Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Sun Jun 02 2019
Valid 12Z Wed Jun 05 2019 - 12Z Sun Jun 09 2019
...A heavy convection/rainfall and flood/flash flooding threat to
spread slowly northeastward next week from the south-central
Plains to the lower and mid Mississippi Valley, Tennessee Valley
and lower and mid Ohio Valley...
...Overview and Weather/Threats Highlights with
Guidance/Uncertainty Assessment...
Split flow remains evident over North America. In an active
southern stream an amplified upper-level trough will be kicked
slowly from the Southwest to Mid South next week together with
tropical moisture currently consolidating over the southern Gulf
of Mexico. This would fuel a potentially heavy pre-event and
system proximity rainfall threat to spread from southern Texas to
the Ohio Valley. Models and ensembles are in decent agreement on
the slow progression of the upper-level trough and associated and
moisture/instability pooling surface low. This pattern by itself
would represent a heavy rain threat. The more uncertain part of
the forecast continues to be with a potential tropical system that
may consolidate over the Bay of Campeche and how much of the
associated moisture will be drawn northward into the southern
Plains and lower MS Valley. Recent GFS runs jave taken the system
toward the Mexican mountains and deposits much of the moisture in
Mexico before drawing the remaining moisture northward into the
Deep South. Recent ECMWF runs tend to track the system near or
just off northern Mexico, then toward up into the West Gulf Coast.
Recent Canadian models represent the most convective solution with
the eastern-most extreme track, taking the system faster and
stronger along the Texas coast next Wednesday and across Louisiana
next Thursday. With the consideration of the upper-level trough
moving slowly eastward across the Plains next week and the
convective nature of the tropical system, the eastern solutions
indicated by at least the ECMWF and cannot be ruled out, but early
indications from the NHC seem to favor system dissipation over
Mexico.
Meanwhile, potentially amplified northern stream flow offers a
mean upper trough over the Northwest and lead upper trough well
downstream over New England, sandwiching warming upper ridging.
The most uncertain part of the forecast concerns amplitude and
progression of these moderate precipitation focusing and cooling
troughs late next week. The ECMWF and to a lesser extent ECMWF
ensembles have been forecasting a more amplified and slower
progressing pattern than other guidance. WPC favors a solution
slightly on the more amplified side of the full envelope of
solutions given overall blocky hemispheric flow pattern
characteristics. This better favors some June snows for the
northern Rockies.
Overall, the WPC medium range product suite was mainly derived
from a 18/00 UTC GFS/GEFS mean and 12 UTC ECMWF/ECMWF ensemble
mean blend. Blend weightings slightly favor amplitude and shift
more in favor of the ensemble means days 5-7. In this pattern
there remains a growing signal in support of a heavy rainfall
threat next week from the south-central Plains to the mid-lower
Mississippi Valley, Tennessee Valley and lower-mid Ohio Valley in
a region already inundated with heavy rainfall and flooding
issues.
Kong/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