime heating and sufficient cape will promote scattered 
afternoon thunderstorms today. Relatively steep low and mid-level 
lapse rates suggest that hail will be possible in the stronger 
cells. The coverage of severe storms is expected to remain low, so 
will maintain the marginal categorical risk. 


$$ 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 231747 
flz000-232015- 


Mesoscale discussion 0310 
National Weather Service Storm Prediction Center Norman OK 
1247 PM CDT Thu Mar 23 2017 


Areas affected...central and southern Florida Peninsula 


Concerning...severe potential...watch unlikely 


Valid 231747z - 232015z 


Probability of watch issuance...20 percent 


Summary...thunderstorms will continue to increase in intensity and 
coverage the next few hours but will pose a low threat for 
marginally severe hail and brief wind gusts through the afternoon. 


Discussion...widely scattered thunderstorms have percolated along 
the East Coast of the central and southern Florida Peninsula through 
the late morning hours ahead of a weak upper-level 
perturbation...with one cell now showing some organization and weak 
mid-level rotation moving southward into St. Lucie County. 
Mixed-layer cape of 500-1250 j/kg aided by mid-level lapse rates of 
7.5-8 c/km...somewhat larger than typical for late March in southern 
Florida...should continue to allow for updrafts strong enough to 
support small hail production. Marginally severe hail and brief 
severe wind gusts are possible in the strongest updrafts that show 
some mid-level rotation. 


As low-level lapse rates steepen in afternoon heating, the larger 
evaporative cooling should strengthen/amalgamate cold pools that 
spread south and southwest to the Gulf of Mexico coast. Weak wind 
shear in the lowest 1 km directed toward the cold pool motion should 
augment the tendency for cold pools to spread rapidly south and 
west. Although mean wind speeds are relatively weak, vertical bulk 
wind shear magnitudes of 25-35 kt in the 1-8 km layer should 
continue to support some thunderstorm organization for the expected 
continuation of south-southwesterly storm motions. Otherwise...the 
primary Mode will be multicellular/pulse in nature with storms 
propagating somewhat discretely along the spreading cold pools. The 
intensity and coverage of the threat is expected to remain low 
enough to prevent a watch. 


.Coniglio/Hart.. 03/23/2017 


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


Attention...WFO...mfl...mlb...key...tbw... 


Latitude...Lon 28038068 27508032 26548003 25708017 25258037 25148081 
25218109 25868156 26348204 26938234 27268249 27728256 
28138234 28308161 28278112 28038068