Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 181833
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT SAT MAR 18 2017


PRELIM DAY 1 QPF DISCUSSION
VALID MAR 19/0000 UTC THRU MAR 20/0000 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1...

...EASTERN U.S...

THE COMPACT UPPER SHORTWAVE MICHIGAN WILL BRIEFLY MAINTAIN A
CLOSED 500 MB CIRCULATION THROUGH THE DAY 1 PERIOD AS IT DESCENDS
INTO THE MEAN LONGWAVE TROUGH POSITION ALONG THE EAST COAST...AND
SLIDES OUT INTO THE ATLANTIC. THE SYSTEM IS WORKING WITH A FAIRLY
AVERAGE AIR MASS IN TERMS OF PRECIPITABLE WATER
AVAILABILITY...MOSTLY OF GULF ORIGIN...AND THOUGH COASTL ALOW
PRESSURE WILL DEVELOP...ITS TRACK HAS BEEN TRENDING FARTHER
OFFSHORE...MAKING IT LESS LIKELY THAT ATLANTIC MOISTURE WILL WRAP
INTO THE SYSTEM WHEN OVER LAND. THE PRIMARY AXES OF
RAINFALL...THEREFORE...ARE EXPECTED ALONG THE LEADING EDGE OF THE
GULF MOISTURE RETURN THROUGH EASTERN NORTH CAROLINA EARLY IN THE
PERIOD...AND THEN ALONG THE TRACK OF THE COMPACT MID LEVEL
CIRCULATION...ALONG THE DIFLUENT EASTERN SIDE OF THE LOW...FROM
CENTRAL PA DOWN THROUGH D.C. TOWARD SOUTHERM MARYLAND. MODEL
SOLUTIONS HAVE REALLY CONVERGED ON A COMMON QPF SIGNAL IN THIS
AREA...WITH THE NORTHWARD EXTENT OF MEASURABLE PRECIPITATION BEING
FURTHER LIMITED INTO NEW ENGLAND COMPARED TO MODEL CYCLES JUST 18
TO 24 HOURS AGO. QPF FROM THE NAM SLID A LITTLE TO THE WEST OF
CONSENSUS...ALTHOUGH THE NEW 12Z ECMWF OFFERS SOME SUPPORT THERE.
THE WPC QPF IS BETTER ALIGNED WITH THE 00Z ECMWF AND CONSENSUS OF
THE 12Z GUIDANCE...ESPECIALLY RELYING ON THE GEM REGIONAL WHICH
MATCHED WELL TO THE GFS/ECMWF HEIGHT FIELDS / FORCING MECHANISMS.
WITH VERY COLD AIR ALOFT AND A TIGHT UPPER LOW THERE MAY BE SOME
CONVECTIVE ENHANCEMENT AT TIMES...BUT WITH PRECIPITABLE WATER JUST
EXCEEDING A HALF INCH...WE ARE NOT MAKING TOO MUCH OF THE
CONVECTIVE POTENTIAL...AND REMAINED CONSERVATIVE WITH
AMOUNTS...MOST PLACES EXPECTED TO SEE LESS THAN 0.75 INCHES LIQUID.


...WESTERN U.S...

A DEEP SHORTWAVE AND ASSOCIATED FRONTAL SYSTEM WERE BREAKING OFF
FROM THE ESTABLISHED MEAN TROUGHING OVER THE GULF OF ALASKA AND
EASTERN PACIFIC. THE SHORTWAVE WILL DRIVE THE GENERATION OF SOME
OROGRAPHICALLY ENHNACED PRECIPITATION OVER THE NORTHERN ROCKIES
THIS AFTERNOON...AND PERHAPS SOME LOW-TOPPED CONVECTION OVER PARTS
OF EASTERN OR/WA INTO IDAHO PER RECENT HI-RES MODEL TRENDS. WITH
TIME...HOWEVER...THE WAVE WILL FLATTEN IN AMPLITUDE AND ALSO LIFT
NORTHWARD WITH THE BULK OF DEEP LAYER LIFT EXITING INTO CANADA.
THE TRAILING FRONTAL ZONE AND MODEST WEST TO SOUTHWEST FLOW WILL
SUPPORT GENERALLY LIGHT PRECIPITATION TONIGHT AND SUNDAY IN A
SWATH FROM NORTHERN CALIFORNIA TO NORTHERN WYOMING. THE GFS
APPEARED TOO HEAVY...THOUGH ITS PLACEMENT WAS GOOD. THE ECMWF HAD
BEEN TOO LIGHT...BUT THE 12Z RUN LOOKED MUCH MORE REASONABLE. WPC
RELIED MORE HEAVILY ON CONTINUITY AND THE GEM REGIONAL...ALONG
WITH OUR IN-HOUSE ENSEMBLE. THE RESULT WAS PRIMARILY TO SHRINK AND
TIGHTEN THE PRECIPITATION SWATH A BIT...GIVEN THE RELATIVELY WEAK
FORCING AND MODEST MOISTURE CONTENT. BETTER ORGANIZED
PRECIPITATION WILL RETURN MONDAY-TUESDAY.

BURKE

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

24HR QP VT 20/00Z
 0.01 451627 456634 458638 460645 460656 457667 454675 451684
      448690 442697 428708 425711 424715 426717 431727 431729
      429733 424732 417733 418731 423729 422719 420717 419719
      416722 410731 411739 415742 424741 432740 434742 434747
      431750 426751 422749 418751 416755 415757 416761 422768
      425772 425781 423789 423799 421808 416815 413824 411826
      408825 416805 420799 421795 419793 418795 411799 404804
      398809 390814 373825 371828 369829 364824 361823 364818
      368813 379800 383796 387792 388787 384785 368782 358784
      355783 351783 347785 342786 335783 329784 325788 318795
      302785 300781 300775 302766 305755 309746 325720 333705
      339696 344688 354678 366666 375657 384648
 0.01 536207 538202 538195 539185 540180 539176 534170 525158
      514146 496133 487126 482122 477122 469121 464123 460127
      456125 458120 459116 464115 466112 465110 464105 465102
      467098 467092 465076 466058 465051 465041 466021 466010
      466002 463003 463008 461013 457032 456037 455041 451051
      449056 445060 439068 436087 430088 426094 421107 419113
      419122 418133 418142 417148 418151 425155 422161 421164
      422166 424172 425178 423188 420192 416198 411199 404210
      399212 396216 396220 393221 386225 381229 379232 376237
      370245 362251 358256 356260 357264 359269 366272 373272
      378271 388265 393260 396257 400256 412251 420247 425245
      428240 432235 438231 447227 458223 463221 470222 485225
      489231 494236 496239 495242 489239 482236 477231 472232
      467234 466236 467242 476251 481255 485261 494275 499280
      503282 506280 511267 512258 512250 510231 505221 497209
      492205 484203 477202 470204 460214 453213 451214 447213
      441212 437212 436209 439195 443192 447190 451190 453188
      457184 460179 465174 471170 477168 485170 489172 492174
      496179 501183 505188 508194 510199 513203 516209 521208
      531209 536207
 0.01 530978 530971 530963 527955 530944 530931 530925 527920
      520920 516929 515939 510960 510967 508973 506983 500000
      499007 500014 502017 504019 509019 512017 515015 517012
      521004 524997 528986 530978
 0.01 485899 485887 483879 480875 478875 476882 471889 469891
      465892 460893 458895 458900 460903 465905 470906 473907
      480907 484902 485899
 0.01 442774 442767 439765 438767 437772 435777 436785 436788
      435792 435797 437799 439796 440791 440784 441779 442774
 0.01 441130 442127 442125 442123 441121 439121 437121 436121
      436122 434122 433123 432124 431125 431128 430130 430132
      431134 433135 434133 436133 438131 440131 441130
 0.01 397933 396924 395917 393911 389906 380900 374899 369902
      367905 367908 369914 373927 370941 368943 368948 368949
      372950 379950 384953 388957 392954 393952 394946 395938
      397933
 0.25 435632 438636 442642 444650 444660 441670 436681 429691
      424696 419700 409706 403706 398705 393703 386703 382702
      379703 377706 376712 379717 381722 383729 384738 383745
      390758 396767 403776 404780 401783 397782 385778 377776
      371774 367770 364765 364756 365748 367740 364740 361744
      357749 353753 342757 336762 332766 324773 320773 318766
      314767 314764 315759 320745 324736 329725 335715 343704
      349696 356687 364680 369674 373669 387654 395647 401643
 0.25 529191 528185 526178 524176 520174 518175 518180 519183
      521185 523187 525190 526191 529191
 0.25 476139 481138 483138 487140 488141 490139 489136 486134
      483134 482133 479133 477133 476133 475134 474136 473138
      474139 475139 476139
 0.25 471155 470150 468145 464142 460143 452146 442143 437143
      435146 433153 434157 437162 440165 448169 452168 455166
      462161 468157 471155
 0.25 454103 453099 451098 446098 441097 438099 435102 433107
      434111 438112 440113 445114 448111 450107 453105 454103
 0.25 418237 416234 416229 416220 414216 411216 408219 406222
      405227 403229 397233 392237 390240 389245 395246 401244
      407241 414239 418237
 0.25 387801 386801 385801 384802 383803 382805 381806 381807
      382807 385804 387802 387801
 0.50 441655 440648 438644 435640 431638 424637 419639 414641
      406645 396651 391656 385663 374678 371686 369689 364692
      361690 357692 349700 340712 334724 330733 328746 330753
      327762 332760 339755 345749 353742 358737 361729 365721
      368716 368709 370701 372697 376695 381695 385696 389696
      394694 398692 401695 404697 407698 412698 415695 419691
      423689 427686 430684 434676 439664 441655
 0.50 451158 451155 450153 447151 445149 442147 440146 438148
      437151 437155 439158 440160 442161 444161 447161 450161
      451158
 0.50 390774 388765 385761 381757 378750 375749 372751 370757
      368761 371765 375771 380772 386774 390774
 0.50 380734 380732 379730 379728 378727 378728 377730 377733
      377735 378735 379735 380734
 1.00 431660 430653 426651 421651 416652 409653 404655 396661
      390671 387676 386681 387686 390687 392686 401680 410681
      413681 415679 418676 422672 426673 429668 431663 431660
 1.00 356705 353706 350708 346714 344721 341729 339736 337745
      337747 341747 346742 350736 353730 356721 356712 356705
 1.50 404663 403663 402664 403664 404663
 1.50 351724 350721 348723 346725 345728 344730 343734 342737
      342739 344739 345737 347734 348732 349729 350727 351724

$$





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