Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 606 AM EDT Wed May 09 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid May 09/1200 UTC thru May 12/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Great Lakes into the OH Valley... There are no significant mass field differences in the latest suite of models with the eastward push of the mid to upper level trof from the Upper MS Valley into the Great Lakes-OH Valley. Fairly well defined upper difluence ahead of this trof in an axis of above average pw values will support a broad area of scattered to organized convection across these areas. Confidence is low with qpf details---with general model consensus for widespread moderate to heavy precip values. The WPC day 1 qpf leaned toward the href mean and in house hi res ensemble mean---with areal average .25-.50"+ amounts depicted. ...Southeast New England... The mid to upper level trof moving off the NC coast early this morning is expected to become increasingly negatively tilted as it pushes northeastward---passing close to Cape Cod and the offshore Island early Thursday morning. The northwest edge of the associated precip with this system may impact southeast New England with moderate totals in the .25-50"+ range. ...Pacific Northwest---Northern Rockies into the Northern High Plains... A lead area of height falls will be pushing eastward Wednesday from the Pacific Northwest into the Northern Rockies and then eastward into the Northern High Plains Wednesday night into early Thursday morning. A concentrated area of large scale uvvs along and ahead of the associated frontal boundary with these height falls will support an organized area of precip pushing eastward across these areas. Model consensus is for .25-50"+ totals from far northeast WA---across northern ID and into western to central MT. Additional upstream northeast Pacific height falls will follow this lead area---pushing into the coastal areas of Washington-Oregon Wednesday night into early Thursday morning. Overall weaker large scale dynamics and lower pw values will support mostly light to moderate additional precip totals late Wednesday into early Thursday for coastal sections of Washington and Oregon. Days 2/3... ...Pacific Northwest... Light to moderate precipitation is expected over the favored terrain of the Pacific Northwest Thursday as a series of shortwaves progress inland from the eastern Pacific. This activity will wane along the WA/OR coast Thursday night as the shortwave starts to amplify downstream and increasing northerly flow shuts down the region's moisture supply. Model guidance remains well clustered in keeping precipitation focused in the terrain and slight downward adjustments were made to continuity per guidance consensus. ...Northern Rockies and Intermountain West... A large scale trough amplifying will close into a low over the interior western U.S. Thursday night and bring both Pacific and Gulf moisture into the Intermountain West. Light to moderate precip will occur with this system, particularly over the northern Rockies of WY/ID where an areal average of around 1 inch is expected Thursday night through Friday night. Ongoing snow melt will raise flood concerns for this area (already under a hydrologic outlook from WFOs in the area), though snow levels will lower Friday and limit the overall flood potential. ...North-central Great Plains and Upper Mississippi Valley... Surface low development east of the CO Rockies Thursday will provide forcing to Gulf moisture laden southerly flow Thursday night through Friday. The greatest threat for any excessive rainfall will be from north-central Nebraska into southern Minnesota and northern Iowa, where the combination of a weak ripple of shortwave energy, strong southerly low level flow, and an axis of anomalous moisture (1 to 1.5 inch PW is 2 to 3 standard deviations above normal) will heighten the risk for a period of heavy rainfall Thursday night into Friday. The Marginal Risk for excessive rainfall was maintained for Day 2 (12Z Thu-12Z Fri) with just a few spatial edits based on 00Z guidance consensus. The southward movement of the amplifying trough/low will maintain surface lows over the central plains well into this weekend with Gulf moisture expected to be diverted farther east ahead of the low with precip tapering off over the plains starting Saturday. ...Upper Midwest to New York State... The positively-tilted and amplifying trough/low in interior west will allow shortwave energy to shift across the north-central CONUS and stretch the warm front associated with a slow moving surface low over KS. This warm front looks to stretch from WI to NY state on Day 3 (12Z Fri-12Z Sat) with a narrow stripe of heavy precip along this front. Instability should be limited south of the front, so the max potential for precip looks to be somewhat limited. A marginal risk for excessive rain was raised along this frontal zone for Day 3. ...Southern Florida... The combination of a weakening frontal boundary and an axis of highly anomalous moisture could result in periods of heavy rainfall over (or just south of) the southern tip of Florida Thursday and Friday. There is some uncertainty with the exact amounts, but 00Z model guidance was still in agreement with keeping the heaviest totals just offshore. Oravec/Jackson Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml