Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1203 PM EDT Sun Mar 31 2019
Valid 12Z Wed Apr 03 2019 - 12Z Sun Apr 07 2019
...Overview...
Today's guidance remains fairly agreeable and consistent in
showing a progression of shortwaves from the Pacific into and
across portions of the Lower 48, with a corresponding series of
surface systems. The northwest periphery of strong low pressure
off the East Coast on Wed may have some influence on New England's
coastal areas as the system tracks northeastward. Then shortwave
energy over the West on Wed will make steady progress and push a
wave/frontal system across the central/eastern states during the
latter half of the week. The northern part of incoming Pacific
energy Thu-Fri should weaken as it heads into a developing western
Canada ridge but the southern part will likely continue across the
southern U.S. and northern Mexico. Then a fairly strong shortwave
should reach the West Coast around Sat with continued progression
thereafter, perhaps followed by yet more energy brushing the
Pacific Northwest late next weekend. The combination of these
systems will likely bring precipitation to most of the CONUS at
some point during the Wed-Sun period, with the southern third or
quarter of the West the most likely area to stay dry.
...Guidance Assessment/Preferences...
Model/ensemble clustering has improved dramatically for the storm
off the East Coast as of early Wed with a location just southeast
of the 40/70 benchmark. However note there are some smaller but
locally significant differences that persist even in the
short-range time frame. Otherwise guidance continues to agree
fairly well with the existence of each feature in the
Pacific/CONUS stream but still displays spread/uncertainty for
specifics. Favored keeping a consensus approach that was obtained
through a blend of the deterministic models (00Z
GFS/ECMWF/Canadian and 06Z GFS/FV3-GFS) along with continuity
during the period. This matched quite well with the ensemble
consensus but with a bit more detail.
The shortwave and associated low pressure reaching the Plains
around Thu agrees fairly well in the guidance up to that time.
Solutions then differ on exactly how energy will be distributed
within the overall trough aloft--along with strength and track of
best-defined surface low pressure. Fast moving northern tier
energy may also feed into the upper trough as it reaches the
eastern U.S., providing added complexity to the forecast. This
type of evolution tends not to be easily resolved in the extended
time frame. Middle ground solution was employed. By early Fri
ensemble members are still varied north-south but have trended
toward a consensus position near southern Indiana between the more
southerly ECMWF ensembles and more northerly GEFS ensembles. That
system should exit off the coast near the NY bight per the best
multi-ensemble overlap.
Farther upstream composite blend represents established consensus
with little continuity change for the southern stream Pacific
shortwave that eventually heads into the southern Plains, as well
as for the vigorous shortwave reaching the West Coast around early
Sat. Establishment of Pacific troughing south of Alaska will
temper height falls a bit into the Pacific Northwest.
...Weather Highlights/Hazards...
The series of systems affecting the West will bring at least two
or three periods of enhanced rain and high elevation snow. Expect
highest totals for the five-day period to be along favored terrain
from northern California/Sierra Nevada through the Pacific
Northwest. Moisture will extend through the Intermountain West
and northern-central Rockies, with some significant precipitation
over these areas as well but with less extreme totals relative to
areas near the coast. The system emerging into the Plains on Wed
and reaching the East Coast toward the end of the week will spread
a broad shield of precipitation across the eastern half of the
country with embedded convection. SPC has noted a 15% chance of
severe thunderstorms on Wed/Thu over OK/lower MS Valley,
respectively. There is still less than desired agreement on areas
of heaviest rainfall but at least localized pockets of moderate to
heavy rainfall may be possible over parts of the sensitive eastern
Plains/Mississippi Valley region and then into the Northeast. The
northern periphery of the moisture shield may contain snow with
best potential from the north-central Plains into New England.
Today's guidance is showing a stronger signal for heavy rainfall
potential over parts of the southern Plains and possibly into the
Lower Mississippi Valley from about Fri night through the weekend.
This activity should be encouraged by the combination of an
approaching southern stream shortwave aloft and low level Gulf
inflow interacting with a front expected to stall near the Gulf
Coast. During the day Wed most precipitation with the western
Atlantic storm should be mostly confined to areas near the New
England coast.
Steady progression of systems across the Lower 48 will provide
some day-to-day variability of temperatures. Within this pattern
the general evolution of mean flow will likely be toward more
above average heights aloft with time, corresponding to increasing
coverage of above average temperatures from midweek through the
weekend. The areas of clouds and precipitation accompanying each
system will tend to favor greater warm extremes for morning lows
with some areas of plus 10-20F anomalies. In terms of five-day
averages the Interior West into the Plains should see warmest
temperatures relative to climatology. Plus 10F or greater
anomalies for highs are most likely over the parts of the Plains
Fri-Sun.
Fracasso/Rausch
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