Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
240 AM EDT Sat Jun 08 2019

Valid Jun 08/0000 UTC thru Jun 11/1200 UTC

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

00Z Model Evaluation...with Confidence and Preferences
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...Overall Pattern Across the CONUS...
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Preference: General model blend
Confidence: Above average

An initially blocky pattern across the eastern U.S. will gradually
break down as a deep layer southern stream closed low and
associated trough moving east from the lower Mississippi Valley
into the Tennessee Valley begins to gradually weaken over the next
couple of days. The system will become increasingly elongated in a
north/south fashion by Sunday and spanning an axis from the Ohio
Valley south to the eastern Gulf coast region. On Monday, a
portion of the trough will actually get suppressed down to the
south and will become focused over the northeast Gulf of Mexico by
the end of the period. The models are in very good agreement with
this scenario and also support a breakdown of the deeper layer
ridging that will be in place this weekend over the Great Lakes,
northern Mid-Atlantic and southern New England.

At the surface, the models do still depict some suggestion of a
weak surface wave on Saturday near or just off the Mid-Atlantic
coast involving an attendant frontal zone. There is some mid-level
shortwave energy that will support this, but this system should be
rather modest. The 00Z NAM tends to be a little more robust with
this coastal feature, but the 00Z ARW/ARW2/NMMB solutions and the
00Z GFS are all a little weaker. The 00Z non-NCEP guidance per the
UKMET, CMC and ECMWF solutions also are a bit flatter.

Meanwhile, a key contributor to the breakdown of the eastern U.S.
block will be the progressive intrusion of northern stream
troughing across the Pacific Northwest and downstream across the
northern Rockies, northern Plains and Midwest through the weekend
and into early next week. All of the guidance shows a trough
swinging through the Great Lakes region by the end of the period
as additional northern stream shortwave impulses dig down across
the northern High Plains in response to upstream ridging along the
West Coast. Model spread is rather minimal with all of this,
including with the details of the a strong cold front that will
advance across the Plains and Midwest through the period. However,
regarding some of the finer details, the NAM, UKMET and ECMWF
gradually begin to lag the model consensus a tad as the initial
surge of height falls cross into the Great Lakes region on Monday.
The GFS overall is most progressive with this energy, but the 00Z
GEFS mean came in a tad slower which suggests overall the GFS may
be a bit too fast.

Based on all of this, a general model blend will be preferred
given the modest model spread across the CONUS for the period, but
acknowledging in particular some of the timing differences that do
appear over the Great Lakes region toward the end of the period
with the northern stream trough.


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

Orrison