Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Sat May 18 2019
Valid 12Z Tue May 21 2019 - 12Z Sat May 25 2019
...Overall Weather Pattern...
The upper level pattern across the continental U.S. will remain
quite 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 Tue/Wed, followed by weaker lows and frontal boundary
meanderings from the Southwest to the Northeast U.S. later week
overtop the Southeast ridge. The pattern offers a periodic local
threat for strong to severe convection and potential for cell
training/excessive rainfall.
...Guidance/Predictability Assessment...
The 06 UTC GFS and 00 UTC ECMWF seem well clustered with
GEFS/ECMWF ensemble solutions Tue into Thu and a composite seems
reasonable, but run to run continuity issues limit forecast
confidence. Opted to quickly tranistion to a blend of the
ensembles later Thu into next weekend amid growing forecast spread
and uncertainty.
...Weather Highlights and Hazards...
Numerous showers and thunderstorms continue to be in the forecast
through the middle of next week from the Plains to the Upper
Midwest then eastward. Multiple rounds of MCS activity are likely
with both of the low pressure systems that are progged to track
across the Plains. This will have the potential to produce very
heavy rainfall capable of producing flash flooding, and severe
weather is also likely across much of the Midwest states based on
recent SPC forecasts. Additional heavy rain is also possible from
the next storm system tracking eastward from the Intermountain
West later in the week, although details on timing and placement
continue to remain less clear at this time.
There will also be a dichotomy of temperature anomalies given the
amplified flow pattern in place. Temperatures are expected to be
well above normal to near record warmth across much of the
southeastern U.S. owing to the strength of the upper ridge, and
this will also serve to keep rainfall chances minimal. Afternoon
high temperatures may exceed 100 degrees for parts of Georgia and
South Carolina by later in the week. The opposite will be the case
across much of the western U.S. and also the northern Plains with
readings on the order of 10 to 20 degrees below climatology, which
will be under the influence of the upper level trough and to the
north of the low tracks. Heavier late season snows are also likely
for the Sierra Nevada to the northern Rockies for the middle of
the week.
D. Hamrick/Schichtel
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