WPC Medium Range Archive
Medium Range Products Valid On:
(Day 7 PMDEPD: Valid 08/11/2018 to 08/15/2018)
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1120 AM EDT Wed Aug 08 2018
Valid 12Z Sat Aug 11 2018 - 12Z Wed Aug 15 2018
...Pattern Overview and Guidance/Predictability Assessment...
Models and ensembles now show better than normal clustering
through the period for the CONUS, bolstering forecast confidence.
The pattern offers an eastern Pacific upper low that moves through
southern British Columbia Saturday as a lead upper low sinks
slowly southward into the Ohio Valley and closes off. Subsequent
Canadian system approach toward the Great Lakes early next week
kicks the lead Midwest system into New England. The WPC medium
range product suite was mainly derived from the 00/06 UTC GFS and
00 UTC ECMWF along with their well paired respective ensemble
means and WPC continuity.
...Weather Highlights and Hazards...
Near or above record high temperatures over the interior
Northwest/northern Rockies/High Plains Saturday will trend cooler
Sunday/Monday as the upper trough and surface cold front push
through. A separated southwestward extension from the OH Valley
upper trough by Sunday/Monday will help fuel organized rain/storms
across Texas westward to the Four Corners region, especially NM/CO
just to the east of the upper high in a region of favorable upper
diffluence. Guidance continues to waver on placement but several
inches of rain are likely over central Texas during the Sat-Wed
A wavy front will linger across the U.S. southern tier during the
period which will help spark afternoon showers/storms and locally
heavy rainfall in the warm/humid airmass. As the upper trough
(eventual closed low) digs/sharpens over the east-central U.S.,
more widespread precipitation may be favored to its east along the
Appalachians to the I-95 corridor. This could develop into a more
widespread heavy rainfall threat considering slow system
translation and amplitude with a southerly fetch of ample moisture
over several days. Closed lows in the summer can be underestimated
in the short and medium range in terms of precipitation
intensity/amounts and longevity.
Upstream, an approaching frontal boundary over the High
Plains/Upper Midwest/Great Lakes next week will act as another
focus for shower/storms just to its south as the leftover weakness
aloft gets absorbed into the next trough.
WPC medium range 500 mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indexes are found at: