Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 240627
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
126 AM EST TUE FEB 24 2015


PRELIM DAY 1 QPF DISCUSSION
VALID FEB 24/1200 UTC THRU FEB 25/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1...


...NEW ENGLAND...

A SHORT WAVE STARTING DAY 1 OVER NORTHERN MANITOBA SWEEPS ACROSS
THE GREAT LAKES...THEN TAKES ON A NEGATIVE TILT AS IT APPROACHES
NEW ENGLAND BY THE END OF THE PERIOD. LIFT ASSOCIATED WITH THE
SHORT WAVE INDUCES CYCLOGENESIS OFF THE MID ATLANTIC COAST. THE
MID LEVEL FLOW ALLOWS THE SURFACE LOW AND ITS INVERTED TROUGH TO
BACK TOWARD THE NORTHERN NEW ENGLAND COAST. THERE IS A FAIR AMOUNT
OF SPREAD CONCERNING HOW FAR WEST TO BRING THE PRECIPITATION
SHIELD ALONG THE INVERTED TROUGH...WITHE 00Z REGIONAL GEM FURTHER
WEST AND THE 00Z UKMET/12Z ECMWF FURTHEST EAST. CONSIDERING HOW
WELL THE MODEL SUITE CONVERGES ON A MID LEVEL SOLUTION...THE WPC
QPF IS BASED ON A MULTI MODEL BLEND.

THE KEY TO THE FORECAST WILL BE THE PLACEMENT OF THE INVERTED
TROUGH STRETCHING FROM EAST OF THE MA COAST INTO CENTRAL ME. AS
THIS POINT...THERE IS FAIRLY GOOD MODEL AGREEMENT WITH THE
PLACEMENT...WITH THE 12Z ECMWF FURTHEST EAST WITH THE FEATURE. THE
INVERTED TROUGH BECOMES THE FOCUS FOR LOW LEVEL MOISTURE (AS
PRECIPITABLE WATER VALUES JUMP UP TO OVER 0.50 INCHES ALONG THE
TROUGH)...AND THERE IS NOW FAIRLY GOOD MODEL AGREEMENT WITH THE
PLACEMENT OF THE 0.10 TO 0.25 INCH AREA EXTENDING FROM EAST OF I95
IN MA ACROSS SOUTHEAST NH AND SOUTHWEST AND CENTRAL ME. THE 00Z
REGIONAL GEM IS THE FURTHEST WEST...BRING 0.25+ INCH AMOUNTS TO
NEAR KBOS THROUGH THE MID COAST OF ME.

THE HIGHER QPF COULD BE DUE TO INCREASED LOW LEVEL CONVERGENCE
WITH THE DEVELOPMENT OF THE A SURFACE LOW ON THE INVERTED TROUGH.
IF THIS OCCURS (AS DEPICTED BY THE 00Z REGIONAL GEM)...A SLIVER OF
0.50+ INCHES OF QPF IS POSSIBLE ACROSS THE MID COAST OF ME.
HOWEVER...SINCE THERE IS NOT YET WELL SUPPORTED...THE QPF ACROSS
CENTRAL ME WAS NOT QUITE THIS HIGH.


...MID ATLANTIC...

A SHORT WAVE TRACKING SOUTHEAST OUT OF THE CENTRAL PLAINS EARLY ON
DAY 1 APPROACHES THE SOUTHERN MID ATLANTIC TOWARD 25/00Z. THE
SHORT WAVE INDUCED CYCLOGENESIS OFF THE SC COAST...WHICH THEN
TRACKS NORTHEAST THROUGH THE END OFF THE PERIOD. THE 00Z/21Z SREF
MEAN WERE THE FURTHEST NORTHWEST WITH THE PRECIPITATION SHIELD
ASSOCIATED WITH THE SURFACE LOW...AND THIS APPEARS TO BE TOO FAR
NORTHWEST INTO THE COLD AIR. THE 00Z GFS/UKMET WERE SIMILAR WITH
AMOUNTS...AND THE 12Z ECMWF WAS THE LIGHTEST WITH QPF HERE. THE
WPC QPF WAS BASED ON A BLEND OF THESE THREE MODELS.

AS THE SHORT WAVE APPROACHES FROM THE MID MS VALLEY AFTER
24/18Z...WARM AIR ADVECTION PRODUCES QPF ACROSS PORTIONS OF
EASTERN TN AND NORTHERN GA. HOWEVER...THE MAIN QPF PRODUCER SPINS
UP ON A LOW LEVEL BAROCLINIC ZONE OFF THE SC COAST TOWARD 25/00Z.
THE TRACK OF THE LOW LEVEL CIRCULATION SUGGESTS THAT THE BEST LIFT
LEVEL FRONTOGENETIC FORCING OCCURS ACROSS SOUTHEAST SC AND
SOUTHEAST NC. AS MENTIONED EARLIER...THE 00Z NAM/12Z SREF MEAN
APPEAR TO BE TOO FAR NORTHWEST WITH THE 0.25 INCH QPF (WITH TOO
MUCH QPF DEEP INTO THE COLD AIR)...AND THE 0.25 TO 0.50 INCH QPF
AREA WAS BASED ON A NON-NAM/SREF MEAN BLEND.


...GREAT LAKES...

A STRONG SHORT WAVE CROSSES THE GREAT LAKES DURING THE FIRST HALF
OF DAY 1. LIFT WITH THE SHORT WAVE RESULTS IN A LARGE AREA OF QPF
ACROSS THE GREAT LAKES. THE FLOW BEHIND THE SHORT WAVE ALLOWS
FAVORABLE LAKE ENHANCEMENT TO DEVELOP ACROSS THE UPPER GREAT
LAKES. FOR THE MOST PART...THERE WAS GENERALLY GOOD MODEL
AGREEMENT WITH RESPECT TO THE OVERALL SYNOPTIC SETUP...SO THE WPC
QPF WAS BASED ON A BLEND OF THE 00Z NAM/21Z SREF MEAN.

LIFT WITH THE SHORT WAVE IS IMPRESSIVE AS IT CROSSES THE GREAT
LAKES DURING THE FIRST HALF OF THE PERIOD. WARM AIR ADVECTION (IN
THE FORM OF ISENTROPIC LIFT ON THE 290K SURFACE) PUMPS A BIT OF
MOISTURE INTO THE REGION AHEAD OF THE SHORT WAVE. THE COMBINATION
OF MOISTURE AND LIFT PRODUCES A LARGE AREA OF 0.10 TO 0.25 INCHES
OF QPF ACROSS THE UP OF MI AND MUCH OF THE NORTHERN PORTION OF THE
LP OF MI. BEHIND THE SHORT WAVE...A RAPIDLY DEEPENING MIXED LAYER
AND STRONG LAKE INDUCED INSTABILITY SHOULD RESULT IN LAKE ENHANCED
QPF EAST OF LAKE MI ACROSS THE NORTHERN PORTION OF THE LP OF MI.
ALONG THE EASTERN SHORE OF LAKE MI...LOCAL 0.25 TO 0.50 INCH QPF
AMOUNTS ARE POSSIBLE. ELSEWHERE...ICE COVER SHOULD INHIBIT MUCH IN
THE WAY OF LAKE ENHANCED QPF...EXPECT FOR LAKE ONTARIO...WHICH
STILL HAS A FAIR AMOUNT OF ICE FREE WATER. EAST OF THIS
LAKE...LOCAL 0.10 TO 0.25 INCH QPF AMOUNTS ARE EXPECTED.


...NORTHERN ROCKIES/NORTHERN PLAINS...

A PAIR OF SHORT WAVES IN THE FAST MID LEVEL NORTHWEST FLOW RESULT
IN AXES OF QPF ACROSS THE NORTHERN ROCKIES AND NORTHERN PLAINS.
THERE WAS DECENT MODEL AGREEMENT WITH RESPECT TO THE TRACK OF THE
SHORT WAVES (AND SURFACE REFLECTIONS)...AS WELL AS THE QPF AXES.
WITH THIS IN MIND...THE WPC QPF WAS BASED ON A MULTI MODEL BLEND.

THE FIRST SHORT WAVE TRACKS FROM MT INTO THE CENTRAL
PLAINS...ALONG A LOW LEVEL ARCTIC BOUNDARY. A SURFACE WAVE SPINS
UP ON THE BOUNDARY IS IT MOVES SOUTH...INCREASING LOW LEVEL
CONVERGENCE AND MOISTURE FLUX ALONG IT. THE INCREASED
MOISTURE...COUPLED WITH THE STRONG MID LEVEL LIFT...SUPPORTS A
SWATH OF 0.10 TO 0.25 INCHES QPF EXTENDING FROM NORTHWEST ND INTO
NORTHEAST NE.

THE SECOND SHORT WAVE CROSSES WESTERN MT AND NORTHERN WY LATE IN
THE PERIOD. WHILE THE LIFT IS STRONG WITH THE SHORT
WAVE...MOISTURE IN THE COLUMN IS FAIRLY SCANT (AS PRECIPITABLE
WATER VALUES REMAINS BELOW 0.25 INCHES). UPSLOPE FLOW ADDS SOME
MOISTURE TO THE COLUMN...SO THAT AXES OF 0.10 TO 0.25 INCHES OF
QPF WERE PLACED ALONG THE ROCKY MOUNTAINS FRONT RANGE IN MT...AS
WELL AS THE GRAND TETONS IN WY.


...SOUTHWEST/SOUTHERN PLAINS...

THE CLOSED LOW OVER EASTERN CA AND WESTERN NV EARLY ON DAY 1
FINALLY WEAKENS AND OPENS UP AS A LONG WAVE TROUGH THAT CROSSES
THE SOUTHWEST AND AND SOUTHERN PLAINS BY THE END OF DAY 1. THERE
IS FAIRLY GOOD AGREEMENT WITH RESPECT TO THE CLOSED LOW CROSSING
THE SOUTHWEST STATES AND OPENING UP AND CROSSING THE SOUTHERN
PLAINS (THE 00Z NAM APPEARS TO BE TOO FAST WITH THIS TRANSITION
AND MOVEMENT...AND WAS NOT FACTORED INTO THE WPC QPF). GIVEN THE
REASONABLY GOOD AGREEMENT... THE WPC QPF WAS BASE ON A BLEND OF
THE 00Z GFS/12Z ECMWF...WITH SOME 21Z SREF MEAN USED TO BETTER
DELINEATE HIGHER TERRAIN QPF ACROSS AZ/NM.

THE CLOSED LOW WEAKENS AS IT CROSSES THE SOUTHWEST STATES DURING
THE FIRST PART OF DAY 1. INITIALLY...THERE IS A SOURCE OF MOISTURE
FROM THE SEA OF CA...BUT THIS ERODES QUICKLY AS THE MID LEVEL
SYSTEM OPENS UP AND MOVES EAST. THE ADDED MOISTURE...LOCAL UPSLOPE
FLOW (AND MARGINAL INSTABILITY...DRIVEN BY STEEPENING MID LEVEL
LAPSE RATES) RESULTS IN LOCAL 0.25 TO 0.50 INCH QPF AMOUNTS ACROSS
EASTERN AZ AND WEST CENTRAL NM...WHICH ARE SURROUNDED BY A MUCH
LARGER AREA OF 0.10 TO 0.25 INCHES OF QPF ACROSS EASTERN AZ AND
MUCH OF NORTHERN AND CENTRAL NM.

FURTHER EAST...THE LOW LEVEL FLOW BACKS AHEAD OF THE LONG WAVE
TROUGH ACROSS CENTRAL AND EASTERN TX. THE FLOW TRANSPORTS 0.75 TO
1.00 INCH PRECIPITABLE WATER VALUES INTO THIS AREA. THE
COMBINATION OF MOISTURE...LIFT FROM THE LONG WAVE...AND RESIDUAL
MID LEVEL INSTABILITY PRODUCES AN XIS OF 0.25 TO 0.50 INCHES OF
ACROSS CENTRAL AND EASTERN TX.


HAYES


GRAPHICS AVAILABLE ON THE WEB AT WWW.WPC.NCEP.NOAA.GOV

24HR QP VT 25/12Z
 0.01 550096 549090 546084 541076 536069 529061 524054 518045
      514038 506032 494016 482002 474996 468990 463984 457976
      444961 437954 433952 428951 422950 419952 416956 415962
      414967 412975 414980 417992 419996 421000 424004 425007
      425011 425019 426025 432023 440017 446025 450032 452035
      453037 452039 448036 444033 440035 436035 434037 434041
      439049 441054 443059 443063 441066 436065 435061 432059
      428060 425056 420055 416057 410063 401066 405074 409076
      415076 417073 414070 415067 418066 421069 426070 433078
      444079 447085 450088 452088 452092 449093 433094 426089
      427092 429097 424110 441115 445119 451120 455121 460123
      468126 472129 474136 479145 482149 485151 488151 494152
      501160 507167 506174 507179 511183 514185 520187 523190
      535194 538193 541188 542183 542176 538164 536161 535157
      535152 534147 535140 535136 534132 534123 534118 538118
      543115 547110 549107 549102 550096
 0.01 504241 503239 501235 500234 498231 497228 496223 494225
      495228 496231 497234 499237 501239 502241 504241
 0.01 495257 494250 491245 484235 478233 472233 467232 462233
      451235 448236 446238 445240 446243 452246 458248 469247
      476256 479257 481254 481249 484248 493257 495257
 0.01 506094 504089 502088 498082 490074 487068 484065 479059
      476054 473049 470046 467043 463043 461045 460047 461049
      468060 470066 472071 478082 483087 486090 491094 494097
      497097 506094
 0.01 485658 484653 480651 473649 465650 457652 453653 451656
      447655 442655 436662 428665 422667 418666 414667 411666
      404665 395666 388669 382674 372683 366689 360696 356698
      351700 348705 338717 325727 316737 308748 302762 297779
      294801 293809 290815 288823 285831 279838 277845 273879
      269886 269896 269919 267930 264939 255949 252955 250964
      249969 251972 256973 258976 261979 262984 262993 266999
      271003 274003 278002 280001 284998 290993 293992 297994
      300998 302003 301015 304032 308040 307045 308048 308054
      306058 306065 304068 303080 306083 310084 312093 315100
      313107 311110 311114 315118 323118 335120 339122 341125
      342127 345125 346120 350121 359124 366127 370130 371134
      372138 374142 377142 378137 379127 376120 374110 375107
      377104 379103 382098 380089 381083 383080 388080 393079
      394075 392071 391068 388069 385071 382072 379066 372060
      370057 372055 381056 379051 371050 362048 352047 360014
      362007 361999 360993 359989 355981 354973 348933 346923
      345915 344910 343905 342897 338886 334880 329876 323870
      325865 328861 333855 347849 353845 358840 362832 365822
      367815 367813 365812 365809 364792 374781 378764 382743
      388739 396736 408726 412719 422716 430714 438710 451704
      465695 467692 467685 467682 468679 470676 478674 480673
      482670 484663 485658
 0.01 494784 492763 488748 486741 483738 480739 478737 471738
      453753 447741 444737 438738 435739 433742 431748 430754
      429762 427768 425771 422772 417774 413779 403785 400788
      398786 393789 376801 372804 372807 371814 375817 379814
      386805 390801 393801 397802 403804 406809 407813 410814
      410823 411827 413830 414837 412845 409852 408859 410861
      410865 413869 428884 435896 438902 444902 449904 453908
      458911 462910 467905 469899 473893 475887 478875 482859
      485845 486837 486827 487819 489811 492800 494784
 0.01 482214 481211 477212 474213 470215 468217 465219 463218
      459219 457222 460223 464221 468220 471218 475217 478216
      482214 482214
 0.01 345008 344991 341973 341960 339958 336959 335967 335975
      336984 335994 335999 334001 333011 331019 329026 329036
      332041 339040 341038 341033 339028 340019 343013 345008
 0.25 520162 518159 515155 512152 509148 506145 503142 500142
      498144 501148 504150 509154 512157 515160 518162 520162
 0.25 509063 507062 507063 509063 509063
 0.25 494140 492139 492137 491136 489137 490138 492140 494141
      494140
 0.25 437693 435691 434687 432686 428687 426688 423689 420692
      419695 421697 423699 426700 428701 432699 433698 435695
      437693
 0.25 413689 413685 412682 409680 406678 401679 384687 379693
      373701 368706 360710 353715 348723 338736 328748 319761
      309775 304782 303791 303802 307809 312814 319815 327809
      333804 344794 356780 356769 358761 363753 366745 371738
      377733 381730 383727 389721 401711 413689
 0.25 374071 375069 375068 373066 371065 371066 373068 374071
      374071
 0.25 361069 362067 360066 359066 357067 358069 360070 361069
 0.25 357082 357078 355073 352071 348068 342068 339067 337069
      337071 339076 343078 345081 350083 353084 355085 357082
 0.25 347099 348094 348090 346088 344087 341086 339087 337089
      335093 334097 335101 336104 337106 341107 343107 345105
      347101 347099
 0.25 325971 326960 326949 324941 323937 319935 315936 313939
      314947 315958 316967 316977 317982 319984 323979 325971
 0.25 293889 293882 292877 292874 290872 289877 287880 285884
      284889 282900 281910 282923 283928 285925 288916 290906
      292895 293889
 0.50 387710 386707 385706 384706 383706 381707 380709 380710
      379711 380712 380713 382714 384713 385712 387710
 0.50 381716 378715 377712 373713 364719 358723 355727 352731
      348734 343737 340742 334750 321767 314776 309786 308792
      309797 310799 315801 321800 329793 336785 347766 358747
      363736 366732 371729 375726 378723 381716
 0.50 342098 343096 342094 340094 338094 337095 338097 340098
      341099 342098

$$





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