Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1105 AM EST Sat Feb 16 2019
Valid 12Z Tue Feb 19 2019 - 12Z Sat Feb 23 2019
...Multi-day threat of heavy rain for the Tennessee Valley to
Southern/Central Appalachians, with wintry precipitation likely on
the northern edge in the Mid-Mississippi/Ohio
Valley/Mid-Atlantic...
...Cold weather will persist in the western to central U.S., with
unsettled weather coming into the Southwest...
...Overview...
Troughing in the western U.S. will be persistent during the medium
range period, reinforced by shots of renewed energy. This feature
plus the unyielding upper high in the western Atlantic will create
a favorable pattern for heavy precipitation in the southeastern
U.S.
...Guidance/Predictability Assessment and Preferences...
Model guidance is generally rather agreeable in the large scale
pattern of potent upper troughs/height falls progressing overtop a
northeast Pacific ridge that then dig sharply southward to
reinforce a western U.S. mean trough. Another mid/upper-level
trough will eject from the Southwest to Northeast Tue-Thu, which
guidance also seems to handle well. The medium range suite was
derived from a multi-model blend of the operational 00Z and 06Z
GFS, the 00Z ECMWF, and the 00Z EC ensemble and GEFS means, with
more of a deterministic component than normal by day 6-7 due to
the good model agreement and to maintain details of strength. The
CMC was excluded from the blend, however, as by day 4-5 a trough
in the Gulf of Alaska became more progressive than other models,
which negatively affected the downstream features across the
CONUS.
...Weather Highlights/Hazards...
Heavy precipitation in the southeastern U.S. will be the main
story across the CONUS next week. Lead deep layered and
anomalously moist southwest flow channeled from the Southern
Plains to the East will act to sustain a Southeast ridge and fuel
multi-day threats of heavy rain/training from the Lower
Mississippi/Tennessee Valleys to the Southern/Central
Appalachians. On the northern edge, a cold surface high and cold
air damming in the Mid-Atlantic region is expected, leading to
frozen precipitation. Potentially heavy snow and ice is a
possibility from the Middle Mississippi Valley to Ohio Valley and
northern Mid-Atlantic region.
With anomalously low heights in the western U.S., much below
average temperatures will prevail for the western and central U.S.
A surface low is progged to make its way into California on day 5
(Thu) and move throughout the Southwest the next couple of days,
which will lead to enhanced precipitation for the Southwest,
including higher elevation snow.
Tate/Schichtel
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation and winter weather outlook
probabilities are found 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