Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
142 AM EDT Fri Mar 15 2019
Valid 12Z Mon Mar 18 2019 - 12Z Fri Mar 22 2019
...Overview...
A blocking mid/upper-level ridge initially centered from the
Pacific Northwest to western Canada early next week is expected to
very slowly shift eastward through the forecast period. With the
ridge axis across western North America early next week, a mean
trough will be in place across the Great Lakes/Northeast, with
numerous small scale shortwaves traversing the larger trough.
Strong westerly flow across the North Central Pacific will split
as it encounters the ridge, with some shortwave energy directed
north into the higher latitudes of Canada, and some separating
into the southern stream. By the latter portion of next week as
the western ridge axis shifts east, this may allow for stronger
height falls from the North Pacific to approach the Pacific
Northwest.
...Guidance Assessment/Preferences...
In general a blend of deterministic models (ECMWF/GFS/CMC/UKMET)
served as a good forecast starting point during days 3-5
(Mon-Wed). Overall, spread was relatively low during this time
frame. Models differed on the amplitude of a northern stream
trough digging into the central U.S. Tue-Wed, but no clear
outliers were evident and a consensus approach was preferred.
Models were also initially very similar with handling of an
amplified southern stream shortwave/upper low approaching
California by Wed. Differences in amplitude emerge as the system
approaches the coast, with the GFS weaker and faster than the
consensus of the ECMWF/UKMET/CMC which show a deeper system and
slower progression. For this reason, the GFS from 12Z Thu (which
was closer to the model/ensemble consensus) was used in the blend
over the later runs. By days 6-7 (Thu-Fri), spread gradually
increases as the southern stream system moves east into the Four
Corners region and stronger height falls approach the Pacific
Northwest. Weighting of the ECENS and NAEFS ensemble means was
boosted during this time period to account for the increased spread
...Weather Highlights and Hazards...
A lingering frontal boundary south of the Florida Peninsula (with
a wave of low pressure developing along it) will support
widespread and potentially heavy rains for the southern half of
the Florida Peninsula Mon-Tue. The southern stream trough/upper
low will spread rain and mountain snow into the Sierra Nevada, the
Great Basin, and the central/southern Rockies by the middle to
latter portion of next week. Precipitation should increase in
coverage across the Pacific Northwest by late the week as the
upper-level trough approaches. Temperatures will initially be 5 to
10 deg F below average early next week across the eastern third of
the U.S. under the influence of the Great Lakes/Northeast upper
trough, but temperatures across these areas will gradually
moderate to near seasonal averages by the mid-latter portion of
the week as the trough lifts out. Much of the West will start next
week 5 to 10 deg above average, and the warm temperatures will
gradually shift east through the week along with the upper ridge.
Temperatures across the Midwest could reach 15 deg above average
by late next week.
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