Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0333 AM CDT Tue Jun 27 2017 Valid 301200Z - 051200Z ...DISCUSSION... On Fri/D4, an upper trough will be centered over the northern Plains, with embedded shortwaves moving from the middle MS Valley into the upper Great Lakes, with a weak surface low over Lower MI by afternoon. A cold front will extend southwestward from this low, with a moist air mass to the east. Indications are that substantial rain and thunderstorms will be ongoing along this front, which lends uncertainty to forecast instability levels. For example, the ECMWF shows much less MUCAPE than the GFS, with minimal instability into Lower MI where the most favorable shear will be. While a Slight risk may eventually be issued, will defer to later outlooks given these uncertainties. Similar predictability issues exist for the next few days as the upper trough gradually shifts eastward, affecting the Northeast on Sat/D5. In the D6-D7 time frame, a northwest flow regime is expected across the Plains, and southerly surface winds will bring substantial moisture back north across the central Plains and mid/lower MO Valley. While some wind/hail threat would exist with this pattern, predictability is low at this time.Read more
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