- Day Three
acus01 kwns 192000
Storm Prediction Center ac 191959
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0259 PM CDT Tue Jun 19 2018
Valid 192000z - 201200z
..there is an enhanced risk of severe thunderstorms across parts of
the Central Plains...
..there is a slight risk of severe thunderstorms outside of the
enhanced risk area in the Central Plains and in the mid-Atlantic...
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.
Several changes have been made to the outlook for this issuance. The
first change is to add a 10 percent tornado probability in parts of
northeastern Colorado. A tornadic supercell is ongoing to the
northeast of the Denver Metro area. This storm is part of a cluster
of storms that are expected to maintain a severe threat and move
eastward across northeast Colorado over the next few hours. The
storms should have potential to produce more tornadoes through early
evening. The second change is to expand the enhanced risk area
including the 30 percent and significant hail contours northwestward
across northeastern Colorado where several severe hail storms are
ongoing. This activity is forecast to move eastward across the
remainder of northeastern Colorado and into western Kansas/southern
Nebraska later this evening. The final change to this outlook is to
trim the northern edge of the slight risk area in the mid-Atlantic
region behind a cold front that is moving southward into northern
Previous discussion... /issued 1129 am CDT Tue Jun 19 2018/
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
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 Maryland 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.
acus11 kwns 191955
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 191954
Mesoscale discussion 0793
National Weather Service Storm Prediction Center Norman OK
0254 PM CDT Tue Jun 19 2018
Areas affected...eastern Colorado
Concerning...Tornado Watch 191...
Valid 191954z - 192200z
The severe weather threat for Tornado Watch 191 continues.
Summary...severe weather threat continues across Tornado Watch 191.
Discussion...severe and tornado warned storms continue across the
northern half of the watch. The storms have strengthened into
supercells and should remain discrete in the coming hours.
Three-inch hail has already been reported in Arapahoe County, and
the severe hail/wind and tornado risk will continue into this
evening. Latest hrrr/rap guidance indicates the storms will
eventually merge and form a mesoscale convective system this evening across far eastern
Colorado, western Kansas, and southwestern Nebraska. Some storms
could redevelop behind these initial storms along the northern Front
Farther south, the cumulus field has struggled to build, but
confidence remains that a discrete storm or two will form along the
southern Front Range and move eastward. There is good potential for
these storms to develop into discrete supercells capable of
producing large hail, damaging winds, and a tornado. Additionally, a
new storm has just formed in far southeast Colorado near the surface
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 41010620 40410575 39950567 39870538 39230540 38810532
38630515 38050506 37890553 37630550 37600524 37260518
36960499 37010203 40990203 40970536 41010620