Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
251 AM EDT Sat Jun 01 2019
Valid 12Z Tue Jun 04 2019 - 12Z Sat Jun 08 2019
...Heavy Rainfall Threat from South-Central Plains to the
Mid-Lower Mississippi Valley, Tennessee Valley and lower Ohio
Valley next week...
...Overview and Weather/Threats Highlights...
Potent North Pacific upper-level jet energies split in approach to
the West Coast of North America. In the southern stream, an
upper-level low/trough will linger over southern California and
the Desert Southwest, only very slowly moving eastward after
midweek. This will nudge eastward a lead hot subtropical ridge
over the south-central U.S. and the Gulf of Mexico. A persistent
and amplified upper low over southeastern Canada will position to
the lee of central Canadian upper ridging. This will allow
incoming northern stream shortwaves to periodically amplify from
the Great Lakes to the Mid-Atlantic/Northeast.
Relatively slow-progressing southern stream shortwaves will
periodically eject eastward from the Southwest low early next
week, reaching the central U.S. and potentially interacting with
amplifying northern stream energy. These waves along with return
flow across a persistent baroclinic zone may continue to support
areas of increased convective risk from the Southern/Central
Plains into the mid-lower Mississippi Valley, Tennessee Valley and
lower Ohio Valley. This offers a risk of episodes of locally heavy
rainfall/flash flooding as well as strong to severe
thunderstorms/MCS activity. This threat may become more widespread
when the upper low/trough over the unsettled Southwest ejects more
bodily to the central U.S. to spawn lead Gulf of Mexico/tropical
moisture return. System ejection is in response to the amplified
approach of kicker Pacific energy upstream across the West Coast.
Kicker trough height falls themselves will support the spread of
moderate and terrain enhancing precipitation across the
Northwest/West later next week in unseasonably cooling and
unsettling late Spring flow.
...Guidance/Uncertainty Assessment...
The WPC medium range product suite was mainly derived from a
composite blend of well clustered 18/00 UTC GFS/FV3/GEFS mean and
12 UTC UKMET/ECMWF/ECMWF ensemble mean guidance in a pattern with
average to below average mass field forecast spread. A main heavy
convective rainfall focus is less predictable within this pattern,
but there is a growing signal supporting a threat from the
south-central Plains to the mid-lower Mississippi Valley,
Tennessee Valley and lower Ohio Valley in a region already
inundated with heavy rainfall and flooding issues.
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