Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 210642
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 AM EDT THU SEP 21 2017


PRELIM DAY 1 QPF DISCUSSION
VALID SEP 21/1200 UTC THRU SEP 22/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1

...FAR SOUTHEAST MASSACHUSETTS AND OFFSHORE ISLANDS...

ANY APPRECIABLE RAIN ASSOCIATED WITH TROPICAL STORM JOSE WILL
REMAIN CONFINED TO SOUTHEAST MASS...MARTHA`S VINEYARD...AND
NANTUCKET. MEASURABLE PRECIPITATION IS FORECAST AS FAR NORTH AS
GLOUCESTER AND AS FAR WEST AS LONG ISLAND THROUGH FRIDAY MORNING.
THE FORECAST TRACK DID NOT CHANGE IN THE 00Z MODELS...BUT THE
MODELS DID ADD SOME QPF BACK INTO THE STORM...LOOKING JUST
SLIGHTLY HEAVIER THAN IN PREVIOUS CYCLES. EVEN WITH THIS
CHANGE...HOWEVER...THE WPC AREAL AVERAGE RAINFALL IS STILL
FORECAST TO BE AROUND 2 INCHES ON NANTUCKET...1 INCH ON CAPE
COD...AND LESSER AMOUNTS ELSEWHERE. FLOODING IS NOT EXPECTED.


...WESTERN U.S...

A LARGE TROUGH WAS TAKING SHAPE OVER THE WEST. EARLY THIS MORNING
A WIDE BAND OF RAIN WAS FALLING WITHIN ENERGETIC MID LEVEL FLOW
FROM THE CENTRAL SIERRAS THROUGH THE NORTHERN GREAT BASIN TOWARD
EASTERN IDAHO. SHARP HEIGHT FALLS WILL OCCUR HERE THROUGH MIDDAY
AS THE TROUGH SWINGS FROM POSITIVE TO NEAR NEUTRAL TILT...FOCUSING
DIFLUENT UPPER FLOW OVER THE NORTHERN GREAT BASIN...WITH EVENTUAL
FORMATION OF A MID LEVEL LOW CENTER STRADDLING OREGON/IDAHO/NEVADA
BY THURSDAY NIGHT. RAIN AND HIGH ELEVATION SNOWS WILL BE FORCED
MAINLY BY THE HEIGHT FALLS...BUT UPSLOPE FLOW INTO THE
NORTH-FACING SLOPES OF THE NORTHERN ROCKIES WILL INCREASE BY
THURSDAY NIGHT AS SURFACE PRESSURES RISE ACROSS MONTANA.
OVERALL...THE SYSTEM IS SOMEWHAT MOISTURE STARVED...WITH
PRECIPITABLE WATER VALUES PEAKING JUST ABOVE A HALF INCH WITHIN
THE PLUME OF DEEP LAYER ASCENT. THE PATTERN WOULD BE FAVORABLE FOR
THUNDERSTORMS OVER SOUTHERN NEVADA AND MUCH OF UTAH THIS
AFTERNOON...EXCEPT FOR VERY DRY LOW LEVEL AIR WHICH WILL LIMIT
INSTABILITY AND THE EFFECTIVENESS OF ANY STORMS THAT MANAGE TO
FORM. WE THEREFORE FOCUSED MOST OF THE QPF WITHIN THE 700-500 MB
LAYER ASCENT REGION BACK OVER EASTERN NEVADA AND NORTHERN
UTAH...WITH MOISTURE WRAPPING TOWARD THE FORMING LOW CENTER IN
EASTERN IDAHO. THE FORECAST WAS DERIVED FROM A BLEND OF PREVIOUS
WPC...WITH THE 00Z GFS AND NAM CONUS NEST. THE GFS MAY BE SLIGHTLY
OVERDONE WITH SOME OF ITS UPSLOPE-ENHANCED ACCUMULATIONS OF
GREATER THAN 2 INCHES LIQUID...GIVEN THE LOW PW ENVIRONMENT. BUT
SPATIALLY THE GFS LOOKED GOOD...AND 00Z ECMWF TRENDED TOWARD IT.
SEE THE WPC HEAVY SNOW DISCUSSION FOR WINTER WEATHER DETAILS.


...PLAINS / MIDWEST / GREAT LAKES...

THE DAY 1 FORECAST PRESENTS SOMETHING OF A DIFFICULT
PATTERN...ALTHOUGH THE STAKES ARE LOW...WITH RELATIVELY BENIGN
AREAL AVERAGE RAINFALL TOTALS. AT 06Z THUNDERSTORMS WERE ONGOING
OVER PARTS OF IA/IL AT THE TAIL END OF A SHORTWAVE LIFTING UP
THROUGH THE GREAT LAKES. THE SAME WAVE IS FORECAST TO PRODUCE
ENHANCED LOW LEVEL MOISTURE TRANSPORT INTO LOWER MICHIGAN DURING
THE DAY...WHERE SYNOPTIC LIFT AIDED PERHAPS BY DIFFERENTIAL
HEATING / LAKE BREEZES MAY BE ENOUGH TO SPUR CLUSTERS OF
THUNDERSTORMS. MODERATE TO STRONG CAPE VALUES AND GREATER THAN
1.50 INCHES PRECIPITABLE WATER SUGGESTS A HEAVY RAIN THREAT TODAY
OVER LOWER MICHIGAN. JUST AS THE DIURNAL ACTIVITY OVER MICHIGAN
WINDS DOWN DURING THE EVENING...A WARM FRONT WILL SHARPEN BACK
WEST ACROSS WI/MN. ISOLATED INITIATION MAY OCCUR NEAR THE WARM
FRONT...WITH MORE WIDESPREAD INITIATION EXPECTED IN THE
STRENGTHENING WARM ADVECTION REGIME / NOSE OF THE PLAINS LOW LEVEL
JET ACROSS CENTRAL MINNESOTA AND ADJACENT PARTS OF THE DAKOTAS.
SIMILARLY...POCKETS OF CONVECTION ARE POSSIBLE OVER THE SOUTHERN
PLAINS ALONG THE EASTERN EDGE OF THE WARMER MID LEVEL TEMPERATURES
WHERE ADVECTION IS MAXIMIZED...AND THEN ALSO ALONG THE LEE TROUGH
/ MOISTURE GRADIENT TOWARD PEAK HEATING. THE OVERALL FORCING IS ON
THE WEAK SIDE...HOWEVER...SO THERE IS SOME SPREAD IN THE TIMING
AND PLACEMENT OF PRECIPITATION AREAS IN THE MODELS. WPC AGAIN
FAVORED A BLEND OF THE PREVIOUS WPC FORECAST WITH 00Z GFS AND NAM
CONUS NEST.


...SOUTHERN U.S...

THE 12Z ECMWF ENSEMBLE QPF PROBABILITIES SEEMED TO DESCRIBE THE
SPATIAL LAYOUT OF THE MOIST PLUMES ACROSS NORTHERN FLORIDA AND
SOUTHEAST FLORIDA...WITH A DRY POCKET OVER CENTRAL FLORIDA. USING
THIS TOOL ALONG WITH PERSISTENCE BASED ON THE COVERAGE OF DIURNAL
CONVECTION ON WEDNESDAY THROUGHOUT THE SOUTHERN U.S...WE ENHANCED
AMOUNTS HERE AND THERE...BUT MADE LITTLE OVERALL CHANGE TO THE
TIMING AND PLACEMENT OF QPF. STRONGER ONSHORE FLOW SHOULD PROMOTE
AN INLAND SPREADING OF SHOWERS OVER TEXAS...AND CYCLONIC FLOW
CHANNELED DOWN THROUGH THE TENNESSEE VALLEY WILL SUPPORT WIDELY
SCATTERED SHOWERS THERE AS WELL.

BURKE

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

24HR QP VT 22/12Z
 0.01 421637 423643 427645 430648 431655 431667 431673 430680
      428705 426709 423712 415719 409726 407729 403733 392736
      386737 381736 377735 374731 372725 372720 366696 367687
      370682 373676 377669 382660 387653 391650 397647 403642
 0.01 544182 545172 545165 543156 541150 539144 538141 535140
      528136 516137 508138 503134 500131 494129 487127 483123
      480118 477113 477103 479094 482081 486070 488064 491058
      495043 493030 501021 514003 525986 532956 532946 530944
      528944 520952 514960 507969 500975 494983 489995 484007
      479022 475039 477041 475044 471048 466050 463054 455059
      446062 440063 437063 435065 432071 431076 430080 425082
      422084 421087 418092 410091 406093 405096 403097 392100
      389107 386110 379113 373115 369119 366121 366125 368131
      365138 366142 371144 374148 374154 371160 369168 370175
      371178 370179 364178 356181 352180 350179 348176 347173
      346169 345165 337164 330163 325165 322169 325174 332181
      337185 339190 343193 347195 352198 355195 357193 361194
      366197 378204 383206 387210 392215 397219 402218 405213
      405206 406202 409202 421205 424208 426205 424198 426194
      428192 432193 434192 438192 441191 446190 449190 452193
      455190 460190 463186 466181 470177 477177 486184 489185
      491183 493184 498180 500178 504179 510180 515179 521181
      524186 531195 537197 539194 544182
 0.01 487218 487212 484209 480206 476208 468210 458213 452212
      449213 439215 430217 426219 421223 422227 427229 428231
      426233 420233 412235 410238 413243 415248 420250 433254
      441253 446253 451251 459249 464247 466242 467233 469227
      473223 478221 487218
 0.01 502924 503916 502907 502903 499898 497892 497885 493873
      484854 474835 471831 470826 470821 469814 467810 463808
      459808 455811 446811 439815 425829 417835 415838 413842
      413848 415854 417858 422858 426856 427863 428869 429874
      438894 441907 444916 443945 445950 446958 446966 444981
      443986 445991 448994 452996 457991 464982 469974 472970
      476968 484966 488964 491959 496948 499937 502924
 0.01 479238 479236 477234 476234 474234 473237 474237 475238
      477239 479239 479238
 0.01 457229 456228 454228 453228 454230 456230 457229
 0.01 453230 452228 451229 449228 447228 446228 445229 444229
      442229 441229 440230 438231 439233 441233 443233 444233
      445232 447232 448232 449232 450231 452231 453230
 0.01 445172 444169 440166 438164 435160 433152 432149 430147
      429149 427158 427162 428165 429168 427170 424173 423175
      424178 428179 431176 437175 439177 443176 445172
 0.01 413959 413948 412943 411942 406936 402929 398923 396921
      393921 389921 385923 380927 372937 368944 365952 366956
      368958 375959 379960 384961 387961 387965 383969 377971
      371975 366980 357989 347000 347002 344006 340010 336015
      336020 338021 360007 365005 370002 371998 375996 381992
      392986 397982 401980 402977 407968 410962 413959
 0.01 401848 400841 396837 392835 386836 382840 378838 375836
      373830 373820 375815 380810 384805 384799 379796 375796
      370798 362805 354813 348819 346815 344811 345807 349796
      351789 356786 357782 357777 355768 351763 348763 340770
      334758 332747 327746 325751 323765 322773 324779 328779
      335777 335781 333785 326794 319803 312807 309810 305814
      297825 294830 292831 290830 284829 277829 272827 269822
      275814 278809 282810 289814 294813 298811 302807 304802
      303784 303776 300772 295770 289774 282780 278784 274788
      263789 256791 253793 248802 245808 243814 242817 244819
      248823 257820 261822 259828 262832 262838 266847 272852
      284854 290856 295860 299874 297881 296884 292885 292890
      294896 289906 288910 290914 297919 301923 303925 306925
      308924 309919 310913 308910 308905 308901 306898 306891
      307884 308877 310871 312865 312858 315847 319839 321837
      322840 325846 325851 327853 334853 340850 340853 338855
      334859 333867 332872 332879 332883 334885 340886 358890
      364889 369887 372881 373872 375865 378860 382859 383857
      387852 391854 395853 398853 400851 401848
 0.01 372227 373225 373223 373222 372220 370217 369215 367214
      365215 363215 362218 363218 364220 366222 367223 367224
      369225 371225 372227 372227
 0.01 381078 381074 379069 377064 374062 370060 367063 366066
      369069 372073 373077 374082 379084 381079 381078
 0.01 321035 321031 319030 315030 312030 308030 305029 303031
      301034 301036 300038 304038 306038 310037 313037 317037
      319037 321035
 0.01 323960 323950 321945 308941 296937 289937 286943 281948
      277951 270955 266960 262961 258962 254961 250961 246963
      242968 241972 242976 247979 257979 263982 271991 277995
      284999 287004 288007 285007 278011 274015 272018 273021
      277024 285027 294028 302002 303992 304988 306987 309985
      311981 314975 323960
 0.01 299067 297062 295060 290059 284061 279065 272062 267058
      262055 256051 252048 249048 247050 244056 244064 246070
      250076 254080 261083 275086 281084 286081 289076 295073
      299067
 0.01 273007 273002 272999 266995 257995 248994 246993 243996
      241998 241004 245009 249014 250018 252020 254020 258017
      260009 262008 265009 269009 273008 273007
 0.25 537174 538169 538161 536153 534149 531147 523146 520146
      517148 515150 511151 509154 509157 514163 520167 525174
      529179 533179 536177 537174
 0.25 493142 492140 491140 490139 489138 488139 488141 488142
      490144 492144 493142
 0.25 481879 481878 481877 480874 479872 479871 478870 477867
      476866 474866 473868 473870 473873 473875 474877 475880
      476881 478882 480882 481881 481879
 0.25 481914 475900 470895 467895 463898 459901 456904 455908
      455917 457923 455929 452947 451958 452969 452978 452981
      455979 458973 463967 466960 469951 470941 470927 473920
      479915 481914
 0.25 457239 458237 457236 455236 454236 453236 451236 449237
      449239 451240 452240 453240 454240 456239 457239
 0.25 471091 473077 472071 470068 466067 462068 455071 450072
      445070 442073 445077 444083 437087 427086 424088 424092
      422099 420105 417108 414109 408105 404110 397116 393118
      390119 386120 383123 382126 384127 388127 387130 385135
      385140 380159 383168 384173 387177 392178 397178 404177
      407175 409169 411164 413160 420156 422153 423149 424142
      426136 430133 433132 435135 436140 438149 441152 446154
      451153 453149 457140 459131 465122 467117 468112 469100
      471091
 0.25 458840 457834 456830 454827 451825 443825 439826 436828
      431835 430843 432850 436856 439859 442858 445856 447853
      447848 451846 456842 458840
 0.25 426669 423659 421653 419648 416644 413643 407644 404648
      389658 384676 379683 377688 376694 378706 379713 381720
      385727 389729 395727 402723 407716 414711 420702 423695
      426684 426676 426669
 0.25 397210 399208 397206 396205 394205 394207 395208 397210
      397210
 0.25 376191 375189 375188 373187 371187 369186 368186 367187
      366189 367190 369191 370192 372192 374193 376191
 0.25 374988 373984 369984 368986 366988 364990 362992 360994
      359996 360998 364997 366995 367994 370992 373990 374988
 0.25 318823 318819 314818 310818 306820 303827 302830 301836
      303845 300850 304853 305851 306846 309839 310835 312833
      317828 318823
 0.25 297800 296794 295791 291791 288792 286791 283787 280789
      277793 273797 268799 262799 257801 254804 253808 255811
      263815 266814 269808 272805 276805 283800 287800 292802
      296802 297800
 0.25 301966 303962 302958 299952 294951 288954 284956 279958
      275962 277967 281971 286974 291975 297974 301968 301966
 0.25 274075 272075 274075 274075
 0.50 532168 532166 532165 531162 529160 528159 526158 525157
      523156 522156 520157 521159 521160 523162 523163 524164
      525166 526166 527169 527170 528171 530171 531170 532169
      532168
 0.50 466090 467085 467079 466077 463075 449078 446086 441088
      436091 429089 427089 426092 427099 428103 426107 421112
      411115 401125 396129 393133 391136 391143 391151 389163
      388167 389171 392173 395171 402161 406155 411150 415146
      418141 422133 426127 433118 435116 439115 447115 451120
      455119 461114 463107 466090
 0.50 466952 466944 465940 463935 459935 457938 455942 454949
      454957 454960 454966 457969 459966 461962 463957 466952
      466952
 0.50 448145 448143 449141 448139 446138 445138 445137 443136
      442137 441138 440139 440141 440143 441144 442146 444147
      445147 447147 448145
 0.50 423675 422664 419654 415648 412647 408648 404652 401655
      397656 391661 389665 390670 387677 383683 380690 380701
      381708 386716 391719 396719 400717 405712 412708 417703
      421695 423688 423677 423675
 0.50 292962 290960 288962 287960 285962 286964 288963 290964
      292962
 0.50 281796 281794 280793 280794 279795 278796 279798 281797
      281796
 0.50 266804 265802 263802 263803 261804 259805 260805 261806
      263807 264807 265805 266804
 1.00 457101 458096 458091 457089 454087 452088 450090 448092
      447094 446099 450099 451101 454103 455103 457101
 1.00 421671 419662 417655 413652 409653 405658 397660 394664
      393668 394673 393678 388683 385687 384690 383694 385703
      386707 389709 394710 397709 401707 405705 413702 416698
      419693 421678 421671
 1.00 428115 426115 424116 422118 420119 417119 415122 413125
      414129 417129 419126 421125 423123 425120 427117 428115
 1.50 419671 418663 416657 412655 410659 407662 404661 399662
      397666 397672 397679 394683 386690 385697 388703 392705
      397705 402704 407701 414694 417690 419683 419671
 2.00 417671 417664 415660 413658 409665 405665 402664 399667
      399672 400678 400683 394687 391688 386693 387697 390702
      394704 400703 405701 409698 415689 417683 417676 417671
 3.00 415679 414672 407673 407681 405687 401692 393693 390694
      390697 394701 400700 405697 409693 412688 415682 415679

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