Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 445 PM EDT Thu Apr 26 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Apr 27/0000 UTC thru Apr 30/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Central Appalachians---Mid-Atlantic---southern NY state into southern New England... The strong vort rotating through the base of the mean eastern trof across the central gulf coastal region/southeast late this afternoon will become increasingly negatively tilted tonight as it races northeastward from the southern Appalachians/southeast into the Mid-Atlantic and then across the coastal Mid-Atlantic into coastal New England on Friday. Strong isentropic lift expected in the region of well defined upper difluence ahead of these height falls. This will support the continued well organized nature to the area of associated precip as it affects areas from the central Appalachians---Mid-Atlantic and into southern NY state and southern New England. The expected fast movement will be a detractor to precip totals---but with pw values above average and overall strong dynamics---moderate to heavy areal average totals likely. Hourly rainfall rates may be as high as .25-.50"+---with potential for isolated runoff issues in the urbanized regions across this area. ...South Florida... The axis of much above average pw values currently lying to the south of south Florida and the Keys is expected to be drawn northward ahead of a southward moving cold front moving across the Florida peninsula Friday. This northward push of higher pw values is related to the next area of mid to upper level height falls that are rotating through the mean eastern trof---pushing into the northern Gulf of Mexico Friday. This northward surge will enhance precip potential ahead of the above mentioned southward moving cold front--supporting scattered convection and locally heavy rainfall potential Friday over South Florida. ...Upper MS Valley---Upper Great Lakes... Strong northern stream height falls dropping from the Upper MS Valley into the upper Great Lakes will help re-amplify the northern portion of the mean eastern trof Friday into Friday night. A fast moving area of enhanced isentropic lift ahead of the associated surface low will support moderate precip totals from the Arrow Head of MN into the western U.P. of MI and from northern to southeast WI. Precip may change from rain to snow over the Arrow Head of MN---supporting light snowfall accumulations. See the latest QPFHSD for additional winter weather information. ...Northwest California into western Oregon and far southwest Washington... The well defined closed low off the northern California coast this afternoon will meander slowly east northeastward tonight into Friday to a position just off the coastal Oregon-California border. Model consensus is for the development of a narrow northwest to southeast oriented precip band to the north northeast of this closed low Friday---affecting areas primarily across Oregon to the west of the Cascades. In the core of this precip area---moderate totals in the .25-.50"+ range possible over Oregon to the west of the Cascades---with lighter values northward into far southwest Washington and southward into northwest California. ...South TX into northeast Mexico... Low level north northeasterly flow expected to strengthen Friday as a secondary front pushes south through south Texas. This will support increased scattered shower activity over south TX into northeast Mexico Friday. Model consensus is for light precip totals affecting south TX--with greater totals south into northeast Mexico where instability and upslope flow is expected to be stronger. Days 2/3... ...Northeast... Weak shortwave energy lifting up the northeastern CONUS phase into an upper trough shifting east over the Great Lakes Friday night. The trough closes into a low as it shifts east from the Great Lakes Saturday into Saturday night. A general model blend was used for QPF with 12Z guidance continuing a trend in improved agreement. The heaviest rainfall looks to be in a swath of about one inch (on areal average) up coastal eastern Maine Friday night. ...Michigan... A brief note on considerations for QPF on the Lower Peninsula. The 12Z GFS is stronger with the low crossing the Great Lakes than other 12Z operational models, which places a heavier QPF over the Lower Peninsula north of Detroit (half to three-quarters inch). This is slightly greater than the 12Z NAM which has similar placement while the 12Z ECMWF/UKMET/CMC are all weaker and south of Detroit. Will need to monitor subsequent model runs for this to be ironed out. ...Northwest... An upper low will drift east across OR Friday night through Saturday night, filling as it goes. The associated precip swath expands as the low occludes with max 24hr precip half to one inch for preferred terrain over northern CA/OR/WA/ID and into MT. A general model blend was used for WPC QPF with decent agreement. ...Rockies into the Southern High Plains... Anticyclonic flow over the central CONUS will allow increasing moisture across central Colorado to New Mexico as it interacts with weak shortwave energy embedded within difluent flow out ahead of the western U.S. low. This activity shifts onto the high plains of CO/NM/KS/OK/TX Saturday night. A general model blend was used for WPC QPF. ...Florida Keys... 1.75 inch PW (two standard deviations above normal) air lingers over or just south of the FL Keys Friday night ahead of a shortwave trough swinging through the Gulf of Mexico to the FL peninsula. Heavy rain may linger over the Keys through this time. Oravec/Jackson Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml