Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
327 AM EDT Sun May 31 2020

Valid 12Z Wed Jun 03 2020 - 12Z Sun Jun 07 2020

...Hot temperatures for the West-Central U.S. and a Gulf of Mexico
feature to monitor...

...Overview and Guidance/Predictability Assessment...

A composite of reasonably well-clustered GFS/ECMWF/UKMET seems
reasonable over the nation Wed into Thu. However, prefer to
quickly switch to an ensemble mean blend later Thu through next
weekend in an effort to mitigate growing smaller-scale model
timing and detail differences. Zonal northern stream flow
amplifies significantly into next weekend with development of West
Coast and Northeast U.S. upper troughs and the blocky nature at
mid-lower latitudes seems to favor the slower side of guidance
spread. The models also continue to overall trend a bit slower
with ejection of closed southern CA upper trough energy late week,
but the GFS/GEFS remain on the faster side of the full solution
envelope. Accordingly, applied much greater weighting in the WPC
blend to the overall less progressive ECMWF ensemble mean in a
pattern with lowering forecast predictability and continuity over
time. The ECMWF ensemble mean also seems a reasonably good fit
with NHC/WPC continuity over the active tropics/Gulf of Mexico.

...Weather/Hazard Highlights...

The pattern/impulses should favor showers/thunderstorms mid-late
week with a focus for locally moderate to heavy downpours from the
Mid MS/OH Valleys to the central Appalachians/Mid-Atlantic in
advance of a southward sinking cold front. Frontal passage will
also act to mitigate lead warm sector heat. The wavy front
extending back to the Northern Plains/Rockies will also provide a
focus for instability/convection with a series of passing
impulses.

Maximum temperatures will remain hot across much of the
west-central U.S. with a broad area of plus 10-15F anomalies and
spotty record values in advance of an approaching/moderating cold
front. Lead southern CA closed low ejection northeastward over the
West late week will increase rainfall coverage and height
falls/moisture and ample weekend West Coast upper trough
amplification will further enhance potential across the West to
the northern Plains.

The Gulf of Mexico should be active with eastern Gulf/FL
convection focusing near an old front mid-late week. WPC and NHC
are also monitoring potential system development into the southern
to western Gulf into next weekend. Deep tropical moisture works
gradually northward to significantly enhance rainfall potential.
The Canadian offers more robust development than other guidance,
while the ECMWF/ECMWF ensemble mean lift a low on a more southern
to western Gulf track more in line with NHC/WPC continuity than
the more eastward shifted GFS/GEFS.

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