Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Tue Jun 19 2018
Valid 12Z Fri Jun 22 2018 - 12Z Tue Jun 26 2018
...Guidance/Predictability Assessment...
Models show above normal agreement with the flow pattern evolution
during the medium range, bolstering forecast confidence. Nrn
stream flow will feature a persistent upper ridge over central
Canada sandwiched by early next week by amplified wrn Canada/nwrn
U.S. and ern Canada/nern U.S. cooling troughs. A modestly
progressive pattern underneath across the CONUS has some tendency
for system amplification. Energy crossing from the Rockies to the
central U.S. offers potential for deepening and/or closing off,
moving through a region of relatively weak upper flow beneath the
Canadian ridge before being forced downstream.
The WPC medium range product suite was primarily derived from a
composite blend of reasonably well clustered model guidance from
GFS/ECMWF, the National Blend of Models, and WPC continuity, with
limited ensemble input.
...Weather Highlights/Threats...
Lead mid-Mississippi Valley closed trough/low energy Friday shears
northeastward through the Ohio Valley and Northeast over the
weekend, and the trailing front sinks down across the ern U.S.
This occurs as an amplifying upstream kicker shortwave trough digs
from the nwrn U.S. southeastward over the Rockies to the
north-central states. Guidance with these systems produce a well
developed series of surface lows along a main frontal boundary
from the Plains to the MS/OH valleys and mid-Atlantic/Northeast.
Expect repeat periods of locally excessive convective
complexes/rains to focus along this boundary and into the warm
sector aided by tropical moisture influx from the Gulf of Mexico.
A late season cooling front next weeks show promise to work into
the nwrn us.
Schichtel
WPC medium range forecasts of 500 mb heights, surface systems,
weather grids, quantitative precipitation, and winter weather
outlook probabilities are 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