MD 1537 CONCERNING SEVERE POTENTIAL…WATCH POSSIBLE FOR NORTHEAST NE…WEST-CENTRAL/CENTRAL IA
Mesoscale Discussion 1537 NWS Storm Prediction Center Norman OK 1114 PM CDT Sun Aug 20 2017 Areas affected...Northeast NE...West-Central/Central IA Concerning...Severe potential...Watch possible Valid 210414Z - 210545Z Probability of Watch Issuance...40 percent SUMMARY...Thunderstorms capable of large hail are anticipated across the region. Trends will be monitored for possible watch issuance. DISCUSSION...Regional radar imagery has shown an increase in thunderstorm activity over the past hour amidst a strengthening low-level jet. This low-level jet will contribute to persistent warm air advection/isentropic ascent within the frontal zone draped across the region. Additionally, the low-level airmass upstream is very moist, evidenced by surface dewpoints in the upper 60s/low 70s and a mean mixing ratio of 16.7 g/kg on the 00Z TOP sounding. Continued isentropic ascent within this moist airmass will result in increasing storm coverage. Based on the 00Z OAX and recent RAP sounding, storm bases will likely be around 850 mb/1 km. These elevated storms will occur in an environment characterized by steep mid-level lapse rates (7.7 deg C per km on the 00Z OAX sounding) and moderate low and mid-level shear. Latest OAX VWP showed strong directional shear within the lowest 3 km. These environmental factors support strong, organized updrafts capable of producing severe hail and a watch may be needed to cover the anticipated severe threat. ..Mosier/Goss.. 08/21/2017 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DMX...FSD...OAX... LAT...LON 41009435 41549572 41769721 42319778 42829726 42829604 42549480 41949340 41149345 41009435
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