Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 512 PM EDT Tue Apr 03 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 04/0000 UTC thru Apr 07/0000 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. Days 2/3 ...Pacific Northwest/California... Weak short wave energy and weak onshore flow, with precipitable water values of 0.75 inches, over the Pacific Northwest will aid in producing maximum qpf amounts ranging from 1.25 to 1.30 inches over the Olympic Peninsula and 1.00 to 1.10 inches over the Northern Cascades from Wednesday evening into Thursday evening. On Thursday evening into Friday evening, onshore flow will start over Northern/Central California with precipitable water values of 1.25 inches that will increase to almost 1.75 inches on the low-level flow increasing from 20 knots to 30 knots into Southern California by Friday evening. Maximum qpf amounts will range from 1.20 to 1.25 inches over the Central/Northern California Coast on Thursday evening into Friday evening. A secondary maximum will develop over parts of the Sierras with maximum qpf amounts ranging from 0.75 to 1.00 inches also on Thursday evening into Friday evening. WPC used a blend of the GFS and the ECMWF as a starting point for the manual graphics. ...Northern Rockies into the Middle/Lower Mississippi Valley... A baroclinic zone moving southward out of West-Central Canada will move to Southern Plains/Lower Mississippi Valley while banked up against the Front Range of the Rockies by Friday evening. Moisture spilling over the top of the continental divide will aid in producing qpf over parts of the Northern Rockies/Northern High Plains on Wednesday evening into Thursday evening producing maximum qpf amounts ranging from 0.50 to 0.60 inches. As the boundary moves southward, upslope flow will develop along the Northern Rockies producing a maximum qpf amounts ranging from 0.75 to 0.90 inches over the Wind River Mountains on Thursday into Friday evening. Additionally, moisture from the Gulf of Mexico will stream northward over the Southern Plains into parts of the Lower Mississippi Valley with precipitable water values of 1.25 to 1.50 inches on Thursday into Friday evening. The baroclinic zone will intersect the moisture over Eastern Oklahoma producing maximum qpf amounts ranging from 1.00 to 1.10 inches on Thursday into Friday evening, too. WPC used a blend of the GFS and the ECMWF as a starting point for the manual guidance. ...Northern Plains/Great Lakes into Northeast... Baroclinic zone moving southward out of Canada will extend from the Northeast across the Ohio Valley by Friday evening. The boundary will move into air with precipitable water values less than 0.25 inches on Wednesday evening into Thursday evening over the Upper Midwest, producing modest amounts of qpf with maximum amounts over North Dakota and Illinois ranging from 0.10 to 0.15 inches. On Thursday, moisture from the Western Gulf of Mexico will move northward over the Southern Plains/Middle Mississippi into the Ohio Valley/Northern Mid-Atlantic by Friday evening with precipitable water values of 0.50 inches. The system will produce a swatch of precipitation along the track of the surface low with maximum qpf amounts ranging from 0.25 to 0.40 inches from the Great Lakes to the Northeast. WPC used a blend of the GFS and the ECMWF as a starting point for the qpf graphics. Fracasso/Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml