U.S. Severe Weather Forecast (Convective Outlook)

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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 232053 
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Mesoscale discussion 0312 
National Weather Service Storm Prediction Center Norman OK 
0353 PM CDT Thu Mar 23 2017 


Areas affected...extreme southeastern Wyoming...portions of the 
Nebraska Panhandle...southwestern Nebraska...extreme northwestern 
Kansas 


Concerning...severe potential...watch likely 


Valid 232053z - 232300z 


Probability of watch issuance...80 percent 


Summary...widely scattered thunderstorms will develop in the next 
few hours. Severe hail and wind gusts are the main threat, but a 
brief tornado or two are possible in a narrow zone near and around 
the warm front. A Severe Thunderstorm Watch will likely be needed. 


Discussion...large-scale forcing for ascent associated with an upper 
low is slowly approaching the area and contributing to a broad area 
of lowering surface pressures across the Central High plains. 
Separate low pressure centers...one near cys and the other over 
southeastern Colorado should consolidate into a single low over 
northeastern Colorado this evening. A dryline stretches from far 
southwestern Kansas to near Oga, where it intersects an east-west warm front 
that has been reinforced by persistent low-level clouds and showers 
from lbf to points east. 


Very steep mid-level lapse rates...from 8.5 to 9 c/km...and a tongue 
of mid-to-upper 50s boundary layer dewpoints...are contributing to 
MLCAPE of 1000-2000 j/kg in the warm, moist air mass. Deep layer 
bulk shear of 50-70 kt oriented at a large angle to the dryline and 
warm front will support discrete supercells. Any storms that 
develop along the dryline south of the warm front will move into a 
high-local environment supportive of severe wind gusts, and steep 
lapse rates will support severe hail with any of the storms. As 
storms move northeast and interact with the warm front...local 
enhancement of low-level shear and lowered LCLs could support 
low-level rotation. However, given the strong reinforcement of the 
cool air north of the warm front and relative fast storm 
motions...35-40 kt...oriented at a large angle to the front, only a 
brief period will exist where a tornado or two will be possible 
before the storms interact with the stable boundary layer. Severe 
hail will still be possible with these storms, however, as they 
become elevated above the front. 


Although the boundary layer is drier over the Nebraska 
Panhandle...with dewpoints in the upper 30s to mid 40s...very steep 
low and mid-level lapse rates are supporting 250-1000 j/kg of 
MUCAPE. Deep inverted-v profiles suggest severe wind gusts and hail 
are the primary threats in this area, although severe hail will also 
be possible. 


Given the above expectation of a severe threat emerging in the next 
few hours, a Severe Thunderstorm Watch will likely be needed for 
parts of the area. 


.Coniglio/Hart.. 03/23/2017 


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


Attention...WFO...Gid...lbf...gld...cys... 


Latitude...Lon 41799879 42199948 42680117 42830256 42710339 42520411 
42210447 41720443 41530428 41140376 41060308 41130226 
41010171 40490120 40330105 40100095 39800072 39670002 
39879901 40569859 41319846 41799879