SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0745 AM CDT Sun Apr 27 2025 Valid 271300Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR MUCH OF THE GREAT PLAINS... ...SUMMARY... Isolated to scattered severe thunderstorms are possible on Sunday evening into early morning Monday across parts of the Great Plains. Large hail, severe gusts, and a few tornadoes are all possible. ...Synopsis... Early morning satellite imagery shows modest upper ridging between a pair of well-defined cyclones, one centered over NV and the other centered over northern NY/VT. The NV cyclone forecast to shift slightly eastward throughout the day as a shortwave trough, and associated jet streak, rotate through its base. Moderate to strong southwesterly flow associated with this shortwave will spread northeastward from the Southwest into central Plains and Mid MO Valley. Recent surface analysis reveals an expansive area of high pressure centered over the Upper Great Lakes covering much of the eastern CONUS. A broad area of low pressure exists over the intermountain West, with several embedded lows. A tight surface pressure gradient exists between these two features across the Plains, and the resultant moderate low-level flow will contribute to northward moisture advection throughout the period. Any large-scale forcing for ascent associated with the shortwave progressing around the NV cyclone will remain west of this better low-level moisture (and associated buoyancy) until later tonight, when it reaches the northern High Plains. Ample buoyancy and moisture will exist across the central and southern High Plains, but the lack of stronger large-scale forcing for ascent will result in a more conditional severe thunderstorm potential. ...Southeast MT...Western Dakotas... A deepening lee trough is forecast to result in surface cyclogenesis in the far eastern MT/WY border vicinity by late this afternoon. Strong boundary-layer mixing is anticipated across the region, promoting airmass destabilization but also likely keeping dewpoints in the 40s across much of the region. Convergence along several boundaries across the region, including a surface trough extending across southeast MT and the lee trough along the eastern WY border vicinity, amid this destabilized airmass will result in thunderstorm development, particularly during the late afternoon/early evening as increasing large-scale ascent complements the low-level convergence. An eastward storm motion should take any storms that develop in better low-level moisture over time, with a strengthening low-level jet helping to maintain favorably moist low-level inflow. Even with this modest improvement in thermodynamics, nocturnal stabilization should result in storms becoming more elevated over time. Primary threat across this region are large hail and damaging gusts. ...Central/Southern High Plains... Mid 60s dewpoints are already in place across the Permian Basin and the general expectation is for low-level moisture to increase throughout the day. 60s dewpoints will likely be in place across all but far western KS by 21Z and into much of central NE by 00Z. Strong heating is anticipated across this region as well, resulting in an area of moderate to strong buoyancy from southwest NE into west TX by the late afternoon. Large-scale forcing for ascent across the region will be nebulous, but low-level convergence along the dryline amid little to no convective inhibition may result in convective initiation. With dryline convergence as the mechanism for convective initiation, predictability is low and convection-allowing guidance has limited utility. Dryline circulations will likely be strongest across the TX Panhandle/West TX where temperatures west of the dryline will be warmest, but low-level coverage will likely maximize in the CO/NE/KS border intersection vicinity near a developing surface low. As a result, these two areas may have a greater risk for thunderstorms today. The overall environment will be very supportive of supercells with any storms that do form, with large to very large hail as the primary risk initially. Strong downdrafts are possible as well. A westward shift of the dryline and strengthening low-level jet will support an increase tornado threat during the evening with any storms that persist (or develop along the retreating dryline). The kinematic environment improves notably across the TX Panhandle, western KS, and western NE between 00Z and 06Z, so any storms that are ongoing may be able to organize considerably before eventually weakening due to nocturnal stabilization. ..Mosier/Broyles.. 04/27/2025