SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0237 PM CDT Sat Jun 18 2022
Valid 182000Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHWEST
TO NORTH-CENTRAL MONTANA...AND THE FLORIDA PENINSULA...
...SUMMARY...
Significant severe hail is possible across portions of northwest and
north-central Montana through this afternoon. Scattered damaging
winds are possible across parts of the Florida peninsula through
early evening.
...20z Update...
Only minor adjustments have been made to the 10 percent general
thunderstorm lines based on convective trends. The Slight and
Marginal risk areas across MT, the south-central states, and the FL
Peninsula remain unchanged. Reference MCD 1215 and 1217 for short
term information, and the previous outlook discussion below for more
forecast details.
..Leitman.. 06/18/2022
.PREV DISCUSSION... /ISSUED 1115 AM CDT Sat Jun 18 2022/
...Northwest/north-central MT...
Large-scale ascent tied to a shortwave impulse ejecting north from
the ID/NV/UT border area should aid in isolated to scattered
thunderstorm development this afternoon along and to the cool side
of a quasi-stationary front extending from southwest to
north-central MT. Boundary-layer dew points holding in the 50s
beneath steep mid-level lapse rates will support a confined plume of
MLCAPE from 750-1500 J/kg near the MT/Alberta/Saskatchewan border
area. Strong deep-layer speed shear yielding a rather elongated,
straight-line hodograph will foster potential for a few discrete
splitting supercells with a primary threat of large hail before
convection crosses into Canada.
...FL Peninsula...
Remnants of decaying morning pre-frontal convection persist across
north FL. Scattered thunderstorms are expected to develop this
afternoon ahead of this activity as surface temperatures warm
through the 90s. Large MLCAPE in excess of 3000 J/kg supported by
relatively steep mid-level lapse rates has already developed across
the west-central portion of the peninsula. While deep-layer shear
will be weak, northerly mid-level winds will support
southward-propagating cold pools in pulse to loosely organized
multicell clusters. A series of damaging downburst winds, especially
along outflow intersections, is possible along with isolated severe
hail.
...Central Gulf Coast and South-Central States...
Isolated to scattered thunderstorms are expected this afternoon
along and west of a backdoor cold front pushing southwest across the
Lower MS Valley. Owing to close proximity of a stout mid-level
anticyclone over eastern KS, deep-layer shear will remain weak,
yielding predominately pulse convection. With the largest MLCAPE
near the frontal zone, localized microbursts are most probable in
this corridor yielding isolated damaging winds.
...Southwest to central Rockies/High Plains...
The Southwest monsoon is underway with a plume of PW near or above 1
inch across eastern AZ/western NM, between the upper trough along
the Pacific coast and the ridge over the Great Plains. Locally gusty
outflow winds will be possible in scattered to numerous
thunderstorms where pockets of stronger surface heating and steeper
low-level lapse rates coincide with convective clusters. The threat
for very isolated severe wind gusts while non-zero does not appear
likely to be greater than 5 percent coverage over such a broad area.
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