Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Fri Apr 05 2019
Valid 12Z Mon Apr 08 2019 - 12Z Fri Apr 12 2019
...Overview and guidance assessment...
The WPC medium range product suite was derived from a blend of the
12 UTC ECMWF and 12z ECMWF/GEFS ensemble means. These guidance
options were well clustered with the forecast evolution of the
larger scale systems. A composite blend provided good run to run
continuity and addresses minor timing/intensity differences.
...Western and Central US...
The models show two primary upper level troughs that move onshore
across the west coast from the eastern Pacific and spread inland.
The initial trough is offshore over the northeast Pacific 12z Mon,
and moves onshore after 00z, an din most solutions onshore by 12z
Tue 09 Apr. The models show steady forward progression across the
Rockies and then high Plains by 12z Wed.
The 12z ECMWF and 18z GFS runs continue to show once the upper
trough reaches the high Plains,
the low reforms in the high central Plains and intensifies into a
strong cyclone Wed as the cyclone moves northeast, reaching the MS
Valley by 12z Thu and then the Great Lakes by 12z Fri 12 Apr. The
12z ECMWF was on the northwest fringe of the suite of forecast
models/members
Upstream, an upper level trough energy reaching the northeastern
Pacific is expected to reach the West Coast Thu 11 Apr, amplifying
as it continues inland on Fri 12 Apr. There is better than average
agreement among the 18z GEFS Mean/12z ECMWF Ensemble Mean, and 12z
ECMWF to warrant a consensus of these solutions to be used in the
forecast (for example, the 12z Fri surface low positions over
southern NV near the AZ border are close among the 12z
ECMWF/19-00z GFS models and the 12z ECMWF and 18z GEFS ensemble
means).
...Eastern US...
A leading upper trough over the Great Lakes Mon with a surface low
and trailing wavy cold front progress slowly east with models
models indicating triple point low development along the New
England coast early Tue and then moving offshore thereafter. The
trailing cold front moves off the southeast coast on Wed with
building high pressure in the lakes producing cold air advection
across the northeast and mid Atlantic.
The next closed low coming out of the central US on day 6 is
forecast to move towards the Great Lakes day 7. The respective
ensemble means from the 18z GEFS and 12z ECMWF produced a low
position in between the operational 12z ECMWF and 18z GFS,
providing an intermediate solution that is where we would usually
indicate a preferred cyclone position in between the 12z ECMWF and
18z GFS forecasts in most cases. The low would induce a warm
front to move north across the mid Atlantic towards Long Island
and southern New England Fri 12 Apr.
The 00z GFS has come in with a forward progression that is much
faster, and appears to be an outlier solution, so is considered
low probability, particularly given .
...Weather Highlights/Hazards...
Areas of terrain-enhanced rain and higher elevation snow are
forecast from northern California and Oregon into Idaho, southern
Montana, and Wyoming early next week. Current guidance suggests
best potential for heaviest activity will be centered along the
West Coast near the California/Oregon border and the Oregon
Cascades.
Continued progression of this system should spread precipitation
across the north-central Rockies, Plains, Mid-Upper Mississippi
Valley, and eventually Ohio Valley and Great Lakes. Some activity
may be heavy and areas with ongoing flooding concerns will need to
monitor this system. In addition there is potential for strong
winds to be an issue north of the low pressure center as it tracks
from the central Plains towards the lakes. There is also a threat
of snow in the northern periphery of the precip shield from the
n-central Plains to the Upper Midwest.
The eastern half of the country will see a broad area of
precipitation with the system progressing eastward from the Lower
Mississippi Valley and central Gulf Coast region and southern
Appalachians early next week. Convection may be strong to severe
over southern areas. Check the SPC outlooks for the latest
probabilities. Significant rainfall is also possible from the
Ohio Valley into northern Mid-Atlantic/Northeast. Snow should be
confined mostly to northern New England Mon-Wed in this pattern as
moisture advects northward into a cooled/receding surface ridge.
The warm sector of the central-eastern U.S. system Mon will
provide much above normal temperatures. Morning lows will be
particularly anomalous with many locations 15-25F above normal Mon
in the Ohio Valley to central Appalachians and daily record warm
low values may be challenged. On Tue the anomalies of 15-20F
above normal for the min temperatures shift to the mid Atlantic
states, and in southern NV to western AZ. As the western system
moves east, those southwest warm temps shift into the southern
Plains for Wed morning, and then lower MS Valley for Thu morning,
followed by the Appalachians to east coast Fri morning 12 Apr.
Petersen
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