Extended Forecast Discussion...amended
NWS Weather Prediction Center College Park MD
350 AM EDT Sun May 19 2019
Valid 12Z Wed May 22 2019 - 12Z Sun May 26 2019
...Overall Weather Pattern...
The upper level pattern across the continental U.S. will remain
amplified and slow to change next week. A hot upper level ridge
over the southeast U.S. becomes anchored over the region and
gradually becomes stronger for the second half of the upcoming
work week. Across the western U.S., a large scale upper trough
will be dominant as multiple shortwave perturbations keep
conditions cool and unsettled. This will also be slow to move
given the expected development of an omega block type pattern
upstream over the eastern Pacific. Lead main weather features
include a strong low pressure system for the Plains and Upper
Midwest mid-week, followed by weaker lows and slow moving fronts
from the Southwest to the Northeast U.S. later in the week on the
western and northern periphery of the Southeast ridge.
...Models and Preferences...
The models and ensemble means are in relatively good agreement on
Wednesday, with the GFS more progressive with the trough axis over
the Desert Southwest and the CMC slower than the model consensus.
By Friday, the GFS becomes an outlier solution regarding the
intensity of an upper low over California, whereas the other
operational guidance, including the FV3, is more indicative of an
open trough over this region. There has also been a westward and
slower adjustment to the surface low over the Plains through the
end of the week, compared to earlier forecasts. By the end of the
forecast period on Sunday, the GFS is suggesting less upper level
ridging over the eastern U.S. compared to the model consensus.
The FV3 was given greater weighting in the forecast process given
its better agreement with the ensemble means, and the ECMWF/EC
mean/GEFS mean were also incorporated into the forecast.
...Weather Highlights and Hazards...
The main things that will make weather headlines for the second
half of the week and extending into next weekend will be the
anomalous heat and humidity building across the southeastern
quadrant of the nation, the unseasonably cool weather expected for
the interior western U.S. and northern plains, and the ongoing
threat of heavy rainfall and potential severe weather across the
central U.S. High temperatures are forecast to be on the order of
10 to 15 degrees above late May averages from the Midwest to the
Southeast U.S., with the hottest readings expected for the Friday
to Sunday time period. There is a good chance that the first 100
degree temperatures of the season could be realized across inland
portions of southern Georgia and South Carolina. The opposite
will hold true for the western U.S. under the influence of the
upper level trough, with daytime highs of 15 to 25 degrees below
normal for mid-week, and then moderating to 5 to 15 degrees below
normal by the end of the forecast period.
Heavy rain will likely be an issue again for parts of the central
plains and Midwest with the stalled frontal boundary in place for
the end of the week and into the weekend. There are some
differences in the model placements of the heaviest QPF axis, but
the consensus is for the heaviest rain to develop from northern
Texas to Iowa with the potential for flash flooding. Strong to
severe thunderstorms are also likely in this same general area.
D. Hamrick
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