Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Sat Jun 08 2019
Valid 12Z Tue Jun 11 2019 - 12Z Sat Jun 15 2019
...Heavy rainfall and flash flood/flooding threats possible over
parts of the Appalachians/East Coast states Tue-Thu...
...Overview and Guidance/Predictability Assessment...
From Tue into Thu expect a strong ridge moving into the West to
promote downstream trough amplification into the east-central U.S.
Incoming Pacific energy (in both northern and southern streams)
will rapidly erode the western ridge and produce a diffuse trough
over the West by Fri-Sat while northeastward progression of the
eastern trough should ultimately yield flat mean flow over the
East by the start of next Sat.
The forecast maintains better than average continuity as guidance
displays similar and consistent ideas for evolution of mean flow
during the period, providing good confidence in the large scale
evolution. However detail uncertainties become gradually more
noticeable with time so some specifics will take added time to be
resolved. The relative agreement of models/means still favors a
consensus approach with a blend consisting of mostly operational
guidance early and then trending toward about half models/half
means to tone down lower confidence details.
During the first half of the period the primary consideration was
to remove the 12Z UKMET from the blend after day 3 Tue as it
became slower than other solutions for the trough amplifying into
the Mississippi Valley. The new 00Z UKMET looks more reasonable
and remaining 00Z guidance conforms well to established consensus.
By Thu-Fri there is still the unresolved question of whether the
amplifying trough energy may at least briefly close off an
embedded low center. Latest operational models seem to be hinting
at increased potential for some separation and a possible upper
low (actual or implied, depending on the height contour used)
whose most likely track would be from the Great Lakes into eastern
Canada. The diffuse upper trough moving into the West has good
agreement/continuity in principle. Confidence is rather low in
specifics though. Operational runs show separate pieces of energy
within different streams plus meaningful differences in amplitude
and timing of each feature. Shortwaves of this scale tend to have
low predictability several days out in time--favoring a
blended/mean approach until details become more refined.
...Sensible Weather Highlights/Threats...
Specifics are not fully resolved yet but there is still a decent
signal for a heavy rainfall threat over areas from the
Southeast/southern Mid-Atlantic northeastward. The trailing part
of a frontal system reaching the East Coast on Tue will stall into
Wed and then a rainfall-focusing wave over the Southeast will lift
northeastward near the coast in advance of the complex surface
system associated with the upper trough amplifying into the
east-central U.S. by early Thu. Best potential for highest totals
currently exists over the Carolinas. The aforementioned trailing
system may bring some locally enhanced activity from the northern
Plains into the Great Lakes. Moisture will persist over Florida
into the weekend but the rest of the eastern states should see a
drying trend by Fri-Sat.
Shortwave energy moving into the West will bring scattered
showers/thunderstorms of varying intensity primarily into the
northern/central parts of the region from Wed or Thu into the
weekend. Currently expect highest totals over and near the
northern half of the Rockies. Shower/storm potential should
expand into the Plains during the late week/weekend time frame but
with low confidence for timing/location of greatest rainfall.
The forecast remains on track for the brief episode of very warm
to hot conditions over the West mainly Tue-Wed in association with
the upper ridge moving in from the Pacific. Most guidance
continues to show a broad area of plus 10-20F anomalies with
locations between and including Portland/Medford having the best
potential to see highs 20-25F or so above normal. Daily records
for highs/warm lows will be possible over the West Coast states as
temperatures reach levels that will likely be the hottest
temperatures so far this year. Readings should moderate later in
the week but somewhat above normal readings may persist over the
Northwest into Sat. On the other hand the pattern will favor
below normal temperatures from the Plains into the East for
multiple days. The central U.S. will be first to see a moderating
trend late in the week and then rapidly flattening flow aloft will
support temperatures closer to normal over the East next weekend.
Rausch
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml