Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
225 AM EDT Sun Apr 14 2019
Valid 12Z Wed Apr 17 2019 - 12Z Sun Apr 21 2019
...Yet another major spring storm mid-late next week will pack a
heavy rainfall and severe weather threat for the central to
eastern U.S...
...Overview...
Potent upper level low will exit the Four Corners region Wednesday
and work its way eastward/northeastward as ridging builds in the
western Atlantic. This will lead to a dynamic spring storm again
for the central states with rain, severe weather, and some
northern fringe snow. Ridging will also push into the West Coast
but be replaced by an upper low late Friday coming into Southern
California with little fanfare.
...Guidance Preferences...
Ensemble spread continued to decrease markedly in the Rockies to
start the period with the ECMWF ensembles largely shifting slower
like the GEFS members have been. Blend of the guidance sufficed to
start, though the Canadian was perhaps too strong with northern
stream flow. Favored a mean position between the ECMWF/GFS and
their ensemble means which differed in how the system evolved east
of the Mississippi. Unclear how much the southern portion of the
upper trough remains separated from the flow to the north, perhaps
slowing the system down even more by the weekend. Pacific
Northwest will see a front push through the region Friday through
the weekend, reaching the Upper Midwest and stretched back to
California. Timing via a consensus has been fairly steady but
deterministic runs have been wavering.
...Weather Highlights/Threats...
Significant precipitation will again increase into Wednesday and
spread from the Mississippi/Missouri Valleys through the East as
low pressure strengthens over the Plains and Corn Belt. Multi-inch
rainfall totals with local flooding are probable (enhanced in
embedded convection) both along/ahead of the front and to the
north/northeast of the surface low. The 12Z GEFS mean was
forecasting 24h precipitation amounts much higher than typical for
this lead time over parts of MN/WI/MI. Consult SPC for the latest
on the severe weather risk. Mild temperatures will precede the
front (10-15F above average) to be replaced by cooler than average
temperatures after its passage.
Fracasso
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