SPC AC 211252

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0752 AM CDT Fri Jun 21 2024

   Valid 211300Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
   HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY AND OVER THE FOUR
   CORNERS REGION...

   ...SUMMARY...
   Scattered strong to severe storms are expected from parts of the
   northern High Plains into the upper Mississippi Valley, mainly this
   afternoon and evening. Scattered strong/severe thunderstorms are
   also possible across the Four Corners vicinity. A few strong storms
   may occur from parts of the lower Great Lakes to southern New
   England.

   ...Northern High Plains...
   A shortwave trough will shift eastward from the Canadian Rockies
   toward Saskatchewan, with southeasterly low-level flow deep into
   Montana ahead of this shortwave trough. Relatively strong (40 kt)
   mid-level flow will develop across central Montana as the upper
   ridge flattens. Scattered robust convection should easily develop
   within a flow regime favorable for supercells. Forecast soundings,
   especially for central Montana, exhibit favorable deep-layer shear
   with strong buoyancy and relatively low cloud bases. Scattered
   supercells should evolve by early afternoon then propagate
   southeastward along the instability axis toward
   eastern/south-central Montana through early evening. Very large hail
   and gusty winds are expected along with some tornado risk.

   ...Middle Missouri Valley/Siouxland to Upper Mississippi Valley...
   Scattered thunderstorms persist this morning regionally in vicinity
   of the convectively modified frontal zone. A mid-level impulse over
   Colorado/southeast Wyoming this morning will reach the Siouxland by
   late afternoon and early evening, all while a south-southwesterly
   low-level jet markedly intensifies after sunset. Strong diurnal
   heating south of the boundary will ease CINH across the warm sector
   and scattered storms are expected to develop and intensify. Updrafts
   may initially develop along the cool side of the boundary but with
   time surface-based storms are expected. Hail, wind, and perhaps a
   couple tornadoes can be expected with supercells occurring near the
   front.

   ...Four Corners Region...
   A seasonally high PW plume will advance into the Four Corners region
   as a low-latitude shortwave trough over southern California/Nevada
   ejects over the Great Basin, strengthening mid-level flow across
   southern Utah into southwestern Colorado. Sustained multicells and
   some supercells should develop along the southern fringe of this
   shortwave trough, where strong shear will support organized
   longer-lived updrafts. Large hail and strong/gusty winds can be
   expected, and some tornado risk may exist as well.

   ...Lower Great Lakes to southern New England...
   Strong boundary-layer heating will once again occur across the lower
   Great Lakes region into portions of southern New England, with a
   southward-shifting front focusing scattered convection into
   early/mid-afternoon. Within a moderately unstable environment,
   localized wind damage will be the primary concern with the strongest
   storms his afternoon through around sunset.

   ..Guyer/Mosier.. 06/21/2024

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