Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
419 PM EDT Mon Jul 08 2019
Valid 12Z Thu Jul 11 2019 - 12Z Mon Jul 15 2019
...Overview and Guidance/Predictability Assessment...
Models consensus remains relatively poor as to the eventual
evolution of low pressure expected across the Gulf of Mexico later
this week into the weekend. In general, a westward trend was noted
in the guidance from overnight, especially among the GFS/ECMWF and
their respective ensembles, while the 00Z UKMET/CMC maintained
solutions that keep the area of low pressure farther to the east.
After assessing the trends and the current ensemble/model spread,
a solutions close to the 00Z ECMWF was preferred at this time,
subject to adjustment this afternoon pending new model guidance
and collaboration with NHC. Fortunately, models showed slightly
above average agreement at the larger scales elsewhere, with the
primary storm track focused within a relatively active jet across
the CONUS northern tier. Timing/amplitude differences were minor
with a series of upper shortwaves crossing the Midwest/Great
Lakes/Northeast through the period. Differences grow through time,
and shortwave energy expected to reach the Pacific Northwest
Sun-Mon, then moving east from there showed somewhat larger
differences among the guidance. Given these considerations, a
multi-model deterministic blend was used initially during days
3-4, with a shift toward a three-way blend of the ECMWF and
ECENS/GEFS ensemble means during days 5-7.
Ryan
...Weather Highlights/Threats...
The heavy rainfall threat continues for some areas along and
inland from the Gulf Coast, with specifics depending on the very
uncertain path of the system expected to track over a portion of
the northern Gulf. Given the diverse guidance spread thus far, it
is important to note that a meaningful potential exists over a
greater area than represented on any single deterministic model or
manual forecast. Latest trends are suggesting there may be a
westward shift in highest rainfall potential but further runs will
be needed for confirmation. Elsewhere, low pressure and trailing
front will bring showers/thunderstorms to the Northeast and
Mid-Atlantic late this week with best dynamics aloft supporting
highest rainfall totals over parts of the Northeast. Some
showers/storms may also accompany another frontal system tracking
from the northern Plains into the East late week through the
weekend. The trailing part of the front may stall over the
northern Plains to provide a longer-term rainfall focus.
Locations along and just inland from the Pacific Northwest coast
may see one or more periods of scattered light rainfall depending
on strength of shortwaves ejecting from the mean trough aloft over
the eastern Pacific. Portions of the Rockies may see scattered
diurnal convection on one or more days.
Most temperature anomalies should be in the single digits through
the period. Aided by warm morning lows in particular, areas from
the interior West through the northern Plains should be
consistently above normal. Frontal progression will provide some
temperature variability over the northeastern quadrant of the
lower 48. Clouds/rainfall may keep high temperatures a little
below normal over some areas along and inland from the Gulf Coast,
depending on the track of the possible Gulf system.
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
Hazards:
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, and the Southern Plains, Thu-Mon, Jul 11-Jul
15.
- Heavy rain across portions of the Northeast and the Great Lakes,
Thu-Fri, Jul 11-Jul 12.
- Flooding possible across portions of the Central Plains and the
Northern Plains.
- Flooding occurring or imminent across portions of the
Northern/Central Plains, the Mississippi Valley, and the Ohio
Valley.
- Flooding likely across portions of the Central Plains and the
Northern Plains.
- Excessive heat across portions of the Southeast, the Lower
Mississippi Valley, the Southern Plains, and the Tennessee Valley,
Thu, Jul 11.
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