Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1129 AM EDT Fri Jul 12 2019
Valid 12Z Mon Jul 15 2019 - 12Z Fri Jul 19 2019
...Tropical Storm Barry expected to weaken as it tracks up the
Mississippi Valley/Lower Ohio Valley but continue to produce areas
of heavy rainfall...
...Overview and Guidance/Predictability Assessment...
...Weather Highlights/Threats...
National Hurricane Center forecasts continue to show Barry
reaching Louisiana in the short range time frame and making its
way northward over the Lower Mississippi Valley leading into the
start of the extended time frame by early day 3 Mon. From Mon
into Wed Barry should slowly weaken as it tracks into the southern
Mid-Mississippi Valley and Lower Ohio Valley. The surface
reflection may become less-defined after Wed though the 00Z ECMWF
still forecasts a discernible center through the period into next
Friday, which is plausible given some similar (or stronger)
ensemble members. There are still very stubborn model and ensemble
differences overall but the 00Z ECMWF was closest to the official
track, closely followed by the Canadian and GFS. Based on this
cluster expect highest rainfall totals from 12Z Mon onward to
extend from northeastern Arkansas/northern Mississippi through
Tennessee/Kentucky, with less confidence to the east-northeast
thereafter. There may be a severe threat over some areas to the
right of the surface low track but with low predictability in
details this far out in time. Later in the week the remnants of
Barry could interact with a wavy northern stream front and produce
enhanced rainfall over the Northeast but this depends on the
strength of Barry in the short term and timing in the northern
stream in several days. Please consult latest NHC products for
updated information on Barry.
Away from Barry the guidance continues to show a fairly typical
summertime pattern with an upper ridge prevailing over the
southern Rockies/central-southern Plains and progressive low
amplitude flow across the northern tier states and southern
Canada. Models/means are advertising a change in the pattern's
character from the Pacific into western North America though, with
a North Pacific jet reaching into the northwestern U.S. mid-late
week underneath a Gulf of Alaska into western Canada upper low.
Some aspects of the northern stream forecast (shortwaves and
associated surface lows/fronts) have maintained consistency to
some degree over recent days but others have not. In particular
there has been difficulty in resolving the specifics of shortwave
energy ejecting from the West Coast upper trough Mon-Wed. Also
consensus has generally trended faster over the past day with
arrival of the North Pacific jet and closed low to the north. The
consensus evolution should bring a period of steadier light to
locally terrain-enhanced moderate rainfall between the Pacific
Northwest coast and Cascades, after lighter and more scattered
activity earlier in the week.
The frontal systems affecting the northern tier states will bring
periods of showers and thunderstorms with some areas of heavy
rainfall, especially from the northern Plains through the Upper
Mississippi Valley and northern Great Lakes in association with a
front that may stall for a period of time. Over this area the
models and ensembles currently show too much spread to depict
especially heavy totals in the manual deterministic forecast.
However operational runs in principle are showing a decent signal
for some multi-inch 5-day totals at some locations so this area
will need to be monitored as details come into better focus.
Consult the latest WPC Hazards chart for more information.
The composite of forecast preferences led to a days 3-5 Mon-Wed
blend based mostly on the 00Z ECMWF as well as some ideas from the
00Z-06Z GFS/00Z CMC and 00Z ECMWF mean. Days 6-7 Thu-Fri
transitioned to a model/ensemble mean blend (including
continuity). This maintained good continuity.
Above normal temperatures with some pockets of plus 10F or greater
anomalies will spread from the northern Plains into Northeast
Mon-Wed with some warmth lingering over the northeast quadrant of
the lower 48 into Fri. Clouds/rainfall associated with Barry will
likely keep daytime highs well below average over parts of the
Lower Mississippi Valley on Mon (perhaps near record low max
values). After Mon confidence decreases for how much daytime
temperatures may be affected by Barry's moisture from the
Ohio/Tennessee Valley into the Mid-Atlantic/Northeast. Expect the
central Plains/Mid-Mississippi Valley to trend hotter by the
latter half of the week with some highs reaching 10-15F above
normal and heat index values potentially high enough to cause
concern (105-110F). The southern Rockies/High Plains should be
5-10F above normal most of the period under the upper high. The
Northwest will trend cooler by Thu-Fri with highs 5-10F below
normal.
Fracasso/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