U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 250518 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1218 am CDT Sat Mar 25 2017 

Valid 251200z - 261200z 

..there is a slight risk of severe thunderstorms today across much 
of the lower and middle Mississippi Valley region... 

..there is a marginal risk of severe thunderstorms across 
surrounding areas of the Mississippi and lower Ohio valleys and Gulf 
Coast states... 

Thunderstorm activity is likely across much of the lower and middle 
Mississippi Valley region today. This may be accompanied by some 
risk for severe wind gusts, hail, and perhaps a tornado or two. 

Much of North America will remain under the influence of split 
westerlies emanating from the mid-latitude Pacific. Although 
northern stream short wave ridging is now building to the north of a 
nearly vertically stacked southern stream closed low, now crossing 
the south Central Plains, the latter impulse appears likely to 
remain slowly progressive today and tonight, as an upstream southern 
stream short wave trough progresses inland of the California coast 
through The Four Corners region. 

In lower levels, boundary layer moisture over the Gulf of Mexico 
remains quite modest, but a gradually moistening and deepening of 
the boundary layer does appear underway. Northward return flow may 
become increasingly cut-off by tonight, due to an increasingly 
westerly component to the low-level flow across the central into 
eastern Gulf Coast states, however a westward return flow through 
the lower Rio Grande Valley may commence in response to surface 
pressure falls to the Lee of the southern rockies. 

..lower and middle Mississippi Valley... 
Models indicate considerable further weakening of the south Central 
Plains lower/mid tropospheric cyclone (and associated wind fields) 
as it turns northeast of the Ozarks through the middle Mississippi 
Valley by late tonight. Within/above the surface warm sector, deep 
layer wind fields are expected to generally decrease into the 30-50 
kt range during the day. 

Boundary layer moisture may be a bit higher than the past couple of 
days within a pre-frontal plume wrapping into the surface low 
center, but this may be mostly confined beneath relatively weak 
mid-level lapse rates, remaining largely displaced just ahead of the 
axis of coldest mid-level temperatures. 

Still, capping likely will be weak, and large-scale forcing for 
ascent may support both discrete thunderstorm development and one or 
more bands of thunderstorms activity overspreading the region today. 
Given the lingering strength of the wind fields, precipitation 
loading coupled with downward momentum Transfer could support at 
least marginally severe wind gusts in strongest storms. Some hail 
also appears possible, and an isolated tornado or two may not be out 
of the question. 

.Kerr/Marsh.. 03/25/2017 


Mesoscale Discussion

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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 250806 

Mesoscale discussion 0328 
National Weather Service Storm Prediction Center Norman OK 
0306 am CDT Sat Mar 25 2017 

Areas affected...parts of northeastern la and western/central MS 

Concerning...Severe Thunderstorm Watch 84... 

Valid 250806z - 250900z 

The severe weather threat for Severe Thunderstorm Watch 84 

Summary...an isolated strong to damaging wind threat continues 
across Severe Thunderstorm Watch 84. A downstream watch/substantial 
extension in area of the current watch into more of central/eastern 
MS does not appear likely. 

Discussion...a surface observation from Greenville MS (kglh) 
revealed a peak wind gust of 49 kt at 0734z with a bowing line 
segment crossing the MS river. Isolated strong to damaging wind 
gusts should remain possible along the length of a line of 
thunderstorms that will move eastward into parts of western/central 
MS over the next couple of hours. Instability becomes more marginal 
with northward and eastward extent across MS, as surface dewpoints 
decrease from the mid 60s to mid/upper 50s. Still, some weak 
instability persists near and just east of the MS river, and the vwp 
from kdgx shows southerly low-level winds of 35-50 kt veering to 
southwesterly at mid-levels, which should support organization of 
the line in the short term. However, the marginal thermodynamic 
environment downstream will likely act to limit the overall severe 
threat into central/eastern MS, and a downstream watch or 
substantial eastward extension in area of the current watch does not 
appear likely. 

.Gleason.. 03/25/2017 

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


Latitude...Lon 31399112 31449192 32589180 33009108 33359096 33689091 
33679031 33638999 31449021 31399112