429  
FOUS11 KWBC 160857  
QPFHSD  
 
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
356 AM EST TUE JAN 16 2018  
 
VALID 12Z TUE JAN 16 2018 - 12Z FRI JAN 19 2018  
 
DAY 1-3...  
 
***SOUTHERN TEXAS TO THE DEEP SOUTH***  
 
STRONG COLD AIR ADVECTION BEHIND AN ARCTIC FRONT SETTLING  
SOUTHEASTWARD ACROSS THE GULF COAST AND THE DEEP SOUTH WILL CREATE  
AN ENVIRONMENT FAVORABLE FOR MAINLY LIGHT WINTRY PRECIPITATION.  
RIGHT ENTRANCE JET DYNAMICS ALOFT COUPLED WITH A POSITIVELY TILTED  
LONGWAVE TROUGH IN THE PRESENCE OF MODEST LEVELS OF MOISTURE WILL  
PROVIDE ENOUGH LIFT TO SUPPORT A BAND OF ONE TO LOCALLY TWO INCHES  
OF SNOW FROM EAST CENTRAL TEXAS TO CENTRAL/NORTHERN MISSISSIPPI,  
AND ALSO PARTS OF ALABAMA AND GEORGIA. ACCUMULATIONS WILL BE  
LIMITED BY THE RELATIVELY SHORT DURATION OF THE EVENT. A  
CONSIDERABLE PORTION OF THE ONGOING EVENT WILL HAVE OCCURRED  
BEFORE 12Z TUESDAY.  
 
FARTHER TO THE SOUTH ACROSS SOUTHERN TEXAS AND CLOSER TO THE  
CENTRAL GULF COAST, THE SUB-FREEZING LAYER WILL BE MORE SHALLOW  
WITH THE 850MB TEMPERATURES SLOWER TO COOL. THIS IS EXPECTED TO  
RESULT IN PERIODS OF LIGHT FREEZING RAIN AND SOME SLEET. AS THE  
BEST LIFT IS EXPECTED TO REMAIN PRIMARILY NORTH OF THIS AREA, ICE  
ACCUMULATIONS ARE EXPECTED TO REMAIN GENERALLY BELOW A TENTH OF AN  
INCH, ALTHOUGH LOCALIZED AMOUNTS EXCEEDING A TENTH OF AN INCH ARE  
POSSIBLE BY THE TIME THE EVENT IS OVER LATER TUESDAY.  
 
***MID ATLANTIC REGION TO NEW ENGLAND***  
 
RELATIVELY LIGHT WARM ADVECTION SNOW IS LIKELY BEGINNING TUESDAY  
MORNING ACROSS THE CENTRAL AND SOUTHERN APPALACHIANS AHEAD OF A  
SURFACE LOW TRACKING ACROSS THE GREAT LAKES REGION. THE POTENTIAL  
FOR MODERATE SNOW INCREASES BY TUESDAY NIGHT AS A NEW COASTAL LOW  
DEVELOPS OFF THE MID-ATLANTIC COAST. THE BEST AREA OF DYNAMIC  
FORCING IS EXPECTED FROM NORTHEAST PENNSYLVANIA TO EASTERN NEW  
ENGLAND THROUGH EARLY WEDNESDAY, WHERE THE BEST POTENTIAL FOR 4 TO  
8 INCHES OF SNOW EXISTS. THE BEST LIFT IS REALIZED LATE TUESDAY  
NIGHT AND INTO WEDNESDAY MORNING ACROSS SOUTHEASTERN NEW ENGLAND,  
AND THIS IS WHEN THE SNOWFALL RATES SHOULD BE THE HEAVIEST. SNOW  
SHOULD COME TO AN END BY EARLY THURSDAY MORNING FOR EASTERN MAINE  
AS THE SURFACE LOW DEPARTS AND DRY AIR ADVECTION ENSUES.  
 
FARTHER TO THE SOUTH OVER PARTS OF VIRGINIA AND NORTH CAROLINA,  
MODELS CONTINUE TO INDICATE THE POTENTIAL FOR ANOTHER WEAK WAVE OF  
LOW PRESSURE TO DEVELOP NEAR THE OUTER BANKS BY WEDNESDAY MORNING  
WITH AN UPPER LEVEL JET STREAK ALOFT. ANOTHER ENHANCED AREA OF  
SNOWFALL AMOUNTS IS POSSIBLE FROM CENTRAL NORTH CAROLINA TO  
EASTERN VIRGINIA TO THE NORTHWEST OF THIS SURFACE WAVE, WHERE 1 TO  
3 INCHES ARE POSSIBLE.  
 
***WESTERN U.S.***  
 
SNOW COVERAGE OVER THE NORTHWESTERN QUADRANT OF THE NATION IS  
EXPECTED TO INCREASE BY MIDWEEK AND ESPECIALLY INTO THURSDAY OWING  
TO STRONG HEIGHT FALLS ALOFT AND MULTIPLE PACIFIC SHORTWAVES  
APPROACHING THE COAST. THE FIRST SHORTWAVE SHOULD REACH THE  
NORTHWEST COAST EARLY TUESDAY, AND DECREASING SNOW LEVELS SHOULD  
SUPPORT LIGHT TO MODERATE SNOW OVER THE HIGHER ELEVATIONS OF THE  
WASHINGTON CASCADES AND THE HIGHEST MOUNTAINS OF NORTHERN OREGON.  
THE SECOND AND MUCH LARGER SHORTWAVE AND ASSOCIATED COLD FRONT  
BEGIN AFFECTING THE PACIFIC NORTHWEST ON WEDNESDAY, AND THEN IT  
WILL WORK ITS WAY INLAND ACROSS THE INTERMOUNTAIN WEST ON  
THURSDAY. THE WIDESPREAD ASCENT FROM THIS DEEP TROUGH AND COLD  
FRONT IS EXPECTED TO RESULT IN HEAVY SNOW FROM THE CASCADES TO THE  
SIERRA NEVADA, WITH SNOWFALL TOTALS APPROACHING A FOOT IN SOME  
CASES BY THURSDAY NIGHT. SIGNIFICANT SNOW ACCUMULATIONS IN EXCESS  
OF SIX INCHES ARE EXPECTED ACROSS THE HIGHER TERRAIN OF CENTRAL  
AND NORTHERN IDAHO, AND WESTERN MONTANA, WITH SNOW BEGINNING TO  
FALL OVER WESTERN WYOMING BY THE END OF THE FORECAST PERIOD  
THURSDAY NIGHT.  
 
THE PROBABILITY OF SIGNIFICANT ICING (0.25 INCH OR MORE) IS LESS  
THAN 10 PERCENT.  
 
D. HAMRICK  
 

 
 
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