Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
235 AM EDT Wed Mar 14 2018


Prelim Day 1 QPF Discussion
Valid Mar 14/1200 UTC thru Mar 15/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Northeast...

Snow continues this morning across much of ME to the west of the
strong offshore low. The low will weaken today as it moves west
into southern Canada...however snow showers will continue
underneath the closed mid/upper level low over much of central and
northern New England. Northwesterly flow on the backside of the
low will result in orographic enhancement to the snow over the
favored terrain of upstate NY and VT/NH...with lake enhancement
also expected off of lake Ontario and Erie. Overall models were in
very good agreement through the day 1 period. WPC QPF was thus
based on a multi model blend.

...West...

Longwave troughing building into the west will continue the
showery pattern through the day 1 period. The better PWATs and
moisture transport will have shifted south and east of the west
coast...thus not anticipating rainfall rates or totals to be that
impressive. However with the trough axis moving ashore, showery
conditions will continue...with a well defined wave on the
southern periphery of this trough helping increase shower coverage
over central CA. Overall model trends have been for less QPF today
across the Sierras...with additional amounts generally forecast
between 0.5"-1". Did increase totals some across the southern CA
mountains though...with increased onshore upslope flow anticipated
today and slightly better PWATS there. Looking at some 1" amounts
over portions of the Transverse and Peninsular Ranges.

Showers will overspread the Great Basin as well though the day.
Falling heights aloft and good upper level divergence ahead of an
approaching jet will provide a favorable environment for
increasing shower coverage. Steepening mid level lapse rates
should also allow for the development of some weak instability
today. Thus would expect scattered convection to
develop...primarily from eastern NV into UT. PWAT values do
increase to around 0.5" over UT as well...which is about as high
as they can get this time of year. Thus would anticipate some
brief heavy rainfall rates to accompany any showers/storms that do
intensify. However storm motions will be very quick...thus not
thinking localized amounts will get much above 0.5" in an hour.
Areal averaged rainfall generally expected to between 0.25"-0.5"
across portions of NV/UT...with amounts approaching 1" over
northern UT where orographic enhancement is expected. Models were
close enough to allow for a multi model blend for QPF over the
west...with more emphasis given to the high res CAMs. 

Chenard