The Weather Prediction Center

Model Diagnostic Discussion

[Abbreviations and acronyms used in this product]
Geographic boundaries:    Map 1- [Color] [B/W Print Version]      Map 2 - [Color] [B/W Print Version]

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1214 PM EDT Sun Oct 20 2019

Valid Oct 20/1200 UTC thru Oct 24/0000 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air

12Z Model Evaluation with Preferences and Confidence

Post-tropical cyclone Nestor
Preference: Non-CMC blend
Confidence: Slightly above average

The remnants of TS Nestor continue to progress through the
Carolinas into SE VA and is expected to shift offshore later
today.  High vertical shearing will separate the low level
circulation and mid-level forcing at the start of the week along
70W, though there remains some small spread especially in the
lower levels/surface.  The CMC remains north of the cluster while
the NAM has finally latched on to similar solutions presented by
the ECMWF/GFS and UKMET.  The remaining low level circulation will
lift north in advance of the approaching frontal zone Wed, again
with the CMC the only stronger and further west solution, so a
Non-CMC blend is preferred at slightly above average confidence.

Rapidly deepening Central Plains cyclone, lifting into Great Lakes
by Tues. Second surface wave lifting along front in Carolinas into
New England 12z Wed.
Preference: General model blend
Confidence: Slightly above average

The strong jet and diffluent pattern across the Western Northern
Plains is supporting rapid cyclogenesis currently and the overall
guidance suite has come into very strong agreement with it.  The
trailing shortwave trof that had been leading to some uncertainty
with the strong surface reflection and low level surge of
moisture/instability over the past few days, has come deeper into
the more dense data network and so as it lifts through the MS
Valley on Monday, there is much stronger agreement.  The overall
spread is tight with the only minor exception being the 12z GFS
which, at the surface, shows a greater cyclonic wobble to the
occluded low center, still this is not an issue overall. 

Even the next surge of upper level jet energy/weak shortwave
inflection drops along out of the Rockies into the base of the
growing large scale trof, by late Monday into Tuesday, eventually
spurring a surface wave to develop along/southeast of the
Appalachians.  This surface wave will lift along the progressive
front into New England, also under fairly solid model agreement. 
As such a general model blend is supported at slightly above
average confidence throughout the forecast period.

Fast moving 'clipper' shortwave entering Northern US Rockies/MT
High Plains late Tuesday and Midwest by late Wed ushering in cold
air plunge across the Northern Plains.
Preference: 00z ECMWF/CMC blend with some 06z GEFS
Confidence: Average

While there was some cold air pulled south very near the upper
low/surface cyclone with the prior system, a strong but fairly
potent shortwave is expected to exiting the Gulf of AK, over-top
the ridge and roll along the spine of the Canadian Rockies.  By
late Tuesday, this will spur a Clipper surface low, that will
skirt through the northern Plains, but in its wake usher a strong
cold surge from an open Arctic stream of low level flow.  The
guidance, has some moderate spread, mainly in the strength of the
lead shortwave energy...the 12z NAM is particularly strong
supported by the UKMET, but is much wetter than the UKMET, making
it a bit suspect toward its negative day 3 bias.  The 12z GFS is
uncharacteristically slow, relative to the other guidance, but
that seems to manifest from initialization of the wave in the
Pacific, favoring the second upstream shortwave over this lead
one.  Given the ECWMF/CMC both are a equal split of the stronger
NAM/UKMET and the 06z GEFS is more ECMWF/ECENS mean-like in
strength/timing will favor an ECWMF/CMC blend at average

Model trends at
500 mb forecasts at


Last Updated: 1214 PM EDT Sun Oct 20 2019