The Weather Prediction Center

College Park, MD

Extended Forecast Discussion

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Mon Mar 18 2019

Valid 12Z Thu Mar 21 2019 - 12Z Mon Mar 25 2019

...Overview and Guidance Assessment/Preferences...

Split flow pattern is expected to persist across North America
during the extended period. Ensemble guidance shows good consensus
that a strong and blocking upper-level ridge axis initially across
the High Plains of the U.S. into Alberta/Saskatchewan will meander
in place over the next week. This will continue to split incoming
energy from the Pacific into northern stream components directed
northward toward Alaska, and southern stream components that
traverse the southern/central U.S., undercutting the ridge.
Downstream of the ridge, the Northeast will be subject to
continued mean troughing, reinforced by a series of energetic
shortwaves. Some guidance suggests that perhaps this northern
stream amplified ridge/trough pattern may begin to weaken by early
next week, but confidence in that is relatively low at this time
given increased spread among the ensemble guidance as to the
intensity and duration of the upper ridge.

Model depictions are now relatively similar with respect to the
upper low/trough crossing the Four Corners Thu-Fri and exiting
into the Plains Fri night-Sat. Farther east, solutions differ more
significantly with respect to small scale northern stream
shortwave energy traversing the larger mean trough, and the
potential for development of a compact/robust surface low off the
Eastern Seaboard Thu night-Fri. Trend in the ensemble guidance has
been toward a bit slower/deeper and closer to the coast solution,
forming a middle ground between the deeper 00Z ECMWF and 06Z
FV3-GFS and weaker/quicker 00Z/06Z GFS and 00Z Canadian/UKMET.
This blend sufficed for the west/central states as well given some
overall minor detail differences. Finally, models show general
consensus that an another shortwave/frontal system should reach
the West Coast Fri-Sat, with relatively minor timing and amplitude
differences through Sat.

Timing differences become more significant Sat-Mon in the West as
subsequent Pacific shortwaves move inland. In general, the 00Z GFS
continued to be quicker than the consensus of other guidance and
was excluded from the forecast. 06Z GFS and 06Z FV3-GFS were
slower like the ECMWF and its ensemble mean, which have been much
more consistent with the cross-continental flow over the past
several runs compared to the GEFS. Used a blend of those slower
solutions with continuity for a starting point which only resulted
in a few minor changes to the fronts, but perhaps more changes to
the PoPs given timing uncertainties of return flow from the Gulf
this weekend.

...Weather Highlights and Hazards...

Rain and high elevation snows are expected across the
southern/central Rockies Thu-Fri as the leading Pacific system
passes the region. Increasing moisture return ahead of the system
will expand coverage of showers and some thunderstorms across the
southern/central High Plains by Friday. The next system will bring
another round of rain/snow to the Pacific Northwest and Rockies
Fri-Sat, with further increased potential for rain and
thunderstorms, some of which could be heavy, from the
southern/central Plains to the Mississippi Valley through the
weekend. Above average temperatures are expected to develop by
late this week across the Upper Midwest and then gradually spread
eastward across the Great Lakes to the Eastern Seaboard through
the weekend as surface high pressure moves offshore. Maximum
temperatures ranging from 5 to 15 deg F above average are
forecast, with minimum temperatures approaching 20 deg above
average for some areas across the Midwest and Mississippi Valley.
Cooler than average temperatures in the Southwest will moderate a
bit late this weekend ahead of the Pacific system just offshore
next Monday.


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:

3-7 Day Hazards Bullets
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, and the Tennessee Valley, Sun-Mon, Mar 24-Mar
- Flooding possible across portions of the Central/Northern
Plains, the Tennessee Valley, the Middle/Upper Mississippi Valley,
and the Great Lakes.
- Flooding occurring or imminent across portions of the
Northern/Central Plains, Mississippi Valley, the Tennessee Valley,
the Great Lakes, and the Ohio Valley.
- Flooding likely across portions of the Upper/Middle Mississippi
Valley, the Great Lakes, and the Northern Plains.

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

Last Updated: 414 PM EDT MON MAR 18 2019