Quantitative Precipitation Forecast
Issued by NWS

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253
FXUS04 KWBC 221830
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM EDT THU SEP 22 2016


PRELIM DAY 1 QPF DISCUSSION
VALID SEP 23/0000 UTC THRU SEP 24/0000 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1

...IOWA / WISCONSIN / ILLINOIS...

FORCING ALONG THE EDGE OF THE CAPPED GREAT PLAINS AIRMASS HAD
GENERATED A VERY HEAVY 2-DAY RAINFALL EVENT OVER THE UPPER
MIDWEST...WITH 48-HOUR TOTALS OF 7 TO 14 INCHES OF RAIN IN SOME
PARTS OF SE MN / NE IA / SW WI. PARTICULARLY HEAVY RAIN FELL SINCE
WEDNESDAY EVENING...WHICH PLACES ADDED IMPORTANCE ON THE EXPECTED
EVOLUTION OF ANY ADDITIONAL PRECIPITATION IN THE SHORT TERM. THE
KEY FEATURE AT THIS TIME WOULD APPEAR TO BE A SHORTWAVE TROUGH
THAT WAS TRACKED COMING OUT OF THE CENTRAL ROCKIES ON
WEDNESDAY...AND WAS PREPARING TO EXIT EASTERN IOWA THIS AFTERNOON.
WARM ADVECTION INTO THE BACK SIDE OF THIS LOW AMPLITUDE WAVE MAY
SUPPORT ADDITIONAL SCATTERED OR NUMEROUS SHOWERS / STORMS THIS
AFTERNOON AND EVENING...ESPECIALLY NEAR THE INSTABILITY GRADIENT
AND COMBINED OUTFLOW BOUNDARIES OR REINFORCED WARM FRONT WHICH HAD
SLIPPED DOWN INTO CENTRAL AND SOUTHEAST IOWA. BASED ON THESE
OBSERVATIONAL TRENDS WPC FAVORED GUIDANCE THAT FOCUSES ADDITIONAL
RAINFALL SOUTH OF HIGHWAY 20 IN IOWA...AND GENERALLY SOUTH OR
DOWNSTREAM - HYDROLOGICALLY - FROM THE AREAS IMPACTED BY HEAVY
RAIN LAST NIGHT. PREFERRED GUIDANCE INCLUDED THE 12Z GFS AND
WRF-ARW. SEVERAL RUNS OF THE HRRR HAVE ALSO SUPPORTED THIS
THINKING...ALTHOUGH CERTAINLY THE LOW LEVEL FLOW ACROSS THE
BOUNDARY MAY YIELD ADDITIONAL LIGHT OR PERHAPS MODERATE RAINFALL
FARTHER NORTH INTO AFFECTED AREAS...WHERE THE PERCENTAGE GOING
INTO SURFACE RUNOFF WOULD BE VERY HIGH. WILL WATCH THIS SITUATION
CAREFULLY...BUT AT THIS TIME A SLIGHT RISK OF EXCESSIVE RAINFALL
WOULD APPEAR SUFFICIENT TO COVER THE COMBINATION OF VERY LOW FLASH
FLOOD GUIDANCE VALUES BUT RELATIVELY LIGHT ADDITIONAL RAINFALL.

THE MORE ROBUST CONVECTION EXPECTED SOUTH OF HIGHWAY 20 WOULD ALSO
SEEMINGLY NOT POSE AS SIGNIFICANT A THREAT AS THERE HAS BEEN OVER
THE PAST TWO DAYS...GIVEN THAT THE SHORTWAVE WILL EXIT THE
REGION...AND DEEP LAYER ASCENT WILL DECREASE ALONG WITH SLACKENING
FLOW DURING WHAT IS USUALLY THE MORE FAVORABLE TIME FOR PRECIP
EXPANSION DURING THE EVENING.


...WESTERN U.S...

AN IMPRESSIVE GREAT BASIN / ROCKIES STORM WILL CONTINUE TO UNFOLD
THROUGH FRIDAY. NEGATIVE HEIGHT ANOMALIES OF UP TO 3 STANDARD
DEVIATIONS WILL SLIDE EAST WITH THE CENTER OF THE DEVELOPING
CLOSED CIRCULATION. THE SYSTEM REMAINS PROGRESSIVE...BUT THE
PROGRESSION IS EXPECTED TO BE SO SLOW...AND WITH A PIVOT OCCURRING
OVER UTAH...THAT QUITE HEAVY AMOUNTS OF RAIN AND HIGH ELEVATION
SNOW ARE EXPECTED. PRECIPITATION EFFICIENCY IS ENHANCED BY THE
INVOLVEMENT OF ANOMALOUS DEEP LAYER MOISTURE HAVING BEEN PUMPED
INTO THE REGION OUT OF THE SUB-TROPICS PRIOR TO ARRIVAL OF THE
NORTHERN STREAM TROUGH...AND STEEP LAPSE RATES OWING TO THE DEPTH
OF THE TROUGH / STRENGTH OF THE DEEP LAYER LIFT.

THE GFS/ECMWF/UKMET ARE SHOWING GOOD LARGE SCALE AGREEMENT AND RUN
TO RUN CONTINUITY. THE NAM IS ALSO IN LINE WITH CONSENSUS THROUGH
DAY 1...SUCH THAT OUR IN-HOUSE ENSEMBLE TOOL WITH PSEUDO BIAS
CORRECTION SHOULD PERFORM WELL. WPC QPF BEGAN WITH A 40/30/30
BLEND OF THE ENSEMBLE TOOL / 12Z GFS / PREVIOUS WPC FORECAST. ONCE
AGAIN THIS REALLY PRESERVED THE LARGE SCALE SHAPE AND INTENSITY OF
THE FORECAST PRECIPITATION...ALTHOUGH SPOT TOTALS WILL HAVE
CHANGED THROUGH USE OF THE NEW BLEND AND THROUGH DOWNSCALING
(LOWER AREAL-AVERAGE AMOUNTS WITHIN THE VALLEYS AND SOME
ENHANCEMENT ACROSS THE WASATCH-UINTAS AND EASTERN SLOPES OF THE
NORTHERN ROCKIES). AREAL AVERAGE 24-HOUR AMOUNTS ARE FORECAST TO
EXCEED 2 INCHES IN A FEW SPOTS OF FAVORED TERRAIN IN UTAH AND
IDAHO...IN ADDITION TO WHAT HAD ALREADY FALLEN AS OF MIDDAY
THURSDAY.


...ELSEWHERE...

THE QPF BLEND USED IN THE WEST AND MIDWEST...BASED ON OUR IN-HOUSE
ENSEMBLE TOOL...THE 12Z GFS...AND PREVIOUS WPC FORECAST...SERVED
AS A GOOD STARTING POINT FOR ORGANIZED PRECIPITATION AREAS
ENTERING THE PACIFIC NORTHWEST COAST...NEW ENGLAND...TEXAS...AND
LINGERING ALONG THE SOUTHERN ATLANTIC COAST AND FLORIDA. TO FILL
IN SOME OF THE DETAILS...PARTICULARLY WHERE LIGHT OR SCATTERED
PRECIPITATION WAS CONCERNED...WE TRUSTED THE DETAIL IN THE
WRF-ARW. THE MOST ORGANIZED AREA OF RAIN WILL AFFECT NORTHERN NEW
YORK AND NEW ENGLAND...ESPECIALLY MAINE...AS NORTHERN STREAM
HEIGHT FALLS ARRIVE COINCIDENT WITH A FETCH OF DEEP LAYER MOISTURE
THAT IS EXITING THE MIDWEST STATES. NUMEROUS MODELS PRODUCE MORE
THAN A HALF INCH AREAL AVERAGE PRECIPITATION OVER MUCH OF CENTRAL
AND NORTHERN MAINE.

BURKE

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

24HR QP VT 24/00Z
 0.01 504311 487307 470304 435302 431302 426300 418297 414293
      413290 410285 406281 406272 409262 404258 404253 406248
      412242 418237 427238 433232 431227 426225 425225 428221
      431219 436220 446221 449218 452217 460214 467213 475209
      483206 489205 499208 502211 506213 513220 518226 520226
      520222 519216 516212 513208 512202 512197 514194 518193
      526197 533203 537209 537214 537221 536224 535225 534228
      533229 532230 531231 530232 528232 526232 525233 526235
      527236 529239 529240 530242
 0.01 543095 542082 541069 533049 529040 525031 519014 509996
      498983 472959 458949 455947 450947 445947 441945 439943
      439940 439934 440928 442925 444920 444913 447903 447896
      445890 445884 445876 445865 448853 449848 449843 454835
      453827 454819 456806 458796 463787 474771 477763 481753
      482744 484732 485723 486710 495691 496686 496678 495666
      494657 495652 492635 488627 485625 481623 477622 472623
      464628 456630 450636 445644 442651 438660 435670 433679
      430689 428700 427706 427713 426722 429726 429731 428738
      426741 425746 428748 429754 429761 429775 429784 431788
      432795 433810 435821 424861 420863 417867 414875 414883
      412888 407898 405903 404908 401918 405941 407949 410959
      414968 420973 423975 427974 431971 434968 438966 442968
      443973 445976 446982 444987 439995 436999 434001 432000
      424994 419994 417996 417003 419006 422015 424021 422026
      417031 410035 403039 397046 391050 387053 384053 383051
      379048 374046 371048 365047 358049 350052 343056 334060
      326063 322065 320069 320074 322077 332077 341074 350073
      359073 355078 329098 324106 322110 322116 324120 327122
      336120 346121 349126 351130 354139 358141 363142 374144
      379145 382148 390162 391168 390175 389187 397192 400194
      403193 415182 424179 432174 440173 450174 456172 464166
      470163 474154 479145 482144 487144 492146 495149 498152
      503154 508154 512153 518149 520146 522141 524136 525128
      524122 526116 528110 534110 539103 543095
 0.01 389725 389723 387723 385724 384726 384727 382729 381732
      379734 380736 382738 383738 385735 387735 387733 388730
      388728 389725 389725
 0.01 365764 363760 360760 356753 354747 352744 347736 342733
      338738 333745 327750 306774 303776 298776 290775 285775
      282777 276784 269785 265786 262788 260791 261792 257795
      253796 246800 243807 241810 242814 248819 255822 263824
      271825 281824 286823 289821 299820 307820 318819 321817
      326816 332813 347806 353801 361797 366791 366787 364782
      362771 365764
 0.01 349831 348831 346831 344833 344834 342836 342838 343838
      345840 346838 348835 348833 349831 349831
 0.01 352987 352982 348978 342978 337979 334980 329981 324978
      314966 314963 316960 314949 314928 312932 310928 307918
      306914 304909 299903 296904 295907 291916 288926 285924
      281925 270937 263939 254941 246943 243945 239949 237951
      237957 242962 248966 255970 272975 279978 282978 286979
      291981 289984 291989 293989 297988 301990 306996 308000
      311003 314005 319005 333998 345994 349990 352987
 0.01 322797 319794 315792 311791 308793 305796 302800 302804
      304808 309807 315806 318804 321799 322797
 0.01 326915 324911 323907 321902 317900 313898 309898 308901
      310905 311907 315909 317915 319918 324917 326915
 0.01 289075 288072 284071 276068 271064 267058 256049 251046
      243047 238051 236059 238067 241073 246078 251082 257086
      263090 269094 276096 282095 286089 286085 285081 289075
 0.01 260008 260004 259000 255995 248992 240990 236991 234993
      234998 235001 239007 245011 249016 251019 254021 256019
      257014 260008
 0.25 522267 518258 512250 508246 505245 495242 486241 481239
      477236 472235 468236 464236 460238 453245 454253 453258
      450261 442262 438263 434267 433274 435280 441282 445282
      454282 465286 474287 485290 492292 497295 502297 506297
      511295 512295
 0.25 526079 527067 525060 520056 515053 511048 508040 507031
      508022 507012 505010 502011 495012 489012 482011 476013
      474015 471014 465008 461011 459018 454032 448036 445041
      440044 442050 443053 442058 441060 437060 431062 427067
      426077 421081 416085 412087 406083 404081 403076 400070
      393070 388071 383072 380069 375066 371065 368068 366070
      367074 369082 374095 375096 378096 381094 385094 388099
      389104 389109 385115 383119 383124 390135 394140 397142
      401144 405144 406148 406154 410158 416162 423162 427158
      429157 433158 440161 454163 483113 488111 495110 504109
      509113 513111 520093 521088 523085 526079
 0.25 482652 481641 476636 470634 463638 457645 453650 449657
      446664 445673 444683 445703 442722 437739 437748 436758
      437769 440779 442782 446780 449775 452767 454758 457749
      457740 457734 458730 460727 462730 462736 461740 461744
      462750 464752 467749 470741 473723 478706 479696 481688
      484680 485676 485669 482652
 0.25 436892 436882 436876 434873 431873 430876 427883 424889
      420894 415898 412903 409911 407919 407929 409938 412945
      416950 420950 421948 423945 423940 424930 426923 432909
      433901 436892 436892
 0.25 433054 432048 427048 422046 417048 414050 411054 412061
      416064 419065 423063 426060 429058 432056 433054
 0.25 353771 352765 350762 346759 342758 334761 330764 329768
      329774 332778 334780 334785 333796 337797 342797 348793
      353786 352781 350778 353771
 0.25 285794 283790 278790 274791 272795 274803 269806 264804
      260804 256806 255809 256811 260813 262815 268816 278813
      280813 283810 277805 280805 281802 283797 285794
 0.25 283962 282960 279959 276959 274960 271962 269964 270967
      272969 274970 277970 279969 281967 283964 283962
 0.25 272087 271083 268079 265076 262074 260071 256069 253071
      254076 256079 260082 264084 268087 271088 272087
 0.50 509288 510284 510280 510273 508267 505263 498255 495251
      490247 487247 482248 475253 473254 472257 473262 472270
      474276 478280 484282 493289 498292 504292 509288
 0.50 514079 514075 514069 511065 506055 498045 495041 491037
      486034 483039 481046 478051 475056 473057 471055 472048
      474040 473034 469030 465031 462036 456047 453053 453064
      452066 449066 442067 438071 442074 447075 452074 456070
      458073 458076 458081 456083 452086 447089 443090 438090
      433092 431096 428101 424100 418101 414102 409100 405097
      400102 397104 393109 390114 389118 389122 392127 394133
      397136 403137 409137 416139 421142 427141 436137 438136
      439139 439141 437147 438150 441153 444154 448154 453154
      458152 461147 460140 458135 457127 457118 461114 471110
      478102 486095 496090 501089 507088 514079
 0.50 477663 476651 475645 474641 469641 466642 459648 455655
      453662 451670 450679 450686 450691 453701 452708 448716
      448726 450729 453726 462715 466714 469711 472705 475696
      475687 477677 477666 477663
 0.50 446759 446756 445755 444754 442754 441755 441757 440757
      440760 440762 440764 441767 443767 443766 445764 445761
      446759 446759
 0.50 419156 420154 420152 419149 417148 416149 415149 413150
      412153 413154 415155 415156 416157 418157 419156
 0.50 426909 427904 424900 419901 416903 413907 412917 410924
      409930 410935 414942 416943 418940 418928 421919 424913
      426909
 0.50 377080 376078 376077 375078 376078 377080 377080
 0.50 278797 277795 276797 277797 278797
 1.00 497281 498276 497273 496270 494267 493264 491260 488262
      487264 486268 489270 490273 491276 493279 494281 497281
 1.00 488073 487072 485073 484074 483075 484075 485075 487073
      488073
 1.00 469666 468661 466659 464659 462657 461659 460663 460666
      460671 458674 458677 459681 461682 464680 466678 467676
      468673 469669 469666
 1.00 473086 472083 471083 470082 469083 468084 467085 466087
      466090 467092 469092 471091 472088 473086 473086
 1.00 462097 463094 462092 460092 459094 457095 456096 455098
      456099 458100 460100 461099 462097 462097
 1.00 444118 445113 444110 438111 434114 429112 425110 419110
      412110 409107 398113 398115 401115 401118 401123 400125
      400128 401131 414130 426136 430132 433127 434120 436119
      439121 441121 444118
 1.50 427125 427121 425118 424116 420115 417116 415117 413118
      411119 408121 406123 409125 412126 416126 419127 423127
      425127 427125

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