323  
FXUS21 KWNC 151926  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST JANUARY 15 2018  
 
SYNOPSIS: DURING THE COURSE OF THE OUTLOOK A FAIRLY SUBSTANTIAL PATTERN CHANGE  
IS ANTICIPATED ACROSS NORTH AMERICA. INITIALLY, MID-LEVEL HIGH PRESSURE IS  
FORECAST OVER THE ROCKIES WITH MID-LEVEL LOW PRESSURE ALONG THE EASTERN  
SEABOARD. MID-LEVEL LOW PRESSURE, FORECAST INITIALLY OFF THE PACIFIC COAST, IS  
FORECAST TO PUSH INTO THE WESTERN U.S. AND LIFT TOWARDS THE GREAT LAKES DURING  
THE COURSE OF WEEK-1, HELPING TO DEVELOP A SURFACE DISTURBANCE OVER THE CENTRAL  
PLAINS. A SECOND AREA OF MID-LEVEL LOW-PRESSURE IS FORECAST TO APPROACH THE  
WEST COAST LATE IN WEEK-1. DURING WEEK-2, MID-LEVEL LOW PRESSURE IS FORECAST TO  
EXTEND FROM ALASKA THROUGH THE WESTERN U.S., WITH MID-LEVEL HIGH PRESSURE  
EXTENDING EAST OF THE MISSISSIPPI RIVER. ALASKA IS FORECAST TO SHIFT FROM A  
RELATIVELY MILD PATTERN IN WEEK-1 TOWARDS A COLDER SOLUTION IN WEEK-2 WITH  
NORTHEASTERLY FLOW ANTICIPATED OUT OF THE YUKON OR ARCTIC OCEAN.  
 
HAZARDS  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE GREAT BASIN, THE NORTHERN ROCKIES,  
CALIFORNIA, AND THE PACIFIC NORTHWEST, THU-MON, JAN 18-JAN 22.  
 
HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES AND THE NORTHERN GREAT  
BASIN, THU, JAN 18 AND MON, JAN 22.  
 
HIGH WINDS ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC NORTHWEST, THU, JAN 18.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF CALIFORNIA AND THE  
PACIFIC NORTHWEST, THU, JAN 18.  
 
HIGH WINDS ACROSS PORTIONS OF THE PACIFIC NORTHWEST, SAT, JAN 20.  
 
HEAVY SNOW ACROSS AREAS FROM THE CENTRAL ROCKIES THROUGH THE WESTERN GREAT  
LAKES, SAT-MON, JAN 20-JAN 22.  
 
HEAVY RAIN ACROSS PORTIONS OF THE MISSISSIPPI VALLEY, THE OHIO AND TENNESSEE  
VALLEYS, THE SOUTHEAST, AND THE GREAT LAKES, SAT-SUN, JAN 20-JAN 21.  
 
FREEZING RAIN ACROSS PORTIONS OF UPSTATE NEW YORK AND NEW ENGLAND, MON, JAN 22.  
 
HIGH WINDS ACROSS AREAS FROM THE FOUR-CORNERS REGION THROUGH THE WESTERN GREAT  
LAKES, SAT-MON, JAN 20-JAN 22.  
 
MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE GULF STATES, THE  
MID-ATLANTIC, AND THE TENNESSEE VALLEY, THU, JAN 18.  
 
HIGH WINDS AND POTENTIAL FREEZING SPRAY FOR ST. LAWRENCE ISLAND, FRI-MON, JAN  
19-22.  
 
HIGH WINDS FOR THE BROOKS RANGE AND DOWNSLOPE AREAS TO THE SOUTHWEST, FRI-MON,  
JAN 19-22.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF CALIFORNIA,  
OREGON, AND NEVADA, TUE-THU, JAN 23-JAN 25.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR THE ALASKA PANHANDLE AND  
MAINLAND ALASKA, TUE-MON, JAN 23-JAN 29.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER MISSISSIPPI  
VALLEY, THE TENNESSEE VALLEY, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, AND  
TEXAS, TUE-THU, JAN 23-JAN 25.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL AND SOUTHERN  
APPALACHIANS, THE TENNESSEE AND OHIO VALLEYS, THE MID-ATLANTIC, AND THE  
SOUTHEAST, THU-SAT, JAN 25-JAN 27.  
 
SEVERE DROUGHT FOR PARTS OF THE GREAT PLAINS, THE SOUTHWEST, THE CENTRAL AND  
SOUTHERN MISSISSIPPI VALLEY, THE SOUTHEAST, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR THURSDAY JANUARY 18 - MONDAY JANUARY 22: ACTIVE WEATHER WITH MULTIPLE  
HAZARDS IS ANTICIPATED FOR THE WESTERN TWO-THIRDS OF THE LOWER-48 STATES  
THROUGHOUT THE FORECAST PERIOD. THESE HAZARDS ARE ASSOCIATED WITH TWO WAVES OF  
500-HPA LOW PRESSURE SHIFTING INLAND FROM THE PACIFIC AND THROUGH THE CENTRAL  
U.S. BEFORE LIKELY SHIFTING NORTHWARD INTO CANADA. THIS EVOLUTION IS LARGELY IN  
LINE WITH THE EXPECTED EVOLUTION OF THE MID-LATITUDE CIRCULATION OVER NORTH  
AMERICA IN RESPONSE TO THE MADDEN-JULIAN OSCILLATION SHIFTING FROM THE INDIAN  
OCEAN TOWARDS THE MARITIME CONTINENT, WITH RIDGING OVER THE EAST AND TROUGHING  
FOR THE WEST. CONTINUATION OF THE LAGGED RESPONSE FROM THIS TROPICAL FORCING  
WOULD SUGGEST RISING 500-HPA HEIGHTS ACROSS THE LOWER-48 STATES IN WEEK-2 AND  
BEYOND, WITH ANOMALOUS TROUGHING FOR ALASKA.  
 
WITH THE FIRST 500-HPA TROUGH SHIFTING INLAND INTO THE WEST, PERIODS OF  
WIDESPREAD HEAVY PRECIPITATION (DAILY LIQUID EQUIVALENT PRECIPITATION TOTALS OF  
2 INCHES OR MORE, WITH SNOW FURTHER NORTH AND AT HIGHER ELEVATIONS AND RAIN  
ELSEWHERE) IS FORECAST FROM THE 18TH THROUGH 22ND. IN EXCESS OF 10 INCHES OF  
LIQUID PRECIPITATION IS POSSIBLE THROUGHOUT THE PERIOD IN SOME AREAS, WITH  
SEVERAL FEET OF SNOW POSSIBLE IN THE SIERRA-NEVADAS AND CASCADES. SNOW LEVELS  
ARE LIKELY TO BEGIN RELATIVELY HIGH, BEFORE DROPPING OVER THE COURSE OF THE  
EVENT (LIKELY 2000-3000 FEET ACROSS OREGON FOR EXAMPLE). THE HEAVY RAIN IS  
LIKELY TO BRING WITH IT THE POTENTIAL FOR MUDSLIDES IN AREAS OF NORTHERN  
CALIFORNIA NEAR STEEP TERRAIN, PARTICULARLY EARLY IN THE PERIOD WHERE THE RAINS  
MAY HELP MELT THE EXISTING SNOWPACK. A PERIOD OF SIGNIFICANT WAVES (EXCEEDING  
20 FEET) ON THE 18TH DUE TO THE SIGNIFICANT FETCH OF WEST-NORTHWESTERLY WINDS  
ACROSS THE NORTH PACIFIC AS THE LOW APPROACHES. THE AFOREMENTIONED WINDS ARE  
ALSO ANTICIPATED REACH HAZARDOUS CRITERIA (EXCEEDING 40 MPH) ON THE 18TH AND  
STRETCH FROM COASTAL REGIONS OF NORTHERN CALIFORNIA THROUGH PUGET SOUND. A  
SECOND 500-HPA LOW IS FORECAST TO APPROACH THE WEST COAST BY THE WEEKEND,  
BRINGING ANOTHER POTENTIAL ROUND OF HIGH WINDS FOR PORTIONS OF THE OREGON AND  
WASHINGTON COASTLINES FOR THE 20TH. FURTHER INLAND, THE BEST MOISTURE SURGES  
FROM THESE EVENTS COULD BRING A PAIR OF DAYS WITH POTENTIALLY HEAVY SNOW  
(EXCEEDING 8 INCHES IN 24 HOURS) FOR PORTIONS OF IDAHO AND MONTANA ON THE 18TH  
AND 22ND.  
 
AS THE FIRST MID-LEVEL TROUGH FROM THE AFOREMENTIONED EVENT SHIFTS INTO THE  
ROCKIES, LEE CYCLOGENESIS APPEARS LIKELY OVER THE PLAINS LATE THIS WEEK. MODELS  
DEEPEN THIS DISTURBANCE AND SHIFT IT NORTHEASTWARD FROM THE CENTRAL PLAINS  
TOWARD THE GREAT LAKES DURING THE REMAINDER OF WEEK-1. THE ECMWF IS DEEPER AND  
FURTHER NORTH WITH THE TRACK OF THE SYSTEM, RELATIVE TO THE WEAKER AND FURTHER  
SOUTH FORECAST FROM THE GFS. WITH THE TROUGH OVER THE WEST ANTICIPATED TO TAKE  
ON A NEGATIVE TILT, AND SURFACE LOW FORECAST TO STRENGTHEN, HIGH WINDS ARE  
INITIALLY LIKELY OVER THE SOUTHWEST ON THE 20TH, WITH A NORTHEASTWARD SHIFTING  
THREAT TOWARDS THE GREAT LAKES THROUGH THE 22ND ON THE BACK SIDE OF THE LOW AS  
THE PRESSURE GRADIENT TIGHTENS. MARGINALLY ENHANCED FIRE WEATHER CONDITIONS FOR  
PARTS OF NEW MEXICO AND TEXAS ARE ALSO POSSIBLE DUE TO DRY, BREEZY CONDITIONS  
IN ASSOCIATION WITH THE MID-LEVEL TROUGH OVER THE WEST ON THE 19TH. AN  
EASTWARD-SHIFTING THREAT FOR HEAVY SNOW (POTENTIALLY UP TO A FOOT OR MORE) IS  
POSSIBLE FROM THE CENTRAL PLAINS THROUGH THE WESTERN GREAT LAKES FROM THE 20TH  
THROUGH 22ND IN ASSOCIATED WITH ELEVATED POTENTIAL INSTABILITY IN THE TROWAL  
REGION OF THE CYCLONE. FURTHER EAST, FREEZING RAIN (EXCEEDING A TENTH OF AN  
INCH) ALONG THE WARM FRONT IS POSSIBLE FOR PORTIONS OF UPSTATE NEW YORK AND NEW  
ENGLAND ON THE 22ND IF THE GFS SOLUTION WERE TO VERIFY. IN THIS SCENARIO SNOW  
WOULD MELT WHILE FALLING THROUGH A LAYER OF WARMER AIR ALOFT WRAPPING IN OFF OF  
THE ATLANTIC, BEFORE REFREEZING ON CONTACT WITH SURFACE TEMPERATURES  
ANTICIPATED TO BE AROUND 30 DEGREES F. FURTHER SOUTH, WITH NORTHWARD FLOW  
FORECAST TO DRIVE MOISTURE POLEWARD AND OUT OF THE GULF AHEAD OF THE LOW, HEAVY  
RAIN (EXCEEDING 1 INCH IN 24 HOURS) IS POSSIBLE FROM THE MISSISSIPPI RIVER  
DELTA THROUGH THE VICINITY OF SOUTHERN LAKE MICHIGAN ON THE 20TH AND 21ST.  
TYPICALLY, WITH A WELL-DEVELOPED TROUGH OVER THE CENTRAL U.S. AND DEEP SURFACE  
CYCLONE LIFTING NORTHWARD A SEVERE WEATHER THREAT WOULD BE POSSIBLE. HOWEVER,  
THE ANTECEDENT COLD-AIR OUTBREAK OVER THE EASTERN U.S. MAY HELP LIMIT MOISTURE  
AND INSTABILITY TO SOME EXTENT, AND WITH IT THE POTENTIAL FOR SEVERE WEATHER.  
 
THE AFOREMENTIONED COLD-AIR OUTBREAK IS LIKELY TO BE LINGERING AT THE START OF  
THE FORECAST PERIOD. THE MOST ANOMALOUSLY COLD AIR IS FORECAST TO BE OVER THE  
SOUTHEAST, WHERE MUCH BELOW-NORMAL TEMPERATURES (MINIMUM TEMPERATURE ANOMALIES  
OF -12 TO -20 DEGREES F) ARE FORECAST ON THE 18TH FROM EAST TEXAS THROUGH THE  
CAROLINAS AND MUCH OF THE FLORIDA PENINSULA. THE HIGHLIGHTED AREAS COULD SEE A  
FROST OR FREEZE THAT IMPACTS AGRICULTURAL INTERESTS BEFORE TEMPERATURES BEGIN  
TO MODERATE WITH A SHIFT TO SOUTHERLY WINDS FOR THE REMAINDER OF WEEK-1.  
 
SURFACE CYCLONES ARE FORECAST IN THE BERING SEA AND NORTHEAST PACIFIC DURING  
THE COURSE OF WEEK-1, BUT OVERALL IMPACTS ON ALASKA ARE LIKELY TO BE MUTED.  
MODELS DO SUGGEST THE POTENTIAL FOR A HIGH WIND EVENT ALONG AND DOWNWIND OF THE  
BROOKS RANGE ON THE 19TH THROUGH 22ND IN ASSOCIATION WITH NORTHEASTERLY FLOW.  
HIGH WINDS COULD ALSO IMPACT ST. LAWRENCE ISLAND ON THE 19TH THROUGH 22ND, AS  
THE BERING SEA HAS NOT FROZEN THAT FAR SOUTH YET THIS SEASON, AND FREEZING  
SPRAY FROM THE STRONG NORTHEAST WINDS COULD DEVASTATE COASTAL COMMUNITIES ON  
THE WINDWARD SHORE. RELATIVELY MILD CONDITIONS ARE FORECAST ACROSS MUCH OF THE  
STATE EARLY IN WEEK-1, BEFORE A SHIFT TOWARDS RELATIVELY COOLER CONDITIONS  
LATER IN THE WEEK.  
 
FOR TUESDAY JANUARY 23 - MONDAY JANUARY 29: DURING WEEK-2, ANOMALOUS 500-HPA  
TROUGHING IS FORECAST TO EXTEND FROM ALASKA THROUGH THE GREAT PLAINS, WITH  
ANOMALOUS RIDGING SITUATED EAST OF THE MISSISSIPPI VALLEY. IN THIS SCENARIO,  
COLD HAZARDS ARE POSSIBLE FOR THE WEST, WITH AN INCREASED RISK OF HEAVY  
PRECIPITATION FOR THE EAST DUE TO FLOW OUT OF THE GULF OF MEXICO.  
 
A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES IS FORECAST ACROSS PORTIONS OF  
OREGON, NORTHERN CALIFORNIA, AND NEVADA FROM THE 23RD THROUGH 25TH. HERE THE  
GEFS PROBABILISTIC EXTREMES TOOL GIVES AT LEAST A 20% CHANCE OF THE DAILY  
MINIMUM TEMPERATURES BEING BELOW THE 15TH CLIMATOLOGICAL PERCENTILE. A SLIGHT  
RISK OF MUCH BELOW-NORMAL TEMPERATURES ALSO EXISTS FOR ALL OF MAINLAND ALASKA  
THROUGHOUT WEEK-2 IN ASSOCIATION WITH LIKELY NORTHEASTERLY FLOW OFF THE ARCTIC  
OCEAN OR OUT OF THE YUKON. HERE THE GEFS PROBABILISTIC EXTREMES TOOL ALSO GIVES  
AT LEAST A 20% CHANCE OF BEING IN THE BOTTOM 15TH PERCENTILE OF CLIMATOLOGICAL  
MINIMUM TEMPERATURES THROUGHOUT THE WEEK. ECMWF REFORECAST GUIDANCE DURING  
WEEK-2 ALSO SKEWS COLD FOR EACH OF THE AFOREMENTIONED REGIONS, FURTHER  
SUPPORTING THE POTENTIAL COLD RISKS.  
 
A NORTHEASTWARD SHIFTING SLIGHT RISK OF MUCH ABOVE-NORMAL PRECIPITATION IS  
FORECAST FROM THE GULF STATES THROUGH THE TENNESSEE VALLEY ON THE 23RD THROUGH  
25TH AND FROM THE TENNESSEE VALLEY THROUGH THE MID-ATLANTIC ON THE 25TH THROUGH  
27TH. THIS AREA IS ISOLATED BY THE ECMWF PROBABILISTIC EXTREMES TOOL WHERE AT  
LEAST A 40% CHANCE OF AN INCH OF RAIN THROUGHOUT THE AFOREMENTIONED PERIODS IS  
POSSIBLE, WHILE ODDS OF PRECIPITATION BEING ABOVE THE 85TH CLIMATOLOGICAL  
PERCENTILE ON THOSE DAYS EXCEEDS 30%. THE GEFS PROBABILISTIC EXTREMES TOOL  
EXHIBITS FAR WEAKER SIGNALS THAT ARE SHIFTED WELL TO THE NORTH, AND APPEAR TIED  
TO A WET BIAS IN THE MODEL, AND THUS IT IS DISCOUNTED HERE.  
 
THE U.S. DROUGHT MONITOR, VALID ON JANUARY 9, 2018 INDICATES AN INCREASE IN THE  
COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2-D4) FROM 7.46% LAST WEEK TO 8.70%  
THIS WEEK. SOME OF THE MORE SIGNIFICANT ADJUSTMENTS MADE THIS WEEK INCLUDE  
IMPROVEMENT (FROM D3 TO D2) IN EASTERN MONTANA, SOME DETERIORATION IN OKLAHOMA  
(D2 TO D3), AND THE INTRODUCTION OF ABNORMAL DRYNESS (D0) IN PARTS OF OREGON.  
 
FORECASTER: CPC FORECASTER  
 

 
 
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