QUANTITATIVE PRECIPITATION FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 149 PM EDT FRI AUG 12 2016 PRELIM DAY 1 QPF DISCUSSION VALID AUG 13/0000 UTC THRU AUG 14/0000 UTC REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR Day 1... Central Gulf Coast ~~~~~~~~~~~~~~~~~~ ...Extremely Heavy Rainfall Continues Across Portions of Louisiana... Abundant moisture remains in place across the Southeast, with exceptionally anomalous 2.5-2.75+ inch PW values along the central Gulf Coast, including an observed 2.79" per the KLIX 12z RAOB. These values are between 3-4 standard deviations above the norm (near record values). The best description of this system is that of a sheared inland tropical depression or a monsoon depression. The upper high once over the system has retrograded into TX, advecting north to north-northeast flow over the top of the system. The best analog is Tropical Depression Five (2010) during its second trip into the Gulf Coast, though this system has proven to be a broader with its rainfall footprint. Given the deep high theta-e/moist profile for optimal warm rain processes (wet bulb zero heights beyond 16,000 feet), the threat for heavy tropical banding rains across this area will continue given the slow westward drift of the low- to mid-level warm core cyclone. WPC maintained a fairly large swath of areal-average QPF between 3-7" across LA and southwest MS. The best match to our QPF pattern was the 12z UKMET, though with a maximum adjusted southwestward. Most of the higher-resolution guidance indicates pockets of much higher amounts, local amounts of 10-20" additional inches of rain between now and Saturday evening. Significant to catastrophic flash flooding should continue/is still anticipated in association with this unusual heavy rain event into Saturday evening. Central and Upper Mississippi Valley - Upper Great Lakes ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The anomalous rich moist profile with adequate deep-layer instability will pose a continued risk of excessive short-term rainfall rates during the new day 1 period (12Z Fri-12Z Sat). PW anomalies continue to be quite high on the western periphery of the broad SE ridge and ahead of the approaching trough currently across the northern High Plains -- as values of 2-2.3 inches is around 3 standard deviations above normal for mid August. Despite the rich moist profile and more than sufficient dynamical support ahead of the trough (broad-scale upper divergence along with increasing right-entrance region upper jet forcing with time), the one limiting factor for widespread areal-average totals over 2 inches across portions of the central-upper MS Valley and into the upper Great Lakes will be the increasing forward propagation of convection with time later today. This occurs as the upper trough and stronger westerly flow pushes across the area tonight, with the strengthening deep-layer shear and negative PW advection (tightening PW gradient along and west of the surface front) favoring a more progressive front and pre-frontal convection with time. Therefore, the main concern with this pattern during day 1 will be the potential for excessive short-term rainfall rates (to the tune of 3" per hour). WPC QPF featured a multi-model blend, nudged in the direction of the 12z guidance, which led to higher values. It should be noted that the bulk of the high-resolution guidance indicate isolated higher totals between 4-7+ inches. Central and Southern Rockies and High Plains ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Have maintained modest areal-average rainfall over this region along the tail end of the cold front, on the back edge of the moisture gradient where the dynamical forcing is not expected to be as robust (weaker flow pattern aloft). Still, with the anomalous PW values in play (2-2.5 standard deviations above normal) along with generally modest instability (mixed layer capes 1000-2000 J/KG) and 850-700 mb frontogenesis and moisture flux, a marginal or more isolated threat for excessive rainfall will continue ahead of the cold front over these areas. Roth/Hurley GRAPHICS AVAILABLE ON THE WEB AT GRAPHICS AVAILABLE ON THE WEB AT www.wpc.ncep.noaa.gov/qpf/qpf2.shtml 24HR QP VT 14/00Z 0.01 459624 465632 469643 471650 473655 478670 481681 483690 482696 485724 487737 487749 487763 486768 487776 488790 489797 490803 505815 510820 517829 519832 521837 523844 526851 530862 532872 533878 535882 537883 539887 540892 541901 543906 545911 545917 542925 540930 539936 536949 531955 528960 525960 522960 517962 509962 501957 495952 492949 492947 489940 487929 487922 485920 482922 474925 471935 469940 467943 463945 460942 463930 463927 461926 457928 453925 449925 447920 451917 453914 452911 448909 443909 438909 433911 426917 421920 417924 410929 403934 400937 398940 395949 392955 390960 382977 379989 378004 377008 378012 380016 384019 392015 399011 408007 412007 418006 423006 425006 425009 428020 429023 431025 434027 439028 442030 445040 443046 438046 431049 426056 418059 415063 410064 396071 387075 383077 381082 378085 373085 363086 358088 355092 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337049 338048 339047 340046 341045 1.00 460775 459765 458758 456755 452756 448761 444765 442770 437782 433795 426805 420807 417811 414817 415823 412849 408862 407866 409869 412875 413877 416878 421874 428865 431860 434854 434847 436840 438833 441828 446824 449824 452818 454812 457798 459786 460775 1.00 450731 448729 447729 446730 445732 447734 448732 450731 1.00 420804 419801 418801 417802 417804 419805 420804 1.00 373911 370911 368913 363918 359925 355931 351936 349940 350945 353946 355944 359938 362931 366925 370918 373911 1.00 347963 347960 348958 346958 345958 345959 343960 343961 342963 341965 341967 343967 345966 346965 346964 347963 1.00 339978 340970 337970 334974 330977 327980 321981 318985 319992 316005 314018 314025 317028 322025 325020 329011 333001 338991 339978 1.00 334930 333921 330913 327906 324899 321897 316897 308899 305900 301899 299896 299891 298886 296888 293893 291897 289901 287908 286916 285927 286932 287935 292940 299941 307941 314941 323941 330939 332937 333932 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