737
FXUS02 KWBC 281906
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
306 PM EDT Sun Jun 28 2026

Valid 12Z Wed Jul 1 2026 - 12Z Sun Jul 5 2026

19Z Update: The latest guidance continues to strongly agree on a
potentially historic heatwave across the eastern third of the
country for the end of the week, and all of the guidance has a
closed 594dm contour that persists for a few days. Some of the
guidance hints at the possibility of all-time record highs,
peaking during the Thursday to Friday time period. The NBM is also
close to all-time records for some areas of the East Coast, but
these are likely to be a few degrees too high given overall pattern
recognition, and the potential for some mid-high level clouds from
convective complexes that develop along the northern periphery of
the ridge. Therefore, NBM max temperatures were generally lowered
by 1-3 degrees for most areas from North Carolina to New England to
give the highest readings in the 100-105 degree range for the end
of the week, and dewpoints were also lowered some during the
afternoon and evening hours to better account for mixing of the
boundary layer. Differences become apparent by next weekend
regarding timing of upper ridge breakdown, with the CMC quicker to
erode the northern periphery of the ridge and bring in slightly
cooler conditions, whereas the GFS and ECMWF maintain the extreme
heat a little longer. The caveat to temperatures over the holiday
weekend will be the presence of convection and its associated cloud
cover, which would ultimately limit how high temperatures get. For
fronts and pressures, a deterministic model blend was used for
Wednesday and Thursday, followed by gradually increasing
percentages of the ensemble means to about 40% by next Sunday. The
previous forecast discussion is appended below for reference.
/Hamrick
----------------------

...Significant, dangerous, and record breaking heat wave expected
next week for the Central to Eastern U.S...


...Pattern Overview...

The period begins Wednesday with a strong ridge anchored over the
eastern half of the country, supporting a sprawling and dangerous
heat wave. Meanwhile an amplified trough will be over the West
becoming reinforced as multiple impulses move through within the
flow, with some energy possibly acting to suppress the Eastern
ridge slightly by next weekend. Showers and thunderstorms will be
most likely across the Gulf Coast/Florida region, the southern
Rockies, and the Upper Midwest to Great Lakes/Northeast.


...Guidance/Predictability Assessment...

Good agreement continues amongst the latest guidance for at least
the large scale pattern, but the details remain uncertain across
the West with various shortwave energies reinforcing the trough.
Confidence and predictability is high for the large upper ridge
centered over the Tennessee Valley later next week. Out West, a
strong shortwave will drop into the Northwest early period, with
the GFS continuing to be much more amplified and slower with this
system as it slowly drifts east-northeastward. By next weekend,
there is some consensus for this energy to ride over the top of the
ridge, acting to suppress it slightly, with an expansion of
ridging westward into the southern Plains as well. The ECMWF
remains less enthused with this late period evolution, wanting to
maintain a stronger ridge over the East than some of the other
guidance would suggest. The WPC forecast used a consensus of the
deterministic and machine-learning guidance early in the period.
Removed the GFS completely by Day 5, and increased weighting of the
ensemble means into the mix to help tone down the less predictable
late period details. Overall, maintaining good continuity with the
previous WPC forecast.


...Weather/Hazards Highlights...

The most impactful weather hazard during the medium range period
will be a long lasting heat wave affecting much of the central to
eastern U.S. spanning the short to medium range period. Widespread
daily record breaking maximum temperatures into the 90s to low
100s, combined with high humidity, will result in heat indices
approaching or exceeding 105-110 in many places. This equates to
widespread Major to Extreme HeatRisk from the Midwest/MS Valley
eastward to the East Coast. Overnight lows will also be quite warm,
with numerous record high minimums possible, bringing little to no
relief from the heat in the nighttime hours. Heat may finally
begin to abate slightly by the end of the period, with above normal
temperatures expanding westward into the Southern and Central
Plains as well. Out West, temperatures will be below to well below
normal underneath of the upper trough.

Rain and thunderstorms associated with a slow moving frontal
boundary will impact parts of the Upper Midwest and Great Lakes
into late next week. Moisture anomalies and instability within
fairly weak flow may support at least a localized flash flood
threat. WPC highlights much of this region within a Marginal Risk
for both the Day 4/Wednesday and Day 5/Thursday Excessive Rainfall
Outlook. Some of this activity will likely make its way into parts
of the Northeast as well as it rounds the northern periphery of the
mid/upper level ridge.

Elsewhere, moisture funneling between the western trough and the
eastern ridge should support showers and thunderstorms across parts
of the southern Rockies and southern High Plains into Wednesday.
Diurnally driven showers and storms are also expected from the
central Gulf Coast to Florida with moisture increasing south of the
upper ridge. Showers may increase across parts of the Ohio Valley
and East late week/next weekend as the upper ridge slightly weakens
and upper level energy tries to intrude into the region.


Santorelli/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 forecast, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key Messages
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
https://www.wpc.ncep.noaa.gov/#page=ovw










$$