Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Sat Jun 10 2023

Valid 12Z Tue Jun 13 2023 - 12Z Sat Jun 17 2023

***Heavy rain and strong storms expected from the Central Plains
to the Mid-South, and early summer heat builds from Texas to
Alabama***

...Synoptic Overview...

A well-defined low is forecast to be in place across the Great
Lakes Tuesday as a shortwave drops south from the Hudson Bay
region.  This will spur surface cyclogenesis across the Ohio
Valley early in the week with a trailing cold front exiting the
East Coast Tuesday morning, and this will likely bring widespread
showers and some storms across the Northeast states.  A second
closed upper low across the southwestern U.S. early in the week is
expected to evolve into a trough and this should reach the
central/southern Plains by Wednesday, and that will likely support
a surface low along the front.  The prospects for widespread
showers and storms increases from Oklahoma eastward across the
Mid-South and the southern Appalachians through the remainder of
the week with episodes of heavy rainfall possible, and building
heat and humidity south of the frontal zone.

...Guidance Evaluation/Predictability Assessment...

The 00Z model guidance suite has consolidated well with the
placement of the upper trough across the Southwest and the low
across Great Lakes region and the corresponding surface features
for the beginning of the week.  The GFS remains slightly more
amplified with the southern stream shortwave crossing the Gulf
Coast region through Thursday, but still has good ensemble
support.  Across the Northwest, the CMC lingers the building upper
trough/closed low compared to the more progressive GFS/ECMWF
solutions.  There is still strong model support for an upper ridge
axis extending northward across Manitoba for the end of the week. 
The WPC forecast incorporated a nearly deterministic model blend
through Wednesday, followed by slightly less weighting of the GFS
and CMC, and more of the ensemble means going into Thursday and
beyond.

...Weather/Hazards Highlights...

The closed low over the Great Lakes and trailing surface cold
front crossing the East Coast will advect copious moisture
northward across the Northeast, and in combination with ample
instability will likely produce storms with locally heavy
rainfall, with a Marginal Risk of excessive rainfall in effect for
Tuesday across eastern New England.  However, the main focus for
heavy rainfall is expected from the Central Plains to the
Tennessee River Valley and the southern Appalachians for the
Wednesday through Friday time period, where an axis of 1-3 inch
rainfall totals with locally higher amounts is likely.  Moisture
advection from the Gulf of Mexico will intersect a
quasi-stationary frontal boundary and shortwave energy aloft will
also aid in ascent.  A few mesoscale convective complexes are
likely to develop near this boundary and result in higher rainfall
rates that could result in instances of flash flooding, and thus a
Slight Risk of excessive rainfall is planned for both Day 4 and 5
from eastern Oklahoma to northern Georgia where the deterministic
guidance and NBM indicate a more concentrated signal for higher
QPF.

In terms of temperatures, the main story that will make headlines
will be the building heat and humidity across much of Texas and
into southern portions of the Deep South states, with the hottest
weather of the season expected thus far.  Widespread mid-upper 90s
are likely from northern Florida to Louisiana, and 100-110 degrees
for much of central and southern Texas away from the coastal
areas.  Some heat indices on the order of 110-120 degrees are
possible across portions of Deep South Texas for the middle to end
of the week with dewpoints well into the 70s.  This heat wave will
likely have some staying power beyond next Saturday based on the
latest forecasts from the Climate Prediction Center.  Elsewhere,
expect pleasantly cooler conditions compared to average across
much of the Southwest to the Central Rockies, and also for much of
the eastern U.S. for the middle of the week, and then a gradual
warming trend going into Thursday and beyond.

Hamrick


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, experimental excessive rainfall
outlook, 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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml