U.S. Severe Weather Forecast (Convective Outlook)

Today
Tomorrow
Day Three

000 
acus01 kwns 210550 
swody1 
Storm Prediction Center ac 210549 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1249 am CDT sun Jul 21 2019 


Valid 211200z - 221200z 


..there is a slight risk of severe thunderstorms across portions of 
the Central Plains and lower MO valley... 


... 
Severe thunderstorms capable of strong wind gusts and isolated hail 
are possible from the Central Plains eastward into the lower 
Missouri Valley today. 


..Central Plains...Lower MO valley... 
recent surface analysis places a low near the Colorado/KS/OK border 
intersection. A composite boundary/stationary front extends 
northeastward from this low across Kansas to another low near the 
Kansas/NE/MO border intersection. Ongoing convective line across MO has 
modified the boundary across northern MO, pushing it southward into 
central MO. Mesoscale convective vortex associated with ongoing showers and thunderstorms 
across southeast Colorado and western Kansas is expected to track 
northeastward along or just north of this stationary front early 
this morning and likely play a role in convective development this 
afternoon. Poor performance within the guidance of convectively 
induced, meso-Beta scale features suggests its evolution is 
uncertain. Current expectation is for the mesoscale convective vortex to drift northeastward 
early this morning before then turning more eastward in response to 
the shortwave trough dropping through the northern plains. 
Thunderstorm development is then anticipated along the southern 
periphery of this mesoscale convective vortex across northeast Kansas and southeast NE. 
Previously mentioned stationary front as well as modified outflow 
may also be in this area, providing additional foci for convective 
initiation. 


The air mass where this convective initiation is expected to occur 
will be warm (temperatures in the 90s), very moist (dewpoints in the 
low to mid 70s), and strongly buoyant (mlcape over 2500 j/kg). As a 
result, strong updrafts are anticipated. Vertical shear will be 
modest, so the initial development will likely become 
outflow-dominant quickly, with subsequent development anticipated on 
the resulting cold pool. Strong wind gusts are the primary severe 
threat but some hail is possible with the early development. 
Presence of several surface boundaries suggests there is a low 
probability tornado threat as well. 


..mid MS and Ohio valleys... 
Weak surface convergence along a slow-moving cold front amidst very 
warm and moist conditions is expected to result in scattered showers 
and thunderstorms from the mid MS valley across the Ohio Valley. 
Vertical shear will be very weak, limiting storm organization and 
longevity. Even so, a few water-loaded downbursts capable of 
damaging wind gusts are possible. 


... 
A subtle speed Max/low-amplitude shortwave trough is currently 
moving into the lower Great Lakes. Lift associated with this 
shortwave is likely contributing to the areas of light reflectivity 
from Lake Ontario southward into north-central PA. This shortwave is 
expected to continue northeastward, reaching Maine later this 
morning. Modest Theta-E advection is expected ahead of this 
shortwave, contributing to enough instability for thunderstorms. A 
few severe storms are probable, with strong wind gusts as the 
primary threat. Some isolated large hail is also possible. 


..Central High plains... 
Thunderstorms are expected to initially develop across the higher 
terrain before moving out into the moist Post-frontal air mass 
across the region. Easterly/northeasterly low-level flow beneath the 
northwesterly flow aloft will contribute to moderate vertical shear 
(highest across northern portions of the region) and the potential 
for a few stronger, more organized storms capable of strong wind 
gusts and isolated hail. 


.Mosier/Bentley.. 07/21/2019 


$$ 

Mesoscale Discussion


000 
acus11 kwns 210945 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 210945 
mez000-211215- 


Mesoscale discussion 1559 
National Weather Service Storm Prediction Center Norman OK 
0445 am CDT sun Jul 21 2019 


Areas affected...portions of ME 


Concerning...severe potential...watch unlikely 


Valid 210945z - 211215z 


Probability of watch issuance...20 percent 


Summary...an isolated large hail and strong/gusty wind threat may 
develop with storms moving eastward this morning. Watch issuance is 
unlikely, although trends will be monitored. 


Discussion...a subtle vorticity maximum embedded within the 
mid-latitude westerlies is supporting isolated convective activity 
across southern Quebec this morning. Even though low-level winds are 
generally weak across ME, they quickly increase above 3 km per kcbw 
vwp and rap forecast soundings. Long, nearly straight hodographs 
owing to mainly speed shear are supporting around 40-50 kt of 
effective bulk shear in a narrow corridor over ME. This shear should 
organize updrafts within cells approaching the international border 
as of 0945z, and a couple supercells appear possible. Still, the 
primary limiting factor that will likely keep the overall severe 
threat isolated is weak instability. Modest mid-level lapse rates 
(5.8 c/km in the 700-500 mb layer) observed on the 00z sounding from 
car and surface temperatures near the diurnal minimum should support 
MLCAPE of no more than 500-1000 j/kg. This combination of weak 
instability and strong shear may allow for isolated instances of 
marginally severe hail and perhaps some strong/gusty winds with the 
most robust storms. Current expectations are for the severe threat 
to remain isolated, and watch issuance appears unlikely at this 
time. 


.Gleason/grams.. 07/21/2019 


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


Attention...WFO...car...gyx... 


Latitude...Lon 45417085 45587072 45787042 46087032 46337021 46216884 
45876741 44986747 44616796 44656892 44806997 45417085