Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 230655
QPFPFD

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


PRELIM DAY 1 QPF DISCUSSION
VALID OCT 23/1200 UTC THRU OCT 24/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1

...GREAT LAKES...

AN IMPRESSIVE SYNOPTIC SETUP AND ABOVE NORMAL MOISTURE WILL RESULT
IN A SWATH OF HEAVY RAINFALL OVER THE GREAT LAKES TODAY INTO
TONIGHT. THE UPPER LEVELS WILL BECOME INCREASINGLY DIVERGENT
THROUGH THE PERIOD...WITH A PERSISTENT AXIS OF SURFACE CONVERGENCE
PRESENT AS WELL AS RAPID CYCLOGENESIS OCCURS THIS AFTERNOON INTO
TONIGHT. 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...AND AS SUCH EXPECTING A CORRIDOR OF 2-4" OVER
PORTIONS OF WESTERN MI. MODELS CONTINUE TO TREND WEST WITH THIS
AXIS OF HEAVIER RAINFALL...AND SOME UNCERTAINTY STILL EXIST ON ITS
EXACT PLACEMENT. BUT FOR NOW FOLLOWED A MULTI MODEL BLEND...WITH
THE MOST WEIGHTING GIVEN TO THE VARIOUS HIGH RES CAM SOLUTIONS.
THIS RESULTS IN A PRETTY SIGNIFICANT WESTWARD SHIFT FROM OUR
PREVIOUS FORECAST. CONFIDENCE IS HIGH IN THIS
ADJUSTMENT...ALTHOUGH AS MENTIONED ABOVE STILL LINGERING
UNCERTAINTY ON THE EXACT AXIS. PORTIONS OF SOUTHWEST MI HAVE SEEN
WELL ABOVE NORMAL RAINFALL RECENTLY...WHICH COULD RESULT IN SOME
FLOODING CONCERNS DEVELOPING DESPITE THE RELATIVELY LOW RATES
ANTICIPATED.


...OHIO VALLEY SOUTHEAST INTO THE MID ATLANTIC AND SOUTHEAST...

A BROAD SWATH OF MODERATE TO LOCALLY HEAVY RAINFALL AMOUNTS IS
EXPECTED FROM THE OHIO VALLEY INTO THE SOUTHEAST. A DEEPENING LOW
OVER THE GREAT LAKES WILL PUSH A COLD FRONT ACROSS THE AREA
THROUGH THE DAY TODAY. 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 AN OROGRAPHIC ENHANCEMENT TO THE RAINFALL TOTALS ACROSS
THE SOUTHERN APPALACHIANS. 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 A NARROW SQUALL LINE DEVELOPING AND QUICKLY
PUSHING 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. 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.

CHENARD


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

24HR QP VT 24/12Z
 0.01 505306 500307 494304 485295 483289 482283 480275 481267
      482258 485252 493243 492235 493230 495228 498224 503220
      506218 513220 518222 522229 523234 524243 524249 525253
 0.01 540208 538201 534196 528195 526195 525199 525206 521207
      521210 524215 524219 526221 530226 532228 534228 536218
      536213 538210 540208
 0.01 527177 526176 526174 525173 524171 524168 522167 521167
      519166 519167 517168 517169 516172 516174 517175 517177
      518178 519179 521179 523180 524180 525179 526178 527177
 0.01 520897 520885 519876 517871 512869 508870 510862 513851
      515845 516841 516836 514827 511820 506805 501793 495779
      493773 489769 475753 466743 462740 456741 451740 447741
      445738 441734 441728 443720 446715 452704 455699 456693
      455691 451695 447699 443699 442697 439695 437695 435703
      433708 427712 414715 410728 408731 405733 399735 385737
      379738 374738 348747 324755 281774 266779 257784 230784
      222785 222788 227799 231810 228814 229820 231831 237830
      238830 239834 242840 245845 248849 250853 249857 249859
      252860 256862 266867 271869 276869 285865 298862 300860
      304861 311861 325860 329860 331862 335866 339872 341878
      343882 349885 358891 364898 374905 378904 384902 387900
      390902 394908 398911 401915 409924 414927 421927 426925
      432924 441928 456928 462928 465928 467933 475952 471957
      467962 470964 476967 480969 486970 492970 495968 502962
      506957 507954 508949 510931 511920 511914 512909 515908
      518905 520897
 0.01 417067 417062 416059 414059 413054 411052 409056 406056
      399055 396060 402060 403059 407059 408063 407065 408070
      415071 417067
 0.25 513292 507298 503299 500295 495286 492276 491271 492264
      496260 501262 502261 502256 503241 506238 510241 515248
      520256 522264
 0.25 506906 505903 505902 503902 502903 500904 498906 498909
      497911 497914 499915 500914 501914 502913 503911 504911
      505908 506906
 0.25 502855 503845 502838 500821 498808 496804 494801 486794
      483792 477792 474792 468791 465788 463782 458772 456766
      453764 446759 437758 433758 431759 432762 434766 437770
      438772 435774 430773 426769 427765 425749 425743 423741
      419739 413739 409742 406745 401751 396754 389756 380755
      375755 371756 362756 358752 354752 347757 344759 339760
      333761 327763 319768 311775 303780 294784 283787 264791
      258793 255793 245791 240790 234792 233797 235804 236807
      237811 241812 245809 249808 252811 255813 255818 253826
      258835 261839 262845 265849 269851 275852 281851 289851
      298848 301846 303848 307852 313852 324852 336852 345854
      362861 367863 371865 375872 381880 377884 373885 373888
      376891 380894 385894 389891 393889 404889 411893 414897
      417899 421902 424906 427909 432909 440906 448899 451896
      456894 460896 462901 461906 462908 464908 466905 468900
      467892 468887 478880 489866 497861 500858 502855
 0.25 490932 490929 489927 487926 486926 484926 484927 483929
      484932 486933 487933 489933 490932
 0.25 460793 459792 457791 456790 454789 452789 451789 450789
      449790 447791 446793 447795 449796 450797 451797 453797
      454797 456797 458796 458795 459793 460793
 0.50 518273 520266 519260 514251 511248 507248 505252 506258
      509267 508274 507277 505276 501269 498271 497274 498278
      502286 505289 508290 512287 514282 515278 518273
 0.50 495820 495812 493808 486803 481798 472799 455804 450806
      447810 444812 442813 440811 439805 436802 429808 423813
      419814 417812 415807 416802 419793 425786 423782 421778
      420770 420764 421754 422748 422745 414743 411744 408747
      402754 393759 391762 394764 392769 389770 381767 375764
      368761 350761 329764 322769 316774 310779 308787 308793
      306798 307803 310806 316809 319810 320812 320819 314825
      311827 306827 300823 293821 282822 272822 268821 263820
      259821 260825 265833 268841 276844 284846 302844 310842
      319843 329845 336848 351853 359856 368857 375860 378864
      382866 390879 395880 400879 406880 419881 427883 432889
      436891 441890 447885 453885 457884 460881 463881 469880
      473877 476874 480866 485856 490848 492842 493835 495820
 0.50 441815 440814 439814 437816 436818 435819 435821 436821
      437822 438820 439818 440817 441815
 0.50 424824 422823 420823 420822 418822 416822 415823 414823
      413825 413826 413827 415828 417828 419827 420826 422825
      424825 424824
 0.50 295813 290803 286800 281798 278795 273795 267794 260795
      256798 253799 250799 247799 245801 248802 253802 258804
      260809 264811 268814 272816 277816 281813 285812 290815
      295813
 1.00 487831 487826 485823 483818 480816 478807 471806 462809
      457813 446826 442832 436836 431840 424841 406843 402842
      400837 398828 399818 399807 399805 395803 395800 398798
      406795 411791 418787 418784 413784 385791 383787 380784
      377785 374787 369791 359792 360789 362788 366787 368786
      367784 365782 349784 341785 332789 326793 323795 321799
      322801 324804 332806 340815 346818 349822 340825 337826
      335828 336830 331835 330839 331842 339843 344846 350849
      357851 374854 382856 387856 390854 396850 400845 403846
      404852 404859 399864 398868 400871 403871 411874 418875
      425873 433873 442875 447873 449872 446870 444867 446863
      451857 455855 459856 460861 459866 459869 462870 464871
      467869 472861 474858 475853 480847 484839 487831
 1.00 413755 412753 410752 408752 407753 405755 405756 405757
      405759 406761 408763 410764 411763 412760 412758 413755
 1.00 385825 385820 385815 382813 382814 381817 379819 377821
      375823 374826 376828 380826 383826 385825
 1.00 338771 338767 336766 333765 331765 329766 325768 324770
      324773 326775 328776 332776 335774 337773 338771
 1.00 299840 300836 299832 296828 289827 283827 278825 271824
      269823 266825 269829 273832 279834 283837 288841 294842
      299840
 1.50 476827 475822 474817 471814 468813 463813 461815 455822
      450828 445834 438839 432843 423845 418845 415848 411855
      408859 408864 410867 413869 421871 426871 430870 438868
      443861 450856 455851 461847 468841 472835 476827
 1.50 390847 390838 389836 385834 380838 373838 370839 366839
      359841 358843 359846 365848 372848 377848 383851 389849
      390847
 1.50 386799 382795 379794 377796 376799 369797 359797 351797
      346797 342799 344803 347805 354808 357811 357814 356819
      353822 347825 340831 337835 339839 345840 352841 356839
      357834 357828 358825 367820 367816 370813 378810 381809
      385806 386799
 1.50 371826 371824 370824 368822 367824 367825 366827 367828
      369828 371826 371826
 1.50 336797 334797 332797 330797 328798 327799 329799 330799
      332799 334799 336798 336797
 1.50 294836 295834 294832 293831 291831 289833 289835 289837
      290838 292839 293837 294836
 1.50 277830 277828 276827 274827 273828 272828 273829 275830
      276830 277830
 2.00 470831 470824 468820 465818 462819 452831 442839 436843
      428847 422848 417855 415858 412860 415865 421868 425869
      429867 436865 441859 446855 452850 463841 467836 470831
 2.00 384802 383800 383799 381800 379802 378803 378805 380807
      382807 383804 384802
 2.00 376803 373801 368800 364802 362805 360812 358820 355822
      351824 349826 348831 346834 348838 350837 353833 356826
      361821 365816 369810 374805 376803
 3.00 448843 446842 442843 437846 432849 429853 425857 424863
      428862 432859 436855 441851 444848 448843

$$





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