SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0301 PM CDT Sat Jul 09 2022
Valid 092000Z - 101200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
CENTRAL MONTANA INTO CENTRAL NORTH DAKOTA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE
NORTHERN PLAINS AND THE SOUTHEAST...
...SUMMARY...
Scattered severe thunderstorms are expected later this afternoon
through tonight across Montana into North Dakota, with damaging
winds and large hail likely. Occasional damaging gusts will also be
possible this afternoon/evening across parts of Alabama and
Mississippi.
...20Z Update...
Mostly minor adjustments were made to the outlook to reflect the
latest observations or model guidance consensus. The one exception
was to expand the Category 3/Enhanced risk into central ND. Some of
the latest HRRR guidance members depict robust convection associated
with a severe bow-echo MCS progressing into central parts of the
state by 12Z. In the 06-12Z period, forecast soundings from several
of the last RAP runs depict 9 C/km 700-500 mb lapse rates (and
resultant 3500 J/kg MUCAPE), with considerable drying in the 800-600
mb layer. Despite a stable boundary layer, adequate evaporative
cooling/ice melting should support strong enough downward momentum
transport for an organized severe wind threat with the bow-echo MCS.
..Squitieri.. 07/09/2022
.PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Jul 09 2022/
...MT/ND late this afternoon through tonight...
Similar to the previous two days, midlevel shortwave troughs will
move around the northwest periphery of the Four Corners midlevel
high, from the interior Northwest across MT to ND through tonight.
Despite overnight convection, boundary-layer dewpoints remain in the
mid 50s to near the higher terrain in west/southwest MT (somewhat
higher dewpoints across eastern MT). Steep midlevel lapse rates
will again be replenished from the southwest, which in concert with
daytime heating, will result in MLCAPE near 1500 J/kg this
afternoon/evening. Deep-layer vertical shear will be fairly strong,
with long hodographs and effective bulk shear in excess of 45 kt.
Much like yesterday, scattered thunderstorm development is expected
near or just after 21z, over and immediately northeast of the
mountains in southwest MT. Some of these storms could develop
supercell structures with an attendant threat for large hail of 2+
inches in diameter. Later this evening, some upscale growth into
one or more clusters is expected, with an increase in the threat for
damaging winds of 75+ mph. Embedded supercells will remain
possible, especially on the southern flank of the convection, as the
cluster(s) move eastward across ND tonight.
...Southeast into TX this afternoon/evening...
Downstream from a midlevel high centered near the Four Corners, a
broad zone of cyclonic flow aloft persists from the MS Valley to the
Mid-Atlantic/Carolinas. Embedded perturbations within this cyclonic
flow, enhanced by prior convection, will continue to move
east-southeastward over the Southeast, as a surface cold front
drifts slowly southward across VA/KY/TN/AR and north TX. Morning
clouds/convection across north GA/northeast AL will produce weak
outflow and differential heating zones that will drive afternoon
thunderstorm development farther south and west from central AL into
the Mid-South along the cold front. Hot afternoon temperatures of
95-100 F and boundary-layer dewpoints in the mid 70s will boost
MLCAPE to 3000 J/kg or greater, with thunderstorm development
expected by early-mid afternoon. Convection will likely grow
upscale into a couple of clusters/lines and spread southward through
late afternoon/evening. Though flow aloft will be weak, the large
buoyancy and DCAPE near 1000 J/kg will support occasional damaging
downbursts.
Farther east, the morning convection across GA may persist into the
afternoon while spreading southeastward, and additional storms are
expected to form along the differential heating zone across the
Piedmont, and along the cold front moving southward into NC.
Vertical shear will remain rather weak (slightly stronger along the
front in NC), and thermodynamic profiles from GA into the Carolinas
will not be quite as supportive of downbursts compared to MS/AL.
Thus, isolated strong/damaging outflow winds will be possible with
multicell clusters this afternoon from GA into NC.
Strong surface heating (afternoon temperatures well above 100 F) and
inverted-v profiles along the slow-moving front across north TX will
support the threat for high-based thunderstorms with isolated severe
outflow winds for a few hours later this afternoon/evening.
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