Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
140 AM EDT Mon Jun 03 2019
Valid 12Z Thu Jun 06 2019 - 12Z Mon Jun 10 2019
...Excessive Rain and Flash Flood/Flooding Threat to slowly spread
Thursday to next Monday from the south-central Plains and
Mid-Lower Mississippi Valley to the Tennessee/Ohio Valleys and
Southeast/Appalachians/Mid-Atlantic...
...Guidance/Predictability and Weather/Hazards Highlights...
An amplified upper-level trough/height falls and surface system in
a split southern stream will track from the south-central Plains
to the Appalachians. Deep moisture return from the Gulf of Mexico
will feed into the system to fuel a widespread threat of heavy
rain and flash flooding/flooding. There is a strong pattern and
guidance signal in support of an excessive rain and flash
flood/flooding event to slowly spread Thursday-next Monday from
the south-central Plains/Mid-Lower Mississippi Valley to the
Tennessee/Ohio Valleys and Southeast/Appalachians/Mid-Atlantic.
This threat will include a risk of repeat/training of convective
cells considering the slow system progression as common in
guidance. Cumulative WPC day 4-7 qpf offers an expansive 2-5" mean
areal rainfall that implies much higher, but less predictable
local amounts. These are partly contingent on the less certain
full extent of deepest tropical moisture to pool into the system
and the National Hurricane Center continues to monitor a
disturbance over the Bay of Campeche.
Meanwhile, models continue to show development of a
significant/anomalous cooling upper trough from the northern
stream flow to move across the Northwest/West to the north-central
Plains late week into early next week. While guidance seems to be
slowly converging on a more clustered forecast, bolstering
confidence, there still remains quite a bit of uncertainty with
respect to the amplitude and evolution of this trough and heavier
precipitation focus. The ECMWF and to a lesser extent ECMWF
ensembles have been forecasting a more amplified and slower
progression than most other guidance. WPC favors a solution
slightly on the amplified side of the full guidance envelope given
overall blocky hemispheric flow pattern characteristics. This
would also favor June snows for the higher elevations of the
northern Rockies in this pattern as highlighted in the WPC medium
range winter weather outlook probabilities.
Overall, the WPC medium range product suite was primarily derived
from a composite of the 12 UTC GFS/FV3/ECMWF/UKMET and GEFS/ECMWF
ensemble mean along with the National Blend of Models, shifting
WPC blend weightings slightly in favor of the ECMWF/ECMWF ensemble
mean over time. This solution maintains good WPC continuity.
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