Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
336 AM EDT Tue Apr 30 2019

Valid Apr 30/0000 UTC thru May 03/1200 UTC

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

00Z Model Evaluation w/Preferences & Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
Preference: General model blend (more weight toward GFS, less
weight to the NAM, especially Day 3)
Confidence: Slightly above average

07z update: No significant changes needed to the model blend
preference with the rest of the 00z guidance now available.

---previous discussion---
The overall pattern across the CONUS through the next 3 days is
generally expected to feature ridging across the southeast US with
troughing over the interior west. Disturbances / shortwaves are
expected to move through the flow across the Plains into the Upper
Midwest and Great Lakes. In the large scale sense, the model mass
fields are in above average agreement through the period, with the
usual biases seen in the timing and strength toward the end of the
period.

The main upper level shortwave currently over the southwest US
will open up as it progresses through the Plains through
Wednesday. As it reaches the Upper Midwest, the NAM holds it
stronger and a bit faster compared to the rest of the
deterministic models. Another shortwave working through the large
scale troughing approaches the northern Plains by Thursday. Here,
most of the deterministic models have the same general idea with
some timing differences noted (NAM fast, GFS slower).

The biggest model differences lie with the QPF fields and the
maxima across the Plains. This will be driven mainly by mesoscale
features and convective boundaries that set up due to prior
thunderstorm activity. With the NAM being fast with the shortwave
/ low pressure on Wednesday, its QPF is spread northeastward
compared to the rest of the guidance.

Overall, with the above average agreement despite the NAM, a
general model blend with less weight toward the NAM, especially on
Day 3, is preferred.


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

Taylor