877  
FXUS21 KWNC 282122  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 28 2017  
 
SYNOPSIS: A MID-LEVEL LOW-PRESSURE SYSTEM IS FORECAST TO MOVE ACROSS THE  
NORTHERN GREAT PLAINS. DOWNSTREAM, A SURFACE LOW-PRESSURE SYSTEM IS PREDICTED  
TO DEEPEN OVER SOUTHEAST CANADA.HIGH PRESSURE IS FORECAST TO BUILD IN ACROSS  
THE EASTERN HALF OF THE CONTIGUOUS 48 STATES, DRIVING A COLD FRONT SOUTHWARD TO  
THE GULF OF MEXICO. ACROSS THE WESTERN PORTIONS OF THE CONTIGUOUS 48 STATES,  
MODEL FORECASTS DISAGREE DURING WEEK-2, SO UNCERTAINTY IS HIGH, THOUGH SOME  
MODELS SHOW IMPACTS TO THE SOUTHWEST. 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 SNOW ACROSS PORTIONS OF THE GREAT LAKES, SUN-WED, DEC 31-JAN 3.  
 
HIGH WINDS ACROSS PORTIONS OF THE MID-ATLANTIC AND THE NORTHEAST, SUN, DEC 31.  
 
HEAVY SNOW ACROSS PORTIONS OF THE NORTHEAST, WED-THU, JAN 3-JAN 4.  
 
HIGH WINDS ACROSS PORTIONS OF THE MID-ATLANTIC AND THE NORTHEAST, THU, JAN4.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE GREAT PLAINS, THE  
MID-ATLANTIC, THE MISSISSIPPI VALLEY, THE CENTRAL AND SOUTHERN APPALACHIANS,  
THE TENNESSEE VALLEY, THE GREAT LAKES, THE NORTHERN ROCKIES, THE NORTHEAST, THE  
SOUTHEAST, AND THE OHIO VALLEY, SUN-TUE, DEC 31-JAN 2.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE MISSISSIPPI VALLEY, GREAT  
LAKES, THE OHIO AND TENNESSEE VALLEYS, THE NORTHEAST, MID-ATLANTIC, AND  
SOUTHEAST, WED-THU, JAN 3-JAN 4.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF SOUTHERN MAINLAND ALASKA, SUN-MON, DEC  
31-JAN 1.  
 
HIGH WINDS ACROSS PORTIONS OF SOUTHERN MAINLAND ALASKA AND THE ALEUTIANS, SUN,  
DEC 31.  
 
HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA, MON-TUE, JAN 1-JAN 2.  
 
MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF MAINLAND ALASKA, TUE-WED, JAN  
2-JAN 3.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF MAINLAND ALASKA, TUE, JAN  
2.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FROM THE GREAT PLAINS TO THE EAST  
COAST, FRI-SUN, JAN 5-JAN 7.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE  
MID-ATLANTIC, THE LOWER MISSISSIPPI VALLEY, THE CENTRAL APPALACHIANS, THE  
TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE NORTHEAST, THE SOUTHERN  
APPALACHIANS, THE SOUTHEAST, THE GREAT LAKES, AND THE OHIO VALLEY, FRI-SUN, JAN  
5-JAN 7.  
 
HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES FOR THE CAROLINAS AND PORTIONS OF  
GEORGIA, FRI-SUN, JAN 5-JAN 7.  
 
HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT LAKES AND  
THE OHIO VALLEY, FRI, JAN 5.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL  
PLAINS, THE UPPER MISSISSIPPI VALLEY, THE NORTHERN PLAINS, AND THE NORTHERN  
ROCKIES, MON-TUE, JAN 8-JAN 9.  
 
SLIGHT RISK OF HEAVY PRECIPITATION SPREADING EASTWARD FROM SOUTHERN CALIFORNIA  
TO THE SOUTHERN PLAINS, SAT-TUE, JAN 6-JAN 9.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL ROCKIES, THE  
CENTRAL PLAINS, AND THE NORTHERN PLAINS, SAT-MON, JAN 6-JAN 8.  
 
MODERATE RISK OF HEAVY PRECIPITATION, INCLUDING SIGNIFICANT FROZEN  
PRECIPITAITON FOR PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL PLAINS, AND THE  
NORTHERN PLAINS, SAT-SUN, JAN 6-JAN 7.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR WEST-CENTRAL ALASKA, SAT-SUN, JAN 6-7.  
 
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 SUNDAY DECEMBER 31 - THURSDAY JANUARY 04: AREAS OF MODERATE TO HEAVY SNOW  
DURING THE WEEKEND ARE PREDICTED DOWNSTREAM OF THE GREAT LAKES. LAKE SURFACE  
TEMPERATURES ARE STILL ABOVE FREEZING IN MOST LOCATIONS THOUGH LIKELY DROPPING  
QUICKLY IN THE COMING DAYS. OPEN LAKES AND COLD AIR SET THE STAGE FOR LAKE  
ENHANCED SNOWS, AND MANY LOCATIONS JUST RECEIVED SIGNIFICANT SNOWS. MITIGATING  
FACTORS WILL BE THE WIND DIRECTION AND DROPPING LAKE TEMPERATURES.  
 
A LOW-PRESSURE SYSTEM IS FORECAST TO DEEPEN OFF THE NORTHEAST COAST. AS A  
RESULT, HIGH WINDS (GREATER THAN 35 MPH OVER LAND) ARE LIKELY FROM THE  
MID-ATLANTIC TO NEW ENGLAND. WIND SPEEDS ARE CONSISTENT WITH MODEL OUTPUT FROM  
YESTERDAY.  
 
BEHIND THIS LOW-PRESSURE SYSTEM, STRONG AND COLD HIGH PRESSURE IS FORECAST TO  
BUILD SOUTHWARD FROM CANADA. MULTIPLE DAYS OF TEMPERATURES AT LEAST 12 DEGREES  
BELOW AVERAGE ARE FORECAST FOR MUCH OF THE EASTERN HALF OF THE CONTIGUOUS 48  
STATES. THE ECMWF ENSEMBLES MEAN IS NOW SLIGHTLY COLDER THAN THE GEFS, WITH THE  
CANADIAN MORE ALIGNED WITH THE ECMWF. ODDS OF FREEZES ARE ANOMALOUSLY HIGH AS  
FAR SOUTH AS THE GULF COAST, ESPECIALLY ON NEW YEAR'S DAY. BY DAY 6, SOME  
MODERATION OF THE AIRMASS IS LIKELY OVER THE PLAINS, SO THE HAZARD ON DAYS 6  
AND 7 IS RESTRICTED TO EAST OF THE MISSISSIPPI VALLEY.  
 
BEHIND THE COLD FRONT, WINDS OVER THE SOUTHERN PLAINS ARE LIKELY TO BE STRONG,  
BUT CERTAINTY ON REACHING HAZARDOUS CRITERIA IS LOW. HIGHER WINDS COULD LEAD TO  
RED FLAG CONDITIONS ON SATURDAY. THE SAME HIGH PRESSURE WOULD ALSO SUPPORT  
STRONG EASTERLY WINDS INTO THE EAST COAST OF FLORIDA, POTENTIALLY INCREASING  
THE THREAT OF RIP CURRENT AND DANGEROUSLY HIGH SEAS NEAR THE GULF STREAM.  
 
ACROSS THE WEST, RIDGING IS PREDICTED TO DOMINATE THROUGH NEXT TUE-WED. SURFACE  
HIGH PRESSURE OVER THE GREAT BASIN SUPPORTS A SLIGHTLY INCREASED RISK OF  
EXCEEDING CRITICAL FIRE WEATHER THRESHOLDS TUESDAY AND WEDNESDAY, JAN 2-3.  
 
LATER IN THE PERIOD, MODELS SHOW ACTIVITY ALONG THE COLD FRONT PREDICTED OVER  
THE GULF OF MEXICO. THE 0Z ECMWF AND CANADIAN MODELS DEPICTED MODERATE TO HEAVY  
SNOW FOR THE NORTHEAST, WITH THE 12Z GEFS NOW WEST OF THE 0Z GEFS, WHICH WAS  
FURTHER EAST AND DRY FOR NEW ENGLAND. THE INCREASING MODEL AGREEMENT AND  
POTENTIAL FOR A HIGH IMPACT EVENT SUPPORTS THE DEPICTION OF A RISK FOR HEAVY  
SNOW FROM CONNECTICUT TO MAINE. SOME MODEL OUTPUTS SHOWS HEAVY SNOW AS FAR  
SOUTH AS THE THE DC METRO AREA. HIGH WINDS FROM THE MID-ATLANTIC TO THE  
NORTHEAST AS ALSO LIKELY WITH THIS NEXT POTENTIAL STORM.  
 
DURING JANUARY 3, ENSEMBLE MEAN GUIDANCE ALSO INDICATE MODERATE PRECIPITATION  
AMOUNTS FOR NORTHERN CALIFORNIA, WITH SOME ENERGY MOVING INTO AND UNDERCUTTING  
THE MEAN RIDGE OUT WEST. AT THIS TIME, QPF AMOUNTS ARE NOT PREDICTED TO BE  
HAZARDOUS.  
 
ACROSS ALASKA, A STORMY PATTERN IS FORECAST FOR SOUTHERN ALASKA. HIGH WINDS (45  
KNOTS) ON DEC 31 OVER THE ALEUTIANS ARE LIKELY TO SPREAD EASTWARD SOUTH-CENTRAL  
ALASKA AND INTO THE ALASKA RANGE WHERE SOUTHERLY FLOW COULD GET ENHANCED BY  
TERRAIN DURING JAN 1-2. THE SOUTHERLY FLOW IS LIKELY TO BRING MUCH ABOVE NORMAL  
TEMPERATURES TO CENTRAL AND WESTERN ALASKA, ALONG WITH HEAVY PRECIPITATION (2-3  
INCHES IN 24 HOURS, FOR MULTIPLE DAYS) TO SOUTHWEST AND SOUTH-CENTRAL ALASKA,  
SOUTH OF THE ALASKA RANGE.  
 
FOR FRIDAY JANUARY 05 - THURSDAY JANUARY 11: 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 MIDDLE OF THE PERIOD. THIS LEADS TO A SLIGHT  
RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE CENTRAL AND EASTERN  
CONUS JAN 5-7 AND A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FROM  
MIDWEST TO THE LOWER MISSISSIPPI VALLEY AND EASTWARD, DURING JAN 5-7. A HIGH  
RISK OF MUCH BELOW NORMAL TEMPERATURES IS INDICATED AROUND THE GREAT LAKES, JAN  
5, AND OVER THE CAROLINAS DURING JAN 5-7. 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. THE  
ECMWF MODEL OUTPUT IS NOW COLDER THAN THE GEFS, WHICH IS COLDER THAN YESTERDAY  
FOR JAN 7, SO THE MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES IS EXPANDED  
TO INCLUDE FLORIDA, WHERE THESE IS AN INCREASED RISK OF CROP DAMAGING FREEZES.  
 
SOME MODEL OUTPUTS SHOW TROUGHING MOVING INTO THE FOUR CORNERS REGION DURING  
THE EARLY PORTION OF WEEK-2. THIS WOULD SUPPORT MODERATE TO POTENTIALLY HEAVY  
RAINS ACROSS INLAND PORTIONS OF SOUTHERN CALIFORNIA, AND POTENTIAL FOR RAINS  
OVER BURN SCARS. ADDITIONALLY IT WOULD SUPPORT SLIGHTLY INCREASED ODDS OF  
HEAVY SNOWS IN ARIZONA, NEW MEXICO, COLORADO, AND THE SOUTHERN HIGH PLAINS.  
ODDS ARE 20-30% ACCORDING TO THE GEFS, WITH ECMWF AND CANADIAN ENSEMBLE MEANS  
ABOUT THE SAME. SOME MODELS INDICATE THE POTENTIAL FOR A NORTHERN STREAM  
VORTICITY MAX TO DROP DOWN TO THE EAST SIDE OF THE ROCKIES, WHICH COULD LEAD TO  
HEAVY SNOWS FOR WYOMING AND COLORADO, JAN 6-7.  
 
MODELS ARE ALSO INDICATING A CONTINUED STORMY PATTERN FOR WESTERN ALASKA. THE  
POTENTIAL FOR PERIODIC HEAVY PRECIPITATION IS HIGHLIGHTED, EARLY IN WEEK-2.  
 
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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