Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
227 PM EDT Fri Jun 09 2023

Valid 12Z Mon Jun 12 2023 - 12Z Fri Jun 16 2023

...Heavy rain and strong storms for portions of the High Plains
and into the Mid-South as deep summer heat builds from Texas to
Alabama...


...Synoptic Overview...

A quite troublesome closed upper low has been anchored in place
across New England downstream of a highly amplified central
continent upper ridge. The low has been a main part of a
long-standing blocky flow pattern over the nation, but will slowly
lift away across the Canadian Maritimes by Monday, with another
well-defined low developing across the Great Lakes 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 reaching the East Coast around Tuesday, and
this will likely bring widespread showers and storms from the
Mid-Atlantic to New England.  A second main closed upper low is
expected to linger across the southwestern U.S. into early next
week and associated energies that should reach the
central/southern Plains by midweek will likely support a surface
frontal low, and this will also tend to increase the prospects for
widespread showers and storms from northern Texas/Oklahoma
eastward with a focus across the Mid-South/vicinity and with an
uncertain axis downstream toward the southern Appalachians
Wednesday through Friday. 

...Guidance Evaluation/Predictability Assessment...

The WPC medium range guidance suite was primarily derived from a
composite blend of reasonably well clustered guidance from the 06
UTC GFS and 00 UTC ECMWF/UKMET/Canadian models along with the 13
UTC National Blend of Models valid for early to mid next week.
This solution has favorable ensemble support and maintains good
WPC product continuity in an overall pattern with seemingly above
normal predictability. Forecast spread/uncertainty remain lower
than normal into later next week, but prompted inclusion of some
of the latest GEFS/ECMWF ensemble guidance in place of the 06 UTC
GFS that seemed too progressive at these longer time frames within
less certain southern stream flow system and convective focus
details. The 12 UTC GFS has trended slower.

...Weather/Hazards Highlights...

A daily risk for heavy showers and strong to severe thunderstorms
from the Southern Plains to the northern Rockies and westward into
the Great Basin is expected to be slow to dislodge through about
mid-week, as tropical Pacific moisture advects northward between a
strong central U.S. upper ridge and an upper low/trough parked
over California/Southwest early in the week.  A weakening boundary
through the region should also help to enhance rainfall totals,
with particular concerns over areas that have seen well above
average rainfall over the past two weeks (northern and central
Rockies/western Great Plains).  A Slight Risk area remains in
place on the WPC Day 4 Excessive Rainfall Outlook across
northeastern Colorado and small portions of neighboring states,
with a broad marginal risk extending from the Intermountain West
to the south-central Plains.

The closed low over the Great Lakes and trailing surface cold
front will advect copious moisture northward across the
Mid-Atlantic and 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
Monday-Monday night, with lingering wrapping into northern New
England into Tuesday.  Antecedent dry conditions and the
progressive nature of the front preclude anything more than a
broad Marginal Risk at this time.  Elsewhere, ejecting shortwaves
from the Southwest also appear to favor additional rounds of heavy
rainfall and convection again around mid-week for parts of the
south-central Plains to the Mid-South and vicinity with copious
Gulf return moisture and instability intersecting a
quasi-stationary/warm front.

There will be two main areas of the U.S. that will likely have
above normal temperatures next week, with the first being across
the Dakotas and into Minnesota, Wisconsin, and Iowa where readings
are expected to be 5-15 degrees above mid-June averages.  The
second and more impactful area should develop and spread across
Texas into the central Gulf Coast region as upper ridging becomes
better established over the region and temperatures slowly
increase to the south of a frontal boundary and associated
convection.  Widespread mid-upper 90s are expected, with values
well into the 100s across the normally warmer locations across
southern Texas, along with increasing humidity levels.  Some daily
record highs are possible, mainly mid-late next week.  This heat
wave will likely have some staying power beyond next Friday and
also expand into the following week toward the Southeast U.S. as
per latest guidance from the Climate Prediction Center. 
Elsewhere, underneath closed upper low development over the Great
Lakes/Midwest and also over the Southwest/California, temperatures
should feel more like the month of May next week.

Schichtel/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