Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
203 PM EDT Wed Apr 11 2018


Prelim Day 1 QPF Discussion
Valid Apr 12/0000 UTC thru Apr 13/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Northern California---Pacific Northwest---Great Basin into the
Northern Rockies...


The strong area of northeast Pacific height falls that will be the
driver of a high impact weather event over the next several days
over large portions of the nation will be pressing inland tonight
across the Pacific Northwest-northern California---eastward into
the Great Basin and Northern Rockies during Thursday.  An axis of
above average pw values along the associated frontal boundary will
support a concentrated region of frontal precip through the
Pacific Northwest-northern California region tonight---across the
northern Great Basin-northern Rockies and northern high Plains
region during Thursdays.  This frontal precipitation will be
followed by post frontal showers from northern California into the
Pacific Northwest to the west of the Cascades as westerly onshore
flow persists across these regions.  Model mass fields are in good
agreement this period with the evolution of this trof---with
subsequent good agreement also with the precipitation distribution
and amounts across these regions.  A broad region of moderate
precipitation potential likely across these areas---with locally
heavier totals in the favored terrain regions from the
Sierra---northwest California coast range---northward through the
Oregon-Washington Cascades and along the Oregon-Washington coast
range into the Olympic range. Locally heavy totals also likely
from the Wasatch of UT---northward into the Northern Rockies from
northwest WY---far eastern ID---central to northern ID---northeast
Oregon and western MT.  See the latest QPFHSD for heavy snow
threat across portions of these regions.

...Upper MS Valley---Great Lakes---northern Mid-Atlantic into
western to central New England...

Ahead of the strong height falls moving into the western U.S. this
period...two areas of height falls will be pushing eastward across
the northern tier of the country from the Northern Plains into the
Upper MS Valley---Great Lakes and into New England.  The lead area
of height fall moving from eastern NY state into New England early
day 1 will be the weaker of the two and have mostly light precip
amounts associated with it from the northern Mid Atlantic---into
NY state and New England.  The second area of height falls pushing
east northeastward from the Northern Plains into the Upper MS
Valley tonight and across southeast Canada Thursday will be
stronger.  This will result in stronger isentropic lift ahead of
the associated surface low moving east northeastward across these
areas.  Model consensus is for an expanding region of overrunning
precipitation to spread across the Upper MS Valley into the Great
Lakes tonight and across NY state into western to central New
England Thursday---with a broad region of moderate precip amounts
in the .10-25"+ range.  Accumulating snow potential will be
confined to the northern edge of this forecast precip region from
northern MN---far northern WI---the U.P. of MI into southeast
Canada. 


Oravec