U.S. Severe Weather Forecast (Convective Outlook)

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000 
acus01 kwns 221948 
swody1 
Storm Prediction Center ac 221947 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0247 PM CDT Mon Apr 22 2019 


Valid 222000z - 231200z 


..there is a slight risk of severe thunderstorms from southeast nm 
into the Texas South Plains and far southwest OK... 


... 
Scattered severe thunderstorms capable of mainly hail and damaging 
winds are possible from southeast New Mexico into parts of West 
Texas and southwest Oklahoma late this afternoon and evening. 
Isolated severe storms will also be possible across parts of 
southern Wisconsin, eastern Iowa, and northern Illinois through the 
evening hours. 


... 


Convection has begun to increase in intensity across eastern Iowa 
where strong heating and modest increases in boundary layer moisture 
has resulted in weak destabilization. An 18z radiosonde observation from dvn indicated 
some weak capping around 850mb but this should be overcome by 
increased ascent spreading over the tri-state region currently. 
Steep midlevel lapse rates and deep boundary layer mixing will 
support a few strong to severe storms capable of marginal hail and 
some locally damaging wind gusts. No changes have been made to the 
previous outlook. For more info, see recently issued mesoscale discussion 419. 


... 


Stronger ascent associated with southeastward progressing upper low 
over the lower Colorado valley will continue to spread northeast into the 
southern rockies/High Plains vicinity late this afternoon into this 
evening. Towering cumulus over higher terrain in nm and northern Mexico 
indicate environment is becoming more favorable for thunderstorm 
development in the next few hours. A corridor of storms from 
southeast nm into southwest OK ahead of a surface front still 
appears favorable for isolated to scattered severe storms through 
this evening. Large hail and damaging wind will be the main concerns 
with this threat. Ongoing forecast remains on track and no changes 
have been made. 


.Leitman.. 04/22/2019 


Previous discussion... /issued 1116 am CDT Mon Apr 22 2019/ 


... 
A couple of mid-level waves will provide impetus for potential 
severe weather later today - one currently centered over western 
Iowa that will migrate northeastward toward lower Michigan and 
another centered over the lower Colorado River valley that will 
migrate southeastward into northwestern Mexico. At the surface, a 
low over northeastern Iowa will migrate eastward across southern 
Wisconsin and into northern lower Michigan today - generally along a 
west-southwest-east-northeast oriented surface warm front. A cold front will extend 
south-southwest from this low across Missouri and Oklahoma, 
ultimately transitioning into a stationary boundary across the Texas 
South Plains and vicinity. Lee surface troughing will extend from 
south-central New Mexico into far West Texas throughout the forecast 
period. 


..eastern New Mexico eastward through central Oklahoma... 
Morning satellite/observations indicate limited solar insolation 
beneath a widespread cirrus shield. However, gradual low-level 
moistening was occurring across portions of southeastern nm and far 
West Texas near the surface trough axis. Surface flow was beginning 
to take on a more easterly component north of the front across the 
Texas South Plains, and these trends should continue throughout the 
day. 


Later today, a shortwave trough currently over northern Mexico will 
eject northeastward toward West Texas. Ascent associated with that 
feature, lift along the stationary front, and low-level upslope will 
result in scattered to numerous thunderstorm development. Though 
low-level wind fields should be weak, steep mid-level lapse rates 
and strong deep shear will result in organized storms capable of 
hail and damaging wind gusts. Storms should grow upscale into one 
or two linear complexes and forward-propagate eastward along/near 
the surface boundary especially within the slight risk area. A few 
storms will also develop into portions of southwestern Oklahoma and 
pose a hail risk. The threat should mostly be diurnally driven, 
although some hail/wind risk may persist overnight given forecast 
strengthening of a low-level jet across West Texas. 


..Wisconsin, Illinois, and far eastern Iowa... 
Continued surface heating along and ahead of the surface low and 
mid-level wave will result in a few thunderstorms this afternoon 
that will spread eastward across the marginal risk area. Modest 
mid-level lapse rates and mid-50s f dewpoints will tend to limit 
buoyancy. However, the deepening low will Foster slightly backed 
low-level flow later today, which may result in a few supercellular 
structures. Damaging winds and perhaps a tornado or two are 
possible with this activity - especially with any updrafts that can 
favorably interact with the warm front over central Wisconsin. 


Later tonight, forcing associated with the amplifying mid-level wave 
may result in a very isolated damaging wind threat in northern lower 
Michigan, although it is unclear if surface-based convective 
updrafts will persist across cold waters of Lake Michigan. 


$$ 

Mesoscale Discussion


000 
acus11 kwns 221942 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 221942 
ilz000-wiz000-iaz000-mnz000-222145- 


Mesoscale discussion 0419 
National Weather Service Storm Prediction Center Norman OK 
0242 PM CDT Mon Apr 22 2019 


Areas affected...portions of eastern Iowa...northwest 
Illinois...southwest Wisconsin 


Concerning...severe potential...watch unlikely 


Valid 221942z - 222145z 


Probability of watch issuance...20 percent 


Summary...isolated severe storms, capable of producing damaging wind 
gusts and marginally severe hail, will be possible over the next 
several hours. A ww is not anticipated at this time. 


Discussion...a 1012 mb surface low is slowly translating across 
Iowa, in tandem with a 500-mb shortwave trough and associated 
differential cva, providing modest deep-layer ascent to portions of 
the upper-Mississippi Valley. Marginal destabilization has 
transpired over the past few hours, with limited solar radiation 
penetrating the upper-level cirrus deck and warming the boundary 
layer. Modest heating is expected to continue, and with the 
continued deep-layer ascent slowly increasing across the area, a 
gradual increase in convection may be expected throughout the 
afternoon hours. 


The vertical thermodynamic profile across the area is relatively 
modest, with steep sfc-3km lapse rates at nearly 8 c/km, and 7 c/km 
lapse rates above 3 km (based on the dvn 18z observed sounding), but 
with mediocre low-level moisture (dewpoints mainly below 60f, with a 
near 20f T/TD spread). As a result, MLCAPE is expected to remain 
around/below 1000 j/kg through the afternoon, amidst 30-45 knots of 
effective bulk shear and weak low-level shear, supporting a marginal 
severe threat. The relatively steep low-level lapse rates may 
promote damaging wind gusts with the stronger downdrafts. Given the 
modest lapse rates above 3 km, a few instances of marginally severe 
hail may also occur. Still, the combination of marginal deep-layer 
ascent, buoyancy, and vertical wind shear, suggests that the severe 
threat will be isolated, with a severe ww issuance not expected. 


.Squitieri.. 04/22/2019 


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


Attention...WFO...lot...mkx...dvn...arx...dmx... 


Latitude...Lon 41308989 41709275 42299280 42869248 43479204 43649129 
43399056 43068988 42358944 41608924 41308989