Quantitative Precipitation Forecast
Issued by NWS

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
000
FOUS11 KWBC 230837
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 AM EDT THU MAR 23 2017

VALID 12Z THU MAR 23 2017 - 12Z SUN MAR 26 2017


DAYS 1 THROUGH 3...


...WEST COAST...

SHORT WAVE ENERGY CROSSING THE PACIFIC NORTHWEST DURING DAY 1 WILL
TAP DEEP PACIFIC MOISTURE...RESULTING IN HIGH ELEVATION SNOWS
ACROSS THE OLYMPICS AND CASCADES OF WA. A LONG WAVE TROUGH COMES
ASHORE ACROSS THE WEST COAST DURING DAY 2...BRINGING WITH IT
LOWERING SNOW LEVELS AND THE POTENTIAL FOR HEAVY SNOWFALL. THERE
WAS GENERALLY GOOD MODEL AGREEMENT WITH RESPECT TO THE OVERALL
SYNOPTIC SETUP...SO THE THERMAL PORTION OF THE FORECAST WAS BASED
ON A MULTI MODEL BLEND. THE QPF PORTION OF THE FORECAST WAS BASED
ON THE MOST RECENT WPC QPF.

DAY 1...
THE BEST LIFT WITH SHORT WAVE ENERGY CROSSING THE PACIFIC
NORTHWEST OCCURS DURING THE LAST PART OF DAY 1. AHEAD OF THE SHORT
WAVE...SNOW LEVELS RISE ABOVE 6000 FEET IN THE WARM AIR ADVECTION
PATTERN. THIS RELEGATES SNOWFALL ACCUMULATIONS OF THE HIGHER
TERRAIN OF OLYMPIC RANGE AND NORTHERN WA CASCADES...WITH LOCAL 6
INCH AMOUNTS EXPECTED OVER THE OLYMPICS. FURTHER SOUTH...A
MOISTURE PLUME AHEAD OF A LONG WAVE TROUGH IMPACTS NORTHERN CA.
SNOW LEVELS RISE AHEAD OF THE LONG WAVE TROUGH...RESULTING IN 2 TO
4 INCHES OF SNOWFALL ACROSS THE HIGHER TERRAIN OF THE TRINITY AND
SISKIYOU MOUNTAINS IN NORTHERN CA.

DAY 2...
THE MAIN THRUST OF THE MOISTURE PLUME IMPACTS NORTHERN AND CENTRAL
CA DURING DAY 2. THE COMBINATION OF UPSLOPE FLOW AND SYNOPTIC
SCALE ASCENT SUPPORT HEAVY QPF ACROSS THESE AREAS...AS SNOW LEVELS
FALL TO 4500 TO 5500 FEET DURING THE DAY. THERE IS ENOUGH QPF TO
SUPPORT AN AXIS OF 8 TO 12 INCHES OF SNOWFALL ACROSS THE HIGHER
TERRAIN OF THE SIERRA NEVADA RANGE IN CA....WITH LESSER AMOUNTS
(GENERALLY BETWEEN 4 AND INCHES) EXPECTED ACROSS THE SHASTA AND
TRINITY MOUNTAINS. THE MOISTURE PLUME IS NOT AS ROBUST ACROSS THE
PACIFIC NORTHWEST DURING DAY 2...BUT SNOW LEVELS HERE ALSO FALL TO
4500 TO 5500 FEET. THIS SHOULD ALLOW STRIPS OF 3 TO 6 INCHES OF
SNOW OVER THE HIGHER TERRAIN OF THE OR CASCADES...WITH 4 TO 8 INCH
AMOUNTS OVER THE WA CASCADES.

DAY 3...
AS THE LONG WAVE TROUGH COMES ASHORE ACROSS THE WEST COAST...MUCH
OF THE MOISTURE IS SCOURED AHEAD OF THE BEST LIFT.
SUBSEQUENTLY...MAINLY LIGHT SNOWFALL AMOUNTS ARE EXPECTED ACROSS
THE NORTHERN WA CASCADES...WHERE LOCAL 2 TO 4 INCH SNOWFALL
AMOUNTS WERE PLACED.


...GREAT BASIN/ROCKIES...

A LONG WAVE TROUGH CROSSES THE WASATCH RANGE IN UT EARLY ON DAY
1...FOCUSING MOISTURE FOR HEAVY SNOWFALL. A CLOSED MID LEVEL LOW
FORMS AT THE BASE OF THE LONG WAVE TROUGH OVER THE SOUTHERN
ROCKIES LATER ON DAY 1...WHICH SPINS UP SURFACE LOW PRESSURE. THE
COMBINATION OF MID LEVEL FRONTOGENETIC FORCING AND UPSLOPE WILL
RESULT IN HEAVY SNOWFALL ACROSS THE CO ROCKIES...AS WELL AS THE
BIGHORN RANGE IN WY. THE EXITING MID LEVEL SYSTEM WILL TAKE THE
MID LEVEL FORCING WITH IT DURING THE FIRST HALF OF DAY 2...BUT
HEAVY SNOWFALL IS STILL EXPECTED OVER PORTIONS OF EASTERN CO
BEFORE IT DEPARTS. FINALLY...ANOTHER LONG WAVE TROUGH CROSSES THE
ROCKIES DURING DAY 3. MOISTURE IS NOT AS ABUNDANT FOR THIS
TROUGH...SO MAINLY LIGHT SNOWFALL AMOUNTS ARE EXPECTED. THERE WAS
GENERALLY GOOD MODEL AGREEMENT WITH RESPECT TO THE OVERALL
SYNOPTIC SETUP...SO THE THERMAL PORTION OF THE FORECAST WAS BASED
ON A MULTI MODEL BLEND. THE QPF PORTION OF THE FORECAST WAS BASED
ON THE MOST RECENT WPC QPF.

DAY 1...
A LONG WAVE TROUGH CROSSES THE GREAT BASIN DURING THE FIRST HALF
OF DAY 1. UPSLOPE FLOW AHEAD OF SURFACE LOW PRESSURE DEVELOPING
OVER UT/CO WILL FOCUS THE MOISTURE IN THE COLUMN ON THE WASATCH
AND UINTA RANGES IN UT. SNOW LEVELS DROP FROM 9000 TO 6000 FEET
ACROSS THESE RANGES...AND THERE IS A MULTI MODEL SIGNAL FOR 4 TO 8
INCHES OF SNOWFALL...WITH THE HIGHEST AMOUNTS OVER THE NORTHERN
WASATCH RANGE AND THE UINTAS. FURTHER NORTH...THE COMBINATION OF
MOISTURE AND LIFT WILL BECOMES FOCUSED BY UPSLOPE FLOW OVER THE
GRAND TETONS AND THE BIG HORN RANGE IN WY...MAINLY DURING THE
MIDDLE OF DAY 1. AGAIN...THERE IS A MULTI MODEL SIGNAL FOR 4 TO 8
INCHES OF SNOWFALL...WITH THE HIGHEST AMOUNTS OVER THE BIG HORNS.

AS THE LONG WAVE TROUGH CROSSES THE CENTRAL AND SOUTHERN ROCKIES
DURING THE SECOND HALF OF DAY 1...A CLOSED MID LEVEL LOW FORMS
OVER SOUTHEAST CO. MOST OF THE 00Z MODEL SOLUTIONS SHOWED THE
DEVELOPMENT OF THE MID LEVEL FRONTOGENETIC FORCING ON THE NORTH
SIDE OF THE CLOSING MID LEVEL LOW...THAT ROTATES TO THE NORTHWEST
SIDE AFTER 24/00Z. THE BEST LIFT IN THE MID LEVEL FORCING OCCURS
DURING THE 24/06Z AND 24/12Z TIME FRAME. THAT AREA OF LIFT IS
AUGMENTED BY INCREASING UPSLOPE FLOW ACROSS THE PALMER DIVIDE OVER
THE CO FRONT RANGE. INITIALLY...BOUNDARY LAYER CONDITIONS ARE WARM
ENOUGH TO RESULT IN A PRECIPITATION PHASE ISSUE ACROSS THE FRONT
RANGE. HOWEVER...THE PRECIPITATION CHANGES TO SNOW AS THE COLUMNS
MOISTENS...AND BECOMES ISOTHERMAL JUST BELOW FREEZING. THERE
SHOULD BE ENOUGH QPF TO SUPPORT AN AREA OF 12+ INCHES OF SNOWFALL
OVER THE HIGHER TERRAIN...TAPERING TO LESS THAN 6 INCHES WHERE THE
CHANGEOVER OCCURS LAST (AIDED BY DYNAMIC COOLING ASSOCIATED WITH
THE CLOSING MID LEVEL LOW. FURTHER SOUTH...LOCAL 4 TO 8 INCH
SNOWFALL AMOUNTS WERE PLACED OVER THE SAN JUAN RANGE IN
CO...MAINLY ABOVE 7000 FEET...AS UPSLOPE FLOW FOCUSES MOISTURE ON
THAT RANGE.

DAY 2...
THE MAIN BAND OF FRONTOGENETIC FORCING WILL PIVOT ACROSS THE FRONT
RANGE OF THE CO ROCKIES DURING THE FIRST PART OF DAY 2...AS THE
CLOSED MID LEVEL LOW EXITS ACROSS THE SOUTHERN PLAINS. THERE COULD
BE SOME PRECIPITATION TYPE PROBLEMS EARLY...UNTIL DYNAMIC COOLING
AND MOISTENING OF THE COLUMN RESULT IN A PROFILE THAT SUPPORTS
SNOW. THERE WAS A MULTI MODEL SIGNAL FOR 6 TO 10 INCHES OF
SNOWFALL NEAR KLIC...EXTENDING NORTH TO SOUTH OF KAKO.  FURTHER
NORTHEAST...MODEL SOUNDINGS WERE NOT COLD ENOUGH TOP SUPPORT AN
ALL SNOW SCENARIO...SO AMOUNTS WERE RAINFALL OFF TO LESS THAN 2
INCHES STRETCHING INTO SOUTHWEST NE DURING DAY 2.

DAY 3...
THE NEXT LONG WAVE TROUGH CROSSES THE GREAT BASIN AND ROCKIES
DURING DAY 3. MOISTURE BECOMES THE LIMITING FACTOR FOR
SNOWFALL...BUT DYNAMIC LIFT AND UPSLOPE FLOW SHOULD MAKE THE MOST
OF THE MOISTURE IN THE COLUMN. LOCAL 2 TO 4 INCH SNOWFALL AMOUNTS
WERE PLACED OVER THE HIGHER TERRAIN OF EASTERN NV...UT INTO THE
ABSAROKA RANGE IN NORTHWEST WY AND SOUTH CENTRAL MT.


...UPPER GREAT LAKES INTO THE NORTHEAST...

MOISTURE STREAMING ACROSS A FRONTAL BOUNDARY EXTENDING FROM THE
UPPER GREAT LAKES TO THE NORTHEAST DURING DAYS 1 THROUGH 3 WILL
RISE UP AND OVER COLDER AIR AT THE SURFACE...RESULTING IN THE
POTENTIAL FOR FREEZING RAIN EACH DAY. THE 00Z ECMWF MAY BE TOO
FAST DROPPING THE FRONT SOUTHWARD...ESPECIALLY ON DAY 3.
OVERALL...THERE WAS GOOD MODEL AGREEMENT ON THE LOW LEVEL
PLACEMENT OF THE COLD AIR...SO THE THERMAL FIELDS WERE BASED ON A
MULTI MODEL BLEND. THE QPF PORTION OF THE FORECAST WAS BASED ON
THE MOST RECENT WPC QPF.

DAY 1...
MOISTURE RIDING UP AND OVER A LOW LEVEL FRONTAL BOUNDARY EXTENDING
FROM SOUTHERN MN INTO WESTERN NY STATE WILL PROVIDE SUFFICIENT
LIFT FOR QPF ALONG AND NORTH OF THE FRONT ACROSS THE UPPER GREAT
LAKES DURING DAY 1. THE BROAD WARM AIR ADVECTION PATTERN PRODUCES
A WARM NOSE ACROSS MN INTO NORTHERN WI AND THE UP OF MI DURING THE
DAY. AS THE VERTICAL MOTION INCREASES...THE WARM NOSE BETWEEN 750
MB AND 800 MB WILL ROB THE COLUMN OF ITS ABILITY TO SUPPORT SNOW
ACROSS THIS AREA. HOWEVER...LOW LEVEL COLD AIR REMAINS LOCKED IN
PLACE BY A LOW LEVEL EASTERLY FLOW. CONDITIONS AT THE SURFACE WILL
INITIALLY BE CRITICAL FOR FREEZING RAIN...BUT COLDER AIR DRAINING
SOUTHWARD AHEAD OF HIGH PRESSURE OVER ONTARIO SHOULD REINFORCE THE
LOW LEVEL COLD AIR IN THE ABOVEMENTIONED LOCATIONS. THIS SHOULD BE
ENOUGH QPF TO SUPPORT AN AREA OF 0.01 TO 0.10 INCHES OF ICE
STRETCHING FROM THE ARROWHEAD OF MN ACROSS FAR NORTHERN WI AND THE
UP OF MI.

FURTHER EAST...THE PRECIPITATION IN THE BROAD WARM AIR ADVECTION
PATTERN MOISTENS THE COLUMN ACROSS WESTERN AND CENTRAL PA INTO
WESTERN AND CENTRAL NY STATE TOWARD THE END OF DAY 1. THE LOW
LEVELS REMAIN COLD DURING THIS PROCESS...BUT MODEL SOUNDINGS
SHOWED A WARM NOSE BETWEEN 750 MB AND 800 MB...WHICH SUPPORTS A
FREEZING RAIN AND SLEET MIX. ICE AMOUNTS ARE EXPECTED TO REMAIN
BELOW 0.05 INCHES.

DAY 2...
THE LOW LEVELS SHOULD WARM ENOUGH TO LESSEN THE THREAT FOR ICING
ACROSS THE UPPER GREAT LAKES DURING DAY 2. PATCHY AREAS OF 0.01
INCHES OF QPF WERE PLACED OVER NORTHERN WI INTO THE UP OF MI.
HOWEVER...AS COLD AIR BLEEDS SOUTH FROM HIGH PRESSURE OVER
ONTARIO...THE COVERAGE OF ICING COULD INCREASE LATE DURING THE
PERIOD.

FURTHER EAST...THE WARM AIR ADVECTION PATTERN MOISTENS THE COLUMN
ACROSS UPSTATE NY INTO NORTHERN NEW ENGLAND DURING THE FIRST PART
OF DAY 2. MODEL SOUNDINGS SHOWED A SATURATED COLUMN JUST BELOW 0
DEGREES C...WHICH SUPPORTS A PERIOD OF SNOW ACROSS THIS AREA. THE
COLUMN EVENTUALLY LOSES THE ABILITY TO SUPPORT SNOWFALL...BUT NOT
BEFORE A GENERAL 1 TO 3 INCHES SNOWFALL STRETCHING ACROSS THE
ABOVEMENTIONED AREAS. COLD AIR AT THE SURFACE BECOMES TRAPPED BY
THE SNOWFALL...SO THAT A PERIOD OF ICING IS EXPECTED THE SNOWFALL
ENDS. ICING AMOUNTS ARE GENERALLY EXPECTED TO REMAIN BELOW 0.10
INCHES.

COLD AIR IN PLACE WILL BECOME TRAPPED IN VALLEYS OF THE TERRAIN
STRETCHING ACROSS THE SOUTHERN TIER OF NY STATE INTO PORTIONS OF
THE LOWER HUDSON VALLEY OF NY INTO NORTHEAST PA AND NEARBY
NORTHWEST NJ. THE COLD AIR SHOULD BE FAIRLY SHALLOW...SO ICING
OCCURS BEFORE 24/18Z...WITH ICE AMOUNTS REMAINING BELOW 0.10
INCHES.

DAY 3...
COLD AIR CONTINUES TO BLEED SOUTHWARD ACROSS THE UPPER GREAT LAKES
INTO UPSTATE AND NORTHERN NEW ENGLAND DURING DAY 3....AS HIGH
PRESSURE MOVES FROM ONTARIO INTO QUEBEC. THE COLD AIR WILL BE
DIFFICULT TO DISLODGE...AS THE NEXT SHOT OF PRECIPITATION CROSSES
THE AREA. MODEL SOUNDINGS SHOWED A WARM NOSE NEAR 3 DEGREES
CELSIUS BETWEEN 800 AND 850 MB...AND THE MODEL SOUNDINGS SHOWED A
FREEZING RAIN PROFILE HERE. LOCAL 0.10 INCH ICE AMOUNTS ARE
POSSIBLE ACROSS PORTIONS OF THE NORTHERN LP OF MI INTO PARTS OF
FAR UPSTATE NY.

HAYES

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.