Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1237 PM EDT Thu Apr 02 2020
Valid Apr 02/1200 UTC thru Apr 06/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation with Preferences and Confidence
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...Western Atlantic closed low and offshore surface low...
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Preference: General Model Blend
Confidence: Above average
Several lobes of vorticity will pivot around a large closed upper
level low currently centered near 40N/62W, with one particular
piece of energy seen in recent water vapor over Quebec/Ontario. In
the highly amplified and blocky pattern, the upper level low will
be slow to move east over the next 24-36 hours across the Western
Atlantic Ocean. The surface low will retrograde and drift
southwest, making its closet approach to Cape Cod by 12Z Friday.
Model differences this cycle are fairly minimal and the most
recent GFS/NAM offer very similar solutions over the next 36
hours. Between 00Z and 12Z Saturday, the upper level low begins to
exit the area. At the surface, the 00Z UKMET is the furthest west
while the 00Z CMC is on the eastern end of the model spread, but
overall there is minimal differences. Given the increased
consensus and model tightening, a general model blend should
suffice for the model mass fields through the next 48 hours.
...Upper Midwest/Great Plains/Mississippi Valley...
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Preference: Non-UKMET blend
Confidence: Average
Large scale troughing over Alberta will push a series of
shortwaves across the northern Rockies into the Upper Midwest and
Great Lakes regions over the period. With a parent surface low
developing well south in the central Plains, a secondary/weaker
low is expected to develop over the Upper Midwest Friday into
Saturday. Aloft, the shortwave is well agreed upon by the latest
model guidance. The GFS and NAM to some degree are a bit faster
than the rest of the guidance, but its differences are fairly
minor. The notable difference however is in the UKMET, which is
not nearly as amplified with the trough axis Friday/Friday night.
QPF differences are most apparent with the NAM, which is further
west with its heaviest QPF axis for the 6-hour periods late
tonight into Friday morning. But overall with the mass fields, the
UKMET remains the biggest outlier and will go with a non-UKMET
blend for this area.
...Northern Rockies...
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Preference: Non-12Z GFS Blend
Confidence: Slightly above average
Large closed low situated over north-central Alberta will have a
couple of shortwaves rounding the base through the northern
Rockies over the next couple of days, one Friday and another
Saturday morning. Models are in fairly good agreement with the
passage of these features with the one notable exception being the
12Z GFS which shows a faster progression than the rest of the
models. The surface low that moves through the area is fairly well
agreed upon as well spatially and temporally. QPF amounts during
this time frame are fairly light and similar between the
GFS/ECMWF/UKMET/CMC but given the timing issue with the GFS, will
continue with a non-GFS blend.
...West Coast...
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Preference: Blend of the 00Z ECMWF, 00Z ECENS, and 06Z GEFS means
Confidence: Slightly below average
A pair of shortwave troughs will drop southeastward from the
eastern Pacific toward the California coast over the next few
days. The first impulse arrives on Saturday and there are some
sizable model differences noted. The 12Z GFS and NAM show a faster
and flatter progression as the energy moves onshore. Meanwhile,
the UKMET/CMC offer a more amplified solution which is slower. The
00Z ECMWF lies in between, more pronounced than the GFS/NAM camp
but slower timing more similar to the UKMET/CMC side. The
deterministic ECMWF actually mirrors fairly well the 00Z ECENS and
06Z GEFS means. So given the timing and spatial spread, the
initial preference for this feature is favored toward the ECENS
and GEFS means along with the deterministic ECMWF.
The second impulse that rotates through is larger and closes off
the California coast by late in the weekend and early next week.
Model differences are notable, with a sizable latitudinal spread
in the low center ranging from the further north UKMET to the NAM
which is on the southern end of the model spread. Here again, the
ECENS and GEFS are fairly agreeable through 84 hours and show
similarities to the deterministic ECMWF.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Taylor