Quantitative Precipitation Forecast
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FOUS11 KWBC 020809
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
308 AM EST MON MAR 02 2015

VALID 12Z MON MAR 02 2015 - 12Z THU MAR 05 2015


DAYS 1 THROUGH 3...


...SOUTHERN PLAINS/LOWER AND MID MS VALLEY/OH VALLEY/MID
ATLANTIC...

SHORT WAVES IN A FAST MID LEVEL FLOW STREAK FROM THE SOUTHERN
PLAINS THROUGH THE MID ATLANTIC ON DAYS 2 AND 3. NORTHERN STREAM
ENERGY DROPS SOUTH ACROSS THE GREAT LAKES DURING THIS
TIME...PUSHING A COLD FRONT ACROSS THE SOUTHERN PLAINS THROUGH THE
NORTHERN MID ATLANTIC DURING DAY 3. THERE IS A FAIR AMOUNT OF
MODEL SPREAD CONCERNING THE POSITION OF THE FRONTAL
BOUNDARY...ESPECIALLY ACROSS THE NORTHERN MID ATLANTIC ON DAY 3.
THE 00Z NAM SEEMS TOO SLOW DROPPING THE FRONT SOUTHWARD...WHILE
THE 00Z GFS MAY BE A TAD TOO AGGRESSIVE PUSHING THE FRONT INTO
VA/MD/DE BY 05/12Z. AT THIS DISTANCE...GIVEN THE SPREAD OF THE
MODEL SUITE...THE THERMAL FIELDS WERE BASED MAINLY ON A BLEND OF
THE 00Z GFS/12Z ECMWF. THIS COMBINATION APPEARS TO BUILD A
CONSENSUS FOR DAY 3 ACROSS THE OH VALLEY AND NORTHERN MID
ATLANTIC. THE QPF PORTION OF THE FORECAST WAS BASED ON THE MOST
RECENT WPC QPF.

DAY 2...
A NORTHERN STREAM SHORT WAVE PUSHES A COLD FRONT ACROSS THE
MIDWEST TOWARD THE SOUTHERN PLAINS AND LOWER AND MID MS VALLEY
DURING DAY 2. HIGH PRESSURE BUILDING IN BEHIND THE FRONT SENDS
SHALLOW COLD AIR AS FAR SOUTH AS THE RED RIVER VALLEY ACROSS THE
LOWER AND MID MS VALLEY. THE SHALLOW COLD AIR IS OVERRUN BY
MOISTURE BEING DRAWN NORTHEAST ACROSS THE REGION. MODEL SOUNDINGS
SUGGEST A FREEZING RAIN PROFILE ALONG THIS AXIS...AND 0.01 TO 0.10
INCHES OF ICE WAS PLACED ALONG THE AXIS.

FURTHER EAST...COLD AIR IN PLACE OVER THE OH VALLEY AND MID
ATLANTIC IS OVERRUN BY WARM AIR ADVECTION (WITH 30 TO 40 KNOT
SOUTHWEST WINDS ON THE 290 ISENTROPIC SURFACE). THE 00Z GFS IS
MORE AGGRESSIVE WITH THE LOW LEVEL WARMING...AND ITS MODEL
SOUNDINGS ACROSS THE OH VALLEY INTO THE NORTHERN MID ATLANTIC
SHOWED A WARM LAYER NEAR 830 MB...WITH A MAXIMUM TEMPERATURE NEAR
3 DEGREES CELSIUS. THIS SUPPORTS FREEZING RAIN...AS THE LOW LEVEL
COLD AIR IS SLOW TO BE SCOURED. THERE IS MULTI MODEL SUPPORT FOR
AN AREA OF 0.10 TO 0.25 INCHES OF ICE IN THE STRONG WARM AIR
ADVECTION ACROSS WESTERN AND CENTRAL PA...AS WELL AS PORTIONS OF
EASTERN WV. THE 00Z GFS ALSO SHOWED THE POTENTIAL FOR MORE THAN
0.25 INCHES OF ICE ACROSS THE VALLEY OF WESTERN PA...WHERE THE
COLD AIR MAY BE TOUGHEST TO SCOUR.

DAY 3...
THE SURFACE BOUNDARY STRETCHES FROM CENTRAL TX THROUGH NORTHERN LA
AND NORTHERN AND CENTRAL MS INTO THE LOWER OH VALLEY DURING DAY 3.
THERE IS STRONG MODEL SUPPORT FOR BRINGING BOUNDARY LAYER
TEMPERATURES TO NEAR FREEZING AS FAR SOUTH AS CENTRAL
TX...NORTHERN LA THROUGH MUCH OF THE INTERIOR DEEP SOUTH INTO THE
INTERIOR MID ATLANTIC. THE MID LEVELS COOL OFF MORE SLOWLY...AS
THE FLOW SLOWLY BACKS. THIS SETUP SETS THE STAGE FOR FREEZING
RAIN...AND MODEL SOUNDINGS STRETCHING FROM CENTRAL TX THROUGH
SOUTHERN AR INTO NORTHERN MS AND NORTHWEST AL SHOWED A CLASSIC
FREEZING RAIN PROFILE ON THIS AXIS. THE ABOVE SUPPORTS AN AREA OF
0.10 TO 0.25 INCHES OF QPF FROM SOUTHERN AR ACROSS NORTHERN
AL...NORTHWEST AL AND SOUTHWEST TN.

FURTHER NORTH...THE COLUMN COOLS ENOUGH FOR SNOWFALL ACROSS THE
MID MS VALLEY INTO THE THE LOWER OH VALLEY AND NORTHERN MID
ATLANTIC. AS MENTIONED EARLIER...THE COLUMN IS IN A STATE OF
TRANSITION...REACHING THE POINT WHERE IT CAN SUPPORT SNOW DURING
THE SECOND HALF OF THE PERIOD. GIVEN THE AMOUNT OF MOISTURE BEING
DRAWN INTO THE REGION (MOISTURE FLUX VALUES ARE VERY HIGH)...THE
POTENTIAL EXISTS FOR HEAVY SNOWFALL FROM PORTIONS OF NORTHEAST AR
THROUGH NORTHWEST TN/KY INTO MUCH OF WV. IN FACT...THE MOST RECENT
ECMWF ENSEMBLE OUTPUT SHOWED A NUMBER OF MEMBERS WITH 12+ INCH
SNOWFALL POTENTIAL CENTERED ON KY AND WV...AND MANY MEMBER WITH 8+
INCH POTENTIAL FROM AR INTO WESTERN PA. SINCE THE SYSTEM WILL BE
IN TRANSITION...LEADING TO A BELOW AVERAGE FORECAST...SNOWFALL
VALUES FOR NOW ARE CAPPED AT LESS THAN A FOOT. HOWEVER...IF THERE
IS MORE IN THE WAY OF MODEL CONSENSUS IN FUTURE MODEL RUNS...THE
POTENTIAL FOR THIS MUCH SNOW MAY RISE.


...NORTHERN PLAINS/GREAT LAKES/MIDWEST/NORTHEAST...

A NORTHERN STREAM SHORT WAVE DROPPING OUT OF WESTERN CANADA DURING
THE SECOND HALF OF DAY 1 SPINS UP LOW PRESSURE ON A LOW LEVEL
BAROCLINIC ZONE STRETCHED ACROSS THE CENTRAL PLAINS INTO THE
MIDWEST. THE SURFACE LOW DEEPENS AS IT FOLLOWS THE LOW LEVEL
BAROCLINIC ZONE ACROSS THE UPPER MIDWEST AND GREAT LAKES DURING
DAY 2...BEFORE REACHING ONTARIO BY THE END OF THE PERIOD. THERE IS
A FAIR AMOUNT OF MODEL SPREAD CONCERNING THE TRACK OF THE MID
LEVEL SHORT WAVE THROUGH DAY 2...SO FOR NOW 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...

ISENTROPIC LIFT AHEAD OF A SHORT WAVE AND COLD FRONT DROPPING OUT
OF WESTERN CANADA BECOMES THE FOCUS FOR SNOW ACROSS MUCH OF SD
INTO SOUTHWEST MN DURING THE SECOND HALF OF DAY 1. MODEL SOUNDINGS
SHOWED MOISTURE AND LIFT AHEAD OF THE SHORT WAVE IN THE DENDRITIC
GROWTH ZONE ACROSS WESTERN AND CENTRAL SD DURING THE 03/00Z TO
03/06Z TIME FRAME. THE COMBINATION OF LIFT AND MOISTURE ACROSS THE
FRONTAL BOUNDARY PRODUCES AN AXIS OF 2 TO 4 INCHES OF SNOWFALL
ACROSS OVER WESTERN AND CENTRAL SD...WITH LOCAL 4 TO 6 INCH
AMOUNTS WHERE THE BEST DENDRITIC GROWTH OCCURS.

DAY 2...

A SURFACE WAVE DEVELOPS ON THE FRONT ACROSS KS EARLY ON DAY 2. THE
WAVE THEN DEEPENS AS IT TRACKS ALONG THE FRONT THROUGH THE UPPER
MIDWEST AND SOUTHERN MI...BEFORE EXITING INTO ONTARIO. THE LOW
LEVEL THERMAL RIBBON IS EXPECTED TO EXTEND ACROSS CENTRAL AND
NORTHEAST IA...SOUTHERN WI AND SOUTHERN MI THROUGH 04/00Z. THERE
WAS SOME SPREAD ON THIS PLACEMENT...AS THE 00Z GFS WAS FURTHER
NORTH WITH THE LOW LEVEL WARM AIR INTO THE GREAT LAKES REGION.
ALONG THE RIBBON...MODEL SOUNDINGS SHOWED A PRONOUNCED WARM NOSE
BETWEEN 850 AND 800 MB...WITH A MAXIMUM TEMPERATURE CLOSE TO 3
DEGREES CELSIUS. THE SCENARIO SUGGESTS A STRIPE OF 0.10 TO 0.25
INCHES OF QPF EXTENDING ACROSS NORTHERN IL AND SOUTHERNMOST WI
INTO SOUTHWEST WI AND NORTHERNMOST IN...WITH LESSER AMOUNTS DOWN
THROUGH THE REMAINDER OF THE OH VALLEY.

NORTH OF THE BOUNDARY...MODEL SOUNDINGS SHOWED A COLUMN COLD
ENOUGH FOR MAINLY SNOW. HOWEVER...THE BEST WARM AIR ADVECTION
ENDS...THE COLUMN LOSES ICE IN THE DENDRITIC GROWTH ZONE...HINTING
AT A PERIOD OF LIGHT FREEZING RAIN/FREEZING DRIZZLE AFTER THE
HEAVIEST SNOW. THE BEST LIFT CROSSES THE REGION DURING THE FIST
HALF OF THE PERIOD ACROSS WI AND MI...WITH MOISTURE AND LIFT IN
THE DENDRITIC GROWTH ZONE FOR ABOUT 3 HOURS. THE ABOVE PRODUCES A
LARGE AREA OF 2 TO 4 INCHES OF SNOWFALL ACROSS EAST CENTRAL
MN...MUCH OF WI AND THE NORTHERN HALF OF MI. WHERE THE BEST
DENDRITIC GROWTH OCCURS...AN AREA OF 4 TO 8 INCHES OF SNOWFALL WAS
PLACED OVER NORTHEAST WI AND THE UP OF MI.

THE BEST LIFT ALONG THE ISENTROPIC SURFACE MOVES INTO NEW ENGLAND
DURING THE LAST PART OF DAY 2. COLD AIR WILL BE ON THE
RETREAT...AS THE STRONG WARM AIR ADVECTION OCCURS. THE BEST LIFT
OCCURS BETWEEN 04/00Z AND 04/06Z ACROSS UPDATE NY AND NORTHERN AND
CENTRAL NEW ENGLAND... AND THE LIFT AND MOISTURE IN THE WARM AIR
ADVECTION COMBINE TO PRODUCE A LARGE AREA OF 2 TO 4 INCHES OF
SNOWFALL. SOUTH OF THE SNOWFALL... AN AREA OF FREEZING RAIN WAS
PAINTED ACROSS THE SOUTHERN TIER OF NY STATE INTO CENTRAL NEW
ENGLAND...WHERE PRECIPITATION CHANGES PHASE FROM SNOW TO FREEZING
RAIN DURING THE BEST LIFT IN THE WARM AIR ADVECTION.


...ROCKIES/SOUTHWEST...

A CLOSED MID LEVEL LOW OFF THE SOUTHERN CA COAST SLOWLY OPENS UP
INTO A LONG WAVE TROUGH ON DAY 1 AS IT TRUNDLES ACROSS SOUTHERN CA
AND AZ DURING DAY 2. THE LOW TO MID LEVEL FLOW AHEAD OF THE LONG
WAVE TROUGH DRAWS MOISTURE NORTHEAST FROM THE PACIFIC INTO THE
ROCKIES AND SOUTHWEST DURING THE TWO DAY PERIOD. THE COMBINATION
OF LIFT WITH THE LONG WAVE TROUGH AND MOISTURE TRANSPORTED INTO
THE SYSTEM IS EXPECTED TO PRODUCE HEAVY SNOW OVER PORTIONS OF THE
ROCKIES AND THE HIGHER TERRAIN OF THE SOUTHWEST. THERE WAS DECENT
MODEL AGREEMENT WITH THE EVOLUTION OF THE CLOSED MID LEVEL SYSTEM
INTO A LONG WAVE TROUGH...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 STREAMS NORTHEAST FROM THE PACIFIC AHEAD OF THE CLOSED
LOW OVER SOUTHERN CA...AS IT TRANSITIONS INTO A SLOW MOVING LONG
WAVE TROUGH. THE MOISTURE COMBINES WITH LIFT FROM SHORT WAVES
EJECTED FROM CLOSED LOW TO PRODUCE SNOWFALL ACROSS PORTIONS OF
CA...AS WELL AS THE GREAT BASIN...SOUTHWEST AND SOUTHERN ROCKIES.
SNOW LEVELS EQUALIZE NEAR 6000 FEET ACROSS THIS ENTIRE
AREA...WHICH NECESSITATED THE INCLUSION OF SNOWFALL ACROSS THE
MOUNTAINS OF SOUTHERN CA. THE HIGHER OF NORTHERN AND CENTRAL AZ
WERE INCLUDED AS WELL...WITH LOCAL 8 TO 12 INCH SNOWFALL AMOUNTS
EXPECTED ON THE NORTH RIME OF THE GRAND CANYON.

THE COMBINATION OF SYNOPTIC SCALE LIFT AND MOISTURE IS AUGMENTED
BY UPSLOPE FLOW ACROSS THE GREAT BASIN AND SOUTHERN ROCKIES TO
PRODUCE HEAVY SNOWFALL. THIS COMBINATION PRODUCES A LONG AXIS OF 6
TO 10 INCHES OF SNOWFALL ACROSS THE WASATCH AND UNITAS RANGES IN
UT. THE UPSLOPE COMPONENT IS MUCH STRONGER OVER THE CENTRAL AND
SOUTHERN ROCKIES...RESULTING IN HIGHER QPF AND HIGHER SNOWFALL
AMOUNTS. SNOWFALL AMOUNTS BETWEEN 1 AND 2 FEET ARE EXPECTED ACROSS
THE ROCKIES OF NORTHERN CO...AS WELL AS THE SAN JUAN RANGE IN
SOUTHWEST CO. THESE AMOUNTS WERE SUPPORTED WELL BY OUTPUT FROM THE
LATEST ECMWF ENSEMBLE...WHICH HAD MEMBERS SHOWING 12+ INCHES OF
SNOWFALL IN THESE AREAS.

DAY 2...
THE LONG WAVE TROUGH CONTINUES TO TRUNDLE EASTWARD ACROSS THE
SOUTHWEST STATES ON DAY 2. HOWEVER...MUCH OF THE MOISTURE WITH THE
LONG WAVE TROUGH HAS BEEN SHUNTED EAST INTO THE PLAINS...LIMITING
SNOWFALL POTENTIAL OVER THE WASATCH AND CENTRAL AND SOUTHERN
ROCKIES. UPSLOPE FLOW ALONG A QUASI STATIONARY FRONT ACROSS THE
CENTRAL AND SOUTHERN ROCKIES ADDS SOME MOISTURE AND
LIFT...RESULTING IN AN AREA OF 4 TO 8 INCHES OVER THE CO ROCKIES.
LESSER AMOUNTS...CLOSER TO 2 TO 4 INCHES...ARE EXPECTED ACROSS THE
WASATCH RANGE IN UT.


HAYES


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