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Categorical Day3 0830Z Outlook
  
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 Forecast Discussion

000 ACUS03 KWNS 200631 SWODY3 SPC AC 200630 Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0130 AM CDT Sun May 20 2018 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN NM AND WEST TX... ...SUMMARY... Isolated strong thunderstorms are expected across eastern New Mexico and west Texas Tuesday afternoon. ...Eastern NM/Western TX... Upper low that is expected to drift into the lower CO River Valley is forecast to weaken and lift northeast into the Great Basin during the latter half of the period. As a result, weak height rises are expected across the southern High Plains as primary corridor of stronger mid-level flow extends across southern AZ into central CO. Model guidance suggest strong boundary-layer heating will be noted across eastern NM/west TX such that convective temperatures should easily be breached by late afternoon. Favorable low-level trajectories will maintain adequate moisture across this region for ample instability required for robust updrafts. Even so, deep-layer shear will be seasonally weak but likely sufficient for isolated severe thunderstorms capable of generating hail/wind. This activity will be strongly diurnal in nature. ...Elsewhere... Unusually weak steering currents for mid may are expected to persist across much of the CONUS outside of the northeastern US. This flow regime leads to low predictability regarding organized severe thunderstorms despite the likelihood for isolated severe in various locations across the country, primarily east of the Rockies. Late evening guidance suggest low-level warm advection may induce deep convection across the northern Plains late and conceivably this activity could generate some hail. Another region where a few severe thunderstorms could evolve will be across portions of the OH Valley along the southwestern flank of stronger flow associated with a short-wave trough. If adequate instability can develop across portions of OH/western PA/western NY there is some concern for robust convection. However, predictability is just too low at this time to issue severe probabilities. ..Darrow.. 05/20/2018 $$