Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1135 AM EDT Sun Jun 23 2019
Valid 12Z Wed Jun 26 2019 - 12Z Sun Jun 30 2019
...Overview and Guidance/Predictability Assessment...
An anomamously amplified closed upper low/trough is forecast to
slowly but steadily move into the Pacific Northwest and then lift
into British Columbia later this week. In this pattern, ample
height falls dig underneath through an unsettled West as upper
ridging builds downstream over the High Plains into the western
Great Lakes. Troughing in eastern Canada will likely also dig into
the Northeast next weekend as in inverted trough develops along
the central Gulf coast and as the upper high settles into AZ/NM.
The latest deterministic models still offer a reasonably
well-clustered starting point for the Wed-Fri period. Thereafter,
switched to a blend of the 06 UTC GFS/GEFS mean and 00 UTC
ECMWF/ECMWF ensemble mean which smoothed out smaller scale timing
and amplitude differences for the lower 48.
...Weather Highlights/Threats...
The amplified upper low/trough 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 next weekend as the upper low moves into Canada.
Temperatures in the northern Plains/Upper Midwest will be 5-10 deg
F above average (80s and some low 90s), but with a daily risk of
showers/storms with locally heavy downpours/cell training as
deeper moisture and instability pool in the vicinity of a warm
front. The Northeast will see cooler temperatures this week as
fronts slip 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 later week into the weekend over a
moistened lower level fetch.
Fracasso/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