Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
133 AM EST Fri Jan 11 2019

Valid 12Z Mon Jan 14 2019 - 12Z Fri Jan 18 2019

...California Heavy Precipitation Pattern Next Week...

...Overview...

Steadily progressive and amplified Pacific flow will bring a
series of significant storms to the West Coast next week. As these
systems move eastward, split flow will emerge around an amplified
downstream Great Basin/Rockies upper ridge. Northern stream energy
will amplify as it enters broad cyclonic upper-level flow east of
the ridge, with frequent shortwaves and mean upper troughing from
the Upper Midwest to the Northeast. Lead Mid-Atlantic coastal low
development this weekend will track northeastward over the western
Atlantic and Canadian Maritimes early next week. Meanwhile, an
active West Coast will feature amplified trough/upper lows to
especially threaten California all next week.


...Guidance Evaluation/Preferences...

The WPC medium range product suite was primarily derived from a
composite multi model and ensemble blend early next week, with
increased emphasis applied to ensemble mean guidance in the days
5-7 timeframe amid quickly growing deterministic guidance run to
run variance. Despite this uncertainty, forecast confidence is
good in the overall pattern including a threat of heavy
precipitation with California focus next week.

...Weather Highlights/Hazards...

A lead coastal low pressure system lifting off the Eastern
Seaboard Mon/Tue will be a maritime threat as the system deepens
offshore. The West Coast will remain quite active given the rapid
frequency of shortwave energies and frontal systems. The heaviest
precipitation (low elevation rain and mountain snow) will be
focused across California, with multiple rounds of precipitation
possible through the forecast period. Total precipitation amounts
over the period could be heavy, with upslope flow enhancing QPF to
4 to 8 inches in the Sierra and Coastal Ranges.

Schichtel


WPC medium range 500 mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indexes 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
https://www.wpc.ncep.noaa.gov/heat_index.shtml