Quantitative Precipitation Forecast
Issued by NWS

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000
FXUS04 KWBC 270701
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST MON FEB 27 2017


PRELIM DAY 1 QPF DISCUSSION
VALID FEB 27/1200 UTC THRU FEB 28/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


DAY 1

...DAY 1 SYNOPSIS...

A FULL LATITUDE LONGWAVE TROUGH BECOMES BETTER ESTABLISHED OVER
THE WEST...SETTING UP SOUTHWEST FLOW AND A VERY SPRING-LIKE
PATTERN EAST OF THE ROCKIES. GULF MOISTURE WILL RETURN NORTHWARD
AND EASTWARD...ALTHOUGH IT WILL ENCOUNTER VERY DRY CONDITIONS
INITIALLY EAST OF THE MISSISSIPPI RIVER...THUS REDUCING THE
EFFECTIVENESS OF SOME PRECIPITATION AREAS. AREAS MORE LIKELY TO
SEE HEAVIER PRECIPITATION INCLUDE THE SOUTHWEST STATES AHEAD OF
THE DIGGING TROUGH AND THE LOWER MISSISSIPPI VALLEY NEAR THE
DEEPER RETURNING MOISTURE AND AIDED BY PERSISTENT UPGLIDE.


...SOUTHWEST U.S...

FOR DAY 1 THE MODEL MASS FIELD SOLUTIONS ARE SIMILAR. THE AIR MASS
WAS INITIALLY VERY DRY...WITH PW BELOW A HALF INCH AND IN MANY
CASES BELOW A QUARTER INCH. THIS WILL CHANGE...PARTICULARLY FROM
SOUTHERN CALIFORNIA TO CENTRAL ARIZONA...AS A PLUME OF PACIFIC
MOISTURE WORKS ITS WAY ONSHORE. THE RESULT IS RELATIVELY HEAVIER
AMOUNTS OF RAIN AND HIGH ELEVATION SNOW AFFECTING THE SAN DIEGO
AREA AND THE MOGOLLON RIM. PROGRESSION OF THE DEEP LAYER TROUGH
AND ASSOCIATED FRONTAL ZONE WILL ALSO SQUEEZE OUT MODERATE TO
HEAVY SNOWS IN MUCH OF UTAH AND WESTERN COLORADO / NORTHWEST NEW
MEXICO. WPC BEGAN WITH A BLEND THAT INCLUDED NEAR EQUAL PARTS OF
THE GFS...THE 12Z WRF-NMM...AND CONTINUITY. OVERALL...QPF HAS BEEN
INCREASING IN THE MODELS FOR CA/AZ...BUT THE MARGINAL PW
VALUES...ALONG WITH LESSER AMOUNTS FROM THE GEFS REFORECAST /
ANALOG EVENT...ARGUE FOR A CONSERVATIVE APPROACH. THEREFORE WE
TRIED TO TREND UPWARD WITHOUT GOING OVERBOARD.

ONE OF THE MORE DIFFICULT ASPECTS OF THIS FORECAST...HOWEVER...IS
FAR SOUTHERN CALIFORNIA...WHERE THE 00Z HI-RES MODELS TRENDED
SIGNIFICANTLY WETTER...TO THE TUNE OF 4-6 INCHES IN ALMOST AN
ATMOSPHERIC RIVER STYLE ONSLAUGHT OF WESTERLY FLOW HITTING THE
LAGUNA MOUNTAINS. PER SATELLITE IMAGERY AND ESRL ATMOSPHERIC RIVER
TOOLS DERIVED FROM THE GFS...THIS EVENT IS NOT LIKELY TO MEET
RIVER CRITERIA...BUT STRONG ONSHORE FLOW COULD NONETHELESS LEAD TO
HEAVY PRECIPITATION IF THE COLUMN CAN MOISTEN SUFFICIENTLY.
LOOKING AT THE UPPER AIR DATA AT 00Z ALONG WITH SATELLITE
TRENDS...THE GRADIENTS IN 850-700 MB FLOW STRENGTH AND MOISTURE
WERE SUPPRESSED QUITE A BIT TO THE SOUTH OF THE U.S. BORDER. THE
DIGGING TROUGH IS DOMINATED BY NORTHERN STREAM INFLUENCE AS
WELL...WHICH WOULD SEEM TO ARGUE FOR CONTINUING A MORE
CONSERVATIVE APPROACH TO QPF...BUT IT IS DIFFICULT TO IGNORE THE
MODEL CONSENSUS...WITH CONSECUTIVE ECMWF RUNS DELIVERING MORE THAN
3 INCHES OF RAIN NORTH OF THE BORDER...AND NOW JOINED BY MORE OF
THE NCEP GUIDANCE. IN THE 06Z QPF RELEASE WE TRENDED UPWARDS A
BIT...BUT WILL LIKELY NUDGE EVEN FURTHER FOR THE FINAL 0830Z QPF.
HOURLY RAIN RATES APPROACHING 0.50 INCHES IN THE NAM CONUS NEST
AND WRF-ARW WILL NECESSITATE AT LEAST A MARGINAL RISK OF EXCESSIVE
RAINFALL TODAY.


...NORTHWEST / NORTHERN U.S...

A NUMBER OF FACTORS FAVOR PRECIPITATION...BUT NOT HEAVY
PRECIPITATION...ACROSS THE NORTHWESTERN / NORTHERN TIER OF THE
COUNTRY. VERY COLD AND SUFFICIENTLY SATURATED AIR ALOFT WILL
PERSIST MONDAY AND MONDAY NIGHT OVER THE NORTHWEST / NORTHERN
ROCKIES / NORTHERN PLAINS. FLOW REMAINS CYCLONIC AND SOMEWHAT
SUPPORTIVE OF LIFT WITHIN A LARGE FULL LATITUDE TROUGH. ONSHORE
FLOW...ALBEIT LIGHT...WILL FAVOR THE CASCADES FOR SOMEWHAT HEAVIER
AREAL AVERAGE PRECIPITATION...BUT EVEN HERE AMOUNTS WILL LIKELY
REMAIN BELOW ONE INCH...AS THE PRECIPITABLE WATER VALUES ARE QUITE
LOW GIVEN THE COLD COLUMN. THE HIGH TERRAIN WILL BE FAVORED FOR
GREATEST COVERAGE OF MORE MEANINGFUL PRECIPITATION AMOUNTS GREATER
THAN A TENTH OF AN INCH LIQUID...BUT LOW ELEVATIONS SHOULD ALSO
SEE SHOWERY WEATHER...AND HEIGHT FALLS SPILLING OUT INTO THE
NORTHERN PLAINS WILL SUPPORT SWATHS OF LIGHT PRECIPITATION FROM
EASTERN MT/WY TO NORTHERN MN. WPC STEERED TOWARD CONSENSUS...BUT
FAVORED THE GFS AND TOOK INTO ACCOUNT NDFD.


...EASTERN / SOUTHERN U.S...

A BROAD REGION OF RETURNING GULF MOISTURE AND ISENTROPIC UPGLIDE
WILL BE SUPPORTIVE OF MESOSCALE AREAS OF PRECIPITATION...MORE
FAVORED WHERE LAPSE RATES ARE STEEPER AND MOISTURE DEPTH
GREATER...GENERALLY WEST OF THE APPALCHIANS AND ESPECIALLY DOWN
TOWARD THE SOUTHERN STATES. BY TUESDAY MORNING...HOWEVER...DEEP
LAYER FORCING AND MOISTURE TRANSPORT WILL INCREASE TOWARD THE
MIDWEST / LOWER GREAT LAKES AHEAD OF DEVELOPING LOW PRESSURE.
THERE WAS NO STRONG EVIDENCE TO TREND THE QPF IN ONE DIRECTION OR
ANOTHER. GENERALLY WE PREFERRED MODELS THAT WERE A LITTLE DRIER
WITH EASTERN EXTENT GIVEN THE DRY INITIAL CONDITIONS. WPC QPF WAS
BASED MAINLY ON CONTUNITY BLENDED WITH THE MOST RECENT 18Z/00Z GFS
AND 00Z WRF-NMM.

BURKE

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

24HR QP VT 28/12Z
 0.01 533198 534189 534182 532176 531172 528167 524163 523160
      520159 519156 516154 510148 507147 505144 505140 504137
      503132 500128 498117 498110 497105 493098 491094 490094
      487096 487101 488104 486108 484103 483097 483090 483082
      482076 483057 485052 485044 486037 484031 488015 489998
      489981 489975 487969 485972 485977 484979 483986 482992
      473009 470014 468018 466023 465031 466042 466056 465068
      465075 466080 468091 472099 475106 476113 476116 475120
      472124 469122 466117 466109 465102 461094 460081 458075
      459067 456056 459042 459032 455011 455004 458998 462991
      467983 472974 477964 483952 485946 487941 489929 491924
      492915 492903 493899 493892 493876 491866 489858 486852
      483848 480847 478852 478860 480865 481872 481879 477883
      475887 471896 462919 462936 459949 454958 451967 448974
      445983 441007 430020 428025 425029 419036 413043 406049
      402052 396051 384052 376047 363047 355049 348054 344056
      340056 338056 342059 343063 347065 350066 352069 349072
      345074 341075 336075 331075 327078 325083 324091 320093
      318095 318100 315103 313108 312116 311124 312130 314138
      314141 313143 309145 303146 299147 296150 294156 295161
      297165 297172 295178 294199 296207 300213 302216 306218
      309220 313220 317218 319214 324206 330197 334193 339191
      343193 346198 347203 350206 354209 352214 354218 356221
      363227 367226 372227 373223 372217 369214 364211 367207
      365205 357202 353199 351195 352191 356189 364195 369203
      372207 376210 383212 389213 393210 396214 399218 404220
      406225 401225 394226 396230 397237 392237 389239 386240
      383245 386248 391249 409254 420257 427256 433256 436255
      446255 465252 470253 474250 479251 481249 484250 491248
      492243 490238 485232 480230 478227 484224 489224 491222
      493217 496213 497203 494199 488197 483195 482191 484189
      487186 490182 494174
 0.01 494174 496172 498169 501168 504168 507169 509172 512174
      515175 518176 521178 522181 523184 524187 525190 527193
      529196 530198 533198
 0.01 513670 512658 511649 508642 504638 501640 500643 497645
      496639 495634 494635 490638 487642 484640 480635 478637
      479647 478657 479665 480670 478674 476679 467689 460701
      458702 456706 451711 448716 449724 453721 457719 458717
      460714 463713 466712 468714 472722 474733 476740 480741
      483741 484736 487730 496722 502718 506714 510708 511702
      512683 513670
 0.01 475197 475191 472187 468188 465190 461192 458195 456199
      455203 456205 459205 464205 468204 471201 474199 475197
 0.01 441207 440205 438204 437202 435201 434201 432201 430202
      429204 429205 430207 431208 432208 434209 436209 438209
      439209 441207
 0.01 450899 449889 447879 443870 438861 434854 429847 424842
      419839 407835 403835 401835 401832 404826 411791 411785
      411781 414772 415767 416762 417757 419752 419747 421743
      423740 424734 425726 426716 425712 421714 419723 416739
      414746 412753 406768 404775 399781 394789 391797 392803
      395805 395811 393814 391816 389812 386811 381810 375812
      371818 365829 362833 359836 356827 352821 343823 338827
      331824 323822 321816 323811 330797 331787 333780 339769
      347765 351762 357759 364754 367755 372755 382752 386747
      390741 392736 393732 396723 396717 394714 386711 378713
      372718 368722 362727 358731 356736 351742 343748 333756
      310779 302791 299799 298802 298807 295809 293807 288802
      283799 276797 263795 254796 253800 255801 263803 272803
      278808 285813 289815 288819 281823 281827 285827 293827
      300828 305832 310834 309841 308850 304859 299872 296889
      291897 288907 293926 297942 308951 305957 305960 306962
      312975 320976 322979 326980 332976 335969 341965 343960
      343953 344947 346945 354941 359938 365932 374924 379925
      383926 384931 361945 357954 357961 361963 366963 375961
      381956 385954 390954 396952 402957 415952 422943 427939
      431938 434936 440930 441925 443921 447909 450899
 0.01 439134 440132 440129 440127 439126 437127 437129 435131
      436133 437134 438135 439134
 0.01 439083 438069 440063 442055 439048 438040 441038 443036
      443031 444021 444017 442014 441016 435028 430039 429049
      428056 426065 425072 426080 426084 428086 435088 438086
      439083
 0.01 420130 419127 416127 413127 411129 410132 408134 406135
      403137 404139 407141 410143 412145 416144 418142 418137
      418133 420130
 0.01 404200 402190 402186 401182 399183 395184 391184 386182
      384177 382172 375175 369158 370151 369148 367147 360152
      353157 347161 347172 347178 350181 368180 372183 376185
      382190 394203 398203 401202 404200
 0.01 334056 332055 330055 328057 330058 332058 334056 334056
 0.25 480216 478211 473211 467212 450215 441215 433217 426220
      423224 423231 416236 411242 414246 418247 427248 443246
      450242 454241 456238 462232 463237 466238 466234 464231
      467228 472221 478219 480216
 0.25 480165 481160 481155 477150 475149 473146 468145 461143
      458145 448153 443154 442159 447164 450170 451176 450180
      449182 447185 448188 453187 458185 462183 465176 466174
      470173 475171 479167 480165
 0.25 444111 444108 444107 442106 440106 439106 437107 436109
      437111 438112 438113 439112 440112 442112 443112 444111
 0.25 429883 429878 428875 425869 421866 416863 412861 408865
      407869 409873 411880 414882 419886 423889 426888 427886
      429883
 0.25 415118 417116 415114 414112 411105 409098 406097 405100
      401104 397106 393110 389112 380120 374122 372123 370121
      353108 353104 354101 359096 367097 372098 377096 386088
      389084 395082 398081 401082 407079 411077 415074 416070
      416066 414061 403060 400065 395062 388063 385067 384070
      381070 378065 369057 370053 365052 359054 355056 356062
      358069 359076 357078 353079 348082 346087 344091 341089
      339085 335082 332081 330083 330092 329097 327098 323104
      322109 324115 324123 324129 328133 329140 329144 332145
      339144 345146 352146 356143 363136 366131 370130 371133
      374140 379139 388132 392130 396126 406121 415118
 0.25 374855 374850 372846 368846 365849 359852 351853 344854
      335856 332857 330854 330845 330841 325842 319846 315851
      313860 312870 310878 303890 299899 297902 297908 300916
      304922 310927 316932 316936 316942 314949 315955 316957
      319956 322949 327934 330925 332923 337921 341923 346928
      349927 353924 355918 353910 354901 358893 360885 363876
      366871 371862 374855
 0.25 358747 357746 356748 355748 356748 358748 358747
 0.25 340172 340168 338165 335161 330157 324154 310152 306152
      304153 302159 304170 304179 302186 302195 303200 306205
      309207 313206 316202 319194 321188 324184 334178 340172
 0.25 325790 324784 321781 318784 316787 313790 310793 306797
      306801 309804 314803 318800 321797 323795 325790
 0.50 462223 462219 459218 454219 448219 442219 436220 432223
      432227 433228 439228 444227 449225 454223 460224 462223
 0.50 407114 407110 405108 402109 400109 398110 394112 392114
      392116 392119 395120 397119 401118 403117 405116 407114
 0.50 410068 408067 407067 405067 406069 408070 410068
 0.50 388123 388122 387123 388123 388123 392116 390116 389115
388116
      388118 390117 392116
 0.50 376078 377076 377073 377071 377069 376068 376066 375064
      374064 373063 371062 370062 368062 366063 366065 366068
      366070 367072 367073 368075 369075 370077 372077 374078
      376078 376078
 0.50 365124 364119 361118 355115 350110 347105 344099 341093
      332086 333093 331101 327107 326109 327111 330117 332123
      334131 334134 338136 350142 354138 358132 359128 362125
      365124
 0.50 359868 357863 353864 346868 330880 326882 325879 325872
      323869 320869 318871 316875 311884 306892 304903 302906
      303911 307920 311923 315921 321913 325905 329896 338893
      340895 343897 346896 351888 354879 359868
 0.50 335171 336167 335165 331162 322157 312154 307155 305159
      308169 309175 308181 306187 306194 308198 311195 313184
      317181 321179 331175 335171
 0.50 321793 322791 320790 320791 320793 321793 321793
 0.50 325928 325926 323926 321930 321932 320937 319940 318943
      319947 321943 321941 323937 323934 324930 325928
 0.50 316794 315794 313794 314796 315794 316794
 1.00 352119 350115 346110 343105 340100 337097 335104 332110
      334115 337121 339127 343129 346127 346123 347119 349119
      352119
 1.00 330170 331166 329164 327163 324161 322160 318159 315157
      311158 310160 310164 312167 313169 315171 318172 322172
      326172 328172 330170
 1.00 321902 321898 320894 318892 315894 313896 313897 313899
      312903 310905 310909 310913 312916 313915 315913 317910
      319907 320905 321902
 1.50 342116 343114 342111 341109 339107 338108 338111 338113
      338115 338116 339117 340118 340117 342116 342116
 1.50 324167 324165 323164 321164 320164 320166 321167 323168
      324167
 1.50 319164 318163 317161 316161 315160 313161 313163 314164
      316165 318165 319164
 1.50 317905 318903 318900 317900 316900 315902 315903 313905
      312907 311908 311909 311911 312912 313911 314909 315908
      316907 317905 317905

$$




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