393  
FXUS01 KWBC 070754  
PMDSPD  
 
SHORT RANGE FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
253 AM EST SUN JAN 07 2018  
 
VALID 12Z SUN JAN 07 2018 - 12Z TUE JAN 09 2018  
 
...HEAVY PRECIPITATION EXPECTED TO IMPACT MUCH OF CALIFORNIA ON  
MONDAY...  
 
...ICE ACCUMULATIONS ARE LIKELY AS FREEZING RAIN SPREADS FROM THE  
MISSOURI VALLEY THROUGH THE OHIO/TENNESSEE VALLEYS AND INTO THE  
MID-ATLANTIC...  
 
...BITTER COLD REMAINS OVER THE EAST COAST ON SUNDAY WITH  
POTENTIAL FOR MORE RECORDS...  
 
A LARGE PATTERN SHIFT IS UNDERWAY AS THE COUNTRY WILL MOVE TOWARD  
A MORE PACIFIC DOMINANT FLOW REGIME. AMPLIFICATION IN THE FLOW  
ACROSS THE PACIFIC SHOULD USHER IN A VERY IMPRESSIVE UPPER LOW  
TOWARD THE CENTRAL CALIFORNIA COAST BY LATE MONDAY. IN ADVANCE OF  
THIS SYSTEM, ABUNDANT SUBTROPICAL MOISTURE SHOULD STREAM  
NORTHEASTWARD TOWARD THE COAST WITH INCREASING ONSHORE FLOW  
EXPECTED. AS USUAL, LOCAL OROGRAPHICS WILL PLAY A KEY ROLE IN  
FOCUSING HEAVIER PRECIPITATION AMOUNTS WHICH INCLUDES THE COASTAL  
RANGES EXTENDING FROM NORTH OF LOS ANGELES UP INTO NORTHERN  
CALIFORNIA. ADDITIONALLY, A SEPARATE AXIS OF HEAVY RAIN AND SNOW  
WILL BE LIKELY ACROSS THE SIERRA NEVADA RANGE WITH UP TO A FOOT OF  
SNOW POSSIBLE THROUGH TUESDAY MORNING. AMONG THE MAJOR CITY HUBS,  
THE SAN FRANCISCO BAY AREA COULD SEE A BRUNT OF THE HEAVY RAINFALL  
WITH OVER 2 INCHES POSSIBLE DURING THE PERIOD. OVERALL, MUDSLIDES  
AND OTHER ASSOCIATED HYDROLOGIC ISSUES WILL BE LIKELY ANYWHERE  
ACROSS THE STATE WHERE BURN SCARS EXIST FROM THE ACTIVE FIRE  
SEASON IN LATE 2017. WHILE THE RAIN IS WELCOME AFTER A SLOW START  
TO THE SEASON, SUCH HYDROLOGIC CONCERNS WILL ALSO NEED TO BE  
MONITORED AS WELL.  
 
A SHARPENING UPPER TROUGH PUSHING THROUGH THE SOUTHERN PLAINS ON  
SUNDAY EVENING WILL GIVE WAY TO A FORMING CLOSED LOW WHICH SPINS  
THROUGH THE CENTRAL GULF COAST THE FOLLOWING MORNING. STRONG  
VERTICAL MOTIONS UNDERNEATH THIS CYCLONIC CIRCULATION WILL SPREAD  
MODERATE RAINFALL INTO THE OZARKS. MEANWHILE, HEAVIER AMOUNTS ARE  
LIKELY ACROSS SOUTHERN LOUISIANA/MISSISSIPPI WHERE STRONG  
LOW-LEVEL CONVERGENCE SHOULD BECOME ESTABLISHED ALONG A MEANDERING  
WARM FRONT. ALONG THE NORTHERN EXTENT OF THE PRECIPITATION SHIELD,  
RESIDUAL LOW-LEVEL ARCTIC AIR WHICH HAS NOT BEEN SCOURED OUT MAY  
LEAD TO SOME FREEZING RAIN ISSUES. WHILE OVERALL PRECIPITATION  
AMOUNTS WILL BE ON THE LIGHT SIDE FROM THE MISSOURI VALLEY  
EASTWARD INTO THE OHIO/TENNESSEE VALLEYS AND MID-ATLANTIC REGION,  
ANY ACCUMULATIONS OF ICE COULD LEAD TO SOME HAZARDOUS ROAD  
CONDITIONS. GIVEN HOW LONG MUCH OF THIS REGION WAS ENTRENCHED IN  
ARCTIC AIR, IT MAY TAKE LONGER THAN EXPECTED TO WARM THE SURFACE  
TO CHANGE PRECIPITATION OVER TO RAIN.  
 
EXCEPT FOR THE FRIGID WEATHER EXPECTED ALONG THE EAST COAST ON  
SUNDAY, MUCH OF THE COUNTRY WILL BE ON THE MILDER SIDE GIVEN THE  
DOMINANCE OF PACIFIC AIR MASSES. WITH AN ARCTIC RIDGE OF HIGH  
PRESSURE IN PLACE EARLY THIS MORNING OVER THE NORTHEASTERN U.S.,  
OVERNIGHT READINGS MAY DIP BELOW 0 DEGREES FROM THE UPPER  
MID-ATLANTIC NORTHWARD AS WELL AS INTO THE CENTRAL APPALACHIANS,  
OHIO VALLEY, AND LOWER GREAT LAKES. WHILE MANY LOCATIONS HAVE SEEN  
WINDS GO CALM, SOME LOCATIONS ACROSS THE NORTHEASTERN STATES HAVE  
A BREEZE IN CONJUNCTION WITH THE FRIGID TEMPERATURES. THUS,  
WIDESPREAD WIND CHILL WARNINGS AND ADVISORIES ARE IN PLACE THROUGH  
AT LEAST THE MORNING HOURS. LITTLE RELIEF IS EXPECTED DURING THE  
DAY AS HIGHS STAY BELOW FREEZING AS FAR SOUTH AS EASTERN NORTH  
CAROLINA. ANOTHER DAY OF RECORDS WILL LIKELY BE APPROACHED OR  
BROKEN, PARTICULARLY FOR THE FRIGID OVERNIGHT LOWS. HOWEVER, A  
WARM UP IS IN STORE FOR NEXT WEEK WITH THE ENTIRE COUNTRY  
EXPECTING TEMPERATURES ANYWHERE FROM CLIMATOLOGY TO AROUND 10 TO  
20 DEGREE ABOVE IT. THESE LARGEST DEPARTURES FROM AVERAGE CAN BE  
FOUND IN THE HIGH PLAINS WHERE DOWNSLOPING FLOW WILL PREVAIL.  
 
RUBIN-OSTER  
 
GRAPHICS AVAILABLE AT  
WWW.WPC.NCEP.NOAA.GOV/BASICWX/BASICWX_NDFD.PHP  

 
 
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