SPC AC 251730
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 PM CDT Mon Jun 25 2018
Valid 261200Z - 271200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
MISSOURI/MIDDLE MISSISSIPPI VALLEY REGION...
Severe storms are possible across the lower Missouri and middle
Mississippi Valley region Tuesday afternoon into Tuesday night. One
or two larger clusters of storms may eventually evolve, accompanied
by the risk for potentially damaging wind gusts and some hail.
Other strong to severe storms are possible across parts of the
southern Appalachians into southern Mid Atlantic coast, as well as
across parts of the northern Plains.
A significant short wave trough, now progressing inland of the
Pacific coast, is forecast to continue pivoting northeast of the
international border through the Canadian Prairies during this
period. In its wake, a seasonably strong and zonal belt of
mid-latitude westerlies appears likely to gradually nose across the
northern U.S. Rockies into the northern Plains. Downstream flow
will remain split, with models indicating that a compact closed low,
within broader scale southern stream troughing, will continue
migrating east/northeast of the middle/lower Missouri Valley region
into the Great Lakes region by 12Z Wednesday. As this occurs,
subtropical ridging may become an increasing influence across parts
of the southern Plains into the Southwest, with an increasingly
prominent embedded high center near the southern Rockies.
Downstream, it appears that subtropical ridging may become at least
somewhat suppressed across parts of the Tennessee Valley and
southern Appalachians into southern Mid Atlantic coast region.
...Lower Missouri/middle Mississippi Valley region...
Considerable uncertainty lingers concerning the potential convective
evolution for Tuesday through Tuesday night. Much will probably
depend on the evolution of convection across this same region
between now and 12Z Tuesday. Widespread convective cloud cover may
be present, at least initially, with convective outflow possibly
impacting a large portion of at least central and southern Missouri
at the outset of the period. This may have at least some impact on
potential destabilization through the day, as a warm frontal zone
begins to advance northeast of the middle Mississippi Valley.
At least some warming at mid-levels is forecast during the day
across much of the region, but perhaps not prohibitive to convective
development, as a seasonably moist boundary layer attempts to warm
and destabilize through late afternoon. South and southwest of the
mid-level closed low, models indicate that clearing skies may allow
for stronger heating that could support moderate to strong boundary
layer destabilization along an axis across central Kansas through
northern Missouri, and perhaps northern Illinois. This seems most
likely to provide the primary focus for renewed convective
development, aided by forcing near the mid-level cyclonic vorticity
center across northern Missouri into northern Illinois, and within a
zone of low/mid-level warm advection in its wake, across east
central Kansas/west central Missouri.
Given the possible large potential instability (CAPE of 2000-3000+
J/kg), and shear associated with a belt of 30-40 kt westerly 850-500
mb flow, discrete supercells are possible initially, but upscale
convective growth may be fairly quick, with one or two larger
convective clusters possibly evolving through Tuesday evening. East
of the middle Mississippi Valley, the tendency should be for
activity to propagate eastward, while veering mid-level flow to the
west supports a southeastward propagation of convection toward the
Ozark Plateau. After an initial hail and, perhaps, isolated tornado
risk, damaging wind gusts probably will become the more prominent
severe weather hazard.
...Southern Appalachians into southern Mid Atlantic coast...
Beneath at least modestly steep lower/mid tropospheric lapse rates,
moderately large CAPE is expected to support scattered vigorous
thunderstorm development Tuesday afternoon and evening. This may be
focused initially near a stalled frontal zone, and across the higher
terrain, with a gradual consolidation into one or more clusters.
These may be accompanied by a risk for potentially damaging wind
gusts as they propagate southeastward through Tuesday evening.
...Black Hills and western Dakotas...
Generally well south of the vigorous short wave trough migrating
across Saskatchewan/Manitoba, thunderstorm coverage remains unclear.
However, an environment characterized by steep lower/mid
tropospheric lapse rates supportive of at least modest CAPE may
promote isolated severe storm development late Tuesday afternoon
into Tuesday night, in the presence of strengthening deep layer
shear associated with the westerlies.
...MAXIMUM RISK BY HAZARD...
Tornado: 5% - Slight
Wind: 15% - Slight
Hail: 15% - Slight
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z