Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Tue Jun 02 2020
Valid Jun 02/1200 UTC thru Jun 06/0000 UTC
...See NOUS42 KWNO (ADMSDM) for the status of the upper air
ingest...
12Z Final Model Evaluation Including Preferences and Confidence
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19Z update...no preference changes.
Upper level low slowly lifting into Oklahoma that drifts east into
Wednesday
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Preference: General Model Blend
Confidence: Moderate-High
A broad upper low currently centered over at the SW Oklahoma and
Texas border will turn more easterly across Oklahoma into Arkansas
into Wednesday as it becomes embedded in the broad upper level
ridge. All global guidance are in close enough agreement on the
main features to merit the use of a multi-deterministic model
blend.
Cut-off low lingering southwest of California through Thursday
before ejecting east
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Preference: General Model Blend, non-GFS Day 3.
Confidence: Moderate-High
A cut off upper low will remain nearly anchored in place through
Thursday west of the ridge axis over the southern Rockies before
beginning to eject east toward southern California Thursday night.
The 12Z GFS remains the fastest with the eastward ejection, a
typical GFS bias of too quick easterly movement of these lows,
while depth and position are in excellent agreement among the rest
of the global guidance. Therefore, the preference for Day 3 is
non-GFS. However, there is little moisture with this system, so
there is not much difference in precip for southern CA.
Active flow pattern across northern Tier of U.S.
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Preference: Non-CMC General Model Blend through Day 2, 12Z
ECMWF/UKMET Day 3
Confidence: Moderate
The westerlies on the northern periphery of the central U.S. ridge
will remain active with three well-defined shortwave disturbances
tracking eastward near the U.S./Canada border through mid-week.
The first system is the remnants of an occluded low moving
currently over far northeast Ontario that will shift southeast
across NY State and southern New England tonight. The second
disturbance is a shortwave over northern Manitoba which will track
south of the Hudson Bay by Wednesday and be directed across
northern Maine by a deep low over Labrador, all the while dragging
a cold front stall over the east-central CONUS and provide a focus
for Day 2 QPF. The third system reaches the British Columbia coast
this afternoon and will track just north of the border and evolve
into an upper low over Manitoba by Wednesday night. This will push
a cold front across the northern Great Plains Wednesday night and
into the Midwest Thursday.
Despite the quasi-zonal and progressive flow pattern in place
across the region, models are in good agreement through Day 2
except for the 12Z CMC which slowed from the 00Z run, but it much
flatter than the rest of the guidance with eastward progression of
the third wave over the Canadian Prairies starting late Wednesday.
There are some more timing and amplitude differences with the
third wave that become apparent on Friday. The 12Z GFS jumps out
ahead of the ECMWF/UKMET/NAM, but the 12Z NAM is deeper than the
UKMET/ECMWF. So the 12Z UKMET/ECMWF is preferred for Day 3.
Closed low drifting south from Gulf of Alaska off BC coast by
Friday.
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Preference: General Model Blend, non-GFS Day 3
Confidence: Moderate-High
Excellent agreement among global guidance for large closed low
drifting south from Gulf of Alaska to a position well off the BC
coast by late Friday except for the 12Z GFS which is the fastest
solution, outpacing the 12Z GEFS mean. Greater differences are
expected by the time the low/trough swings into the Pacific
Northwest over the weekend.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Jackson