WPC Medium Range Archive
Medium Range Products Valid On:
(Day 7 PMDEPD: Valid 05/19/2019 to 05/23/2019)
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
403 PM EDT Thu May 16 2019
Valid 12Z Sun May 19 2019 - 12Z Thu May 23 2019
1530 UTC Update...
Models showed broad agreement on the large scale features
throughout the medium range, with differences primarily confined
to timing and amplitude of various features. This setup was
well-suited for use of a multi-model deterministic blend (00Z
ECMWF/CMC and 06Z GFS/FV3) through much of the period, with a
gradual trend toward heavier ensemble weighting (ECENS/NAEFS
means) through time. Overall, changes to forecast continuity were
relatively small. Hemispheric standardized 500 hPa anomalies show
the long wave pattern becoming more amplified and locked in place
toward late in the medium range, with a mean trough in the West
and a strengthening ridge anchored across the Southeast,
supporting a continued stormy setup from the West to the central
U.S. and Midwest.
Previous Discussion (issued at 0606 UTC)...
The initial cyclone this weekend is forecast to cross from the
upper MS Valley to the Great Lakes Sunday and across the northeast
and into the Canadian Maritimes Mon into Tue. The overall trend
was for slightly faster motion than prior forecasts.
Given good agreement among the 12z ECMWF and its ensemble mean,
the progs gave more weighting to these solutions. The 12z UKMET
was the southern most solution and given the least weighting.
Model and ensemble solutions continue to show above normal
forecast spread with respect to northeastern U.S. flow through
The anticipated upper trough moves onshore Sun in the Pacific
with the surface reflection crossing the Great Basin Sun and Mon.
As a wave emerges as the system crosses the southern Rockies, lee
cyclone development occurs Mon with the new system moving across
the southern and central Plains Mon into Tue, continuing north
northeast across the Plains to the upper MS Valley by Wed 22 May.
The 12z ECMWF/18z GFS offer good forecast agreement with their
ensemble means and Canadian global tracking the mid-upper low
The next in the series of 500 mb wave may move onshore into CA Thu
23 May, according to the 12z ECMWF/GFS/Canadian Ensemble Means.
Downstream from the series of cyclones developing within the
western US trough, a developing mid level anticyclone is forecast
over the southeast US, which gradually becomes stronger in the
middle of next week. Excellent clustering of solutions exist, so
confidence is above normal in the developing anticyclone.
The WPC product suite for temperatures, dewpoints, etc. was
derived from a blend giving more weight to the 12z ECMWF/ECMWF
Ensemble Mean with lower weighting to the 18z GEFS Mean and 18z
...Weather Highlights and Hazards...
Several rounds of showers/storms are expected in the central US,
with Sat-Sun targeting the eastern Southern to central Plains to
the Upper MS Valley , then into the Upper Great Lakes and lower MS
Valley Sun. Locally heavy rain is possible in these areas. The
next system entering the southern Plains Mon triggers the next
round of showers/storms. See the Storm Prediction Center severe
weather outlooks for each day's severe convective potential. As
the system moves north the activity spreads from the central into
northern Plains Tue and into the MS Valley before moving
downstream into the upper Great lakes Wed 22 May.
Upstream, a dynamic mid-upper level trough will produce rainfall
in CA/Pacific northwest to the Great Basin over the weekend. On
Monday the slow moving frontal system targets the ranges of
eastern NV across UT/CO/WY/ID with valley showers and mixed
rain/snows at higher elevations. On Tue the precipitation is
focused in the pacific northwest to northern CA inland into the
northern great Basin and northern Rockies.
On Wed the focus of valley showers and mixed precip at higher
elevations moves into the northern Rockies and high Plains, then
gradually spreading into the northern Plains and upper MS Valley.
The building mid level ridge in the southeast leads to growing
confidence about hot temperatures developing in the southeast.
The first forecast 100 degree readings popped up in both the 12z
ECMWF and ECMWF Ensemble Mean in southern GA next Wed 22 May and
Thu 23 May, marking an early season developing heat wave. There is
potential for record setting heat in the southeast and southern
Appalachians the latter half of next week. Along with the heat
comes a dry spell in AL/GA and the Carolinas, with below normal
chances of rain.
Persistent cold is forecast in the west to the northern Plains
this weekend thru the middle of next week. Large areas of -10 to
-20 degree anomalies for daily high temperatures remain forecast
across the Great Basin and northern Plains Sun, continuing into
the early and middle portions of next week. Overnight minimum
anomalies are not as high a magnitude but still below normal over
large portions of the west to the northern Plains.
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
- Heavy precipitation across portions of the Central Rockies, the
Central Plains, the Northern Plains, and the Northern Rockies,
Sun-Mon, May 19-May 20.
- Heavy rain across portions of the Plains and Mississippi Valley,
Mon-Tue, May 20-May 21.
- Heavy rain across portions of the Northern Rockies, Wed-Thu, May
- Heavy rain across portions of the Central Rockies, Mon, May 20.
- Heavy rain across portions of the Upper Great Lakes, Sun, May 19.
- Severe weather across portions of the Central and Southern
Plains, Mon, May 20.
- Severe weather across portions of the Central and Southern
Plains, Middle and Lower Mississippi Valley, Tue, May 21.
- Severe weather across portions of the Great Lakes and the Ohio
Valley, Sun, May 19.
- Flooding possible across portions of the Central Plains, the
Upper and Middle Mississippi Valley, the Northern Plains, and the
Northern Great Basin.
- Flooding occurring or imminent across portions of the
Mississippi and Missouri River basins, the Southern Plains, and
- Flooding likely across portions of the Northern Rockies.
- Excessive heat across portions of the Southeast, Thu, May 23.
- Much below normal temperatures across portions of California and
Central Intermountain West, Sun-Thu, May 19-May 23.
- Much below normal temperatures across portions of the Northern
and Central Plains, and Upper Mississippi Valley, Sun-Tue, May
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at: