Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
240 PM EDT Thu Apr 12 2018


Prelim Day 1 QPF Discussion
Valid Apr 13/0000 UTC thru Apr 14/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Northern to Central High Plains...

There is overall good agreement in the latest model suite with the
evolution of the multifaceted early spring storm expected to
affect large portions of the nation over the next several days. 
The strong trof moving into the Great Basin this afternoon is
expected to continue amplify into a strong closed low over the
northern to central Rockies tonight---pushing into the central
high plains during Friday.  The developing comma head/deformation
precip area over the Northern Rockies---northern high plains this
afternoon will continue to expand eastward farther into the
Northern Plains overnight and then begin to redevelop farther
southward into portions of the Central High Plains as the closed
low reforms across this area. This will result in a fairly large
heavy precipitation region from southeast MT---southwest ND---much
of SD into western to northern Nebraska.  Heavy snow likely in
this axis with max totals in the 12-18" range possible. See the
latest QPFHSD for additional winter weather information. 

...Upper MS Valley into the Great Lakes...

To the east of the developing deep layered low over the Central
Plains---a strong frontal boundary will extend west to east into
the Upper MS Valley to lower Great Lakes region.  Strengthening
moist west southwest low level flow will overrun this front---with
an expanding region of precip developing to the north of the front
across the Upper MS Valley and into the Great Lakes.  There is
more spread among the latest operational and ensemble members with
respect to amounts and the axis of the qpf in the vicinity of this
boundary.  A qpf solution closer to the in house ensemble mean and
href mean was used to mitigate the spread in solutions---with
areal average .25-50"+ a amounts depicted.  Accumulating snow
potential will be confined to the northern edge of this precip
region from central MN into northern WI and the northern L.P. of
MI.

...Eastern portions of the Southern Plains toward the Lower MS
Valley...

The low level south southwesterly flow will be strengthening
considerably day 1 across the Southern Plains ahead of the above
mentioned amplifying closed low---raising pw values to 1 to 2
standard deviations above the mean across portions of the Southern
to Central Plains towards the Lower MS Valley.  Strengthening
upper difluence and boundary layer convergence along and ahead of
the dry line/cold front to the east and southeast of the closed
low will support increasing convective activity Friday afternoon
across eastern portions of Southern Plains toward the Lower MS
Valley.  Moderate to heavy precip totals possible from northeast
TX--northwest LA---eastern OK into central to western
AR---southern MO.  This active convection will continue to enhance
past the end of the day 1 period---with a greater potential for
more widespread heavy totals into the Lower MS Valley/Lower TN
Valley during day 2.

...Pacific Northwest...

Onshore west southwest low level flow will be re-strengthening
into the Pacific Northwest tonight into Friday to the southeast of
a developing closed low just to the south of the Gulf of AK. This
will support moderate to heavy precip values from the
Washington-Oregon Cascades---west to the northern Oregon coast
range into the Olympic Range.

Oravec