Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Fri Mar 22 2019
Valid 12Z Mon Mar 25 2019 - 12Z Fri Mar 29 2019
...Overview...
The 00Z and 06Z suite of models continued to portray general
agreement in the overall pattern of an upper low in the eastern
Pacific (off the U.S. West Coast), ridging into the western and
central CONUS, and a deep upper low in eastern Canada that creates
troughing in the eastern CONUS on day 3 (Mon). This pattern will
be slow-moving on days 3-5 (Mon-Wed), before the upper low in the
eastern Pacific begins breaking down and sends energy into the
western CONUS by Thu and the central CONUS on Fri.
...Guidance Assessment/Preferences...
Days 3-5 in the medium range were marked by general model
agreement between the 00Z/06Z GFS, 00Z GEFS, 00Z ECMWF/its
ensemble, and the 00Z UKMET, so was able to include components of
all these models in the blend, rather than attempting to select
which model's small-scale features would prevail. Did exclude the
CMC from the blend as it broke down the eastern Pacific upper low
more quickly than the other models, by day 5/Wed. Model spread
increases quite a bit as the upper low moves into the West and
weakens/becomes associated with a deep trough in central Canada,
as each model handles shortwaves embedded in the trough
differently. Thus by day 6-7 we leaned toward the 00Z GEFS and EC
means, with a lower percentage of the operational ECMWF from 00Z.
The 00Z GFS strengthened a trough in the central CONUS more than
other models, while the 06Z GFS focused on a trough oriented
differently in the western U.S. The 00Z ECMWF seemed like a
compromise of these features and seemed similar enough to the
means to incorporate some of it, and wanted to stay away from the
inconsistency of the GFS runs.
...Weather Highlights and Hazards...
This medium range period starts Monday/Tuesday as a southern
stream front with several moisture/enhanced precipitation focusing
waves ejects across the South/Southeast/and Mid-Atlantic. These
waves cut underneath/interact with a cooling northern stream
frontal drape whose post-frontal high pressure builds down through
the central and eastern U.S.
Meanwhile, a protracted series of Pacific systems with associated
height falls and enhanced precipitation swaths will track onshore
and across much of the West early through mid next week in advance
of an mean closed low/trough reinforced just off West Coast.
Expect heaviest precipitation/heavy mountain snows threats from
northern California/Oregon to the northern Rockies. Indication
that the bulk of Pacific trough energy will eject through the West
Wed/Thu to emerge over the Plains later next week to induce
cyclo/frontogenesis. This may occur just as a renewed northern
stream may force cool air down into the unsettled n-central
states. This airmass would prove to be in stark contrast to a
rapidly warming airmass spreading over the e-central U.S. where
moist Gulf return flow may fuel an expanding risk of enhancing
rains/convection channeling between the surging fronts and
retreating eastern U.S. high pressure. Thus, heavy rain is
possible somewhere in the Mississippi Valley/Midwest (where
flooding is ongoing) by late in the medium range period, but
uncertainty remains high regarding rainfall amounts and placement
of the heaviest rainfall.
Tate/Schichtel
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