Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Thu Apr 05 2018


Prelim Day 1 QPF Discussion
Valid Apr 06/0000 UTC thru Apr 07/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Pacific Northwest/California...
...Central/Northern Rockies and adjacent High Plains...

The models bring an area of low pressure toward the West Coast
over the next 24 to 36 hours in association with a gradually
amplifying upper trough. The trough will be interacting with a
substantial pool of subtropical moisture and this will set the
stage for a strong atmospheric river to impact the West Coast
tonight through Friday, with enhanced moisture transport and
strong forcing helping to focus heavy rainfall across the coastal
ranges of central and northern California, and extending up across
foothills and upslope areas of the northern Sierra-Nevada. The
850/700 moisture flux anomalies are forecast to increase to over 5
standard deviations above normal along the coast which will be
aided by the arrival of a 40 kt low level jet. Additionally, the
precipitable water values are forecast to rise to between 1.5 and
1.75 inches across coastal areas of central California and
extending offshore which in itself would be over 5 standard
deviations above normal. A combination of increasing onshore flow
and enhanced rainfall efficiency given the depth of subtropical
moisture will result in heavy rainfall. Expect as much 2 to 4
inches of rain locally through late Friday, with some areas
possibly exceeding 5 inches involving the central/northern
California coastal ranges and northern Sierra-Nevada. Runoff
problems and flooding concerns are expected given the amounts. The
influx of Pacific moisture will extend well inland and all the way
through the central and northern Rockies where some lead shortwave
energy coupled with the moisture will be interacting with an
Arctic cold front draped up against the eastern slopes of the high
terrain. A combination of warm air advection and associated
isentropic lift along with relatively deep frontogenetic forcing
should support a stripe of light to moderate precipitation,
including accumulating snowfall, out across the High Plains. WPC
leaned toward a multi-model consensus with a bit more weight
toward the ARW and ARW2 hires solutions. Please consult the latest
QPFHSD for more details on the expected winter weather impacts.


...Southern Plains/Lower Mississippi Valley...

Increasingly moist southerly flow ahead of a developing area of
low pressure over the southern Plains will set the stage for heavy
convective rainfall beginning late tonight in an elevated fashion
late tonight over far eastern Oklahoma and western Arkansas, and
then expanding east across much of the lower Mississippi Valley on
Friday with focused impacts on central and southern Arkansas and
into central and northern Mississippi. The convection will be
enhanced by the arrival of a strong cold front from the northwest
and the development of a separate west/east oriented stationary
front ahead of the surface low. These boundaries will focus
precipitable water values of up over 1.5 inches and foster
stronger lower level convergence which will take advantage of the
pooling of instability for heavier rainfall rates and convective
organization. WPC generally leaned toward the wetter hires CAM
guidance with a focus on the ARW2 in particular. The environment
is conducive for back-building and training convective cells, and
thus expect heavy to excessive totals. As much as 2 to 4 inches of
rain through Friday evening is expected with locally heavier
amounts possibly approaching 5 inches. This will drive concerns
for runoff problems and flash flooding.


...Great Lakes/Northeast...

Low pressure and an associated shortwave trough will traverse the
Great Lakes region before lifting northeast across southeast
Ontario through late Friday.

...Florida...

Some lingering showers are possible along the southeast coast of
the Florida peninsula this period with some low level convergence
and pooling of modest instability along a weakening front. The
amounts should be generally light.






Orrison