Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
236 AM EDT Sun Jun 17 2018
Valid 12Z Wed Jun 20 2018 - 12Z Sun Jun 24 2018
...Heavy rain threat for southern Texas and the north-central
U.S...
...Pattern Overview and Guidance/Predictability Assessment...
Short range western U.S. closed low energy and height falls eject
to the Plains midweek and Mississippi Valley late week. Strong
Pacific Northwest ridging shifts eastward as a shortwave trough
breaches the Northwest Friday. Meanwhile, the northern periphery
of downstream ridging over the East/Southeast is eroded by
northern stream cyclonic flow over the Great Lakes and the
Northeast, which should suppress the oppressive heat and humidity
expected early this week.
Overall, the models and ensembles show a reasonably similar larger
scale pattern over the next week, but smaller mid-scale embedded
features still offer a bit of forecast spread. This cycle of the
WPC medium range suite was mainly derived from a blend of the
latest runs of the GFS/ECMWF with their ensemble means. Leaned
weighting in this composite in favor of the ensemble means and
euro guidance to de-emphasize the less predictable smaller scale
features which still remain highly uncertain. This forecast
methodology maintains good WPC continuity.
...Weather Highlights/Threats...
A main and persistent/wavy frontal boundary remains
quasi-stationary this week from the Plains to the Ohio Valley and
Mid-Atlantic. Periods of locally excessive convection will focus
along this boundary and in the warm sector aided by early period
tropical moisture influx from the Gulf of Mexico. WPC medium range
QPF forecasts show the heaviest potential over southern TX due to
a potential tropical wave/disturbance now followed by NHC.
Moisture streaming inland intersects the wavy boundary to the
north to fuel strong/severe convection as per SPC and periods of
potentially excessive rainfall centered over the N-central U.S. As
the trough and front shifts slowly eastward into later week, the
heaviest rainfall may increasingly spread along the surface
boundary as enhanced by any potential wave developments/convective
system propagations into the Midwest/Ohio Valley states and
Mid-Atlantic.
Schichtel
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