Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1144 AM EDT Fri Jun 15 2018
Valid 12Z Mon Jun 18 2018 - 12Z Fri Jun 22 2018
...Heavy rains possible for portions of the northwestern Gulf
Coast and portions of the central/northern Rockies and adjacent
plains...
...Hot/humid for portions of the Midwest to the Mid-Atlantic and
Southeast early next week...
...Pattern overview and guidance assessment/preferences...
An upper level low over the Great Basin on Monday should slowly
begin to weaken as ridging in the East gives way to cyclonic flow
through the Great Lakes. This brings a surface cold front slowly
southward out of the Great Lakes on Monday, eventually lingering
across the Mid-Atlantic and back to the Plains through the rest of
the week. To the south, a weakness aloft and a tropical wave at
the surface is expected to produce heavy rainfall along the
northwest Gulf Coast region next week.
For days 3-5, the GFS/ECMWF and their ensemble means were in very
good agreement so a majority deterministic GFS/ECMWF blend served
as a good starting point. By days 6-7, the most notable difference
was the 06z GFS was faster to erode the western low and eject the
energy eastward into the plains. The ECMWF along with the EC and
GEFS ensemble means would support holding back the low across the
Great Basin even into Day 7. The GFS the past few days has been
flip-flopping both solutions, so for days 6-7 the WPC blend leaned
heavily towards the ECMWF/GEFS ensemble means and the
deterministic ECMWF all of which have showed better overall
run-to-run continuity.
...Weather highlights/hazards...
Locally heavy (and regionally modest) rain is probable for the
northwestern Gulf Coast as the broad trough/area of disturbed
weather moves onshore early in the period. Multi-inch rainfall
totals appear possible, focused over portions of southeastern
Texas and southwestern Louisiana. To the west and northwest, the
upper low and moisture from (by then) the remnants of Bud will
combine to produce several days of wet weather for the
central/northern Rockies and the adjacent High Plains. Moisture
may also pool eastward along the quasi-stationary frontal boundary
as it lingers across the central Plains for much of the period.
Totals of 1-2+" may be common for the 5-day QPF total.
Temperatures in the east will be well above average (+10 to +20F)
to start the medium range (Monday) from the Midwest to the
Northeast/Mid-Atlantic with readings well into the 80s/north and
90s/south, and approaching 100 in some locations. Many daily
record maxes will likely be tied/broken along the I-95 corridor.
With dew points ranging from the upper 60s to mid 70s, heat
indices will be over 100F and close to 110F for some areas. The
Pacific Northwest will also see well above average temperatures
(especially inland) as they will be located to the northwest of
the upper low and coincident with ridging moving out of the
northeast Pacific. Temperatures will rise into the 70s/80s west of
the Cascades and 90s in the interior of Washington/Oregon.
Meanwhile, across the Intermountain West and much of the Plains
states, temperatures are forecast to be below normal under the
influence of the stubborn upper low and copious amounts of
moisture streaming into the region.
Santorelli/Fracasso
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