Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 021830
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM EDT WED SEP 02 2015


PRELIM DAY 1 QPF DISCUSSION
VALID SEP 03/0000 UTC THRU SEP 04/0000 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1...

...PACIFIC NORTHWEST...

THERE WILL BE LITTLE MOVEMENT OF THE LARGE SCALE TROUGH AXIS ALONG
THE WEST COAST THROUGH THURSDAY...BUT THE DOWNSTREAM RIDGE WILL
SHOW FURTHER AMPLIFICATION AND A SHORTWAVE WILL CARRY HEIGHT FALLS
THROUGH THE EASTERN SIDE OF THE TROUGH...IN THE ENTRANCE REGION OF
A STRENGTHENING UPPER JET. THUS...IN ADDITION TO THE SHOWERY
REGIME IN WESTERN WASHINGTON...A SWATH OF ORGANIZED PRECIPITATION
IS FORECAST ACROSS NORTHERN IDAHO AND WESTERN
MONTANA...ESSENTIALLY ALONG THE BROAD 850-600 MB FRONTAL ZONE AS
THE ASSOCIATED SURFACE FRONT PUSHES INTO THE PLAINS AND GREAT
BASIN. OUR BIAS-CORRECTED ENSEMBLE IS ON THE DRY SIDE...BUT
SEVERAL DETERMINISTIC MODELS PRODUCE SPOTS OF 0.75-INCH PLUS
PRECIPITATION IN NW WA / ID / MT. WPC QPF IS SOMEWHERE IN
BETWEEN...WITH 0.50 INCH AREAL AVERAGE FORECAST IN
SPOTS...EMBEDDED WITHIN MORE WIDESPREAD 0.25 INCH AREAS. THIS
NOTION IS SUPPORTED BY THE GEFS REFORECAST...ANALOG...DATA ACROSS
ID/MT...ALTHOUGH THAT TOOL IS DRIER OVER WESTERN WASHINGTON.
OVERALL WE INTRODUCED VERY LITTLE CHANGE TO CONTINUITY OVER THIS
REGION.


...UPPER MIDWEST...

THUNDERSTORMS PRODUCING HEAVY RAIN RATES WILL OCCUR AHEAD OF A
COMPACT MID LEVEL TROUGH...BUT ALSO IMMEDIATELY BEHIND THE TROUGH
IN AN AREA OF ENHANCED LOW LEVEL INFLOW. THE TROUGH WILL TRACK
FROM THE VICINITY OF THE MN/WI BORDER EARLY WEDNESDAY AFTERNOON TO
LOWER MICHIGAN BY THURSDAY MORNING...WITH THE LEADING THUNDERSTORM
ACTIVITY MIGRATING ALONG A LOOSELY DEFINED WARM FRONT FROM THE
WESTERN END OF LAKE SUPERIOR DOWN TO LOWER MICHIGAN. THE TRAILING
ACTIVITY WILL REDEVELOP EASTWARD AND SOUTHEASTWARD FROM EAU CLAIR
WISCONSIN TOWARD NORTHERN INDIANA. MANY OF THE MODEL FORECASTS
WERE THOUGHT TO NOT BE PROGRESSIVE ENOUGH...AND LIKELY DISPLAY A
SLIGHT NORTHWARD BIAS TO THEIR QPF. WPC BLENDED THE PREVIOUS
FORECAST TOWARD THE 12Z GFS AND 12Z WRF-ARW. THE GFS WAS MORE
PROGRESSIVE AND MORE LIBERAL WITH THE SOUTHWARD EXTENT OF
PRECIPITATION...BUT IT DID BECOME PROBABLY TOO DRY BY THURSDAY
AFTERNOON.

GENERALLY THE SHORT WAVELENGTH OF THE MID LEVEL TROUGH...ALONG
WITH REASONABLY STRONG DOWNDRAFT CAPE...SHOULD PROMOTE FORWARD
PROGRESSION...AND ACT AGAINST FLASH FLOODING...ALTHOUGH
PRECIPITABLE WATER VALUES NEAR 1.5 INCHES WILL SUPPORT BRIEF
STRONG RAIN RATES. THE GREATEST CONCERN FOR FLASH FLOODING MAY BE
WITH THE NARROW BANDS OF CONVECTION WHICH FORM ON THE TRAILING
SIDE OF THE TROUGH...IN THE BETTER LOW LEVEL INFLOW. ONE SUCH BAND
HAD SET UP WEDNESDAY AFTERNOON IN WESTERN WISCONSIN.


...GULF COAST...

A SMALL SCALE CIRCULATION EMBEDDED IN A MID LEVEL TROUGH HAD
FLARED UP WITH CONVECTION FOR A SECOND STRAIGHT MORNING ALONG THE
TEXAS GULF COAST. GALVESTON MEASURED A RAPID ACCUMULATION OF MORE
THAN 2 INCHES OF RAIN IN THE EARLY MORNING HOURS BEFORE OUTFLOW
PUSHED THE CONVECTION OFFSHORE. HEAVY...EFFICIENT RAINFALL WAS
ALSO NOTED ALONG THE LOUISIANA COAST FARTHER UP THE LENGTH OF THE
TROUGH AXIS...AND AGAIN WITHIN A WEAK ONSHORE FLOW COMPONENT AT
LOW LEVELS. THE LARGER SCALE MID LEVEL TROUGH WILL REMAIN IN
PLACE...STUCK INSIDE A MEAN RIDGE POSITION...BUT IT WILL START TO
FRACTURE AS RIDGING OVER THE GULF BRIDGES TO RIDGING IN THE PLAINS
STATES TO FORM A COL POSITION OVER SOUTHERN LOUISIANA. THIS WILL
FAVOR PROLONGED WEAK ASCENT OVER LOUISIANA...CAPABLE OF SUPPORTING
HEAVY RAIN THROUGH TONIGHT. ALONG THE TEXAS PORTION OF THE TROUGH
THE SMALL CIRCULATION MAY NOT PERSIST IN ITS PRESENT FORM...BUT
PERSISTENT ONSHORE FLOW SHOULD AGAIN FAVOR ISOLATED
HEAVY RAINFALL WEDNESDAY NIGHT. WPC USED A COMBINATION OF THE 12Z
NSSL WRF...GEM REGIONAL...AND GLOBAL MODEL CONSENSUS TO DERIVE THE
QPF IN THIS REGION.


...SOUTHWEST...

A MONSOONAL PLUME HAD BECOME FIRMLY ESTABLISHED IN BETWEEN A GREAT
PLAINS RIDGE CENTER AND A DEEPENING TROUGH ALONG THE WEST COAST.
WEDNESDAY AND WEDNESDAY NIGHT AGAIN HOLD POTENTIAL TO BE
ACTIVE...ESPECIALLY WITHIN THE PLUME OF 1.25 TO 1.65 INCH PW
VALUES OVER CENTRAL AND EASTERN ARIZONA AND WESTERN NEW
MEXICO...BUT ALSO POTENTIALLY EXTENDING TOWARD SE UT / SW CO WHERE
PW VALUES WILL APPROACH 1.00 INCH. THERE IS SOME WEAK CONNECTION
TO HIGH ALTITUDE MOISTURE STREAMING NORTHWARD FROM TROPICAL
DEPRESSION 14-E. MODELS DIFFER IN THE DETAILS...BUT ALL FORECAST
ENHANCEMENT OF MID LEVEL CYCLONIC VORTICITY ACROSS EASTERN AZ
TODAY...WITH AN EVENTUAL TRACK OF THE RESULTING SHORTWAVE TOWARD
THE FOUR CORNERS. THIS MAY ORGANIZE PRECIPITATION ONTO LARGER
SCALES...MAKE IT MORE PERSISTENT OVER A GIVEN LOCATION...AND
ENHANCE INFLOW NEAR THE TOP OF THE BOUNDARY LAYER. UNIDIRECTIONAL
FLOW IN THE CLOUD LAYER ALSO ARGUES FOR SOME TRAINING. THE MODEL
PRECIPITATION SIGNAL IS NOT PARTICULARLY STRONG IN THIS REGION IN
TERMS OF MAXIMUM AMOUNTS...BUT SEVERAL MODELS ARE GENEROUS WITH
COVERAGE OF AT LEAST 0.25 INCH PRECIPITATION...AND MANY OF THE
INGREDIENTS ARE IN PLACE FOR AN ORGANIZED FLASH FLOOD RISK ON
LOCAL SCALES. WPC QPF TRENDED TOWARD THE 12Z GFS AND NAM...BUT
ULTIMATELY MADE LITTLE CHANGE TO CONTINUITY.

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

BURKE

24HR QP VT 04/00Z
 0.01 528247 527243 522242 517242 516239 517235 520229 525228
      534223 536218 539211 540206 541195 541181 540174 538169
      535158 530147 528140 525134 521130 516128 511128 507129
      503132 498132 495132 493129 497123 499119 502116 506114
      511113 514111 518107 523094 524086 526084 526078 525072
      523068 518067 515072 512077 509081 505078 502080 500082
      497084 495082 492083 486083 476084 463084 459088 455091
      453093 447094 441093 437094 433095 429099 446128 444133
      441135 442141 442149 443155 442162 433166 425170 421173
      419177 416181 415190 413197 411207 415210 419210 418223
      422222 425219 429216 432211 436209 438204 441198 443194
      453189 461181 463178 465171 468167 472165 476161 477159
      480160 481163 484166 483171 486182 488187 489193 488197
      487200 483203 472206 468210 464212 461214 457215 447216
      442216 437218 435223 440225 442227 448227 453226 454231
      451232 441235 438239 439246 439253 443257 452258 456258
      461260 477272 489295 492300 497303 501302 505301 508297
      510291 510284 513280 515275 517272 520271 528247
 0.01 476694 475680 473665 471658 468653 465650 461651 458660
      459675 460682 460689 459696 456698 451704 449699 446696
      438694 431696 426699 423701 420704 416714 413724 412729
      413737 415750 415757 414762 412767 410772 412777 413781
      411784 407792 407796 405797 401794 397786 395782 392779
      389778 385780 377784 371791 368795 365801 361809 359814
      355816 347822 341827 339836 339843 341847 343849 349850
      355848 359844 367839 375835 379838 381842 383849 385853
      391857 393864 395872 398881 395898 394911 391930 389947
      392958 398953 403937 407926 411921 417913 420911 423910
      425911 432914 437913 441911 444909 447909 450908 452906
      456901 460896 461890 463878 463864 462849 458840 450834
      444825 439818 437815 435812 436809 436794 436788 440791
      442793 447793 453787 460780 464770 464762 465756 467744
      467738 470733 474725 476717 476709 476700 476694
 0.01 430025 430021 429018 426012 424010 420010 416010 413012
      404020 395030 392034 388039 381042 378043 375042 372041
      369043 366048 363049 358047 353045 347043 340042 332043
      325045 317045 313047 311049 310054 310059 312062 315067
      315072 312074 296071 267070 262068 254068 250069 250074
      253079 257084 261088 270096 275100 276102 279103 283099
      285094 290094 297095 301096 304097 300102 299105 298109
      300116 303121 309125 311127 316127 324128 327129 330128
      342133 346131 350126 355127 358126 363123 368118 372113
      373103 374100 377099 381099 383097 387093 397084 402081
      408079 414076 416074 418071 421067 422057 420055 415053
      409051 405049 403047 407042 419037 426032 430025
 0.01 411108 410098 408093 402099 398104 391106 385110 381115
      380120 381124 385125 388123 392119 398115 405112 408111
      410108 411108
 0.01 377776 376770 371768 367765 363760 357754 349747 340746
      335748 329751 325753 321757 308760 303768 301773 298779
      290784 280789 268791 257787 246785 241787 238791 236796
      238799 248803 254802 258799 261800 260801 256804 250806
      251809 249814 252818 260823 270825 275826 278828 278830
      286838 295841 300843 301848 302853 305856 309860 312865
      319860 322850 320844 321839 324825 327815 330810 333811
      337808 340804 345792 347788 352785 359784 364786 368787
      373783 377776
 0.01 316939 316919 316910 314903 312896 307890 302888 299882
      295878 292876 288875 281877 278883 275888 273896 273902
      275910 280923 282930 280937 272947 263954 252961 248965
      248972 250974 254975 261977 274976 277981 283985 294981
      303971 309960 313948 316939
 0.01 261004 258998 254992 250987 244982 237981 234982 232985
      232995 234003 238009 241010 245011 248012 252012 257008
      261004
 0.25 533187 534182 533176 530170 526163 524155 521148 516144
      513143 510146 508154 498161 494166 493170 493176 493179
      495182 502184 508188 513193 520207 521209 525209 528204
      528188 532188 533187
 0.25 524184 525182 525179 525177 525175 524174 523173 522171
      520170 519169 518169 517172 516174 516177 516178 517180
      517182 517183 519183 521184 522185 524184 524184
 0.25 514158 514155 512155 513158 514158
 0.25 504234 503223 500216 496210 489210 482211 477214 475216
      474221 477223 477226 467237 464244 467250 469253 472254
      475253 477250 484250 487248 488244 488241 486237 482235
      483232 487228 493233 496236 499238 504234
 0.25 488136 488123 485122 482122 477124 473126 469131 461141
      457143 454147 450153 448160 449168 453171 457169 461165
      465162 470159 476149 485141 488136
 0.25 450741 449738 447738 442737 439736 435736 432740 431745
      432752 433759 436761 438762 441760 443757 444752 446746
      448743 450741
 0.25 442711 441706 440706 436707 435709 433711 432713 429716
      428719 430723 432724 434725 435725 438722 440720 441717
      442713 442711
 0.25 454874 455867 454859 453854 451850 446841 442834 430820
      425820 421823 416830 421837 424841 424848 424853 420857
      415863 412873 411885 410890 410894 415895 418898 422899
      427897 432891 435889 441887 444887 449884 453879 454874
 0.25 406061 406058 403057 397056 391056 388060 384064 381065
      376063 370063 367068 367074 369078 370084 371086 374088
      379087 386081 390082 393079 397074 399069 401064 405062
      406061
 0.25 363776 362772 360769 359767 357765 356764 354761 351762
      350764 351766 351769 351773 353774 355775 358777 361777
      363776
 0.25 343098 342092 339087 334085 330090 326094 322093 321090
      317089 313092 309098 307104 308111 311117 316118 321117
      322111 330110 340111 341109 339107 336102 341103 343098
 0.25 322788 320778 318774 315770 312770 309773 305780 298787
      291793 286798 276801 266804 260807 258810 259813 262817
      266818 272816 279813 288814 290816 292822 294826 298826
      300823 305823 307825 312824 317817 319808 322788
 0.25 304085 304083 301081 298080 294080 290079 287079 283079
      280080 283082 284083 288084 292085 295085 299086 303086
      304085
 0.25 301914 300905 298897 295889 289885 284891 283895 282899
      283906 285914 290931 291939 288945 284952 281960 281966
      286967 288964 296953 298950 299945 299935 299924 300916
      301914
 0.25 278092 278090 277086 277084 274081 272081 270081 268083
      265084 267087 269088 271089 273092 275094 278094 278092
 0.25 252002 251998 249996 248994 246992 244991 240990 237991
      236993 236997 238999 240001 242003 245004 247004 249004
      252002
 0.50 507177 507174 507172 507171 507169 506167 504167 503166
      501167 500167 499168 498169 497170 497172 496174 497176
      497177 498178 500179 501179 503179 505179 507177 507177
 0.50 497229 497227 497226 496223 496222 495220 493219 492219
      491219 491220 492222 493223 494225 494226 495228 496228
      497231 497229
 0.50 489219 488217 487216 485216 483216 483217 481218 481219
      483220 484221 486221 488221 488220 489219
 0.50 479238 479236 478234 476235 475237 475238 477239 478239
      479238
 0.50 467155 469152 468150 467150 466150 464151 463151 462152
      461153 460155 460157 461157 463157 465157 467155 467155
 0.50 450867 448861 445853 441847 439839 435834 431830 429827
      427827 427830 428841 430849 432857 431861 427862 422865
      418871 416877 415882 416886 422889 424891 427890 431885
      435880 442878 448875 450869 450867
 0.50 380078 381076 381074 380072 380070 379069 378068 376067
      376066 375066 373066 372066 372068 373069 373071 373073
      373075 373077 374080 375082 377082 379080 380078
 0.50 339095 338093 337092 336093 336094 337095 338096 339095
 0.50 319791 318786 316782 312784 309786 304788 300790 295796
      292800 292803 298804 301806 302808 299812 299816 302817
      304814 307813 310814 314811 315807 317797 319791
 0.50 319104 318101 318100 316101 314103 315104 317104 319104
 0.50 314105 314104 312104 312105 314105 314105
 0.50 295912 296908 295903 294901 293897 292895 291893 288893
      286895 286900 286904 287908 288911 289914 291916 293917
      295914 295912
 0.50 278807 277805 274804 270805 267806 265808 264810 263813
      265815 268815 271814 273813 275811 278809 278807

$$





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