- Day Three
acus01 kwns 220601
Storm Prediction Center ac 220559
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1259 am CDT Fri Jun 22 2018
Valid 221200z - 231200z
..there is an enhanced risk of severe thunderstorms from eastern Colorado
into central OK...
..there is a slight risk of severe thunderstorms across portions of
the lower MS valley...southeast...and mid-Atlantic...
Scattered severe storms will be possible across parts of the
central/Southern Plains, southeast and mid-Atlantic states today.
..southeast into the Ohio Valley and mid-Atlantic...
Upper low currently moving through the middle MS valley is expected
to gradually move northeastward through the Ohio Valley while
devolving into an open wave. A series of vorticity maxima will
rotate around this upper low, accompanied by anomalously strong
mid-level flow, which is expected to spread across northern portions
of the southeast and into the mid-Atlantic.
Thunderstorms will likely be ongoing at the beginning of the period
as one of the lobes of vorticity moves into the lower MS valley,
providing the impetus for convection within the moist and
low-inhibition airmass. Despite the unfavorable timing, the airmass
will likely be moderately unstable with temperatures in the low 80s
and dewpoints in the mid 70s helping support MLCAPE over 2000 j/kg.
As previously mentioned, seasonally strong flow aloft will increase
bulk shear and the potential for more robust, longer-lived updraft
organization. Consequently, these early storms will likely pose a
severe threat from northern la/southern Arkansas eastward across central
MS and Alabama. Water-loaded downbursts and hail are the primary threats.
A tornado or two cannot be ruled out, particularly on the western
periphery of any convective line where enhanced storm-relative
helicity from any southwestward progressing storms could contribute
to locally higher tornado threat.
Vorticity maximum responsible for these early day storms will
continue eastward, likely reaching the Piedmont around or just after
peak heating. Attendant forcing for ascent coupled with airmass
destabilization will likely contribute to increased thunderstorm
coverage in this region into the evening. Farther north, more subtle
forcing may contribute to afternoon storms in the vicinity of The
Wedge front. While the overall bulk shear will be modest,
easterly/southeasterly winds near the boundary could enhanced
low-level shear while also increasing vertical vorticity along the
boundary itself. As a result, a small area of relatively enhanced
tornado probability exists across southeast Virginia.
Fast-moving shortwave trough currently entering the western Great
Basin will continue eastward, moving through the High Plains during
the afternoon and through the plains overnight. Strong Lee
cyclogenesis is anticipated ahead of this system across southeast Colorado
with resulting southerly flow encouraging moisture return into the
Central Plains/High Plains. High 50s dewpoints, possibly low 60s,
will likely arc into southeast Colorado along the northern periphery of
the surface low. Steep mid-level lapse rates advected ahead of the
approaching shortwave atop this at least moderately moist low-level
airmass will result in moderate to strong instability during the
afternoon. Additionally, increasing mid-level flow attendant to the
approaching shortwave trough atop easterly/southeasterly results in
strongly sheared environment. 0-6 km bulk shear over 50 kt is
likely. All of these factors point to the potential for
thunderstorms capable of hail over 2 inches in diameter and wind
gusts over 60 kt across eastern Colorado. Tornadoes are also possible,
particularly if storms are able to remain discrete.
Strong cold pool generation coupled with the strong forcing for
ascent and fast-moving shortwave trough all point to likelihood for
quick upscale growth into what could be a significant mesoscale
convective system. Steep mid-level lapse rates downstream into OK
coupled with a strong low-level jet also point to the potential for
a well-organized system capable of tracking much farther east than
would normally be expected given the increased convective
acus11 kwns 220706
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 220706
Mesoscale discussion 0818
National Weather Service Storm Prediction Center Norman OK
0206 am CDT Fri Jun 22 2018
Areas affected...Texas and Oklahoma panhandles...extreme northeast
New Mexico...southeast Colorado...and southwest Kansas...and far
Concerning...severe potential...watch possible
Valid 220706z - 220830z
Probability of watch issuance...40 percent
Summary...ongoing thunderstorms are increasing in coverage across
the Oklahoma and Texas panhandles. An isolated large hail or gusty
thunderstorm wind will be possible through the night. Trends will be
monitored for a possible Severe Thunderstorm Watch.
Discussion...initial thunderstorms developed during the evening
hours across southeast Colorado, northeast New Mexico, and the
northwest Texas Panhandle in response to modest warm-air advection
atop a stationary front across the area. These thunderstorms
organized into 2 or 3 primary thunderstorm cores, with the strongest
moving southeast across Dallam County, TX, and Cimarron County, OK.
Large hail is likely with this thunderstorm.
Additional thunderstorms are developing to the northeast of this
initial band of convection, with the strongest across Hansford
County, TX, as the persistent warm-air advection allows
surface-based parcels to isentropically ascend to their level of
free convection. Given the larger-scale environment across the area
-- 1000-1500 j/kg of most-unstable cape and 40-60 knots of effective
deep-layer shear -- updraft organization is possible for any
persistent updraft. Given the elevated nature of the thunderstorms,
large hail should be the primary threat, although brief, gusty
thunderstorm outflow cannot be ruled out. These thunderstorms are
expected to continue to develop/persist through the morning hours as
they move east, before weakening after sunrise as the low-level jet
veers and the warm-air advection/isentropic ascent weakens.
Trends will continue to be monitored for possible severe
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 35870316 36830332 37420286 37630194 37250060 36549940
35189948 34830037 34980232 35870316