SPC Jul 21, 2017 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0340 AM CDT Fri Jul 21 2017

Valid 241200Z - 291200Z

...DISCUSSION...
Medium-range models continue to remain in generally good large-scale
agreement early in the medium-range period, with a trough crossing
the Northeast, a second traversing the Canadian Prairies and
brushing the north-central states, and a third moving onshore over
the west.  

However, details on the smaller scale remain sufficiently
out-of-phase to render the forecast uncertain -- even at the start
of the period.  Day 4/Monday, both models hint that isolated
afternoon/evening severe risk may evolve over the northern Plains. 
However, with the upper low/trough progged to remain north of the
international border, development should remain isolated -- and thus
not warranting an areal highlight.  Farther east, the upper trough
slowly crossing the northeast U.S. will support showers and
thunderstorms -- and possibly some severe risk per the slower GFS
solution.  The model differences however cast sufficient uncertainty
so as to preclude an areal delineation of severe risk at this time.

Convective risk appears likely to diminish substantially across the
Northeast by Day 5, while a few storms -- and possibly isolated
severe potential -- could linger over the north-central states as a
cool front drifts south.  With this risk appearing too low/uncertain
for an areal highlight, and with model agreement further diminishing
through the rest of the period, no forecast areas will be
highlighted at this time.

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