Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 222028
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
327 PM EST THU JAN 22 2015

VALID 00Z FRI JAN 23 2015 - 00Z MON JAN 26 2015

DAYS 1 TO 3...

...CENTRAL APPALACHIANS/MID-ATLANTIC/NEW ENGLAND...

A LOCALLY SIGNIFICANT WINTER STORM IS EXPECTED TO IMPACT AN AREA
FROM THE CENTRAL APPALACHIANS THROUGH THE NORTHERN MID-ATLANTIC
AND INTO NEW ENGLAND THIS WEEKEND.

AN UPPER TROUGH CURRENTLY OVER THE LOWER MS VALLEY WILL ADVANCE
EAST INTO THE TN VALLEY ON FRIDAY BEFORE THEN CROSSING INTO THE
MID-ATLANTIC ON SATURDAY. ALL THE WHILE THE ENERGY WILL BE
ATTAINING AN INCREASINGLY NEUTRAL AND NEGATIVE TILT. ON
SUNDAY...THE NEGATIVELY TILTED TROUGH WILL MOVE JUST OFFSHORE OF
SOUTHERN NEW ENGLAND AND LIFT RAPIDLY TOWARD THE CANADIAN
MARITIMES WHILE CONTINUING TO DEEPEN. THE AFOREMENTIONED ENERGY
WILL FOSTER CYCLOGENESIS OVER THE NORTHERN GULF OF MEXICO WHICH
WILL THEN LIFT NORTHEAST JUST OFFSHORE THE MID-ATLANTIC AND NEW
ENGLAND COASTS WHILE STEADILY DEEPENING. THE STRONGEST PERIOD OF
INTENSIFICATION SHOULD BE WHEN THE LOW MAKES ITS CLOSEST APPROACH
TO NEW ENGLAND LATER SATURDAY AND SUNDAY.

THE SNOWFALL POTENTIAL AHEAD OF THIS STORM SYSTEM IS EXPECTED TO
BE PROBLEMATIC IN PARTICULAR FOR THE CENTRAL APPALACHIANS AND
MID-ATLANTIC FRIDAY NIGHT AND SATURDAY AS THERE IS EXPECTED TO BE
A RELATIVE LACK OF COLD AIR...ESPECIALLY SINCE HIGH PRESSURE WHICH
WILL BE OVER THE REGION ON FRIDAY WILL BE QUICKLY ERODING AND
MOVING OFFSHORE. THE CONSENSUS OF THE 12Z MODELS...INCLUDING THE
NAM AND GFS...TRENDED WARMER WITH THEIR THERMAL PROFILES OVER THIS
REGION...AND A LITTLE WEAKER WITH THE ENERGY ALOFT. WEAKER
DYNAMICS ALOFT WITH THE TROUGH SUGGESTS SOMEWHAT LOWER
PRECIPITATION TOTALS BUT ALSO LESS DYNAMIC COOLING THAT COULD
OTHERWISE HELP SERVE TO PROMOTE A GREATER RISK FOR ACCUMULATING
SNOW IN LIEU OF THERE BEING A LACK OF COLD HIGH PRESSURE OVER THE
AREA. NEVERTHELESS...AND DESPITE VERY MARGINAL THERMAL
PROFILES...THERE IS EXPECTED TO BE JUST ENOUGH COLD AIR THROUGH
THE COLUMN FOR A PERIOD OF SNOW AND SLEET ACROSS AREAS OF THE
CENTRAL APPALACHIANS AND THE ADJACENT FOOTHILLS...WITH
PRECIPITATION AT LEAST PERIODICALLY CHANGING BACK AND FORTH
BETWEEN FROZEN AND LIQUID AS DICTATED BY THE DEGREE OF DYNAMIC
COLUMN COOLING THAT OCCURS THROUGH THE EVENT. THIS WOULD INCLUDE
CENTRAL AND EASTERN WV...WESTERN VA...NORTHERN AND WESTERN MD AND
SOUTHERN AND EASTERN PA. A FEW INCHES OF ACCUMULATING SNOW IS
POSSIBLE AT LEAST LOCALLY WHERE STRONGER DYNAMICS ALOFT/COOLING
PERSISTS...AND SO A LOW RISK OF 4 INCH SNOWFALL AMOUNTS IS
GENERALLY DEPICTED. THERE IS ALSO A MARGINAL THREAT FOR FREEZING
RAIN AND GENERALLY LIGHT ICING FOR THE SAME AREAS AS THE GUIDANCE
SUGGESTS ENOUGH WARMING ALOFT FOR PERIODS OF LIQUID PRECIP...BUT
COINCIDING WITH BOUNDARY LAYER TEMPERATURES NEAR OR JUST BELOW
FREEZING. THE BEST POTENTIAL MORE CONCENTRATED ICING CURRENTLY
APPEARS TO BE OVER PORTIONS OF FAR EASTERN WV AND WESTERN VA
INVOLVING SOME OF THE HIGHER ELEVATIONS OF THE CENTRAL
APPALACHIANS.

FARTHER NORTHEAST UP ALONG THE I-95 INVOLVING NY AND SOUTHERN NEW
ENGLAND...COLD AIR WILL BE MODESTLY ENTRENCHED AS PRECIPITATION
ARRIVES...AND SNOW IS EXPECTED INITIALLY AS THE PRECIPITATION
SHIELD OVERSPREADS THE AREA. COLD AIR ALOFT IS EXPECTED TO BE
ERODED ENOUGH THAT MOST AREAS ALONG AND EAST OF I-95 AT LEAST MIX
WITH OR CHANGEOVER TO A PERIOD OF SLEET AND RAIN....AND THEN BACK
TO SNOW AS THE REGION GETS INTO THE STORMS DEVELOPING/INTENSIFYING
DEFORMATION ZONE. A LOW TO MODERATE RISK OF 4 INCH SNOWFALL
AMOUNTS IS DEPICTED. THE THREAT OF FREEZING RAIN/LIGHT ICING AGAIN
IS EXPECTED TO BE IN PLACE MAINLY FOR EARLY SATURDAY AS THE
BOUNDARY LAYER TEMPERATURES WILL BE NEAR OR SLIGHTLY BELOW
FREEZING. THE MAIN FOCUS FOR ANY ICING WILL BE GENERALLY WEST OF
I-95 AND INTO THE ADJACENT FOOTHILLS. THE AFOREMENTIONED
DEFORMATION ZONE THOUGH IS EXPECTED TO DRIVE A MORE STRONGLY
DEFINED THREAT OF HEAVY SNOW FOR AREAS OF INTERIOR SOUTHERN NEW
ENGLAND NORTHEAST INTO EASTERN NEW ENGLAND LATER SATURDAY THROUGH
SUNDAY. THIS WILL INCLUDE AREAS OF NORTHERN CT...CENTRAL/NORTHEAST
MA...SOUTHEAST NH AND ESPECIALLY ACROSS EASTERN ME. HEAVY BANDED
SNOWFALL IS EXPECTED THROUGH HERE AS STRENGTHENING FRONTOGENETIC
FORCING...INCREASING ATLANTIC MOISTURE TRANSPORT AND STRONG JET
DYNAMICS ALOFT COME TOGETHER OVER THIS REGION. A LOW TO MODERATE
RISK OF 8 INCH SNOWFALL AMOUNTS IS DEPICTED HERE...WITH SOME
POTENTIAL LOCALLY FOR AMOUNTS REACHING 1 FOOT.


...UPPER MIDWEST TO THE UPPER OHIO VALLEY...

A NEW TROUGH AND ASSOCIATED AREA OF LOW PRESSURE IS EXPECTED TO
DIG SOUTHEAST FROM THE UPPER MIDWEST SATURDAY NIGHT TO THE UPPER
OH VALLEY LATE SUNDAY. THE 12Z MODELS SUGGEST STRENGTHENING WARM
ADVECTION AND JET DYNAMICS ALOFT WILL FAVOR A STREAK OF LIGHT TO
MODERATE SNOW ACROSS ALONG AND NORTH OF THE SURFACE LOW TRACK
THROUGH THE PERIOD. MOISTURE TRANSPORT WILL GENERALLY BE LACKING
FOR THIS SYSTEM...BUT SUFFICIENT FORCING THROUGH THE COLUMN
COUPLED WITH A DEEPER PROFILE OF COLD AIR SHOULD RESULT IN
RELATIVELY HIGHER SNOW-TO-LIQUID RATIOS AND THUS LOCALLY HEAVY
SNOWFALL TOTALS. AS A RESULT...A LOW TO MODERATE RISK OF 4 INCH
SNOWFALL AMOUNTS IS DEPICTED AT THIS TIME.


...NORTHERN ROCKIES...

SOME MOISTURE AND ENERGY ALOFT TRAVERSING THE MEAN RIDGE AXIS OVER
THE WESTERN U.S. WILL DROP DOWN OVER PORTIONS OF THE NORTHERN
ROCKIES SATURDAY AND SUNDAY. THIS WILL FOSTER SOME SNOW SHOWERS
FOR MAINLY THE HIGHER TERRAIN OF THE BITTERROOTS. A FEW INCHES OF
SNOW IS EXPECTED LOCALLY...AND THUS A LOW RISK OF 4 INCH SNOWFALL
AMOUNTS IS DEPICTED.

ORRISON

$$




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