Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
154 AM EST Fri Mar 09 2018


Prelim Day 1 QPF Discussion
Valid Mar 09/1200 UTC thru Mar 10/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...Eastern Great Lakes - Northeast...

Snow showers will continue across much of central and northern New
England and NY through the day 1 period. Anticipate one local
maximum across northern Maine as the closed mid level low tucks an
area of surface low pressure westward into southern Canada.
Elsewhere more showery conditions underneath the closed low in the
northwesterly flow can be expected. Local maximums will occur
where lake enhancement and orographic impacts are maximized.
Models were close enough that WPC utilized a blend of the high res
and global guidance...with more weight given to the high res
guidance where lake effect and orographic enhancement are
expected. 


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

Moderate showers will continue this morning across portions of
northern CA and southern OR as a weak wave moves ashore. However
anticipate mid level ridging to build into the pacific northwest
through the day...which should result in a decrease in shower
coverage and intensity as we go through the morning hours. The
focus for light QPF amounts will shift east into the northern
Rockies and portions of Montana. A pretty compact wave will move
across these areas...but limited moisture and progressive forcing
will limit QPF magnitudes.


...MS valley into the OH and TN Valley...

Mainly light QPF amounts are expected through the day 1 period
from the central Gulf Coast north northeastward into Kentucky.
Precipitation should break out this evening across portions of the
Ohio Valley...shifting east into portions of southern WV and
southwest VA. Note a pretty good upper jet moving southeastward
placing the region in the favorable left exit region...along with
an increase in 850mb moisture transport. Do note some model
differences...with the 12z ECMWF and 0z UKMET quite a bit drier
than the GFS. The 0z suite of high res models are more in line
with the wetter GFS. Went with a compromise solution...although
given the upper jet and frontogenesis forecast...did lean more
towards some of the wetter solutions.  

The approach of the exit region of an upper jet quickly moving
east out of the Pacific, and a weak mid level wave...will result
in increasing southerly flow across the lower and mid MS valley by
tonight. This should result in the development of some light
showers...with any heavier convection expected to remain offshore
in the Gulf through the day 1 period.

Chenard