Severe Weather Likely Friday Nov 17, 2017
Latest runs of the GFS and ECMWF appear very internally consistent,
with respect to runs from 24 hours ago. However, they remain
similarly inconsistent each other with respect to timing as was the
case yesterday. As the developing surface cold front crosses the
central U.S. late Day 4 (Thursday 11-16) and then Day 5 (Friday
11-17), and finally across the eastern U.S. Day 6 (Saturday 11-18),
a 9 to 12 hour timing difference persists between the two models.
With that said, the overall pattern continues to suggest a linear
band of frontal convection, occurring within a pre-frontal
environment featuring modest CAPE but very strong flow from the
lower troposphere to upper levels. As such, damaging winds would be
the main severe potential, with degree of risk at least partially
modulated by the degree of CAPE and associated intensity of the
convection. Given this potential, a 15% risk area is being
introduced at this time, from the Midwest to the Arklatex vicinity.
Partially due to timing differences between the models, a rather
large area is being included in the risk, with fine-tuning of the
lines left for later outlooks as evolution becomes more certain.
At this time, an outlook area will not be included for Day 6 over
the eastern U.S., as the GFS shows the front moving offshore during
the first few hours of the period, while the ECMWF depicts the front
still lying west of the Appalachians through midday. Depending upon
the actual evolution, a risk area may be required in later