Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Thu Mar 08 2018


Prelim Day 1 QPF Discussion
Valid Mar 09/0000 UTC thru Mar 10/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...Eastern Great Lakes - Northeast...

The occluding cyclone off the coast of Maine early this afternoon,
north of the closed mid-upper level circulation, will pivot slowly
westward across Maine during the day 1 period. After 00Z Friday,
additional light-moderate liquid equivalent precipitation totals
(0.25-0.50") will fall across northern Maine early in the period
(i.e. through tonight) -- owing to the slowly-retrograding
shortwave (lingering DPVA) and deep moist easterly flow/elongated
Atlantic fetch. At this stage, the models are fairly well
clustered in terms of the QPF axes, though the GFS is one of the
wetter pieces of guidance across northern ME. The WPCQPF was
essentially a consensus of both global and high-res models, most
notably the 12Z GFS, ECMWF, local bias-corrected ensemble QPF,
HREF mean, and recent NBM, which tended to temper the wetter
output offered by the GFS.

Elsewhere, lake and/or diurnally-enhanced snow showers will bring
additional modest accumulations (with the orographic enhancement)
into the northern Appalachians-Laurel Highlands as well as the Tug
Hill Plateau-Adirondacks, along with another area of 0.25-0.50+
inch liquid equivalent totals across northeast OH, northwest PA,
and western NY downwind of Lake Erie with the predominant WNW low
level flow.


...Northern CA and Pacific Northwest eastward into the Northern
Rockies...

Satellite shows a compact area of low pressure along the PAC NW
coast early this afternoon. This low will continue to move
northeastward and weaken with time later this afternoon and
tonight. Precipitation intensity should pick up along the WA/OR
coast by 15z and linger through the day. Onshore westerly flow
will be around the climatological 99th percentile for a period
today...thus should see good orographic enhancement to
precipitation totals and see rates as high as 0.3"-0.4" in an
hour. The lack of anomalous PWATs and a quick progression of the
strongest forcing/onshore flow will limit the overall magnitude of
rainfall. However anticipate a longer duration of showery
conditions given continued mid level troughing overhead...thus
looking at amounts within the 1-3" range both along the coastal
ranges and the Cascades through 12z Friday.

Should see decent QPF further inland across the northern Rockies
as well...as the deep layer zonal west to east flow is favorable
for orographic enhancement. Thus anticipate some 1" totals in the
more favored locations.

Model agreement was pretty good across this region. Thus WPC was
able to utilize a multi model blend for QPF.

Hurley/Chenard