Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Tue Apr 03 2018


Prelim Day 1 QPF Discussion
Valid Apr 04/0000 UTC thru Apr 05/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Great Lakes and Ohio valley to the mid-Atlantic/Northeast...

Dynamics associated with the morning convection across southern
IL/IN/OH will continue to fade as the upstream surface low and
cold front take the focus for convection/precip this afternoon and
past 00Z. That will push most of the rainfall into cooler air over
southern Ontario this evening and through southern Quebec late
tonight before pushing through northern New England tomorrow (as
snow -- see the latest QPFHSD for more on the winter weather
aspect). Comma head/deformation precipitation band will expand
east-northeastward overnight out of WI and through MI into
Ontario. Hi-res guidance offered a good starting point (via
blended HREF mean) with QPF axis from lower Michigan across
southern Canada through northern Maine by tomorrow.


...Eastern Texas/lower MS valley/lower TN valley eastward...

Convection taking off over eastern TX this afternoon will continue
past 00Z but wane later this evening as right entrance region of a
110kt subtropical jet accompanies a strong cold frontal passage.
Precipitable water values 1.25-1.50" (+1 to +2 standard
deviations) will support locally heavy rain with embedded
convection but progressive nature should limit excessive rain
threat amid relative high Flash Flood guidance (with the typical
sensitivity to urban areas). Split focus of QPF between
southeastern TX and again from northern MS into middle TN based on
recent RADAR/satellite and hi-res guidance trends since yesterday
(lead convection in TX vs frontal precip/convection to the north).
12Z hi-res guidance appears to be too far south with current TX
convection so expanded the 1" line to the northeast into central
LA vs the HREF mean. Marginal risk should cover isolated local
flash flooding concerns this afternoon into this evening.


...Pacific Northwest/northern Rockies...

A warm frontal boundary will be pressing slowly east-northeastward
toward the Pacific Northwest tonight. Increasingly west-southwest
low level flow with this boundary (PW values increasing to over
0.75" or about +1.5 standard deviations) will support an area of
expansive showers overnight through Wednesday from coastal OR/WA
inland (where there was more disagreement in the guidance). Model
consensus is for modest totals over 0.75" in the Coastal Range and
Cascades with at least some light precip inland in interior WA
(under 0.1"). Better consensus existed farther east into northern
ID where the HREF mean was a reasonable starting point.


Fracasso