Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1219 PM EDT Tue Jun 05 2018
Valid 12Z Fri Jun 08 2018 - 12Z Tue Jun 12 2018
...Pattern overview...
Guidance shows a general trough-ridge-trough pattern aloft
persisting through a majority of the forecast period. Passage of
a vigorous shortwave trough across the Northwest during the
weekend followed by low amplitude North Pacific flow will likely
serve to flatten/broaden the overall mean trough over western
North America late in the period and push the downstream ridge
into the east-central part of the continent. However northeastern
U.S. mean troughing may be reluctant to depart in spite of the
broadening evolution to the west. Mean ridging aloft anchored
over the southern Plains may weaken a bit during the weekend and
rebuild over/near the southern Rockies around next Tue. Farther
east there will be a weakness aloft over the eastern Gulf of
Mexico/Florida. This feature will weaken gradually through the
period.
...Model guidance/predictability evaluation/preferences...
For the days 3-5 Fri-Sun part of the forecast a blend of latest
operational model guidance represented consensus well for features
that have a reasonable degree of synoptic predictability. The
western-central pattern will sharpen as the strong upper trough
and leading surface cold front reach the western U.S. while the
central Canada ridge builds. This will start the process of
reloading the eastern trough aloft with initial weak northern U.S.
energy contributing to frontal waviness that reaches the East by
Sun. Wave details will have low predictability and likely display
meaningful run to run variability.
By days 6-7 Mon-Tue the forecast starts to incorporate GEFS/ECMWF
means along with latest operational runs as detail uncertainties
increase. Timing spread develops for the western trough with
ECMWF/CMC ensemble members tending to show faster ejection than a
majority of GEFS members, while solutions are all over the place
for the shortwave details of low amplitude flow immediately
upstream. Issues with the western trough ultimately affect the
front that reaches the Plains. The average of guidance yields a
faster adjustment versus continuity but would like to await
confirmation from further runs before trending as fast as the 06Z
GFS/00Z ECMWF runs. Models/means appear somewhat more agreeable
for persistence of the northeastern U.S. trough but some
individual ensemble members show potential for higher heights
aloft late in the period. At this time prefer the majority
scenario that favors persistence of this trough.
...Weather highlights and hazards...
Ridging aloft will support hot temperatures from the Desert
Southwest eastward into the Plains, though with anomalies for
daytime highs tending to be less than plus 10F. Greater anomalies
for max/min readings are likely to extend from the Intermountain
West into the northern-central Plains from Fri into Mon ahead of
the cold front that pushes into the West. This cold front will
bring some chilly temperatures into the West with the weekend
likely featuring some highs up to 10F or so below normal from the
northern half of the West Coast northeastward. Upper troughing
will promote near to below normal readings near the East Coast.
Multiple mesoscale complexes will likely extend from the Northern
Plains into the Great Lakes/Ohio Valley region. The wavy front
from the Plains to East Coast late this week through the weekend
will provide a significant focus for locally heavy/strong
convection. Amplifying upper troughing will also promote wet
conditions over the East during the weekend. Farther south,
expect showers/storms across Florida and parts of the Southeast,
especially late this week into the weekend in association with the
weakness aloft. The strong upper trough/surface front affecting
the West will bring abundant precip to the Pacific
Northwest/northern Rockies and eventually may generate some
convection over the northern Plains.
Rausch
WPC medium range forecasts of 500 mb heights, surface systems,
weather grids, quantitative precipitation, and winter weather
outlook probabilities can be found at:
http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4