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 15 16 17 18 19 20 21 22 23 24 25 26 27
000
FOUS11 KWBC 030904
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 AM EST TUE MAR 03 2015

VALID 12Z TUE MAR 03 2015 - 12Z FRI MAR 06 2015


DAYS 1 THROUGH 3...


...GREAT LAKES/MIDWEST/NORTHEAST...

STRONG WARM AIR ADVECTION AHEAD OF A NORTHERN STREAM SHORT WAVE
CROSSING THE NORTHERN PLAINS PRODUCES LIFT AND MOISTURE ACROSS THE
GREAT LAKES AND MIDWEST DURING THE FIRST HALF OF DAY 1...THEN
RACES EASTWARD AND AFFECTS NY STATE AND NEW ENGLAND DURING THE
SECOND HALF OF THE PERIOD. WHILE THERE ARE SOME TIMING DIFFERENCES
CONCERNING JUST HOW QUICKLY THE WARM AIR ADVECTION PRECIPITATION
AFFECTS NEW ENGLAND...BLENDING THE 00Z GFS AND 12Z ECMWF MITIGATES
SOME OF THE DIFFERENCES...AND THESE MODELS WERE USED AS A BASIS
FOR THE THERMAL PORTION OF THE FORECAST. THE QPF PORTION OF THE
FORECAST WAS BASED ON THE MOST RECENT WPC QPF.

STRONG WARM AIR ADVECTION (WITH 35 TO 55 KNOT SOUTHWEST WINDS
RIDING UP THE 290 K ISENTROPIC SURFACE) TRANSPORTS MOISTURE FROM
THE WESTERN GULF OF MEXICO UP AND OVER COLD AIR IN PLACE ACROSS
THE MIDWEST AND GREAT LAKES DURING DAY 1. THE BEST LIFT WITH THE
WARM AIR ADVECTION AND LIFT AHEAD OF A NORTHERN STREAM SHORT WAVE
CROSSES THE GREAT LAKES AND MIDWEST BEFORE ABOUT 03/18Z. A LOW
LEVEL THERMAL RIBBON STRETCHING ACROSS NORTHEAST IA THROUGH
SOUTHERNMOST WI AND SOUTHERN MI MARKS THE TRANSITION ZONE FROM
SNOW TO SLEET AND FREEZING RAIN. NORTH OF THE LINE...THE COLUMN
REMAINS COLD ENOUGH FOR SNOW ACROSS NORTHEAST WI...AND NORTHERN
MI...AND THE LIFT AND MOISTURE SUPPORT A LARGE AREA OF 3 TO 6
INCHES OF SNOWFALL ACROSS THIS AREA.

FURTHER SOUTH...ACROSS NORTHERN IL/NORTHERN IN AND NORTHWEST
OH...STRONG WARM AIR ADVECTION IN THE LOWER LEVELS POKES A WARM
NOSE IN ABOVE THE SHALLOW COLD AIR IN THE 850 TO 800 MB LEVEL. THE
WARM AIR CUTS OFF THE ABILITY OF THE COLUMN TO SUPPORT SNOWFALL.
THE ABOVE RESULTS IN A STRIPE OF 0.10 TO 0.20 INCHES OF ICE ACROSS
NORTHEAST IL...NORTHERN IN AND A SMALL PORTION OF NORTHWEST OH. AS
THE WARM AIR ADVECTION ENDS...LIGHT FREEZING RAIN/FREEZING DRIZZLE
IS POSSIBLE.

AS THE WARM AIR ADVECTION/LIFT WITH THE SHORT WAVE MOVES EAST...IT
CROSSES NY STATE AND NEW ENGLAND BETWEEN 03/18Z AND 04/06Z. THE
BEST LIFT OCCURS ACROSS NY STATE AND WESTERN NEW NEW
ENGLAND...BEFORE IS TRACKS INTO QUEBEC. MODEL SOUNDINGS HERE
SHOWED A 3 HOUR WINDOW OF MOISTURE AND LIFT IN THE DENDRITIC
GROWTH ACROSS CENTRAL AND NORTHERN NEW YORK STATE...SUPPORT A
LARGE AREA OF 4 TO 6 INCHES OF SNOWFALL. FURTHER SOUTH...THE WARM
AIR ADVECTION FLOODS THE COLUMN...ROBBING OF ITS ABILITY TO
SUPPORT SNOWFALL ACROSS THE SOUTHERN TIER OF NY STATE...NORTHERN
NJ...THE LOWER HUDSON VALLEY OF NY AND SOUTHERN NEW ENGLAND. IN
THESE AREAS...1 TO 4 INCHES OF SNOWFALL IS FOLLOWED BY LOCAL 0.10
INCH ICE ACCUMULATION.


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

SHORT WAVE ENERGY RIDING THROUGH A FAST SOUTHERN STREAM TRANSPORTS
GULF OF MEXICO MOISTURE UP ALONG A FRONTAL BOUNDARY EXTENDING FROM
THE SOUTHERN PLAINS THROUGH THE MID ATLANTIC STATES. A NORTHERN
STREAM SHORT WAVE PUSHES COLD AIR SOUTH ACROSS THE PLAINS AND
MIDWEST INTO THE SOUTHERN PLAINS...LOWER AND MID VALLEY...OH
VALLEY AND MID ATLANTIC STATES DURING THE NEXT THREE DAYS. THERE
ARE STILL FAIRLY SIGNIFICANT SPREAD IN THE 00Z MODEL SOLUTIONS
CONCERNING HOW QUICKLY THE COLD AIR RUSHES IN BEHIND THE
FRONT...WHICH DICTATES PRECIPITATION TYPE CHANGE AND SNOWFALL
AMOUNTS...ESPECIALLY FROM THE OH VALLEY EASTWARD ACROSS THE MID
ATLANTIC AND SOUTHERN NEW ENGLAND. THE 00Z NAM (AND THE 21Z SREF
MEAN) REMAIN THE SLOWEST AND MOST AMPLIFIED SOLUTIONS WITH RESPECT
TO THE LONG WAVE TROUGH DEVELOPING ACROSS THE NORTHERN
PLAINS...SLOWING THE ADVANCE OF THE COLD AIR INTO MID MS
VALLEY...OH VALLEY AND MID ATLANTIC STATES. THE 00Z GFS/12Z ECMWF
OFFER A MORE UNIFIED SOLUTION CONCERNING TIMING OF THE COLD AIR
(AND PREDOMINANT PRECIPITATION TYPES) IN THESE AREAS...SO THESE
MODELS WERE USED FOR THE THERMAL PORTION OF THE FORECAST. THE QPF
PORTION OF THE FORECAST WAS BASED ON THE MOST RECENT WPC QPF.

DAY 1...
SHALLOW PLUNGING SOUTH BEHIND A COLD FRONT ACROSS THE SOUTHERN
PLAINS INTO THE MID MS VALLEY DROPS BOUNDARY LAYER TEMPERATURES
BELOW FREEZING BY THE END OF DAY 1. MODEL SOUNDINGS SHOWED THAT
THE MID LEVELS REMAIN TOO WARM FOR SNOWFLAKE PRODUCTION BEHIND THE
FRONT (WITH NO ICE IN THE CLOUD IN THE DENDRITIC GROWTH
ZONE)...PRODUCING A FREEZING RAIN PROFILE. MOISTURE IS FAIRLY
LIMITED DURING DAY 1 ACROSS THIS AREA...SO ICING AMOUNTS SHOULD
AVERAGE LESS THAN 0.05 INCHES.

FURTHER EAST...IN SITU COLD AIR OVER THE MID ATLANTIC BECOMES
TOUGH TO SCOUR...EVEN AS SURFACE HIGH PRESSURE MOVES TO THE EAST
OF THE REGION. THE 00Z NAM WAS THE MOST STUBBORN WITH THE LOW
LEVEL COLD AIR...AS MOISTURE FUNNELED FROM THE OH VALLEY OVERRUNS
IT. THE BEST MOISTURE AND LIFT CROSS THE NORTHERN MID ATLANTIC
DURING AFTERNOON AND EARLY EVENING HOURS. THE TIME OF DAY (AND
INCREASING INSOLATION FROM THE EARLY MARCH SUN) MAY TEND TO
MITIGATE PROBLEMS ACROSS PORTIONS OF CENTRAL AND SOUTHEAST
VA...BUT THE COLD AIR REMAINS LOCKED IN LONGER EAST OF THE
APPALACHIANS IN WV/VA INTO PORTION OF CENTRAL AND EASTERN PA...AS
WELL AS NORTHERN NJ. IN THESE LOCATIONS...ICE AMOUNTS BETWEEN 0.01
AND 0.10 INCHES ARE EXPECTED...WITH THE HIGHEST AMOUNTS OVER
CENTRAL PA.

DAY 2...
MOISTURE STREAMS NORTHEAST ALONG THE COLD FRONT EXTENDING FROM THE
SOUTHERN PLAINS THROUGH THE OH VALLEY INTO THE INTERIOR PORTIONS
OF THE MID ATLANTIC DURING DAY 2. AT THE SAME TIME...FALLING MID
LEVEL HEIGHTS ACROSS THE OH VALLEY INTO THE MID ATLANTIC ALLOW THE
PRECIPITATION PHASE CHANGE TO BEGIN FROM NORTH TO SOUTH. AS
MENTIONED EARLIER...THERE IS MODEL SPREAD CONCERNING HOW FAST THIS
OCCURS...WITH THE 00Z NAM/21Z SREF MEAN SHOWING THE SLOWEST
TRANSITION. THIS TREND HAS BEEN THE CASE FOR THE PAST FEW
CYCLES...AND THE TREND WOULD APPEAR TO MAKE THESE SOLUTIONS LOW
PROBABILITY EVENTS. A BLEND OF THE 00Z GFS/12Z ECMWF ALLOWS THE
TRANSITION TO OCCUR SOONER...AND 00Z GFS MODEL SOUNDINGS SHOWS
DEEP MOISTURE AND LIFT IN THE DENDRITIC GROWTH ZONE FROM SOUTHEAST
MO ACROSS KY/NORTHWEST TN INTO SOUTHERN OH...NORTHERN WV AND
SOUTHWEST PA. SNOWFALL AMOUNTS BETWEEN 6 AND 12 INCHES WERE PLACED
ALONG THIS AXIS. THESE AMOUNTS WERE WELL SUPPORTED BY MEMBERS OF
THE LATEST ECMWF ENSEMBLE OUTPUT...WITH NORTHERN KY AND SOUTHERN
OH IN THE CROSS HAIRS FOR 12+ INCH AMOUNTS.

THE SOUTHERN EDGE OF THE SNOWFALL AMOUNTS WERE TOUGHER TO
DETERMINE...AS EVEN THE COLDER GFS/ECMWF MODEL SOUNDINGS SHOWED A
TRANSITION ZONE WHICH FEATURED AN INCH OR TWO OF SLEET...EXTENDING
FROM SOUTH CENTRAL AR INTO NORTHERN MS AND SOUTHWEST TN. SOUTH OF
THIS LINE...THE SHALLOW COLD AIR RUSHES SOUTHWARD...WITH MOST 00Z
MODEL SUITE MEMBERS SHOWING BOUNDARY LAYER TEMPERATURES DROPPING
BELOW FREEZING FROM CENTRAL TX ACROSS MUCH OF LA AND MS.
HOWEVER...WARM AIR REMAINS IN THE MID LEVELS...AS THE FLOW REMAINS
WEST SOUTHWEST. 00Z GFS MODEL SOUNDINGS SHOWED WARM AIR BETWEEN
750 AND 700 MB WITH PEAK TEMPERATURES NEAR 5 DEGREES
CELSIUS...SUPPORTING A FREEZING RAIN SCENARIO. THERE WAS A MULTI
MODEL SIGNAL FOR 0.10 TO 0.25 INCHES OF ICE EXTENDING FROM
SOUTHERN AR/NORTHERNMOST LA THROUGH WESTERN TN...WITH LOCAL 0.25
INCH AMOUNTS POSSIBLE ACROSS SOUTH CENTRAL AR.

DAY 3...
BY DAY 3...THE PLACEMENT DIFFERENCES WITH THE FRONT ARE MOST
IMPORTANT ACROSS THE MID ATLANTIC. THE 00Z GFS REMAINS THE MOST
AGGRESSIVE DRIVING THE COLD AIR SOUTH THROUGH THE DC METRO AIR
INTO SOUTHERN MD...WHILE THE 12Z ECMWF WAS NOT QUITE AS BULLISH.
THE BEST LIFT/MOISTURE ALONG THE FRONT IS ASSOCIATED WITH A WEAK
SURFACE WAVE TRACKING ALONG IT FROM NC THROUGH THE SOUTHERN
DELMARVA. NORTH OF THAT LINE...MODEL SOUNDINGS SHOWED COLD AIR
DEEP ENOUGH IN THE COLD FOR SNOW STRETCHING FROM NORTHERN AND
CENTRAL VA THROUGH EASTERN MD...SOUTHEAST PA...CENTRAL AND
SOUTHERN NJ...LONG ISLAND NY INTO SOUTHERN NEW ENGLAND. THERE ARE
SIGNALS FOR LIFT/MOISTURE IN THE DENDRITIC GROWTH ZONE EXTENDING
FROM SOUTHERN MD THROUGH DE...CENTRAL AND SOUTHERN NJ INTO EASTERN
LI. THIS COULD MITIGATE INITIALLY RELATIVELY LOW SNOW TO LIQUID
RATIO VALUES (IN A TRANSITION ZONE) TO THOSE CLOSER TO
13:1....SUPPORTING AN AREA OF 4 TO 6 INCHES OF SNOWFALL IN THE
ABOVEMENTIONED AREAS.

FURTHER SOUTH...THE COLD AIR DRIVES INTO PORTIONS OF SOUTHEAST VA
AND NORTHEAST NC BEFORE THE MID LEVELS CAN COOL OFF...RAISING THE
POTENTIAL FOR ICING. THE GFS/ECMWF POINT TO THE POTENTIAL FOR 0.10
TO 0.25 INCHES OF ICE IN THIS AREA...BUT GIVEN SOME UNCERTAINTY IN
THE LOW LEVEL THERMAL FIELDS...THESE AMOUNTS COULD END UP BEING
HIGH.


...ROCKIES...

A STRONG CLOSED MID LEVEL LOW OFF THE SOUTHERN CA COAST EARLY ON
DAY 1 OPENS UP AND TRUNDLES ACROSS THE SOUTHWEST STATES DURING DAY
1. AHEAD OF THE LONG WAVE TROUGH...MOISTURE IS TRANSPORTED FROM
THE PACIFIC UP ACROSS THE ROCKIES. THE COMBINATION OF MOISTURE AND
LIFT PRODUCES SNOWFALL ACROSS THE ROCKIES DURING THIS TIME. WHILE
THERE WERE SOME TIMING DIFFERENCES CONCERNING HOW QUICKLY TO OPEN
UP THE CLOSED SYSTEM AND MOVE IT EASTWARD...THERE WAS ENOUGH
AGREEMENT TO USE THE 00Z GFS/12Z ECMWF AS THE BASIS FOR THE
THERMAL PORTION OF THE FORECAST. THE QPF PORTION OF THE FORECAST
WAS BASED ON THE MOST RECENT WPC QPF.

AS THE CLOSED MID LEVEL SYSTEM OPENS UP AND MOVES EAST...IT SHUNTS
THE PACIFIC MOISTURE SOURCE ACROSS THE ROCKIES TO THE EAST AS
WELL. THE LIFT ASSOCIATED WITH THE OPENING MID LEVEL SYSTEM (WHICH
INCLUDES STEEPENING MID LEVEL LAPSE RATES)...COMBINED WITH THE
MOISTURE FROM THE PACIFIC (AS WELL AS LEFTOVER MOISTURE FROM
UPSLOPE FLOW) PRODUCES AN AREA OF 5 TO 10 INCHES OF SNOW ACROSS
THE CO ROCKIES. FURTHER WEST...WHERE THE MOISTURE IS NOT AS
ROBUST...SYNOPTIC SCALE LIFT AND UPSLOPE FLOW PRODUCE 3 TO 6
INCHES OF SNOW OVER THE WASATCH AND UNITAS MOUNTAINS IN UT.


HAYES

$$





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