Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Sat Apr 28 2018


Prelim Day 1 QPF Discussion
Valid Apr 28/1200 UTC thru Apr 29/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1


...Northeast...

Shortwave energy pivoting across the Ohio Valley early Saturday
will further amplify the longwave trough, as the vort lobe
ultimately ends up rotating around the the eventual closed
mid-upper low. With the main warm conveyor belt (wcb) off the
Atlantic coast, a secondary wcb will develop ahead of the
amplifying trough -- though with moisture anomalies (PW, low-mid
layer moisture flux) negligible this time around. The
slowly-evolving setup will nevertheless prolong the shower and
embedded thunderstorm activity, resulting in modest 24 hour QPF
totals per a multi-model blend (0.25-0.50+ inch) straddling the
Hudson Valley.

 
...Northern California...Pacific Northwest...Central-Northern
Rockies...

The latest model guidance continues to denote good agreement with
the gradual east-northeast progression of the closed upper low
currently along the northern California/southern Oregon coast
early this morning. By the end of the period (12z Sunday), the
circulation will broaden a bit as it moves across OR-WA. A broad
region of showery conditions will continue in the difluent upper
flow east and northeast of this closed low, particularly across
orographically-favored terrain. areas where the flow is more
orthogonal to the elevated terrain. Highest areal-average totals
(0.50-1.0+ inch) were noted across northwest CA and the
Olympics-northern Cascades in WA, with a broader area of
0.25-0.50" over the remainder of the coastal ranges and western
slopes of the Cascades.

Hurley