Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1127 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...
1530 UTC Update...
Models have remained relatively consistent through the medium
range, and the forecast was not changed significantly in this
update. A blend of the 00Z ECMWF/06Z GFS was used to incorporate
the latest deterministic guidance through much of the forecast
period, with a gradual increase in weighting of ECENS/GEFS
ensemble means during the mid to latter portion of the period.
Forecast confidence is slightly above average at the large scales
with the overwhelming majority of solutions showing an upper ridge
axis rebuilding off the Pacific Northwest coast by early next
week, with an amplified upper trough axis shifting into the
Northern Plains, and from the Ohio Valley north toward Hudson Bay.
The main points of contention among the guidance are the specific
track/timing of slow-moving southern stream shortwave energy
moving from the Southern Plains to the Mississippi/Ohio Valleys
Thu-Sun, and its interaction with whatever is left from the system
currently in the Bay of Campeche as it moves north. Further, while
solutions are similar in terms of large scale timing of the
amplified western trough, detail differences remain as to the
specifics of individual shortwaves traversing the larger trough
and their impacts on where the strongest height falls occur and
when. Given no clear outliers, the aforementioned model blend
should smooth out some of these differences and represent a
consensus at this time. See previous discussion below for further
details on the excessive rain/flash flooding threat expected
across much of the central/eastern U.S. during the medium range.
Ryan
Previous Discussion (issued at 0540 UTC)...
...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