Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 231900
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MON OCT 23 2017


PRELIM DAY 1 QPF DISCUSSION
VALID OCT 24/0000 UTC THRU OCT 25/0000 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1

...UPPER GREAT LAKES...

AN IMPRESSIVE SYNOPTIC SETUP AND ABOVE NORMAL MOISTURE WILL RESULT
IN A SWATH OF HEAVY RAINFALL OVER THE GREAT LAKES THROUGH
TONIGHT...WITH THE NEGATIVELY TILTED TROUGH ALONG WITH LINGERING
RIGHT-ENTRANCE REGION UPPER JET FORCING ALLOWING FOR ROBUST UPPER
LEVEL DIVERGENCE AND DEEP-LAYER ASCENT. AS THE SECONDARY UPPER
SHORTWAVE CURRENTLY DROPPING SE FROM THE NORTHERN PLAINS PHASES
WITH THE TROUGH OVER THE MID MS VALLEY...CYCLOGENESIS WILL RAMP UP
AS A CLOSED MID-UPPER LEVEL LOW ENSUES OVER THE UPPER MIDWEST. THE
LATEST SATELLITE IR LOOPS EARLY THIS AFTERNOON ALREADY SHOW THE
CLASSIC BAROCLINIC LEAF/"S" PATTERN TAKING SHAPE...WITH THE
WESTWARD EXTENSION OF THE WARM CONVEYOR BELT (EVOLVING TROWAL)
LIFTING NW INTO THE UPPER MIDWEST AND UPPER GREAT LAKES REGION. A
LACK OF INSTABILITY WILL CAP THE UPPER LIMIT OF RAINFALL
RATES...WITH AMOUNTS EXPECTING TO PEAK IN THE 0.25"-0.5" IN AN
HOUR RANGE. HOWEVER WILL BE A PROLONGED PERIOD OF THIS STEADY
RAINFALL...WITH A LARGE SWATH OF 1-2+ INCHES OF ADDITIONAL
RAINFALL ACROSS UPPER AND WESTERN LOWER MICHIGAN. IN TERMS OF THE
QPF...THE MODELS CONTINUED TO TREND TOWARD A CONSENSUS FOR THE MON
NIGHT-TUE PERIOD... AND AS SUCH A MULTI-MODEL BLEND WAS
UTILIZED...ESPECIALLY THE HIGH-RES GUIDANCE. BEHIND THE AMPLIFYING
TROUGH AND SURFACE OCCLUDED FRONT... NORTHERLY FLOW LAKE
ENHANCEMENT WILL ENSUE ACROSS CENTRAL AND WESTERN UPPER MI WITH
THE N/NNW LOW LEVEL FLOW AND 850 MB TEMPS DROPPING TO -3 TO -6C
(DEEPENING LAKE-INDUCED CBL). THE HIGH-RES CAMS...INCLUDING THE
HREF AND VERSION 2 OF THE HREF MEAN... APPEAR TO BE HANDLING THE
MESOSCALE DETAILS FAIRLY WELL ON TUE...WITH THE ENHANCEMENT IN QPF
DOWNWIND OF LAKE SUPERIOR IN CENTRAL AND WESTERN UPPER MI.


...EASTERN U.S....

A BROAD SWATH OF MODERATE TO LOCALLY HEAVY RAINFALL AMOUNTS IS
EXPECTED ACROSS THE EASTERN U.S. FROM THE OH VALLEY...CENTRAL AND
SOUTHERN APPALACHIANS...AND MID ATLANTIC EARLY IN THE PERIOD
(THROUGH THIS EVENING/OVERNIGHT)...AND WILL THEN LIFT INTO THE
NORTHEAST ON TUE. THE AMPLIFICATION OF THE UPPER LEVEL TROUGH WILL
RETARD THE EASTWARD PROGRESSION OF THE WCB AND SURFACE FRONT FROM
THE MID-ATLANTIC SEABOARD NORTHWARD ON TUE...WHICH WILL ALLOW THE
FAVORABLE LOW-MID LAYER MOISTURE FLUX AND ANOMALOUS PWS (+2 TO +3
STANDARD DEVIATIONS) TO LINGER. THE DYNAMICS WILL BE PRETTY
IMPRESSIVE WITH A NEGATIVELY TILTED TROUGH AND DIVERGENT FLOW
ALOFT. WILL ALSO HAVE STRONG LOW LEVEL SOUTH TO SOUTHEASTERLY
FLOW...WHICH WILL RESULT IN A CONTINUED OROGRAPHIC ENHANCEMENT TO
THE RAINFALL TOTALS ACROSS THE SOUTHERN APPALACHIANS EARLY IN THE
PERIOD. INSTABILITY IS MARGINAL...BUT GIVEN THE INCREASED NEGATIVE
TILT...ANTICIPATE WE WILL BE ABLE TO REALIZE ENOUGH INSTABILITY
FOR CONVECTION AND LOCALLY ENHANCED RAINFALL RATES. THE DEPICTION
SHOWN BY THE VARIOUS HIGH RES CAM SOLUTIONS SEEM REASONABLE...WITH
THE BROAD AREA OF CONVECTION EVOLVING INTO A NARROW SQUALL LINE
THIS AFTERNOON...WHICH WILL QUICKLY PUSH OFF TO THE NORTHEAST.

IN GENERAL THE PROGRESSIVE NATURE OF THE SYSTEM AND THE EXPECTED
CONVECTIVE LINE SHOULD CAP THE UPPER LIMIT OF RAINFALL
TOTALS...WITH AMOUNTS GENERALLY FALLING INTO THE 1-2" RANGE. THUS
IN GENERAL THE FLASH FLOOD THREAT FROM THIS SETUP SHOULD BE
MARGINAL..WITH 1 HOUR RAINFALL TOTALS GENERALLY MAXING AT AROUND
1-1.5". THE EXCEPTION COULD BE ACROSS PORTIONS OF THE SOUTHERN
APPALACHIANS...WHERE OROGRAPHICALLY ENHANCED RAINFALL WILL PRECEDE
THE CONVECTIVE LINE...RESULTING IN A LONGER DURATION OF STEADY TO
HEAVY RAINFALL. EXPECTING A SWATH OF 2-4" ALONG THE UPSLOPE
FAVORED PORTIONS OF THE SOUTHERN APPALACHIANS...WITH MORE
LOCALIZED 4-6" AMOUNTS A POSSIBILITY IN THE MOST PRONE AREAS. THE
DRY ANTECEDENT CONDITIONS OVER THIS AREA SHOULD LIMIT THE OVERALL
FLOOD THREAT...ALTHOUGH AMOUNTS OF THIS MAGNITUDE COMBINED WITH
THE POSSIBILITY OF RATES APPROACHING 1.5" IN AN HOUR...SUGGESTS
THAT AT LEAST SOME FLASH FLOOD RISK DOES EXIST. FOR THAT REASON
WILL CARRY A SLIGHT RISK ACROSS PORTIONS OF THE SOUTHERN
APPALACHIANS FROM NORTHEAST GA INTO WESTERN SC/NC...SOUTHWEST VA
AND SOUTHEAST WV. THE NARROW CONVECTIVE LINE SHOULD BE ABLE TO
MAINTAIN ITSELF THROUGH MUCH OF THE MID ATLANTIC...THOUGH RAINFALL
AMOUNTS SHOULD GENERALLY DECREASE AS YOU GO NORTHEAST AS THE LINE
NARROWS AND SPEEDS UP.

WPC QPF FOR THIS REGION LEANED MORE HEAVILY TOWARDS THE HRW
ARW...HRW ARW2 AND THE EXPERIMENTAL HRRR...WITH SMALLER
CONTRIBUTIONS FORM THE GFS/ECMWF/UKMET. OVERALL THIS RESULTS IN A
FORECAST QUITE A BIT QUICKER THAN OUR PREVIOUS FORECAST. GIVEN
CURRENT RADAR TRENDS AND THE EVOLUTION SHOWN BY ALL THE HIGH RES
CAM SOLUTIONS...THERE IS HIGH CONFIDENCE IN THIS QUICKER TREND
VERIFYING.

HURLEY/CHENARD


GRAPHICS AVAILABLE ON THE WEB AT
WWW.WPC.NCEP.NOAA.GOV/QPF/QPF2.SHTML

24HR QP VT 25/00Z
 0.01 497326 495317 494303 494299 493294 490284 485261 486257
      488252 491248 494246 497247 500247 501244 501238 499232
      501230 506231 514236 517239 519240 520239 522233 522226
      521214 521208 522200 523193 524188 526182 528177 533169
      534163 536158 538153 541151 546152 548156 550159
 0.01 553146 553143 552140 552135 551132 548129 545128 545125
      546120 546117 548115 551115 552113 554111 556108 558106
      559103 560097 556095 554092 550084 545077 542068 540057
      539046 539032 540027 538024 533016 527010 524004 522999
      520994 518986 517980 517975 518972 518969 519965 525960
      533959 536957 541957 547958 555960 559962 563963 567969
      569972
 0.01 535716 523702 519698 516693 509685 507682 505683 502682
      499682 492684 487688 477696 467701 464702 462699 460691
      458687 453688 450688 446688 446684 444683 441683 439685
      438691 432703 428706 422707 414710 410713 397721 393723
      387725 384725 382724 383718 379714 373714 368715 363718
      358723 356727 355733 350736 325749 307758 303762 299765
      291766 287766 281767 275771 273774 268779 263781 256782
      242780 239780 233781 228782 226787 223798 222804 222811
      224818 224825 222832 224839 224843 226846 226850 229851
      234853 239852 243853 248853 253855 258855 263853 277838
      282833 287831 291828 296825 306820 321815 325813 332811
      344810 352809 357811 366815 371816 378816 385816 388817
      388820 383833 373837 370843 370849 376857 380860 383866
      386877 397904 402913 407916 414919 458919 462923 466925
      479922 491917 496916 500911 507904 513898 518884 520873
      520869 522868 527863 535852 541843 544839 548833 552827
      556818
 0.01 271013 271007 269004 264998 257993 249990 239989 236991
      235995 240001 247006 252012 258017 269017 271013
 0.25 508302 505297 502291 499285 496279 496273 498267 503265
      504263 506258 508249 509246 511246 516249 522253 525254
      534228 534226 533225 533222 533221 532219 532216 532214
      532212 532211 532210 533208 534206 535204 536201 537200
      537199 539198 539197 540196 542196 543195
 0.25 545787 545782 544777 542772 539765 536761 530761 525763
      516770 509779 503784 496784 489784 482786 476788 469787
      464785 461781 460776 460767 459762 460760 466757 470753
      473747 482738 486733 487726 486723 483721 477720 472717
      467718 463720 458723 451725 445725 442722 443716 445709
      444705 440709 433718 419720 413723 406727 400731 394734
      380738 367741 355744 347746 342748 329755 317760 294775
      274786 268789 261790 255791 249792 236789 233793 234799
      237804 236809 235818 236823 238827 241830 248830 259833
      266834 269834 273832 275829 276822 279817 284813 299815
      314810 327805 339800 345798 349798 356799 361801 372804
      384808 399811 424815 428817 432821 433824 431826 426829
      421832 414834 400835 396837 391842 388848 388852 390855
      395858 398860 399865 400876 401885 404891 407895 417900
      427905 439908 454908 464914 468909 472903 476898 482894
      494891 501883 515864 523852 530842 533835 536828 541810
      543798 545787
 0.25 455796 454795 453796 452796 453797 454796 455796
 0.25 436777 435777 434775 432774 430775 429776 430778 430779
      432780 433780 434780 436778 436777
 0.25 431793 431790 430788 429788 428788 426790 425791 425793
      424794 423796 425797 427797 428796 430795 431793
 0.50 511294 509293 508290 507287 506284 506279 507277 509272
      510270 510265 511262 511260 513256 516257 519259 523260
      524260
 0.50 530811 530802 529794 527790 519788 514786 509789 495794
      484796 475799 470800 466801 463803 459806 454816 449824
      443829 435834 425838 416841 409845 405847 404851 405857
      407861 409867 408873 408880 409885 414893 417896 422897
      431900 439903 444902 446899 449894 453892 455893 456896
      458902 460906 463909 466906 468902 474893 481888 491887
      497882 509866 519851 524841 528830 528820 530811
 0.50 476730 473725 468724 463725 457728 450731 443732 437731
      433727 428726 422726 415727 408730 402734 395738 382741
      375744 371747 358747 345751 331758 320762 315765 309768
      300776 289785 266794 260796 256801 254806 256814 260816
      267815 278811 289805 294803 299804 305805 311806 316804
      328800 336797 341795 350794 357795 368799 378803 384804
      393805 406806 418805 421804 419802 416798 420792 423785
      421768 422762 426759 431759 438758 444754 451751 459749
      464747 468744 471740 475734 476730
 0.50 270826 270824 269822 268822 267822 266823 265824 265825
      266827 267827 269827 270826
 0.50 262821 261820 259819 259820 260821 261822 262821
 1.00 522267 520268 518270 517273 516275 516278 517279 517281
 1.00 512838 511830 506826 505821 505818 504808 502805 498805
      491806 478813 466809 462812 461815 458823 455830 451835
      445839 439842 425847 419851 417858 416863 417868 421873
      432882 438883 444882 451879 458881 460886 462895 463901
      466900 469893 473887 478884 483878 487871 497864 502859
      507853 510846 512838
 1.00 468732 466729 462730 455734 449736 442736 426738 421734
      418733 413733 407736 401741 396746 394750 394754 398759
      405762 408763 412761 418756 424752 433751 440748 446744
      452740 461737 466735 468732
 1.00 413788 412784 408783 401786 394790 386790 378789 376792
      377796 384799 392800 399800 406797 411792 413788
 1.00 360752 352753 349754 346758 344761 342762 334762 325764
      318767 313770 307776 303782 303785 305787 313788 315790
      314794 316797 319798 324794 335784 341781 345779 346776
      349771 347763 358754 360752
 1.00 283796 282796 281795 279794 277795 275796 274797 275798
      276799 277799 279799 281799 282798 283796 283796
 1.50 495817 492814 487816 482820 475821 471819 467815 465817
      463822 462829 458840 455846 449848 438848 432850 427854
      423857 420861 426862 431866 439871 443872 447871 452869
      456871 459875 463881 465890 467893 469887 473881 477877
      479873 478866 479852 487844 490839 493833 495817
 1.50 437743 435741 434741 432742 432744 434746 436745 437743
      437743
 1.50 424746 423741 419738 415737 410739 407741 404745 403749
      404752 407756 411756 413753 417751 421749 424746
 1.50 335769 333765 329765 325767 322769 317771 313774 310777
      310781 314782 318783 321781 325777 328775 331773 335770
      335769
 2.00 472855 468855 465857 462861 461866 461873 464878 465883
      466885 469880 470875 469869 469863 470859 472855
 2.00 449860 449858 448857 447858 446859 445860 446863 447863
      448862 449860
 2.00 412746 411746 409746 409747 410747 411747 412746
 2.00 332768 331767 329768 327770 327771 329771 330770 331769
      332768
 2.00 319776 320774 319773 317774 315776 315777 315778 317778
      319776 319776

$$





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