Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 170956
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
455 AM EST TUE JAN 17 2017

VALID 12Z TUE JAN 17 2017 - 12Z FRI JAN 20 2017

INTERIOR OF WASHINGTON/OREGON/IDAHO...

HIGH PROBABILITIES OF 0.25 INCHES OF ICE ARE DEPICTED BY A
COMPOSITE OF ALL DETERMINISTIC AND ENSEMBLE GUIDANCE FOR THE
PORTLAND AREA EASTWARD THROUGH THE COLUMBIA RIVER GORGE THEN ALONG
A BROAD STRIP OF THE BASIN AND FOOTHILLS THROUGH
TODAY/TONIGHT/WEDNESDAY BEFORE WANING. WHILE THE PROBABILITIES OF
0.25 INCHES OF ICE ARE HIGH...THEY WOULD LIKELY BE EVEN HIGHER AND
SUPPORT HIGH PROBABILITIES OF HIGHER THRESHOLDS OF 0.5/0.75/1.0
INCHES IF THE MEMBERSHIP CONSISTED OF HIGHER RESOLVING
GUIDANCE...WHICH ARE NEEDED TO SIMULATE THE SHALLOW SUB-FREEZING
AIR AND TERRAIN OVER SMALL DISTANCES. THE MODELS WHICH ARE HIGHEST
RESOLVING HOLD ON TO FAVORABLE CONDITIONS FOR ICE LONGER IN THE
ABOVE MENTIONED AREAS COMPARED TO THE GLOBAL GUIDANCE. BEST
ESTIMATES OF ICE STORM TOTALS ARE FOR BROAD AREAS OF 0.25 TO 0.5
INCHES WITH TOTALS POSSIBLY EXCEEDING 1 INCH IN PARTS OF THE
COLUMBIA RIVER GORGE AS WELL AS SNOQUALMIE PASS...WITH THE SNAKE
RIVER PLAIN IN SOUTHWEST IDAHO NEXT IN LINE TO RECEIVE HIGH
PROBABILITIES OF 0.25 OF ICE FOR WEDNESDAY AND WEDNESDAY
NIGHT....WITH THE MAJORITY OF THE ENSEMBLE MEMBERSHIP ONCE AGAIN
TOO COURSE TO ADEQUATELY RESOLVE THE LOW LEVEL TEMPERATURE
PROFILES. REFER TO LOCAL WFO WATCHES/WARNINGS FOR MORE SPECIFIC
INFORMATION/UPDATES/POTENTIAL IMPACTS FROM THE ICE.

REST OF THE PACIFIC NORTHWEST/CALIFORNIA/INTERMOUNTAIN WEST...

MODERATE TO HIGH PROBABILITIES OF 8 AND 12 INCHES OF SNOW WILL
DEVELOP ACROSS THE HIGHER ELEVATIONS OF THE WEST BEGINNING
WEDNESDAY AS SNOW LEVELS DROP WITH THE ARRIVAL OF THE NEXT MAJOR
UPPER TROUGH. THROUGH TUESDAY NIGHT...THE ENSEMBLE SYSTEMS AGREE
WITH THE EMPHASIS FOR SNOW ACROSS THE NORTHERN CASCADES OF
WASHINGTON...WITH THE SREF ARW MEMBERS GENERALLY LESS SUPPORTIVE
COMPARED TO THE SREF NMMB MEMBERS AS WELL AS THE GEFS/ECMWF
ENSEMBLE MEMBERS. FOR WEDNESDAY AND WEDNESDAY NIGHT...THE HIGHEST
PROBABILITIES OF SNOW AFFECT THE SISKIYOUS/SIERRAS/BLUE
MOUNTAINS/SAWTOOTH/BITTERROOTS...WITH GENERALLY CLOSE CLUSTERING
OF ALL ENSEMBLE MEMBERS. FOR THURSDAY AND THURSDAY NIGHT...LOW AND
MODERATE PROBABILITIES OF 8 AND 12 INCHES OF SNOW ARE DEPICTED FOR
THE SIERRAS AND SOUTHERN WASATCH...WITH MODERATE PROBABILITIES OF
4 INCHES ACROSS MOST ELEVATIONS OF THE INTERMOUNTAIN WEST ABOVE
ABOUT 500O THOUSAND FEET...WITH THE ENSEMBLE SYSTEMS ONCE AGAIN IN
GOOD AGREEMENT WITH CLUSTERING AND SHOWING MINIMAL SPREAD.

NORTHEAST/NEW ENGLAND...

MODERATE TO HIGH PROBABILITIES OF 0.25 INCHES OF ICE EXTEND ACROSS
PORTIONS OF THE ADIRONDACKS/CATSKILLS/BERKSHIRES FOR TODAY/TONIGHT
WITH THE HIGHER RESOLVING SREF/ECMWF ENSEMBLE MEMBERS MORE
SUPPORTIVE OF ICE COMPARED TO THE COARSER RESOLVING GEFS MEMBERS.
REGARDING SNOW...LOW PROBABILITIES OF 8 INCHES EXTEND ACROSS
PORTIONS OF NH/VT/NORTHEAST NY...WITH THE VARIOUS ENSEMBLE SYSTEMS
FAIRLY DISPERSIVE...SUGGESTING LOW CONFIDENCE IN THE 8 INCH
TOTALS. SIMILARLY...THE ENSEMBLE SYSTEMS ARE MORE SUPPORTIVE OF 4
INCH PROBABILITIES...WITH THE SREF/GEFS MEMBERS A LITTLE FARTHER
NORTH WITH THEIR CENTROID OF HIGHEST CHANCES COMPARED TO THE ECMWF
ENSEMBLE MEMBERS WHICH ARE A LITTLE FARTHER SOUTH. OVERALL
HOWEVER...THE SPREAD IN MINIMAL AND HELPS TO ACCOUNT FOR THE RANGE
OF POSSIBILITIES WITH THE TRACK AND SPEED OF THE LOW TRANSFERRING
TO THE COAST.

JAMES

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