368  
FXUS21 KWNC 252054  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 25 2017  
 
SYNOPSIS: A MID-LEVEL LOW-PRESSURE SYSTEM IS FORECAST TO MOVE ACROSS THE  
NORTHWEST LATER THIS WEEK. DOWNSTREAM, A SURFACE LOW-PRESSURE SYSTEM IS  
PREDICTED TO MOVE ACROSS THE NORTHEAST DURING THE WEEKEND AND PUSH A COLD FRONT  
TO THE GULF OF MEXICO. HIGH PRESSURE IS FORECAST TO BUILD IN BEHIND THAT COLD  
FRONT, BEFORE THE FRONT SLOWLY LIFTS NORTHWARD DURING THE EARLY PORTIONS OF  
WEEK-2. A SURFACE LOW-PRESSURE SYSTEM IS FORECAST TO IMPACT THE ALEUTIANS EARLY  
IN THE PERIOD BEFORE MOVING EASTWARD AND IMPACTING SOUTH-CENTRAL MAINLAND  
ALASKA COASTAL REGIONS.  
 
HAZARDS  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST, THU-FRI, DEC  
28-DEC 29.  
 
HEAVY SNOW ACROSS PORTIONS OF THE PACIFIC NORTHWEST, THE NORTHERN ROCKIES, AND  
THE NORTHERN GREAT BASIN, THU-FRI, DEC 28-DEC 29.  
 
HEAVY SNOW ACROSS PORTIONS OF MAINE, SAT, DEC 30.  
 
HIGH WINDS ACROSS PORTIONS OF THE MID-ATLANTIC AND THE NORTHEAST, SAT-SUN, DEC  
30-DEC 31.  
 
MUCH BELOW NORMAL TEMPERATURES FROM THE GREAT LAKES TO THE MID-ATLANTIC AND  
NORTHEAST, THU, DEC 28.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN AND CENTRAL  
PLAINS, AND THE NORTHERN ROCKIES, THU-FRI, DEC 28-DEC 29.  
 
MUCH BELOW NORMAL TEMPERATURES FROM THE NORTHERN AND CENTRAL ROCKIES TO THE  
SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY AND EASTWARD TO THE MID-ATLANTIC AND  
NORTHEAST, SAT-MON, DEC 30-JAN 1.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF MAINLAND ALASKA, SUN-MON, DEC 31-JAN 1.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FROM THE EASTERN ROCKIES TO THE  
EAST COAST, TUE-FRI, JAN 2-JAN 5.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT  
PLAINS, THE MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE OHIO VALLEY, THE  
CENTRAL AND SOUTHERN APPALACHIANS, THE GREAT LAKES, THE NORTHEAST, THE  
MID-ATLANTIC, AND THE SOUTHEAST,TUE-THU, JAN 2-JAN 4.  
 
HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE LOWER AND  
MIDDLE MISSISSIPPI VALLEYS, THE TENNESSEE VALLEY, THE OHIO VALLEY, THE GREAT  
LAKES, THE SOUTHERN AND CENTRAL APPALACHIANS, THE NORTHEAST, THE MID-ATLANTIC,  
AND THE SOUTHEAST, TUE-WED, JAN 2-JAN 3.  
 
SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE LOWER MISSISSIPPI VALLEY, THE  
CENTRAL GREAT BASIN, THE NORTHERN PLAINS, HAWAII, THE NORTHERN ROCKIES, THE  
MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE SOUTHWEST.  
 
DETAILED SUMMARY  
 
FOR THURSDAY DECEMBER 28 - MONDAY JANUARY 01: A TROUGH IS FORECAST TO MOVE  
ACROSS THE PACIFIC NORTHWEST NEAR THE START OF THE PERIOD, BRINGING HEAVY  
PRECIPITATION (UP TO 3.5 INCHES LIQUID EQUIVALENT IN 48 HOURS) TO THE PACIFIC  
NORTHWEST. SNOW LEVELS ARE LIKELY TO BE QUITE LOW, AT OR BELOW 1000 FEET.  
SNOWFALL ACROSS THE CASCADES IS LIKELY TO EXCEED 6 INCHES. ACROSS THE  
BITTERROOTS AND INTO YELLOWSTONE, HEAVY SNOW (GREATER THAN 8 INCHES) IS LIKELY  
DURING A 2 DAY PERIOD.  
 
THAT TROUGH IS FORECAST TO MOVE ACROSS THE NORTHERN TIER, WITH SOME WEAK  
LEE-SIDE CYCLOGENESIS POSSIBLE FRIDAY. THE WEAK LEE-SIDE LOW COULD SUPPORT  
SLIGHTLY INCREASED WIND SPEEDS (GREATER THAN 20 MPH) OVER THE SOUTHERN GREAT  
PLAINS, SO A MARGINAL FIRE WEATHER THREAT IS NOTED.  
 
AS THE TROUGH MOVES EASTWARD AND MOVES INTO THE BASE OF THE MEAN TROUGH,  
LOW-PRESSURE IS LIKELY TO DEEPEN OVER THE NORTHEAST DURING SATURDAY. HIGH WINDS  
(GREATER THAN 35 MPH OVER LAND, AND POTENTIALLY AS HIGH AS 45 KNOTS OVER NEAR  
SHORE WATERS) ARE LIKELY FROM THE CHESAPEAKE BAY TO MAINE, WITH SOME HEAVY  
SNOWS POSSIBLE ACROSS MAINE. THE STRONG LOW-PRESSURE SYSTEM SHOULD DRIVE A COLD  
FRONT SOUTHWARD TO THE GULF OF MEXICO.  
 
BEHIND THE COLD FRONT, TEMPERATURES ARE LIKELY TO BE 12-20 DEGREES BELOW NORMAL  
FROM THE ROCKIES TO THE EAST COAST. THE COLD AIR IS LIKELY TO SPILL SOUTHWARD  
ALONG THE NORTHERN ROCKIES, WHERE SOME MODERATION IS LIKELY TOWARD JAN 1.  
SUBFREEZING TEMPERATURES ARE FORECAST AS FAR SOUTH AS CENTRAL TEXAS AND CENTRAL  
LOUISIANA TO START THE NEW YEAR.  
 
A LOW-PRESSURE SYSTEM IS FORECAST TO MOVE ACROSS THE ALEUTIANS. WIND SPEEDS IN  
THE GFS APPROACH 40 KNOTS, BUT THE ECWMF SOLUTIONS ARE CLOSER TO 30 KNOTS, SO  
NO HAZARD IS INDICATED AT THIS TIME. AS THE LOW MOVES TOWARD SOUTHERN ALASKA,  
MOISTURE WILL BE PULLED NORTHWARD AND PRECIPITATION AMOUNTS APPROACHING 3  
INCHES IN 24 HOURS ARE LIKELY DURING DEC 31 TO JAN 1.  
 
FOR TUESDAY JANUARY 02 - MONDAY JANUARY 08: A DEEP TROUGH IS FORECAST TO  
DOMINATE MUCH OF THE CENTRAL AND EASTERN CONUS FOR MOST OF WEEK-2, ALTHOUGH IT  
IS EXPECTED TO WEAKEN TOWARDS THE END OF THE PERIOD. THIS LEADS TO A SLIGHT  
RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE CENTRAL AND EASTERN  
CONUS JAN 2-5, AND A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FROM THE  
SOUTHERN GREAT PLAINS TO THE GREAT LAKES, AND EASTWARD TO MOST OF THE EAST  
COAST, FOR JAN 2-4. A HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES IS INDICATED  
FROM THE GREAT LAKES TO NEW ENGLAND AND SOUTHWARD TO A LINE FROM CENTRAL  
MISSISSIPPI TO ABOUT SAVANNAH, GA DURING JAN 2-3. TEMPERATURES ARE EXPECTED TO  
MODERATE OVER THE WESTERN AND CENTRAL CONUS DURING THE PERIOD, SO THE WESTERN  
EDGES OF THE SLIGHT AND MODERATE THREAT AREAS ARE LESS CERTAIN FOR LATER IN  
WEEK-2. ADDITIONAL UNCERTAINTY IS EVIDENT OVER FLORIDA WHEN COMPARING THE  
ECWMF, GEFS, AND CANADIAN MODELS, SO THE OFFICIAL OUTLOOK IS NOT AS INTENSE AS  
THE GEFS PROBABILITIES.  
 
THE U.S. DROUGHT MONITOR, UPDATED ON DEC 19, SHOWS AN INCREASE IN AREAS OF  
EXCEPTIONAL DROUGHT (D2-D4) TO 6.97% FROM 6.49%. MOST OF THE NEWLY INDICATED  
SEVERE DROUGHT WAS OVER THE SOUTHERN PLAINS.  
 
FORECASTER: MATTHEW ROSENCRANS  
 

 
 
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