Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1158 AM EDT Tue May 29 2018
Valid 12Z Fri Jun 01 2018 - 12Z Tue Jun 05 2018
...Record heat expected across the southern Plains...
...Guidance and uncertainty assessment...
Model and ensemble guidance offer a reasonably well clustered
range of solutions in the day 3/4 (Fri-Sat) time frame in a
pattern with near average expected predictability. Increasing
model to model run inconsistency and overall guidance forecast
spread into the days 5-7 time frame suggests a transition to below
normal predictability for smaller-mid scale systems, but some
common themes remain to support the overall larger scale flow
evolution.
Accordingly, the WPC medium range product suite was primarily
derived from a composite blend of the quite compatable 06 UTC
GFS/GEFS mean and 00 UTC ECMWF/ECMWF ensemble mean days 3/4.
Transitioned to much higher ensemble mean weighting days 5-7 amid
growing forecast uncertainty. Leaned a bit more on the ECMWF then
ECMWF ensemble mean overall in these blends in an effort to
maintain as much WPC continuity as possible consistent with the
expected larger scale flow evolution.
...Weather Highlights and Threats...
An upper low/trough will likely drop southeast into the
Mid-Atlantic States and Carolinas, setting the stage for wet
weather for the Mid-Atlantic and Southeast states. A lingering
lead/wavy surface front over the from the southern plains through
the southeastern U.S. into the western Atlantic will also provide
a focus for deeper moisture pooling and some heavier local
convective downpours. Upstream, a general trough over the
Northwest composed of a few active shortwaves should generate some
late season rainfall over northern parts of the West late this
week and locally heavy convection over the Plains well into next
week. Ejecting western U.S. impulse energy will play an uncertain
role in rainfall distribution/intensity downstream over the
central and eastern U.S. through the period.
The dominant focus of the temperature forecast will be on a
multi-day southern Plains heat wave whose influence may extend at
times westward into the Rockies and eastward into the lower MS
Valley and western Gulf coast. Hot afternoon readings in the
100-110F range should be most common in the southern High
Plains/lower Rio Grande, with Saturday setting up to be the
hottest day. It is likely that record values for max/warm min will
be reached/exceeded on multiple days, with some of the
record-breaking heat also extending for a time farther
north/northeast. There should be some southward suppression of the
heat in Texas with time from Sunday into Monday as a front settles
southward, though it should rebound by Tuesday. On the other
hand, mean troughing aloft will tend to keep highs near to below
normal near the West Coast and by the weekend/early next week over
the East.
Schichtel
WPC medium range forecasts of 500 mb heights, surface systems,
weather grids, quantitative precipitation, and winter weather
outlook probabilities can be found at:
http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4