U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 230534 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1234 am CDT Thu Mar 23 2017 


Valid 231200z - 241200z 


..there is a slight risk of severe thunderstorms late this 
afternoon and evening across central and southern portions of the 
High Plains... 


..there is a marginal risk of severe thunderstorms across 
surrounding areas of the central and Southern Plains into the middle 
Missouri Valley... 


..there is a marginal risk of severe thunderstorms today across 
parts of southern Florida... 


... 
Strong thunderstorms are expected from parts of the central and 
Southern Plains into the mid Missouri Valley late this afternoon 
into tonight, accompanied by potential for severe hail and damaging 
surface gusts. Thunderstorms with a risk for severe wind and hail 
are also possible across parts of southern Florida. 


... 
Much of the nation will remain under the influence of split 
westerlies emanating from the mid-latitude Pacific. Within this 
regime, one prominent northern stream trough is forecast to continue 
to progress away from the Atlantic Seaboard. As it does, models 
suggest remnant southern stream troughing will linger over the 
Bahamas/parts of southern Florida and the Caribbean, while short 
wave ridging builds to its northwest (across the southeast), ahead 
of a more significant southern stream short wave trough forecast to 
progress east of the southern Great Basin/lower Colorado valley, 
through the southern rockies/High Plains by 12z Friday. 


In association with this latter feature, models generally indicate 
that significant surface cyclogenesis will initiate across parts of 
northeastern Colorado during the day today, before redeveloping 
southeastward into western Kansas tonight, in closer proximity to a 
lower/mid tropospheric cyclone developing within the larger-scale 
trough as it crosses the southern rockies. This should be 
accompanied by considerable strengthening of southerly low-level 
flow through portions of the plains into Mississippi Valley, 
particularly by tonight, when speeds around the 850 mb level are 
expected to reach 50-70 kt across much of the southern into Central 
Plains. 


Despite the favorable evolving large-scale flow, a substantive 
return flow of moisture from the Gulf of Mexico appears unlikely 
during this period due to recent drying across much of the Gulf 
region. This probably will limit the extent of the convective 
potential today and tonight. However, steep mid-level lapse rates 
associated with a plume of elevated mixed-layer air emerging from 
the southern rockies/Mexican plateau region may contribute to 
sufficient destabilization to support at least some risk for severe 
storm activity across the central and Southern Plains into the mid 
Missouri Valley. A remnant plume of elevated mixed-layer air, which 
has advected considerably south and east of the plains, may also 
contribute to some severe weather potential across parts of southern 
Florida. 


..central and Southern Plains into mid Missouri Valley... 
The lack of substantive deep return flow of moisture, coupled with 
downward mixing of dry lower/mid tropospheric air, will be 
problematic with regard to severe thunderstorm potential today. 
Guidance continues to suggest that the most substantive 
boundary-layer moistening may be confined to a narrow corridor along 
the Lee surface trough across parts of western Kansas (perhaps as 
far south as parts of the Texas/Oklahoma Panhandle region) into 
southwestern Nebraska by the 21-23z time frame this afternoon. Even 
this may be characterized by surface dew points only on the order of 
55-60f. However, beneath steep mid-level lapse rates, this may be 
sufficient for a corridor of mixed-layer cape up to around 1000 
j/kg, as a 50-70 kt southwesterly mid-level jet streak noses across 
the region. 


While the primary upper impulse may still be lagging near or to the 
west of The Rockies, the environment along/east of the sharpening 
dryline probably will be conducive to discrete supercell 
development. Some risk for at least weak/brief tornadoes may exist 
with initial development, but severe hail may be the most prominent 
risk with this activity as it develops northeastward/eastward 
through early evening. 


As the main impulse/developing mid-level circulation emerges from 
the intermountain region this evening, storms with severe hail 
potential may become focused within an area of strengthening 
low-level warm advection across north central and northeastern 
Nebraska. Additional storm development may become focused on the 
leading edge of stronger lower/mid-tropospheric cooling, from parts 
of western Kansas into the Texas South Plains. In the presence of 
intensifying environmental wind fields, potentially damaging wind 
gusts seem likely to be the primary threat with an evolving squall 
line. This could continue into the overnight hours, eastward toward 
the Lower Plains, but it remains unclear at this time if instability 
will remain sufficient to support vigorous convection east of 
western Kansas/Oklahoma and northwest Texas. 


..South Florida... 
Relatively steep mid-level lapse rates associated with remnants of a 
plume of elevated mixed-layer air, and cold air aloft, could 
contribute to an environment conducive to storms capable of 
producing severe hail and wind gusts. This may be aided by forcing 
for ascent associated with an impulse digging into lingering upper 
troughing across the region. However, this remains at least one 
Point of considerable spread among the model output, and severe 
weather potential remains too uncertain for more than 5 percent 
severe probabilities at this time. 


.Kerr/Dean.. 03/23/2017 


$$ 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 222030 
wyz000-utz000-idz000-nvz000-222230- 


Mesoscale discussion 0308 
National Weather Service Storm Prediction Center Norman OK 
0330 PM CDT Wed Mar 22 2017 


Areas affected...northern Utah...northeast Nevada...southeast 
Idaho...southwest Wyoming 


Concerning...severe potential...watch unlikely 


Valid 222030z - 222230z 


Probability of watch issuance...5 percent 


Summary...an increase in thunderstorm coverage and intensity is 
expected through about 00z, with small to marginally severe hail 
possible. 


Discussion...sporadic weak thunderstorm activity has been noted 
ahead of a cold front over central Nevada and within a surface trough 
from southern Nevada across Utah. Strong heating along with cooling 
temperatures aloft have resulted in a steep lapse rate environment, 
which is helping to create several hundred j/kg of MUCAPE despite 
dewpoints only in the 30s in most areas. Shear profiles are 
favorable for cellular activity, with increasing mid to high level 
flow elongating hodographs. This should help aid in hail production, 
mostly small. However, a cell or two could produce marginally severe 
hail and gusty winds over the next few hours as heating persists 
especially across northern Utah into southeast Idaho and southwest Wyoming. 


.Jewell/Hart.. 03/22/2017 


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


Attention...WFO...riw...slc...pih...lkn... 


Latitude...Lon 41450875 40191207 39891371 40001477 40521580 40981554 
41241449 42091358 42831240 42811128 42600981 42230909 
41450875