Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Wed Oct 16 2019

Valid Oct 16/0000 UTC thru Oct 19/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Great Lakes closed low and developing Northeast coastal surface Low
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM and higher weight toward ECMWF
Confidence: Slightly above average

07Z update: Continued good clustering with the rest of the 00Z
guidance now available. The NAM remains a bit too deep initially
and then too slow as the low moves north of Nova Scotia. A non-NAM
blend with higher weight toward the ECMWF remains the preferred
blend.

---previous discussion---
Closed upper low currently over eastern Wisconsin will take on
more of a negative tilt as it approaches the Northeast U.S. by
Thursday. The increasing diffluent pattern aloft will support
rapid surface cyclogenesis along or just offshore the Mid-Atlantic
coast and will track inland across New England. The 00Z NAM
continues to show the most vertically stacked and deepest
solution, which may be related to better higher resolution of warm
Gulf Stream air, but this very strong signal departs rapidly from
the other guidance members and ensemble suite/trend, leaving it
out of the preference (though it may not be fully unrealistic).
The rest of the guidance offers fairly good clustering through 60
hours as the low lifts northeast through Maine and into Canada. As
such, will continue to lean on previous preference toward the
ECMWF and continued less weighting of the NAM at this time.

Record for low pressure are for non-tropical cyclone pressures in
October...Post-Tropical Sandy is included in this database, so
records across the lower Hudson and Mid-Atlantic are at much lower
risk of being broken...please see
www.wpc.ncep.noaa.gov/research/roth/SLPrecords.html.


Short wave energy affecting Texas through midweek shearing thru
eastern Gulf States by Fri
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Slightly below average

07Z update: Better agreement now with the weak surface wave
lifting from the southwestern Gulf toward the central Gulf Coast
by Saturday. The GFS remains on the right side of the model spread
while the ECWMF is west, but the overall spread has lessened.
Although the NAM/CMC/UKMET offer a favorable consensus approach,
some inclusion of the GFS and ECMWF would be acceptable as well
despite some lower confidence by Day 3.

---previous discussion---
Troughing currently moving into the Texas Panhandle will gradually
reach the Gulf Coast by later this week. Interaction with an area
of disturbed weather in the southwestern Gulf will eventually lead
to a weak surface wave lifting northeast toward the central Gulf
Coast. There is a fair amount of spread in the eventual track of
any surface wave with the latest ECMWF slower/westward compared to
the faster/east GFS, while the CMC lies in between. The 00Z NAM
offered a good compromise/consensus approach as well. There
remains above normal uncertainty in how this evolves over the
coming days and what sensible weather impacts there will be, but a
blend of the latest NAM/CMC/UKMET represents the consensus
approach the best at this time.


Western U.S. longwave trough (Wed-Thurs) shifts into Rockies with
Northern Plains cyclogenesis Thurs into Fri
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Slightly above average

07Z update: No significant changes noted with the rest of the 00Z
guidance now available and a general model blend is still
preferred.

---previous discussion---
Positively tilted trough will cross into the western U.S. late
Wednesday and push into the central U.S. by this weekend. Model
spread is average to slightly above average at this point, with
the largest differences seen in timing as the shortwave moves east
of the Rockies. Typical model biases are noted, with the GFS being
slightly faster compared to the ECMWF/CMC/UKMET, but compared to
previous cycles, the differences are not as significant. As such,
a general model is preferred given the better than average model
agreement.


Pacific Northwest reinforcing shortwave late Thurs into Fri with
broad/strong westerly Pacific jet thereafter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Slightly above average

In the wake of the initial longwave trough across the Pacific
Northwest, a stronger/compact shortwave piece of energy pushes
into the region late Thursday into Friday. In the previous
forecast cycle, the 12Z UKMET was too amplified and was not
considered for the preferred blend. The new 00Z is considerably
less amplified and now is in much better agreement with the rest
of the deterministic models and within the model spread. A general
model blend can be used here.


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

Taylor