Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1153 AM EDT Mon Apr 15 2019
Valid 12Z Thu Apr 18 2019 - 12Z Mon Apr 22 2019
16Z Update: The deterministic models remain in above average
agreement across the continental U.S. through Saturday with an
amplified upper level pattern in place. The 6Z FV3 GFS solution
is closer to the ensemble means with the main surface low across
the Great Lakes for the end of the week, whereas the operational
GFS is farther south with the closed low over the Tennessee River
valley, so more of the FV3 was incorporated into the forecast.
The operational ECMWF has indicated better run-to-run continuity
with the East Coast storm system compared to the other guidance,
and was also part of the forecast process. The more uncertain
aspect to this forecast relates to the likely development of a
secondary low off the East Coast by Sunday, and the models are
still resolving this potential feature. By the end of the
forecast period next Monday, a new surface low will likely evolve
across the High Plains in response to the next Pacific trough
moving across the western U.S., with the operational GFS among the
most amplified solutions. This storm system may be the next
significant weather event going into the beginning of next week.
The previous overnight discussion is appended below for reference.
Hamrick
...Overview...
Progressive but amplified pattern will support a dynamic system
moving through the central states Thu/Fri into the east by the
weekend but possibly taking until next week to fully move
offshore. The west will see a front move into Washington/Oregon
early Friday and then progress eastward and southward into the
Plains and southern Rockies late this weekend into next Monday.
...Guidance Preferences...
Blend of the 18Z GFS/GEFS and 12Z ECMWF/ECMWF ensemble mean
offered a reasonable starting point to the medium range period,
with a deterministic-centered blend including the UKMET/Canadian
to start and a 2/5ths ensemble weighting by next Monday. This
maintained good continuity overall as the pattern remains fairly
well-handled by the ensembles after earlier uncertainties. Still,
questions remain in how the eastern system evolves depending on
the strength/track of mid-level shortwaves not easily resolved at
this lead time. Ensemble clustering suggested a slowing of the
front along or just off the east coast with a new surface low/wave
developing near the Mid-Atlantic before turning northeastward.
Residence time near New England should be limited due to the
approaching system from the west by that time.
...Weather Highlights/Threats...
Multi-inch rainfall totals with local flooding are probable
(enhanced in embedded convection) along/ahead of the front over
the lower Mississippi Valley (possibly into parts of the Southeast
and Mid-Atlantic) with lesser amounts in a local max area to the
north/northeast of the surface low across Wisconsin. Consult SPC
for the latest on the severe weather risk. Mild temperatures will
precede the front (10-15F above average) to be replaced by cooler
than average temperatures after its passage. The Northwest will
see generally light precipitation along a front push through the
Great Basin and central Rockies this weekend into next Monday.
Fracasso
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