Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1140 AM EDT Mon Jun 24 2019

Valid 12Z Thu Jun 27 2019 - 12Z Mon Jul 01 2019

1600 UTC Update...

No significant changes were made from the previous shift. Models
continue to show relatively good agreement on the overall synoptic
scale pattern over the CONUS in the medium range. This cycle for
the WPC progs used a blend of the latest deterministic guidance
with previous shift continuity through Day 5, with increasing
weighting of the ensemble means thereafter to mitigate the less
predictable detail and timing differences. See previous discussion
below for pattern assessment and notable weather highlights and
threats.

Santorelli

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

An initially deep closed upper low is forecast to slowly but
steadily move through the Pacific Northwest and then into British
Columbia later this week and weekend. Upper ridging will build
downstream over the High Plains into the western Great Lakes while
troughing in eastern Canada (Hudson Bay) will dig into the
Northeast next weekend. Along the Gulf Coast, an inverted trough
develops and will move westward as an upper high settles into
AZ/NM. The latest deterministic models offer a reasonably
well-clustered starting point for the Thu-Sat period. Thereafter,
incorporated the GEFS/ECMWF ensemble means which smoothed out
smaller-scale timing and amplitude differences for the lower 48.


...Weather Highlights/Threats...

The amplified upper low and lingering troughing will favor cooler
than average temperatures in most of the West (especially Pacific
Northwest into the Great Basin/Intermountain West) and scattered
rain/storms with some very high elevation snow. Temperatures
initially 5-15 deg F below average will moderate back toward
typical late-June values by late next weekend as heights rise.
Temperatures in the northern Plains/Upper Midwest will be 5-10 deg
F above average (80s to low or even mid 90s), but with a daily
risk of showers/storms with locally heavy downpours in the
vicinity of a warm front. The Storm Prediction Center highlights a
15% area for severe thunderstorms on Thursday across parts of the
Northern High Plains along the warm front before it lifts north
and eastward into the Upper Midwest by this weekend. The Northeast
will see cooler temperatures by Sunday as a front sinks through
the region. The Southeast and lower MS Valley/Gulf Coast region
will see a daily chance of showers/storms in typical summertime
fashion, but that may be enhanced as the upper trough moves
westward as lower level moisture slowly increases from the Gulf.


Fracasso


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