Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Fri May 17 2019
Valid 12Z Mon May 20 2019 - 12Z Fri May 24 2019
...Overall Weather Pattern...
A stormy and unsettled weather pattern is expected across much of
the central U.S. during the medium range period with a large scale
upper trough becoming established over the Intermountain West and
a building upper level ridge over the southeastern states. Three
well defined storm systems are expected next week, with the first
affecting the northeastern U.S. on Monday. The second storm
gathers strength across the Plains on Tuesday and tracks towards
the Great Lakes, and the third one develops over the Intermountain
West midweek and reaches the Plains by the end of the week.
...Guidance/Predictability Assessment...
Models and ensemble means indicate decent overall agreement on the
synoptic scale on Monday. By Tuesday, the 00Z UKMET begins to
differ with the surface low well to the south of the model
consensus across the southern Plains, and farther north with the
next low over the eastern Pacific. By the middle of the week,
noteworthy differences are apparent with the next upper level
trough crossing the West Coast region, with the ECMWF/EC mean
slower with the progression of the closed low, and the 00Z GFS
more amplified and faster across the Desert Southwest. The
feature with the greatest predictability will be the upper level
ridge over the Southeast, where a general model blend suffices.
Elsewhere, the forecast was derived from a blend of the
ECMWF/GFS/parallel GFS and increasing percentages of the GEFS and
EC mean for the second half of the forecast period.
...Weather Highlights and Hazards...
Numerous showers and thunderstorms continue to be in the forecast
going into next week across the central/southern Plains and
extending to the Upper Midwest. 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 flash flooding, and severe
weather is also likely from northern Texas to the Midwest based on
recent SPC forecasts. The greatest chance of flooding would be
from the Texas Panhandle region to Iowa with the strong low
pressure system for the early to middle part of the week.
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 are less certain.
There will also be a dichotomy of temperature anomalies given the
amplified flow pattern in place. Temperatures are expected to be
well above normal 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. The opposite will be the case across
much of the western U.S. and also the northern Plains that will be
under the influence of the upper level trough and to the north of
the low tracks. Late season snow is likely for the Sierra Nevada
and the northern Rockies.
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