Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Mar 07 2018


Prelim Day 1 QPF Discussion
Valid Mar 08/0000 UTC thru Mar 09/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...Great Lakes - Northeast...

"Miller B" type cyclogenesis is well underway early this
afternoon, as the decaying Great Lakes surface low continues to
give way to the rapidly intensifying low off the mid Atlantic
coast (just east of the DELMARVA at 1800 UTC). The deep upper low
across the Great Lakes and associated negatively tilted trough
axis pivoting southeast-east will provide robust deep-layer Qs
vector forcing -- i.e. strengthening DPVA and low-mid layer
waa/theta-e advection leading to steepening easterly moist
isentropic ascent (strong 850 mb negative U-wind or easterly flow
anomalies). The new day 1 WPCQPF comprised a multi-model blend of
the 12Z guidance -- including the GFS and ECMWF as well as the
high-res WRF-ARW, ARW2, HREF mean, and the NBM. The variance
between all aforementioned solutions is as low as it has been thus
far for this event -- not surprising given the timing (now within
24-30 hours). Highest additional totals after 00Z Thursday
(1-1.5") will be across coastal New England from eastern MA though
eastern ME.


...Northern CA/Northwest...

Onshore flow with precipitable water values of 0.5-0.75" near and
ahead of a frontal boundary is expected to lead to moderate-heavy
totals across northern CA into the coastal ranges in OR and the
coastal-Cascade ranges in WA (max areal-average totals of 1-1.5+
inches).  Used a blend of model guidance and WPC continuity to
come up with the QPF in this region, which ended up best
resembling the 12Z GFS, ECMWF, HREF mean, and NBM.

Hurley