Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
239 PM EDT Sun Mar 25 2018


Prelim Day 1 QPF Discussion
Valid Mar 26/0000 UTC thru Mar 27/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1


...Pacific Northwest...

A rather impressive short wave trough moving rapidly across the
nern Pacific towards British Columbia will yield zonal moist
onshore flow into WA and extending south into OR over the next 24
hrs. This upper disturbance and lower heights will not dig much at
all, due to the mammoth upper ridge over the eastern Pacific and
extending into the northwest quad of the country. However, an
anomalous long fetch of Pacific moisture flux will begin reaching
the coast overnight and persist through Monday. Overall WPC
followed a blend of the GFS/ECMWF with the 12z hi-res package for
areal avg totals of 1 to 2 inches with locally higher values in
the coastal ranges, Olympics and Cascades.

...Central Rockies into Plains/Mississippi Valley...

An amplified split flow upper trough will move slowly through the
West over the next day, while the leading edge of upper height
falls and upper disturbance along the subtropical jet emerge into
the central portion of the country. This will be the start of a
multi-day active convection and heavy to excessive rainfall event,
truly a spring pattern. While moisture and precip will increase
throughout the period from large scale warm advection and ideal
broad swrly upper difluence, a couple of spots may see more
enhanced qpf amounts. The first area is across WY into western SD,
as a mid to upper low and well-defined 500mb vort tracks across
the state into the front range of the northern to central Rockies.
The guidance captures a wave of surface low pressure or inverted
surface trough sliding through WY to enhance the vertical lift and
upslope/orographic flow. Expect areal avg amounts up to an inch,
locally higher, from the Wind River range to the Big Horn mtns to
the nern portion of the state to western SD. Meanwhile, out over
the Plains and/or invof a warm front lifting north and dry line
remaining relative stationary, expect an increase in moisture
pooling and instability leading to convective heavy rains from
sern NE/swrn IA through eastern KS/western and central MO and
slicing through nern OK to north central TX. Overall WPC used a
blend of the GFS/ECMWF/HREF Mean and NBM with the NAM Nest and ARW
for coverage and amounts across the entire region.

...Eastern Gulf Coast States...

A quasi-stationary frontal boundary from nern FL back into
southern AL/MS may yield locally heavy rain with overall a light
steering mechanism. The hi-res shows a signal for locally heavy
amounts and WPC increased qpf amounts over the global models from
JAX to MEI/JAN.

Musher