Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 200721
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 AM EST TUE FEB 20 2018


PRELIM DAY 1 QPF DISCUSSION
VALID FEB 20/1200 UTC THRU FEB 21/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1

...LARGE SCALE HEAVY RAIN / FLOOD EVENT...

...EASTERN PLAINS / MID-UPPER MS VALLEY / GREAT LAKES / UPPER OHIO
VALLEY...

A SYNOPTIC PATTERN THAT SHOULD SPARK GREAT CONCERN OVER HEAVY
RAINFALL CONTINUES TO COME INTO PLACE...WITH LARGE SCALE
AMPLIFICATION OF THE WESTERN U.S. TROUGH, BLOCKED BY A 594
DECAMETER RIDGE IN THE ATLANTIC, ALLOWING FOR PROLONGED, ELONGATED
MOISTURE TRAJECTORIES EMANATING FROM THE CARIBBEAN BEFORE
ENCOUNTERING A SLOW MOVING FRONTAL ZONE IN THE MIDDLE OF THE
NATION. MOISTURE QUALITY LOOKS MORE LIKE MARCH OR APRIL.
PRECIPITABLE WATER INCREASING TO AT LEAST 1.50 INCHES SOUTHERN
GREAT PLAINS AND TAPERING ONLY TO AROUND 1.30 INCHES TO THE
SOUTHERN GREAT LAKES WOULD REPRESENT MAX VALUES FOR LATE FEBRUARY
PER GEFS M-CLIMATE DATA. EXPECT REPEATED WAVES OF MODERATE
RAINFALL...AND EMBEDDED INCREASINGLY HEAVY RAINFALL FROM LATE
TONIGHT THROUGH WED/THU IN SOME AREAS...RESULTING IN A WIDE SWATH
THAT WILL INDUCE LOCAL FLASH FLOODING AND MAY OVERWHELM SOME MAIN
STEM RIVERS. ESPECIALLY CONCERNED IN THE SOUTHERN PLAINS / LOWER
MISSISSIPPI VALLEY WITH THE GREATEST AVAILABLE INSTABILITY...AND
THE SOUTHERN GREAT LAKES WHERE DEEP FROST DEPTH / FROZEN GROUND
AND SOME SNOW MELT WATER WILL EXACERBATE THE RUNOFF / FLOOD
SITUATION.

ALTHOUGH THE QPF WAS NOT OVERLY COMPLICATED ON THE LARGE SCALE
WITH THE SYNOPTIC PATTERN DRIVING THE SITUATION, OF GROWING
CONCERN PER THE 00Z GUIDANCE IS THE INCREASED W-E SPREAD WITH THE
AXIS OF HEAVIEST RAINFALL, PARTICULARLY OVER THE SOUTHERN
PERIPHERY WHERE THE CAMS (INCLUDING THE HIGH-RES MEANS) ARE
TRENDING A BIT FASTER WITH THE EASTWARD PROGRESSION IN LIGHT OF
(MOST LIKELY) SOME CONVECTIVE FEEDBACK. FOR DAY 1, WPC UTILIZED A
BLEND OF THE ECMWF, IN-HOUSE ENSEMBLE QPF, AND THE PREVIOUS
FORECAST, WHICH CONTINUES TO KEEP THE MAX QPF AXIS A LITTLE
FARTHER WEST THAN THE ENSEMBLE OF HIGH-RES GUIDANCE. THIS IDEA
REPRESENTS A RELATIVELY SMOOTH TRANSITION FROM CONTINUITY
(PREVIOUS FORECAST), AS GIVEN THE HIGHLY-AMPLIFIED PATTERN
(DEEP-LAYER S-SW FLOW) ALONG WITH LIMITED INSTABILITY, FEEL MORE
CONFIDENT IN A SLOWER EASTWARD PROGRESSION. THIS RESULTED IN A
CONTINUAL SWATH OF 1.0 TO 2+ INCH AREAL AVERAGE 24-HOUR RAINFALL
FROM TEXAS TO MICHIGAN, WITH HEAVIEST AMOUNTS (AREAL-AVERAGE 3+
INCHES) FOCUSED FROM NORTHEAST TX-EASTERN OK INTO NORTHWEST AR AND
SOUTHERN MO, WHERE MODEST DEEP-LAYER INSTABILITY WILL BE PRESENT
TO ENHANCE THE RAINFALL RATES. OVER THESE AREAS, PER THE MAJORITY
OF HIGH-RES CAMS, LOCALIZED 24 HOUR TOTALS EXCEEDING 5 INCHES ARE
LIKELY -- AND AS SUCH WPC WILL MAINTAIN THE MODERATE RISK OF
EXCESSIVE RAINFALL FROM YESTERDAY`S DAY 2 EXCESSIVE RAINFALL
OUTLOOK IN THE NEW DAY 1 ERO.


...ELSEWHERE...

LITTLE CHANGE TO THE FORECAST OUT WEST BENEATH THE DIGGING UPPER
TROUGH. THE SAME BLEND USED FOR THE EASTERN U.S. WAS APPLIED HERE
AS WELL. SOME OF THE HEAVIER SNOWFALL SHOULD OCCUR IN
WESTERN/CENTRAL COLORADO AND NORTHERN NEW MEXICO... SEE QPFHSD FOR
DETAILS.

BURKE

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



THIS DISCUSSION WILL TRANSITION TO MIXED-CASE FEB 26, 2018.  THE
LISTING OF ISOHYET POINTS CONTAINED BELOW WILL ALSO BE ELIMINATED
FROM THE PRODUCT FEB 26, 2018.  ISOHYET GRID INFORMATION WILL
CONTINUE TO BE GENERATED IN A VARIETY OF BINARY FORMATS AND MADE
AVAILABLE THROUGH THE WPC GIS PAGE.

24HR QP VT 21/12Z
 0.01 397304 402304 407306 416304 419302 421298 424285 424280
      424273 423269 425266 429267 438265 445265 464264 467268
      471269 474267 477263 481237 479228 477223 477215 476210
      474205 472201 467198 462196 459192 455186 448179 445181
      442187 433203 427210 424215 423222 424227 422234 418234
      414235 408241 404244 400246 389243 379239 374237 372237
      367239 364241 359249 358255 359260 379289 384296 389302
 0.01 530175 530169 528164 526159 523157 517150 511144 504137
      500136 497136 496138 497144 501152 505156 507159 510163
      514164 520170 523174 528176 530175
 0.01 528721 525708 521697 517684 513671 503656 494643 492639
      489636 482634 479632 473633 466634 454637 450637 447640
      443644 441646 441653 440658 437667 435678 433690 433697
      434705 434717 434723 433727 430730 431735 426743 422751
      422758 422762 422770 421775 417788 414797 412805 408814
      402820 389833 378849 374855 368861 359874 348888 343895
      341898 337900 334896 329893 327891 326888 329887 335882
      340878 343875 348873 354866 361858 364854 366850 367847
      363847 356848 346853 342853 338852 330844 328842 324843
      318851 311856 309858 306858 298857 294857 291859 287866
      288880 289891 282896 284900 287903 293906 297908 300911
      302914 306914 316915 324917 329919 327922 323925 317926
      311926 308929 304931 299932 296930 293932 290940 287949
      275961 277972 277976 273980 266984 258988 251988 244985
      230990 232995 235999 244003 246007 248011 250020 255024
      259029 321019 326013 328009 326005 325000 326995 329992
      333991 354988 368980 382969 390963 397957 418933 424926
      430918 434916 437917 445923 452928 457934 459938 459945
      458957 455962 454966 450976 443999 441003 443005 453006
      460003 466000 484992 492975 496967 500956 507940 511930
      513925 514919 516888 516880 515875 515867 517863 522859
      526853 525837 527831 526825 526810 526797 525778 526772
      525765 524749 524741 524736 525729 526726 528721
 0.01 489836 487831 487828 485826 483822 482822 478820 475823
      477827 477830 478835 479837 481841 484841 488838 489836
 0.01 477157 478152 476149 475146 473145 470143 468142 466142
      466145 467150 469152 470155 472156 473159 475159 477157
 0.01 450112 447106 444102 441098 440095 437095 432095 428091
      424091 426096 427101 423102 420102 416106 413104 413100
      413096 412094 409089 405088 404083 403079 404075 409071
      411070 409065 410063 414066 413061 409059 406053 403050
      406049 410045 410039 407035 401035 391038 386040 382046
      381051 382056 384058 384062 379062 368060 365061 364065
      364067 365070 369073 372079 373084 373087 376089 382091
      385095 389091 390088 394087 401090 403093 404097 404102
      402104 394111 389113 384117 382122 383127 393122 402127
      409129 412124 415123 418124 421129 425133 428138 433148
      436148 438146 441142 439136 437131 433127 431120 435114
      436111 438110 442115 445116 450112
 0.01 392059 391058 390058 388059 389060 391060 392059
 0.01 376751 374748 370747 364752 360755 355757 352759 346760
      341764 350767 352775 355775 359772 365767 370761 375753
      376751
 0.01 372053 372050 369050 367052 363052 361054 359054 356055
      357058 359058 363056 365054 368055 370055 372053
 0.01 363818 363812 360809 356810 353813 348820 342827 337833
      333837 333841 336845 339846 345846 348843 355838 359835
      361832 362827 362821 363818
 0.01 344089 345084 344082 342080 339080 335081 332080 329078
      325078 317077 310078 304080 297082 293085 289089 289093
      290096 292098 296099 302098 309096 314094 320095 326094
      329093 332094 332099 335101 341102 340097 339094 341091
      344089
 0.01 338060 337057 336055 332054 329054 327053 325053 323055
      321057 319061 319063 319065 321065 323063 325061 328060
      332061 335061 338060
 0.01 330874 328872 327870 326869 326868 324867 323868 321868
      319869 318870 318873 319874 320875 320877 321879 322881
      323883 325881 325880 327878 328876 330874
 0.01 308841 307831 302825 294820 289814 286810 288806 281802
      277799 275797 270789 265782 262778 260778 258783 259789
      261793 261798 255799 252801 252805 258804 264804 267806
      273810 281825 293837 301842 307844 308841
 0.01 262852 261845 260840 255830 249822 244814 240803 237799
      236804 236808 237814 240818 241823 244835 248847 252857
      257857 260857 261854 262852
 0.25 513707 513697 511687 508682 503678 496671 491664 486661
      482660 474662 455658 453664 454673 454683 454691 444710
      442715 443720 442724 439728 438731 442734 441740 434749
      433756 433765 432782 428793 424803 419813 414824 408834
      402841 373874 360890 346906 331925 317938 286964 281990
      284994 290995 300998 305000 311000 315997 319993 334982
      339980 346978 351981 358979 366973 373967 387953 395945
      402936 416918 422910 427902 438882 443870 448858 450853
      450843 450836 453828 462808 466796 469783 474755 475747
      476740 479725 482720 484719 486720 488725 490732 489747
      492753 497753 504746 508737 512722 513707
 0.25 469240 467233 466224 465215 464213 460211 454212 450211
      448213 440224 433238 429243 425249 420252 417254 418259
      422258 427256 434257 440256 451252 457249 462246 469240
 0.25 255002 253001 251000 249999 247999 246998 244997 243998
      244998 245000 246000 247001 248002 249002 251003 253003
      255003 255002
 0.50 478706 477699 474696 471696 465697 453707 451711 451717
      451723 449726 453730 452735 450739 446741 441748 439760
      438771 436781 433792 429800 423815 418825 413833 404846
      394858 381870 369883 359895 349909 339922 333928 327935
      316946 306957 294968 290977 291982 293985 308992 312992
      317990 324986 335977 343973 349973 353976 357976 360974
      365970 377959 388947 394940 400932 409920 414913 418906
      427889 432880 436871 442854 446834 450825 454816 457807
      461796 462787 462780 462774 463762 466753 466746 466738
      467729 475718 477712 478706
 0.50 453243 454240 453240 451240 449240 448241 447242 445243
      444245 445246 446246 447246 448246 450244 452244 453243
 0.50 440246 441244 441242 440240 439239 437240 435242 434244
      434245 435247 435248 437248 438248 439246 440246
 1.00 449794 447783 445789 445796 440800 434802 431807 428814
      422827 417837 410847 403856 394865 386873 377880 369888
      354907 341926 332935 324943 316952 310962 308969 308975
      312979 316982 323981 328977 337972 348966 358962 360964
      364964 369961 377953 392934 398925 404912 412901 417891
      429869 434856 438843 441829 446816 448805 449794
 1.50 444810 440806 435806 433811 431816 429824 426829 421837
      408855 401862 393872 384879 377884 369892 363901 360905
      356910 350918 344926 336934 328942 321949 316959 314964
      313971 315976 321977 330973 348963 357957 364951 369949
      375950 381943 381938 384932 387929 390924 396915 403908
      411891 421872 428861 430855 432850 435838 437823 444810
 2.00 430840 430833 426834 421840 411855 405862 400869 390883
      384889 376892 372894 370894 367898 365902 344928 338935
      332941 326947 321954 317962 316967 317973 321974 325973
      333969 347960 361950 381922 402894 413880 422865 425859
      427853 430840
 3.00 375918 374913 371914 364918 358920 355923 350928 337939
      331945 326952 321960 321964 323964 327956 330952 332952
      334956 332960 330963 329966 330967 343958 356947 360944
      362941 366933 375918

$$





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