Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
419 PM EST Wed Feb 27 2019
Valid 12Z Sat Mar 02 2019 - 12Z Wed Mar 06 2019
...Pattern Overview...
Broadly cyclonic mean flow across the CONUS at the start of the
weekend should transition toward increasingly amplified troughing
over the East by the middle of next week as an upper ridge reaches
the Rockies and a trailing trough approaches the West Coast.
...Guidance Evaluation/Preferences...
Forecast was kept fairly close to continuity in this update with
only minor adjustments. Models continue to show good agreement at
the larger scales through the period, but with some significant
differences surrounding smaller-scale features. Fast-moving and
low amplitude shortwave energy arriving at the West Coast on day 3
(Sat) is key in the evolution of a wave of low pressure across the
eastern U.S. Sun-Mon. The deterministic 00Z ECMWF was a bit faster
with this energy than the consensus throughout this time frame,
which ends up resulting in a surface wave tracking farther
north/west across the eastern U.S. by Sun. Models have shown a
trend toward a less suppressed system across the East Sun, with
the GFS lagging the trend. The solutions best clustered with the
ensemble consensus throughout with respect to this feature seemed
to be the 00Z UKMET/CMC and 06Z FV3-GFS, and a blend of these
solutions formed a basis for the forecast during days 3-5. The
eventual track of this surface low by Sun-Mon will have
significant implications in terms of p-type for portions of the
Mid-Atlantic and Northeast, including the major cities, the
forecast for which is highly uncertain at this time. Later in the
forecast period, as arctic high pressure continues to spread cold
air south into the central and portions of the eastern U.S., the
most active weather will shift to the West coast, with general
consensus that a low pressure system should approach the coast by
the middle of next week. Solutions differ rather substantially on
timing, however, while the ensemble means show a bit more
consensus. Thus, the forecast during days 6-7 (Tue-Wed) placed
heavy emphasis on the 00Z ECENS/06Z GEFS ensemble means.
...Weather Highlights/Hazards...
Across the West the primary axis for heaviest rain and higher
elevation snow will extend from California eastward through the
central/south-central Rockies with the Sierra Nevada likely seeing
the highest 5-day totals. Two systems will affect the region
during the period, one arriving early in the weekend and spreading
moisture rapidly eastward then followed by a second arriving
Tue-Wed. As moisture from the second system spreads northward
there may be potential for wintry precipitation at low elevations
over interior portions of the Northwest given the cold air likely
to be in place.
The system affecting the Northeast during the weekend should bring
some snowfall to the region but weakening and possibly offshore
trends for low pressure as well as fast progression may limit
accumulations. Southern stream energy interacting with the
trailing front may produce a period of heavy rainfall over parts
of the Southeast with the weekend into early Mon time frame the
most likely period for this activity. Guidance has not yet fully
converged for details so confidence is only moderate thus far.
Snow will be possible in the northern part of the moisture
shield--from the south-central Mississippi Valley into the
Mid-Atlantic. Lighter rainfall could linger over parts of the
extreme Southeast/Florida into next week.
Within the widespread area of extremely cold air over the central
U.S., expect the most extreme anomalies to be over the
northern-central Plains during Sat-Mon with anomalies of 30-45F
below normal. Especially on Sun-Mon many places over the Plains
and Midwest should challenge or exceed daily record
values--especially for cold highs but also for morning lows at
some locations. Less extensive coverage of daily records may
continue into Tue. The eastern U.S. will see a modified form of
this cold air by the first half of next week with readings "only"
10-20F below normal. Localized parts of the interior Northwest
may see temperatures 10-30F below normal. Relative warmth will be
confined to the southern half of the West and more so for morning
lows than afternoon highs.
Ryan/Rausch
Hazards:
- Heavy precipitation across portions of the Northeast, the
Central Appalachians, the Middle Mississippi Valley, the
Mid-Atlantic, the Great Lakes, and the Ohio Valley, Sun-Mon, Mar
3-Mar 4.
- Heavy rain across portions of California, the Central Great
Basin, the Pacific Northwest, and the Southwest, Sat-Wed, Mar
2-Mar 6.
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the
Southeast, and the Ohio Valley, Sat-Sun, Mar 2-Mar 3.
- Heavy snow across portions of the Northeast, the Central Great
Basin, the Pacific Northwest, the Northern Great Basin,
California, the Great Lakes, and the Southwest, Sat, Mar 2.
- Heavy snow across portions of the Southern Rockies, the Central
Rockies, the Central Great Basin, the Central Plains, and the
Southwest, Sat-Sun, Mar 2-Mar 3.
- Flooding possible across portions of the Southeast and the
Mid-Atlantic.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley, the Tennessee Valley, the Great Lakes, the
Middle Mississippi Valley, the Mid-Atlantic, the Upper Mississippi
Valley, the Southeast, the Pacific Northwest, and the Ohio Valley.
- Flooding likely across portions of the Southeast, the
Mid-Atlantic, and California.
- Much below normal temperatures across much of the eastern
two-thirds of the country including the interior sections of the
Pacific Northwest, Sat-Wed, Mar 2-Mar 6.
- High winds across portions of mainland Alaska and the Aleutians,
Mon-Tue, Mar 4-Mar 5.
- High winds across portions of the Aleutians, Sun-Mon, Mar 3-Mar
4.
and Wed, Mar 6.
- High significant wave heights for coastal portions of mainland
Alaska, Mon-Tue, Mar 4-Mar 5.
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml