Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1123 PM EST Fri Mar 01 2019
Valid Mar 02/0000 UTC thru Mar 05/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Preference and Forecast Confidence
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...Surface low offshore New England Saturday...
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Preference: Non-NAM blend
Confidence: Above average
GOES-16 WV suite depicts nice baroclinic leaf along the
Mid-Atlantic indicative a deepening surface wave just off the
mouth of the Chesapeake that will track toward the 40N70W
benchmark. Only the NAM remains out of phase with this thinking
initially SE of the otherwise tightened deterministic packing,
then bending back westward under deeper cyclonic development
generally outpacing the other guidance. The 00z GFS remains a bit
weaker, which has been a weakness throughout this winter, but
remains within the overall fold to support an above average
confidence non-NAM blend for this cycle.
...Coast to Coast southern stream shortwave with sharpening
northern vortex enhance fast moving deepening surface wave from
Mid-South through Nova Scotia (Tues)
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Preference: 00z GFS and 12z CMC/UKMET blend (heavy weighting
toward CMC)
Confidence: Average
Southern stream shortwave currently approaching the
Central/Southern CA coast will continue a progressive eastward
track through the Southwest into the Southern Plains by Sunday,
shearing into the increasing zonal flow with time. Concurrently,
the deep global vortex over Ontario will begin to shift eastward
and open southeasterly trajectory of deep cold airmass over
Southern Canada at this time; pouring into the Central Plains and
northern Great Lakes (modifying a bit in the increasing solar
insolation of the day). Some guidance is a bit more progressive
pressing the inner core of the vortex east (GFS/UKMET), allowing
the southern stream system to press eastward and intersect return
Gulf moisture further south. ECMWF/ECENS mean both continue to
stand out with a stronger/sharper northern stream trof through the
Plains (subsequent shortwave ridging downstream in the Northeast),
this is fairly high consistency over the last few ensemble cycles.
This enhances increased overrunning across the TN Valley into KY,
and with increasing dual jet features (given tightening of the low
level temp gradient upstream in the Plains). This allows for a
very strong surface response in the Mid-Atlantic early Monday.
Upper level mass-fields support this evolution, of course, but the
sharpness of the 150+ kt jet evolution Monday, leaves some pause
for concern this may be a bit too aggressive, particularly in
persistent progressive flow (and no significant downstream
blocking ridge over the Northwest Atlantic). It is interesting,
the 00z NAM, which initially is further south and more in line
with the CMC/UKMET, shows typical day 3 over amplification bias.
While faster than the ECMWF (which seems more reasonable without
the block), there are quite a few similarities to the upper level
jet structure/mass fields. Knowing this bias, this does not bode
well for the more extreme nature of the ECMWF. The 12z CMC is
more middle ground, especially in QPF, and is not as aggressive
pressing the closed low over Ontario (and southward extending
northern stream shortwave trofs). Mass-wise, the CMC is closer to
the UKMET and 00z GFS now that it has a slight northward shift,
slowing and strengthening. As such will continue to favor a 12z
CMC heavy blend with the 00z GFS and 12z UKMET.
...Closed mid-level low nearing the coast of Washington on
Monday...
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Preference: Non-GFS blend
Confidence: Slightly above average
At the tail end of the northern stream trof (west of the cold air
and terrain), anti-cyclonic wave brake occurs with a closed low
along the Pacific Northwest coast by the end of day 3. A typical
eastward bias (faster flow east with the jet/trof) seen in the 00z
GFS leads the closed low to develop over WA, which is generally
out of phase with the otherwise tight clustering of the other
deterministic guidance. As such, a non-GFS blend is supported
here, though sensible weather is quite limited with this feature.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina