Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1141 AM EDT Thu Jul 11 2019
Valid 12Z Sun Jul 14 2019 - 12Z Thu Jul 18 2019
...Tropical Storm Barry to bring heavy rain to the Lower
Mississippi Valley this weekend into early next week...
...Overview and Guidance/Predictability Assessment...
...Weather Highlights/Threats...
The National Hurricane Center is issuing advisories on Tropical
Storm Barry over the northern Gulf of Mexico. Current forecast
shows the system tracking into Louisiana and then continuing
northward slowly but steadily in fairly weak flow aloft. Late in
the medium range period the southern edge of the westerlies across
the northern U.S. may begin to have some influence on the track,
with an increasingly large spread among the ensemble members.
Guidance clustering has been improving gradually but there is
still meaningful spread (with the 00Z UKMET continuing to stray
west of the majority). Models/ensembles have generally had
greater than average difficulty in forecasting this system's track
thus far, so further adjustments to the most likely track are
easily possible over coming days. For this forecast the 00Z ECMWF
and Canadian were closest to the official NHC track through the
first half of the period. Then inclusion of the 00Z GFS was used
to help temper the quicker ECMWF as the system lifts through
southeastern Missouri and then likely northeastward next week.
Barry (and its remnants) should produce an axis of heavy rainfall
from the Lower Mississippi Valley into the southern
Mid-Mississippi Valley/Lower Ohio Valley as it retains Gulf inflow
for several days. Precipitation intensity and coverage should
slowly decrease as the remnants of Barry crest the Appalachians,
but interaction with a front across the Lakes/Northeast next week
may at least enhance precipitation late in the period. A weakening
front to the north of the system in the lower MS Valley Sunday
could help to enhance rainfall Sun-Mon and lingering Gulf inflow
could support pockets of moderate/heavy rainfall along parts of
the Gulf Coast away from the center. Please consult latest NHC
products for updated information on Barry.
Meanwhile upper ridging should remain over the southern Rockies.
Shortwaves ejecting from an eastern Pacific into northwestern U.S.
mean trough will continue around the ridge, crossing the northern
U.S./southern Canada and feeding into a broad/weak mean trough
over the Northeast. Strong flow to the south of an upper low
tracking across the Gulf of Alaska may reach the Pacific Northwest
by day 7 Thu and help to push along the leading trough near the
West Coast. There is reasonable continuity for an initial
ejecting Northwest shortwave that should support southern Canada
low pressure and associated warm/cold front crossing the northern
tier. Thus far guidance has had more difficulty in resolving the
next shortwave which should be near the Pacific Northwest as of
early day 5 Tue. Ensembles have trended quicker with this feature
stemming back to its progression across the Aleutians. Continue
to expect episodes of showers and thunderstorms across the
northern states with the waves/fronts, with locations from the
northern Plains into Upper Great Lakes seeing the best potential
for some locally heavy rainfall. The Pacific Northwest will see
periods of scattered and mostly light rainfall with the shortwaves
brushing the region early-mid week. By Thu rainfall could become
a little more organized over or just north of the region as flow
aloft strengthens.
Based on combined preferences for Barry and features in the
northern stream, the latest forecast for days 3-4 Sun-Mon started
with 00Z ECMWF/Canadian with inclusion of the 00Z GFS by day
5/Tue. Increasing detail uncertainty by days 6-7 Wed-Thu led to a
blend of the quicker ECMWF with the slower Canadian as remnant
Barry moves through the Ohio Valley with some ensemble mean
weighting due to its less-detailed depiction.
An area of above normal temperatures will likely expand from the
northern Plains into the Northeast during the period with most
anomalies in the plus 5-15F range. Clouds and rainfall associated
with Barry should produce an area of daytime highs as much as
10-15F below normal over the Lower Mississippi Valley Sun-Mon.
Some below normal highs may extend farther northeastward after Mon
but with lower confidence.
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