Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
213 AM EDT Thu Apr 11 2019
Valid 12Z Sun Apr 14 2019 - 12Z Thu Apr 18 2019
...Heavy Rainfall Threat for the Mid-Lower Mississippi/Ohio
Valleys this weekend and again in the middle of next week...
...Weather Highlights/Hazards and Guidance/Predictability
Assessment...
An upper trough crosses the southern Plains through the mid-lower
MS/OH Valleys this weekend, bringing widespread rains with
potential of excessive rainfall, flash flooding, and strong to
severe lead warm sector convection over the South. The potent low
and precipitation shield will track over the Northeast Monday,
with the trailing cold front moving across the southeast and
offshore into the Gulf of Mexico and western Atlantic. A blend of
the 18z GFS/18z GEFS Mean/12z ECMWF/12z ECMWF Ensemble Mean was
used due to good clustering of these solutions.
Meanwhile upstream, models/ensembles overall agree to bring
another potent mid-upper level trough/ample height falls/frontal
precipitation into the West Coast Sunday.
The upper trough amplifies with time as it crosses the Great basin
Monday
and into the Rockies Tuesday. Height falls on the high plains
induces cyclogenesis with
a renewed return flow of deepening Gulf moisture and ascent
leading to enhanced rainfall in eastern OK/TX extending downstream
into the lower MS Valley.
Given a similar cyclone track and upper level trough track,
similar areas hit by rain this weekend are expected to received
additional rains in the middle of next week.
This could result in a renewed flooding/flash flooding threat
across eastern OK/TX into the lower MS Valley. The models spread
grows for this system as the ensemble means have more emphasis on
low pressure along the wavy front further north in the Midwest
while the operational GFS/ECMWF heave more emphasis on low
pressure under the southern stream portion of the upper trough Wed
17 Apr to Thu 18 Apr. An equal blend of the 12z GFS/12z ECMWF
models/ 18z GEFS/12z ECMWF Ensemble means was used to mitigate the
differences until better agreement develops.
The developing western trough leads to an area of below normal
temperatures in the northwest and northern Rockies Mon 15 Apr that
expands southeast across the Great Basin
and then central Rockies Tue and then the Plains Wed, with
readings commonly several degrees below average. The building
west coast ridge leads to warm temperatures in CA/OR/WA next Thu.
The southerly flow east of the central US storm leads to an area
of above normal temperatures near the east coast next Wed 17
Apr-Thu 18 Apr.
Petersen
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