RAH --- model problems and forecasting for NC.
That Arctic front, analyzed at 20Z this afternoon from cntl WI swwd
to srn IA, then wnwwd across srn and wrn NE and cntl WY, will be
preceded by an increasingly closely-spaced but separate front
analyzed from nern OH swwd across cntl IN/IL/MO, sern KS, and the OK
and TX panhandles. A distinction between the two is critical for two
related reasons regarding how quickly cold, particularly Arctic air,
arrives in cntl NC: 1) the models tend to depict hypergradients
about such closely-spaced fronts as one and 2) how the models (fail
to accurately) resolve the Appalachian mountains yields a premature
Arctic air surge in the lee of the mountains. Consider the past two
early season Arctic frontal passages in cntl NC, for example, from
Halloween night and last Thu/Nov 7. In both cases the models rushed
the cold air east of the Appalachians prematurely relative to
reality.
These model failures are one of the chief reasons that a pattern
such as the one described above, with "cold air chasing the
moisture", fails to produce wintry precipitation in cntl NC.
Nevermind that it's still Nov. And it provides an opportunity for
failure of even the best of NWP ensemble systems that depict
accumulating snow in cntl NC, and for a human to add forecast skill
and value. With that in mind, a band of anafrontal rain, driven by
the right entrance region of a strong (125-150 kt) swly upr jet
streak from the cntl Appalachians to the Labrador Sea, behind the
lead front described above, will edge ewd across cntl NC late Mon
night and (particularly early) Tue - in a pattern very similar to
the band of anafrontal rain that occurred last Thu/Nov 7. The Arctic
boundary will then sweep sewd across cntl NC through early-mid
afternoon Tue, with following much below average temperatures,
including teens to low-mid 20s Wed morning, and highs only in the
upr 30s to low-mid 40s on Wed.