Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Mon Jun 10 2019
Valid 12Z Thu Jun 13 2019 - 12Z Mon Jun 17 2019
...Overview and Guidance/Predictability Assessment...
The one fairly agreeable and stable aspect of the forecast is the
amplified eastern U.S. upper trough and associated surface
reflection lifting northeastward from early Thu onward. Otherwise
the expected transition of the pattern to a lower amplitude regime
with embedded medium to smaller scale features (having low
predictability) continues to cause significant difficulty in
resolving important details. The one common signal comes from
teleconnections relative to the best defined height anomaly
centers in the D+8 means--positive ones northeast of Hudson Bay
and off Vancouver Island along with a negative one associated with
a mean upper low near the Aleutians--all suggesting broadly
cyclonic flow over the eastern U.S. Model/ensemble spread and
variability among consecutive runs keep confidence fairly low for
the time being, but over the past 24 hours there has been a
strengthening signal that the pattern could support heavy rainfall
potential over parts of the south-central Plains and extending
east/northeast. This emerging threat will require close
monitoring given the high sensitivity of some of these areas to
any significant rainfall.
Within the overall eastern trough aloft which should trend more
shallow with time, the key uncertainty remains with the energy
that starts the period early Thu in the vicinity of northern
Ontario/southern shore of Hudson Bay. Individual solutions are
too varied to describe in detail but essentially break down into
one of two scenarios, the feature either remaining over Canada or
else at some point dropping farther south and brushing the
northeastern quadrant of the Lower 48. Adding to the confusion,
multiple models have switched between the two ideas in consecutive
runs. The ultimate path of this energy will determine the
southward extent/timing of a front expected to reach at least as
far as the northern tier states and possibly much farther south.
Meanwhile shortwaves from multiple streams will filter across the
West and into the Plains from late week onward. Compared to
yesterday the guidance as a whole has suggested a somewhat weaker
and faster trend for this energy in the days 3-5 Thu-Sat time
frame. Then by days 6-7 Sun-Mon solutions still diverge
considerably over the eastern Pacific/western U.S., involving flow
at the leading edge of the broad North Pacific upper low (more
eastward elongation in the ECMWF/CMC) and then details of ridging
that may build over the eastern Pacific and corresponding response
downstream. Most individual solutions could be plausible from a
multi-day mean perspective incorporating the late extended/early
week two period. However established consensus indicates the new
00Z GFS/FV3 GFS could become a too strong with the eastern Pacific
ridge by next Mon, leading to the deepest West Coast trough.
For the latest forecast update the multitude of low confidence
detail issues required a steady increase of ensemble input after a
multi-model consensus to start day 3 Thu, with the 18Z GEFS and
12Z ECMWF/NAEFS means used exclusively by days 6-7 Sun-Mon. This
provided more subtle adjustments from continuity than following
any particular model scenario.
...Sensible Weather Highlights/Threats...
The system affecting the Great Lakes/Northeast early in the period
will bring rainfall of varying intensity Thu-Thu night. Emerging
consensus indicates highest totals may remain offshore while
system progression could limit rainfall accumulations as well.
Then the rainfall focus will shift westward as weak shortwaves
move into/through the West and emerge over the central U.S. This
energy may produce at least a modest surface low/frontal system
while southern Canada/northern U.S. flow east of the Rockies could
push a separate front southward. Expect periods of
showers/thunderstorms on multiple days over the northern
two-thirds of the West with best organization likely in the
northern-central Rockies. Farther east there is still
considerable uncertainty over specifics of surface features that
will serve to focus convection. However in principle guidance
over the past day has trended toward higher potential for heavy
rainfall within an area extending from the south-central High
Plains into the Ohio Valley. Some individual solutions display
such potential elsewhere as well. Currently the ensembles as a
whole focus the greatest probability of highest totals for the
five-day period over parts of Kansas/Oklahoma/Missouri/Arkansas.
Expect the Florida peninsula to be another favored area of
meaningful rainfall during the period.
Temperatures over the West should remain above normal though to a
lesser extreme than expected through Wed. Some scattered plus
10-15F anomalies for highs will be possible from extreme northern
California into the interior Northwest and extreme northern
Rockies while the West will see a broader expanse of plus 5-15F
anomalies for morning lows from late week into next Mon. Below
normal readings will prevail over much of the eastern half of the
country Thu-Fri. Then anticipate temperatures closer to normal
though perhaps averaging slightly below average overall.
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