WPC Medium Range Archive
Medium Range Products Valid On:
(Day 7 PMDEPD: Valid 11/18/2019 to 11/22/2019)
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 PM EST Fri Nov 15 2019
Valid 12Z Mon Nov 18 2019 - 12Z Fri Nov 22 2019
...Pattern Overview and Guidance/Predictability Assessment...
The large scale pattern will feature moderately progressive
northern stream flow with a tendency for upper troughing in the
East, while some energy nearing the West Coast will drop southward
into a slow-moving closed low. One upper low already west of Baja
California at the start of the period early Mon will promote a
northward flow of moisture associated with Tropical Storm Raymond.
Some energy within a trough nearing the West Coast by early Tue
should brush the northern tier while the rest drops into an upper
low forecast to close off over or near California, and in the
process eject the upper low initially to the south. The
California upper low should drift slowly eastward late next week.
Northern tier/Canada trough energy should reach the East by Fri,
replacing the amplified trough over the East during Mon-Wed.
Ahead of the initial eastern trough aloft, guidance continues to
show two defined systems but with poor clustering/continuity. The
first one, tracking close to New England Mon-Mon night, has had a
wide track spread (due to smaller scale detail differences aloft)
with significant influence on the degree of sensible weather
impacts over the Northeast. Majority model/ensemble clustering
and continuity leaned toward latest ECMWF/GFS runs and their means
so the updated forecast put greater emphasis on that scenario.
However UKMET/CMC runs including the 12Z cycle and a number of 00Z
CMC ensembles have advertised a farther west track and could have
some validity. For updated model preferences based on 12Z data
please refer to the Model Diagnostics Discussion PMDHMD. Models
and ensembles still show a second system developing off the East
Coast from about late Tue onward but with 24-hour trends showing a
farther offshore track and less impact on the East Coast.
Details differ but there is fair agreement that some leading
trough energy coming into the West by Tue will cross the
northwestern U.S. while the rest drops into a closed low over or
near California. Latest CMC runs have been showing the farthest
west track with the 00Z ECMWF a little eastward, while remaining
solutions are along the coast or inland. By late in the week the
GFS and ECMWF have varied with their timing of ejection. The old
12Z/14 ECMWF was faster than most other recent runs while the 00Z
GFS was closer to the 00Z ECMWF than the 06Z run. The combination
of ridging to the north/northwest of the upper low and
distant/weak nature of upstream Pacific energy seem to favor
timing in the middle to slower half of the spread--leaving the 00Z
ECMWF/00Z GFS (CMC not out of the question but perhaps a tad
extreme) as the closest operational models fitting this idea.
Toward the end of the week the operational models and ECMWF/CMC
means provide a good signal for what could be a fairly vigorous
system reaching the Great Lakes-New England and/or southeast
Canada in association with the shortwave energy reaching western
North America earlier in the week. GEFS means have been much less
defined with the system.
Based on above considerations the forecast blend during the first
half of the period emphasized the 00Z ECMWF and a little less 00Z
GFS, with modest CMC/UKMET input. By days 6-7 Thu-Fri the
forecast blend transitioned to a model/mean blend incorporating
the 00Z ECMWF/GFS/CMC in order of highest to lowest weight along
with more ECMWF mean than GEFS mean.
The most prominent signal for significant focused precipitation
exists over the Southwest and vicinity, near and ahead of the
mid-late week upper low. The best model/ensemble agreement for
highest totals remains over the favored terrain of central
Arizona. Depending on the exact path of the upper low there may
also be a period of significant precip along the coastal ranges of
southern California and possibly over other locations between
southern California and southern Nevada/Utah/Colorado. Moisture
from T.S. Raymond could enhance precipitation totals. Expect
mostly rain over southern areas with some higher elevation snow
possible over the Great Basin/central Rockies. Highest elevations
to the south could see a little snow if the upper low is
Northern parts of the West will see rain and high elevation snow
during the first half of the week with snow levels decreasing as
precip trends lighter. Some of this moisture should extend
eastward across the northern tier in the form of snow around
midweek. Developing low pressure later in the week may produce
higher amounts--snow north and rain south--over parts of the Great
Lakes/Northeast but with sensitivity to exact surface low track.
Rainfall of varying intensity should accompany the trailing cold
front over the central/eastern states.
The leading system tracking near/offshore New England should bring
some precipitation into the Northeast early in the week, with some
snow possible over higher elevation/inland areas and rain closer
to the coast. The tight pressure gradient around the
northern/western side of the system may produce a period of strong
winds. Poor agreement with exact track keeps confidence lower
than desired for the coverage and intensity of effects over the
Northeast. There is lingering uncertainty for the second offshore
system around midweek but at the moment there is better agreement
that most effects should bypass New England.
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
- Heavy rain across portions of the Southwest, Wed-Fri, Nov 20-Nov
- Flooding occurring or imminent across portions of the Northern
- High winds across portions of the Mid-Atlantic and the
Northeast, Mon, Nov 18.
- Much above normal temperatures across portions of the Central
Plains, the Central Great Basin, the Northern/Central Rockies,
California, the Northern Great Basin, the Pacific Northwest, and
the Southwest, Mon-Tue, Nov 18-Nov 19.
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at: