Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8

FXUS10 KWNH 230506

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
105 AM EDT Fri Mar 23 2018

Valid Mar 23/0000 UTC thru Mar 26/1200 UTC

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

00Z NAM/GFS evaluation...including preliminary preferences

...Shortwave trough crossing the Mid Atlantic coast today...
Preference: General Model Blend
Confidence: Above Average

The models show similarly with this feature.

...Deep trough / closed low offshore the Northwest today...opening
into a Series of shortwaves moving into the Intermountain West
this weekend...
Preference: Blend of 00Z GFS, 12Z UKMET, 12Z ECMWF
Confidence: Average

The more significant differences with this feature are tied to a
stronger mid-level shortwave forecast to reach the West Coast near
00Z/25. As this feature moves inland, the 00Z NAM shows less
amplitude in the 500 mb heights compared to the remaining
deterministic and ensemble consensus. The 00Z NAM is also slightly
quicker here, but given the highly meridional flow pattern over
the eastern Pacific, would tend to think a slower/more amplified
progression would fit better to conceptual thinking. The ensemble
spaghetti data also shows the 12Z CMC as faster with the leading
shortwave as it crosses the Rockies. A 00Z GFS, 12Z UKMET and 12Z
ECMWF blend fits well with the latest ensemble data.

...Southern stream shortwave currently over the
Southwest...ejecting into the Plains this evening and deamplifying
toward the East Coast Saturday night as stronger shortwave drops
south into the northern Mid-Atlantic states...
...Lee cyclogenesis in the Plains; surface low moving across the
middle Mississippi River valley on Saturday and redeveloping off
of the Southeast coast early Sunday morning...
Preference: 00Z GFS, 12Z ECMWF, 12Z UKMET blend with initial
surface low
            00Z NAM/12Z ECMWF/12Z UKMET blend with redeveloped
surface low
Confidence: Average

Trends in the NAM have been slower since yesterday concerning the
shortwave as it crosses the Mississippi valley. The 00Z NAM looks
the strongest with the mid-level wave as it nears the Mississippi
valley, but the more significant trend has been with the
corresponding surface low which has trended south valid 00Z/25
compared to older model cycles. This trend has been noted in the
ensemble scatter low plots as well but the NAM lies toward the
north side of the ensemble guidance. Ensemble spread is more west
to east valid 00Z/25 than north to south, so the NAM is considered
too far north here. A blend of the 00Z GFS, 12Z ECMWF and 12Z
UKMET looks like a better fit to trends and the latest ensemble

Forecast models show a surface low redeveloping off of the
Carolinas coastline late Saturday night/early Sunday morning. The
GFS/GEFS are faster with a northern stream shortwave amplifying
southward over the northern Mid-Atlantic region, which coincides
with the surface low off of the Carolinas pushing out east more
quickly into the Atlantic. While differences grow quite rapidly
into the Atlantic, all models keep the impacts largely away from
the coast as Sunday night approaches. Ensemble scatter low plots
show greater support for a 00Z NAM/12Z ECMWF/12Z UKMET blend with
the redeveloped surface low through 00Z/26.

Model trends at
500 mb forecasts at


$$ is the U.S. government's official web portal to all federal, state and local government web resources and services.