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Day 1 Outlook Convective Tornado
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Categorical Day1 1630Z Outlook
  
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 Forecast Discussion


540 
ACUS01 KWNS 191630
SWODY1
SPC AC 191629

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1129 AM CDT Tue Jun 19 2018

Valid 191630Z - 201200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EASTERN COLORADO AND WESTERN KANSAS...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE NORTHERN
VIRGINIA AREA...

...SUMMARY...
Severe thunderstorms are expected across the Central Plains this
afternoon and evening, while marginally severe thunderstorms are
expected from the Midwest into the Mid Atlantic region.

...Central Plains...
Upper low over the northern Rockies is forecast to move eastward and
open into a short-wave trough as stronger winds on the southern
periphery of the low translate eastward into the Central Plains
through tonight.  Water vapor imagery indicates a speed maxima
moving eastward across southern Utah at this time, and this feature
is expected to move into the central High Plains by late
afternoon/evening, enhancing large scale ascent over the area.

A surface low over southeast Colorado is expected to move slowly
eastward with a frontal boundary extending across western Kansas
into southeast Nebraska.  This will maintain an easterly component
to the low-level winds into the Plains of southeast Wyoming and most
of eastern Colorado with ample moisture continuing north of the
boundary.  Visible imagery shows limited clouds over much of eastern
Colorado, western Kansas into southwest Nebraska which will permit
stronger diabatic heating to occur this afternoon.  With moderately
steep mid-level lapse rates in place, the environment will become
moderately unstable with MLCAPE values reaching 1500-2500 J/kg this
afternoon.

Several clusters of storms are expected to develop over parts of
eastern Colorado, southeast Wyoming and western Kansas during the
mid-late afternoon as heating combined with approaching large scale
ascent aloft and upslope flow weaken the cap.  Wind profiles will
exhibit strong directional shear with height with effective shear of
40-50 kt which will enhance storm organization and intensity.  A few
supercell storms are likely to develop and spread eastward,
especially over parts of eastern Colorado into far western Kansas
and southwest Nebraska.  These will pose a threat for very large
hail, damaging wind gusts, and possible tornadoes during the late
afternoon and early evening.  12Z CAM/HREF guidance indicates
potential for storms to grow upscale into one or two eastward moving
linear MCSs this evening with damaging winds becoming the greater
threat.  Activity will continue to progress eastward into the
overnight hours with a gradual weakening trend developing by 03-06Z.

...Southern Maryland and Northern Virginia area...
Despite warm mid-level temperatures, strong diabatic heating of a
very moist low-level air mass is resulting in moderate instability
with MLCAPE of 1500-2000 J/kg.  Storms are forming along a southward
moving cold front that will move into the area this afternoon, with
additional storms expected to develop over the mountains and move
east-southeastward.  Sufficient west-northwest winds above the
surface coupled with low-level inverted-V soundings and large DCAPE
values indicate potential for damaging wind gusts to occur with
stronger cells this afternoon and evening.  See MD 789 for
additional short-term details.
 
...Middle Mississippi Valley to the Upper Ohio Valley...  
A very warm and moist low-level air mass remains in place along and
south of a front that extends across the region.  Weak winds aloft
and limited vertical shear indicate potential for weakly organized
and pulse storm characteristics, however, continued low-level
heating will result in moderate instability with MLCAPE of 1500-2000
J/kg.  Potential will exist for a few wet microbursts to develop as
storms continue to develop from Missouri into the upper Ohio Valley
region this afternoon but uncertainty regarding overall storm
organization will preclude introduction of higher wind probability
values at this time.

..Weiss/Nauslar.. 06/19/2018

$$

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