U.S. Severe Weather Forecast (Convective Outlook)

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acus01 kwns 210601 
swody1 
Storm Prediction Center ac 210600 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0100 am CDT Wed Aug 21 2019 


Valid 211200z - 221200z 


..there is a slight risk of severe thunderstorms from the northern 
Middle Atlantic States into New England... 


... 
Severe thunderstorms are possible across parts of the northern mid 
Atlantic coast states into New England today. Additional strong to 
severe storms are possible in a corridor from the Central Plains 
into the lower Ohio Valley, and near The Rockies. 


... 
A relatively progressive upper pattern is anticipated across the 
northern third of the Continental U.S. With a pair of deep shortwave troughs 
advancing eastward and amplified shortwave ridging between them. The 
eastern shortwave trough is expected to move through the upper Great 
Lakes, central/eastern Ontario, and into southern Quebec while the 
western shortwave trough moves through the Pacific northwest into 
the northern rockies. 


At the surface, a cold front currently extends from southeast Colorado 
northeastward to a low centered near the Iowa/MN/WI border 
intersection. A warm front then extends from that low eastward 
across central lower Michigan through northeast PA and central Delaware. The 
cold front will likely remain in place through this afternoon before 
then pushing southward/southeastward into the lower Ohio Valley and 
northern portions of the Southern Plains. The eastern portion of the 
warm front will gradually lift northward throughout the day, placing 
a warm and moist air mass over much of New England by the late 
afternoon. 


..New England into the northern mid-Atlantic... 
While the vertical ascent and enhanced flow aloft with the shortwave 
described in the synopsis will remain predominantly north of the 
region, a low-amplitude, lead shortwave trough (currently moving 
through the Ohio valley) is expected to move into New England this 
afternoon. Warm and unstable air mass will be in place ahead of this 
shortwave, and the expectation is for multiple bands of convection 
to move across the region this afternoon. Some modest strengthening 
of the low-level flow (i.E. Around 30-35 kt at 850 mb) is 
anticipated ahead of this shortwave trough, lengthening hodographs 
and contributing to 0-1 km srh around 100-150 m2/s2. Overall, wind 
profiles support occasional supercell structures within 
predominantly linear multicells. Primary severe threat will be 
damaging wind gusts but isolated hail and a tornado or two are also 
possible. 


Vertical shear and forcing for ascent decrease with southern extent, 
but a warm, moist, and diurnally destabilized air mass will support 
widely scattered to scattered thunderstorm development. Wet 
downbursts capable of damaging wind gusts are possible within the 
strongest storms. 


..Central High plains into the Central Plains 
the mesoscale convective system currently moving into the NE Panhandle is expected to 
continue eastward, reaching central NE by 12z this morning. Isolated 
threat for hail and strong wind gusts will exist with this system as 
it continues into eastern NE. 


Later this afternoon, scattered thunderstorms are expected to 
develop across Kansas along the front as it begins to push southward. A 
deeply mixed air mass characterized by temperatures in the upper 
90s/low 100s and dewpoints in the low/mid 60s is anticipated ahead 
of the front. Given the amount of dry air entrainment expected and 
the lack of stronger vertical shear, updrafts will likely be 
short-lived. Even so, isolated strong wind gusts are possible. Hail 
could occur within the strongest updrafts. 


At the same time, thunderstorms are expected to develop along the 
Lee trough from south-central Colorado into central Wyoming. Mid-level flow 
here will be the same as areas farther east (across the central 
plains), but vertical shear will be stronger due to northeasterly 
surface winds. A few supercells capable of large hail and/or strong 
wind gusts are possible and a tornado cannot be completely ruled 
out. Uncertainty regarding severe thunderstorm coverage precludes 
higher probabilities with this outlook. 


..mid MS valley into the southern Ohio Valley... 
Outflow from the mesoscale convective system across NE this morning will likely move into 
southern MO and western Kentucky this afternoon. A very moist and buoyant 
air mass will be in place, with dewpoints in the 70s and MLCAPE in 
excess of 3000 j/kg. Vertical shear will be weak, limiting storm 
persistence, but updrafts are expected to be strong enough to result 
in water loading and a resulting threat for isolated strong/damaging 
wind gusts. 


.Mosier/nauslar.. 08/21/2019 


$$ 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 210815 
nez000-210945- 


Mesoscale discussion 1824 
National Weather Service Storm Prediction Center Norman OK 
0315 am CDT Wed Aug 21 2019 


Areas affected...western/central NE 


Concerning...Severe Thunderstorm Watch 608... 


Valid 210815z - 210945z 


The severe weather threat for Severe Thunderstorm Watch 608 
continues. 


Summary...some severe wind risk will continue with Bow echo moving 
across western Nebraska. Gradual weakening is expected with time, 
and downstream watch issuance is unlikely. 


Discussion...a Bow echo is moving eastward out of the NE Panhandle 
as of 08z, with increasingly disorganized elevated convection 
ongoing downstream into central NE. Relatively steep pressure rises 
and cold temperatures (falling into the 50s f) in the wake of the 
Bow suggest a somewhat well-organized cold pool, though radar 
velocities indicate that the rear-inflow jet is not overly strong, 
and observed wind speeds (where available) have been subsevere over 
the last 1-2 hours. 


While the airmass immediately downstream of the Bow likely remains 
strongly unstable (mucape of around 3000 j/kg), convectively 
overturned air emanating out of western Kansas and also central NE is 
likely to erode this instability with time, resulting in a general 
weakening trend. Some severe wind risk will persist given the 
well-established cold pool, but a general decrease in the wind risk 
is expected with eastward extent. With these factors in mind, 
downstream watch issuance into central NE is unlikely. 


.Dean/Edwards.. 08/21/2019 


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


Attention...WFO...Gid...lbf... 


Latitude...Lon 42170210 42270103 41739899 41319816 40609818 40419843 
40359896 40369949 40419997 40460068 40820154 41160159 
41370162 41670177 42010217 42170210