Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1231 AM EDT Wed May 09 2018

Valid May 09/0000 UTC thru May 12/1200 UTC

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

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

The 12Z CMC has initially higher heights than the other models
across various parts of the central and eastern CONUS. This
initialization issue and height differences grow with time, and
thus the CMC is not included in the preferences for any of the
systems in these regions.


...Trough lifting through the Mid Atlantic today, and past the
Northeast on Thursday...
...Associated weak surface low off the East Coast...

Preference: Non-CMC blend
Confidence: Above average

Models show similarity for this system and a general model blend
is preferred with high confidence.


...Northern stream shortwaves consolidating over the Upper Midwest
today, and pushing into the Northeast on Thursday...
...Surface low moving through the Great Lakes with cold front
sweeping across the northern tier of states...

Preference: Non-CMC blend
Confidence: Above average

Models appear to have come into better alignment as the multiple
shortwaves across the Upper Midwest are in the process of
consolidating now. They show fairly good agreement with their mass
fields, and thus a general model blend is preferred to account for
any lingering small uncertainties.


...Upper level trough near the Pacific Northwest followed by
general evolution over the western U.S. to zonal flow...
...Followed by redevelopment of closed low into Great Basin by
late Friday with emerging surface wave in the Plains...

Preference: Non-NAM blend
Confidence: Slightly above average

There is also substantially better agreement tonight with the
model forecasts for the flow pattern over the western U.S. as it
evolves over the next few days. The primary difference seems to be
with the 00Z NAM, which pushes the developing closed low faster to
the southeast, and spreads height falls further east than the
other models. Given the general trend toward an increasingly cut
off low by Saturday as a ridge builds over the top of the low, the
preference is to lean toward slower models (which also happens to
be the global model consensus). The 12Z CMC does not appear to
have the same initial height differences over the West as it does
further east, and thus it is included in the preference at this
time.


...Pacific shortwave quickly moving from California Thursday, into
the Great Lakes by Friday...

Preference: Non-CMC blend
Confidence: Average

This low amplitude shortwave should have a significant impact on
precipitation across the Midwest into Friday. Models do show some
differences on the strength of the associated mid-upper level vort
max, with the 12Z ECMWF generally the weakest. There is not enough
of a systematic bias to discount specific models, and thus a
broader blend is preferred to account for this uncertainty. The
CMC is not preferred as its height fields are notably higher than
the other available models across the region, which could affect
precipitation placement.


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

Lamers