Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1236 PM EDT Mon Oct 08 2018

Valid Oct 08/1200 UTC thru Oct 12/0000 UTC

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

12Z Model Evaluation...with latest preferences and confidence
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...Overall Pattern Across the CONUS...
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Preference: Blend of the 12Z GFS and 00z UKMET/ECMWF
Confidence: Average

The large scale synoptic pattern across the CONUS remains highly
amplified and active with a longwave trough positioned across the
Intermountain West / Four Corners region while a subtropical ridge
continues to hold strong over the Southeast US and Mid-Atlantic
regions. In between, a couple waves of low pressure were analyzed
across the southern Plains with a stationary boundary draped
across the central Plains into the Upper Midwest where rounds of
heavy precipitation have occurred and are ongoing.

Over the next 24 hours, the western US trough will begin to shift
eastward while a strong piece of upper level energy drops into the
Pacific NW Tuesday. These systems will begin to phase and the
trough will begin to take on a positive tilt across the Upper
Midwest while the surface low deepens and treks toward the western
and northern Great Lakes region.

For the details, the models are overall in decent agreement with
the evolution of the longwave trough through Thursday morning.
There are some timing and placement differences in the surface low
track and cold front position across the Upper Midwest. The 12z
NAM and GFS are a bit slower by Wednesday with the front placement
compared to the 00z ECMWF/CMC/UKMET and continue to be slower
through the end of Day 3 (12.00z). Though it is noted that the 12z
GFS has trended faster compared to its previous runs, while the
12z NAM is fairly similar to its previous run for the low track
and frontal position.

By Day 3 (Thursday), the surface low is forecast to be well north
of the Great Lakes with its trailing cold front moving across the
East Coast. Interactions with Hurricane Michael introduce some
spread in forecast models on how the front ultimately progresses
through and any potential axis of heavy rainfall. In its wake,
strong Canadian high pressure building into the northern Plains is
well agreed upon by the forecast.

Based on the latest model spread and solutions across the CONUS
(outside of tropical activity...see below), a general blend of the
12z GFS with the 00z ECMWF/UKMET is preferred.

...Tropical Storm Michael...
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Preference: See the latest NHC forecast advisory

In this cycle, the spread in the deterministic guidance decreased
with the track of Michael as it moves northward into the Gulf of
Mexico. The hurricane is forecast to track due north or
north-northwesterly before making a northeastward turn into the
Florida Panhandle on Wednesday. The storm is then forecast to
quickly trek north-northeastward through the Southeast US and
Carolinas before heading off the Mid-Atlantic coast.

There is better agreement in the track of the hurricane compared
to the previous forecast model cycle. The main forecast challenge
is the forward speed. The 12z GFS continued to be faster than the
consensus while the 00z ECMWF and 12z NAM was much slower. The 00z
UKMET is a decent proxy for the current NHC track and speed,
though a tad to the right to the official forecast. See the latest
NHC forecast advisory for more details on Hurricane Michael.

...Hurricane Sergio...
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Preference: See the latest NHC forecast advisory

Hurricane Sergio is forecast to track east-northeastward this week
toward the Baja California peninsula by early Friday morning
according to the latest NHC forecast advisory. There is reasonable
agreement between the various global deterministic models in the
forecast track. The 12z NAM was faster compared to the current
suite of forecast models and also well to the right of the NHC
forecast while the 00z CMC was a slower solution. Here, a blend of
the 00z ECMWF/UKMET and 12z GFS would yield a forecast
track/motion similar to the NHC forecast. See the latest the NHC
forecast advisory for more details on Hurricane Sergio.


Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

Taylor