Quantitative Precipitation Forecast
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000
FXUS04 KWBC 162058
QPFPFD

Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
458 PM EDT Mon Apr 16 2018


Prelim Day 1, Day 2 and Day 3 QPF Discussion
Valid Apr 17/0000 UTC thru Apr 20/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr

Day 1

...Mid Atlantic into the Northeast and Great Lakes...
A negatively tilted mid/upper level trough supports strong upper
level divergence, strong low-level inflow, and ample moisture
which moves through New England today and tonight.  CAPE should be
harder and to come by rain translates northeast, instability
slowly fades, and the moisture feed slowly winnows, though it
should be enough to allow for continued embedded heavier
convective cores within the rain shield.  Localized rates peaking
in the 0.5"-0.75" in an hour range early on will slowly fade with
time.  Further northwest under the closed mid/upper level low,
will continue to see precipitation into the Great Lakes region.
Overall, a compromise of continuity, the 12z ARW, the 14z National
Blend of Models, the 12z GFS, and the 00z ECMWF were used for the
precipitation pattern, with a strong lean towards the National
Blend of Models near the Great Lakes themselves where global
guidance can underestimate lake effect.


...West...
A trough will continue moving east into the Great Basin and
northern Rockies with associated low- to mid-level frontogenesis
supporting modest precipitation over much of the area.  WPC QPF
used a compromise of continuity, the 12z ARW, the 14z National
Blend of Models, the 12z GFS, and the 00z ECMWF were used for
precipitation amounts.


Days 2/3

...West Coast/Intermountain West...

Upper-level low off the West Coast will move southeastward to the
Great Basin/Southwest by Thursday evening.  Onshore flow over the
Pacific Northwest will end and become offshore by Wednesday
morning.  The precipitable water values along the coast are 0.50
inches that will drop off to near 0.25 inches by Thursday morning.
The qpf will be generally light with maximum qpf amounts over the
Northern Cascades and the Olympic Peninsula with maximum qpf
amounts ranging from 0.25 to 0.30 inches from Tuesday evening into
Wednesday evening.  The Upper-level low will move onshore over
California moving into parts of the Great Basin Wednesday evening
into Thursday evening.  A week plume of moisture will pass along
the Southern California Coast with precipitable water values of
0.50 inches with the low-level flow of 20 knots from early
Thursday morning through late Thursday morning when the plume
moves into Northwestern Mexico.  The qpf will be modest with
maximum qpf amounts ranging from 0.25 to 0.35 inches over parts of
the Great Basin on Wednesday evening into Thursday evening.  WPC
used a blend of the GFS and the ECMWF as the starting point of the
manual graphics.


...Northern/Central Plains eastward to the Northeast/Northern
Mid-Atlantic...

A baroclinic zone over the Middle Mississippi Valley and the
Central/Southern Plains will move northeastward off the East Coast
by Thursday evening.  A plume of moisture from the Western Gulf of
Mexico will intersect the boundary with precipitable water values
of 0.75 inches that will pool along the boundary until the front
and the moisture plume move off the East Coast by Thursday
morning.  The low-level flow will increase from 15 to 20 knots to
35 to 40 knots on Wednesday morning over the Middle Mississippi
Valley.  The storm will produce a maximum qpf over parts of the
Upper/Middle Mississippi Valley with maximum qpf amounts from 1.00
to 1.20 inches on Tuesday evening into Wednesday evening.  A
secondary maximum will develop over parts of the Lower Great
Lakes/Northern Appalachians under a deep upper-level low over the
Northeast with maximum qpf amounts ranging from 0.25 to 0.45
inches also from Tuesday evening into Wednesday evening.  As the
upper-level energy associated with the baroclinic zone moves
eastward the energy forms a new upper-level low over the Northeast
by Thursday evening.  The boundary will aid in producing a broad
region of qpf from the Lower Great Lakes to New England Coast with
maximum qpf amounts ranging from 0.25 to 0.50 inches from
Wednesday evening to Thursday evening.  WPC used a blend of the
GFS and the ECMWF as the starting point for the manual qpf.


...Southern High Plains into the Rio Grande Valley...

As the aforementioned upper-level low over the West Coast moves
inland, circulation around the upper-level low will pull moisture
from the Western Gulf of Mexico westward into the Southern High
Plains Wednesday evening into Thursday evening.  Precipitable
water values will increase from below 0.25 inches to 1.00 inches
by Thursday evening.  The system will produce some qpf over parts
of Northeastern Mexico that will drain into the Rio Grande.  The
heaviest qpf during the period will occur late on Thursday
afternoon into Thursday evening over parts of the Southern High
Plains with maximum qpf amounts ranging from 0.25 to 0.40 inches.


Roth/Ziegenfelder


Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml

$$





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