Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
104 PM EDT Sun Oct 27 2019

Valid Oct 27/1200 UTC thru Oct 31/0000 UTC

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

12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Departing mid-level trough currently over southern
Ontario/Quebec...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The latest model guidance is in good agreement with the track of
the negatively tilted shortwave over the Great Lakes region on 12Z
Sunday and it's associated parent surface low weakening into
Canada as a secondary low develops near the coast of New England
Sunday night. A general model blend will be preferred.


...Mid-level trough ejecting into the central Plains on Monday...
...Surface cold front over the lower/mid MS Valley by Tuesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Slightly above average

Although there remain some minor timing differences with a
shortwave reaching the central Plains from the Great Basin on
Monday, there is enough agreement to support a general model
blend. Overall spread in the deterministic/ensemble guidance has
reduced enough to where any future adjustments should be minor and
within the noise of model run to run variability.


...Shortwave/clipper low over MT/ND by Monday evening...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

No significant differences exist with this system and run to run
continuity has been good so above average confidence exists for a
general model blend.


...Powerful closed low in the Intermountain West Tuesday into
Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: non 12Z GFS blend
Confidence: Slightly above average

Ensemble spaghetti 552 dam heights at 500 mb show shrinking spread
valid Wednesday over their past 4 cycles (12Z/00Z only). The 12Z
GFS however, jumped significantly east/faster with this system and
is an outlier outside of the latest ensemble envelope. Non 12Z GFS
solutions are in relatively good agreement in line with the
shrinking ensemble guidance, so therefore a non 12Z GFS blend will
be preferred for this system.


...Potential disturbance in the Gulf of Mexico early next week...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Average

There is currently an area of disturbed weather just east of the
Yucatan Peninsula which some of the models track around the
western side of the subtropical Atlantic ridge and into the Gulf
of Mexico. The latest models are in sufficiently good enough
agreement here to support a general model blend.


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

Otto