Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EDT Sun Mar 17 2019
Valid 12Z Wed Mar 20 2019 - 12Z Sun Mar 24 2019
...Overview and Guidance Assessment/Preferences...
Models/ensembles show broad agreement that an anomalous upper
ridge axis initially extending from the Canadian Rockies and
prairies south into the north central U.S. by the midweek should
slowly shift eastward during the forecast period, while perhaps
weakening of disbursing somewhat. Shortwave energy from the
Pacific will undercut the ridge, slowly progressing east from
California to the Mississippi Valley Thu-Sun. A mean trough will
persist downstream of the ridge, reinforced across the lower Great
Lakes and the Northeast late in the week by a vigorous shortwave
traversing the northwesterly flow late in the week. Meanwhile, as
the ridge slides east, height falls should reach the Pacific
Northwest by the weekend, bringing a return to a more active
weather pattern for the West Coast.
A blend of the ECMWF/GFS/CMC was used a basis for the forecast
through much of the period. Models have continued to trend deeper
with shortwave energy crossing the Midwest and Mississippi Valley
Wed-Thu, with some continued timing and structural differences.
Consensus has improved over recent days with respect to the
southern stream shortwave as well, with guidance in general
agreement that an upper low should close off across the Southwest
by Thu then slowly drifting east into the central U.S. Again, some
timing differences are evident but solutions are generally
well-clustered around the ensemble means, lending at least some
degree of increased confidence to solutions within the center of
the spread. Finally, while there is broad agreement on height
falls and a cold front reaching the West Coast by next weekend,
models continue to show variability on the structure of the trough
and the embedded smaller-scale shortwaves. Given these
considerations, weighting of the ECENS and NAEFS ensemble means in
the forecast was increased significantly by days 6-7 (Sat-Sun).
...Weather Highlights and Hazards...
The southern stream system will bring rain and mountain snows from
California to much of the Four Corners region Wed-Thu. As moisture
increases ahead of the system across the Southern Plains Fri-Sat,
showers and thunderstorms are expected to become more widespread
across that region, with the potential for some areas of heavy
rain. Rain and mountain snow should spread into the Pacific
Northwest and northern California by Fri-Sat as the upper trough
and cold front approaches, with heavy precipitation possible in
favored terrain areas. Gradually warming temperatures are expected
across much of the northern tier. The warmest temperatures will
initially be across the Pacific Northwest, with highs 5-15 deg F
above average Wed-Thu. The warm conditions will spread east along
with the upper-level ridge, with high temperatures anomalies of
similar magnitude reaching the Midwest by Fri-Sat, and portions of
the Mid-Atlantic and Northeast by next Sun.
Ryan
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