Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EDT Wed May 16 2018
Valid 12Z Sat May 19 2018 - 12Z Wed May 23 2018
...Guidance and Predictability Assessment...
Model and ensemble clustering has improved some with the last few
cycles at medium range time scales and a composite blend of the
latest GFS/ECMWF and GEFS/ECMWF ensembles seems to provide a
reasonable basis for the WPC product suite. Embedded systems still
offer timing/emphasis variance, but overall uncertainty has
recovered to near normal levels.
...Weather/Threats Highlights...
Weekend srn stream shortwave trough energy/height falls ejecting
northeastward from the Rockies to the N-Central U.S. will interact
with nrn stream trough energy digging to the lee of a persistent
wrn Canadian upper ridge. The wavy frontal boundary will focus
some heavier local convection on the leading edge of cooling
post-frontal high pressure spilling southward over the Plains.
Upstream, guidance is in better agreement that an amplifying ern
Pacific trough should dig into CA and the s-central Great Basin
Mon-Wed to form a closed low aloft to support modest widespread
precipitation mainly along/north of the system.
Downstream...anomalously deep moisture from the Gulf of Mexico and
western Atlantic will likely spread showers and storms from the
Southeast to up the Appalachians and Mid-Atlantic/Northeast into
the weekend. The models forecast widespread showers when the
moisture intercepts the front across Long Island and adjacent
southern New England/nearby islands. The wavy frontal zone will
persist and be periodically reinforced from the Plains to the MS
Valley, OH Valley, and Northeast. Hot and moist conditions persist
to the south of the front. Late week record high temps are
expected in parts of Texas to the mid-lower MS valley before the
airmass modifies early next week. Record warm minimum temps are
possible for the Mid-Atlantic in the warm, humid airmass.
Instability and moisture pooling along the front supports showers
and storms with potential for locally heavy downpours. Other
showers/storms should develop in the TX/OK panhandles near the
dryline and return low level southerly flow advects moisture into
the region. Also, FL should experience diurnal showers/storms as 2
inch precipitable water values develop to fuel locally heavy
downpours where best sea/lake breeze convergence occurs.
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
Schichtel