Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 242024
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
422 PM EDT FRI MAR 24 2017

VALID 00Z SAT MAR 25 2017 - 00Z TUE MAR 28 2017

DAYS 1 THROUGH 3...

...WESTERN U.S....

THE WEST WILL BE AFFECTED BY A COUPLE MID/UPPER-LEVEL TROUGHS
THROUGH THE DAY 1-3 FORECAST PERIOD. THE FIRST SHORTWAVE WILL MOVE
ONSHORE THIS EVENING, WITH HEIGHTS DROPPING AS THE TROUGH MOVES
INLAND, BUT THEN QUICKLY RECOVERING IN THE WAKE AS SHORTWAVE
RIDGING BUILDS BACK INTO THE REGION. SNOW LEVELS WILL DROP AS THE
TROUGH AND ASSOCIATES SURFACE COLD FRONT MOVE INLAND TONIGHT, BUT
WILL BEGIN TO RISE AGAIN BY LATE SATURDAY. MODERATE TO HEAVY
SNOWFALL IS FORECAST ON DAY 1 (00Z SAT-00Z SUN) AT THE HIGHER
ELEVATIONS OF THE NORTHERN CASCADES, PORTIONS OF THE SIERRAS, AND
THE HIGHEST ELEVATIONS OF THE NORTHERN ROCKIES, WHERE 5 TO 10
INCHES ARE POSSIBLE.

THE WEST COAST WILL SEE SOMEWHAT OF A REPRIEVE ON DAY 2 (00Z
SUN-00Z MON) AS THE MID/UPPER TROUGH CROSSES THE ROCKIES AND THEN
BEGINS TO AMPLIFY OVER THE CENTRAL PLAINS. SOME RELATIVELY
SNOWFALL AMOUNTS ARE EXPECTED ON DAY 2 ACROSS PORTIONS OF THE
CENTRAL AND NORTHERN ROCKIES, BUT AMOUNTS WILL BE LIMITED BY
DURATION OF THE BEST VERTICAL VELOCITIES AS ENERGY ASSOCIATED WITH
THE SYSTEM QUICKLY MOVES EAST INTO THE PLAINS.

A SECOND, AND MORE SUBSTANTIAL MID/UPPER-LEVEL TROUGH IS FORECAST
TO MOVE ONSHORE ALONG THE WEST COAST EARLY ON DAY 3 (00Z MON-00Z
TUES). HEIGHTS AND SNOW-LEVELS WILL DROP ACROSS MUCH OF THE WEST
AS THE TROUGH MOVES INLAND AND THEN BEGINS TO FURTHER AMPLIFY
ACROSS THE GREAT BASIN BY LATE MONDAY. ALONG THE COAST, LOW-LEVEL
ONSHORE FLOW OF 20-30 KT IS FORECAST TO PERSIST INITIALLY AS THE
TROUGH MOVES INLAND, BUT THIS FLOW SHOULD BEGIN TO WEAKEN DURING
THE DAY ON MONDAY WITH PRECIP ACROSS THE CASCADES, SIERRAS, AND
COASTAL RANGES WANING. SNOWFALL AMOUNTS OF 5 TO 10 INCHES WITH
LOCALLY HIGHER AMOUNTS ARE POSSIBLE ON DAY 3 FROM THE OR CASCADES
TO THE NORTHERN CA COASTAL RANGE AND THE NORTHERN SIERRAS. FARTHER
INLAND, HEAVY SNOW WILL ALSO BE POSSIBLE ACROSS PORTIONS OF THE
GREAT BASIN/INTERMOUNTAIN WEST AND THE NORTHERN ROCKIES, WITH 5 TO
10 INCHES POSSIBLE AT THE HIGHER ELEVATIONS. WHILE SNOW LEVELS
WILL LOWER BY DAY 3, RAIN IS STILL FORECAST TO FALL AT VALLEY
LOCATIONS.

THE WPC FORECAST WAS BASED ON A MULTI-MODEL BLEND INCLUDING THE
NAM/GFS/ECMWF. THE NAM CONUS-NEST WAS WEIGHTED HEAVILY WHEN
PRODUCING THE THERMAL PROFILES DUE TO THE IMPROVED RESOLUTION IN
AREAS OF TERRAIN.

THE PROBABILITY OF RECEIVING A QUARTER INCH OF FREEZING RAIN IS
LESS THAN 10 PERCENT.


...UPPER GREAT LAKES TO THE NORTHEAST...

A MULTI-DAY PRECIPITATION EVENT IS FORECAST ACROSS PORTIONS OF THE
CENTRAL AND EASTERN U.S. A CLOSED UPPER-LEVEL LOW IS FORECAST BY
ALL MODELS TO BE CENTERED ACROSS THE SOUTHERN PLAINS THIS EVENING.
THE LOW IS FORECAST TO DRIFT SLOWLY NORTHEASTWARD TOWARD THE LOWER
GREAT LAKES THROUGH THE WEEKEND. ADDITIONALLY, THE SHORTWAVE
CROSSING THE WESTERN U.S. ON SATURDAY WILL REACH THE CENTRAL U.S.
ON SUNDAY AS IT FURTHER AMPLIFIES. AT THE SURFACE, MULTIPLE CENTER
OF LOW PRESSURE ARE FORECAST TO DEVELOP ALONG A FRONTAL BOUNDARY
ACROSS THE PLAINS  BY SUNDAY, WHICH ARE THEN FORECAST TO MOVE EAST
INTO THE GREAT LAKES/OHIO VALLEY BY LATE MONDAY. AT THE SAME TIME,
AN UPPER-LEVEL RIDGE AXIS IS EXPECTED TO DEVELOP BY SUNDAY FROM
JAMES BAY SOUTHEASTWARD TO THE EASTERN GREAT LAKES. THE
IMPLICATIONS OF THIS AT THE SURFACE ARE THAT COLD HIGH PRESSURE
WILL BE REINFORCED FROM EASTERN CANADA AND EXTENDING INTO NEW
ENGLAND, BEHIND A COLD FRONT WHICH WILL CROSS THE REGION EARLY
SATURDAY BEFORE BECOMING STATIONARY ACROSS THE MID-ATLANTIC BY
SATURDAY NIGHT/SUNDAY.

SOME LIGHT FREEZING RAIN IS POSSIBLE ON DAY 1 FROM PORTIONS OF THE
UPPER GREAT LAKES TO NEW ENGLAND AS THE COLDER SURFACE AIR MASS
BEGINS TO MOVE IN, AND BROAD ISENTROPIC LIFT PRODUCES A SHIELD OF
PRECIPITATION. THE MORE SUBSTANTIAL WINTER PRECIP ACROSS THESE
AREAS WILL HOLD OFF UNTIL DAYS 2 AND 3, HOWEVER, AS THE SURFACE
LOWS ACROSS THE CENTRAL U.S. TAKE SHAPE AND MOIST LOW-LEVEL FLOW
AHEAD OF THE SYSTEM INTO THE OHIO VALLEY/GREAT LAKES AND
EVENTUALLY THE NORTHEAST BEGINS TO RAMP UP. RELATIVELY LIGHT
FREEZING RAIN ACCUMULATIONS OF A HUNDREDTH UP TO A TENCH OF AN
INCH ARE POSSIBLE ON DAY 2 FROM THE NORTHERN GREAT LAKES EAST INTO
PORTIONS OF NEW ENGLAND. ACROSS THE GREAT LAKES, THE FREEZING RAIN
AMOUNTS WILL BE LIMITED BY THE INCREASING STRENGTH OF LOW-LEVEL
WARM ADVECTION AHEAD OF THE STRENGTHENING MULTI-PRONGED LOW
PRESSURE SYSTEM. ACROSS THE NORTHEAST, HOWEVER, THE LOW-LEVEL COLD
AIR MAY PERSIST FOR LONGER AS THE ARCTIC SURFACE HIGH REMAINS
ANCHORED ACROSS SOUTHEASTERN CANADA. ON DAY 3, FREEZING RAIN
AMOUNTS EXCEEDING A TENTH OF AN INCH ARE POSSIBLE ACROSS MUCH OF
THE INTERIOR NORTHEAST, WITH THE POTENTIAL FOR AMOUNTS REACHING A
QUARTER INCH FOR SOME AREAS. THERE IS A SLIGHT PROBABILITY OF
FREEZING RAIN AMOUNTS EXCEEDING A QUARTER INCH ACROSS THE
CATSKILLS ON DAY 2, AND A SLIGHT TO MODERATE PROBABILITY ACROSS
MUCH OF INTERIOR NORTHERN NEW ENGLAND ON DAY 3.

IN ADDITION TO THE FREEZING RAIN, PORTIONS OF NORTHERN NEW ENGLAND
WILL SEE THE POTENTIAL FOR SNOWFALL ON DAY 3. THE COLD AIR WILL
PERSIST LONGEST ACROSS CENTRAL/NORTHERN MAINE, AND THIS IS WHERE
THE POTENTIAL FOR THE HEAVIEST SNOWFALL EXISTS. A SLIGHT TO
MODERATE PROBABILITY OF SNOWFALL AMOUNTS EXCEEDING 4 INCHES IS
FORECAST ON DAY 3 FROM NORTHEASTERN NEW HAMPSHIRE TO MUCH OF
MAINE. ADDITIONALLY, WPC PROBABILITIES INDICATE LOW PROBABILITIES
(5-10%) FOR SNOWFALL AMOUNTS EXCEEDING 8 INCHES ACROSS PORTIONS OF
CENTRAL MAINE ON DAY 3. THE EXACT EVOLUTION OF THE LOW PRESSURE
SYSTEM ACROSS THE CENTRAL U.S./OHIO VALLEY ON DAYS 2 AND 3 AND THE
RESULTANT STRENGTH OF THE LOW-LEVEL WARM ADVECTION, ALONG WITH THE
STRENGTH OF THE ARCTIC HIGH ACROSS SOUTHEASTERN CANADA WILL
DETERMINE THE EXACT PROPORTIONS OF SNOW VS. FREEZING RAIN FOR NEW
ENGLAND DURING THIS EVENT. AT THIS TIME, A SIGNIFICANT AMOUNT OF
UNCERTAINTY EXISTS WITH RESPECT TO THESE FACTORS AND THUS, THERE
IS ROOM FOR CHANGES IN THE FORECAST P-TYPE FOR ANY GIVEN LOCATION
WITH CONSECUTIVE FORECAST UPDATES.

THE WPC FORECAST WAS BASED ON A MULTI-MODEL BLEND INCLUDING THE
NAM/GFS/ECMWF.

RYAN


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