Threats Assessment Discussion

028 
FXUS21 KWNC 162023
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST JANUARY 16 2018
SYNOPSIS: A REGION OF MID-LEVEL LOW PRESSURE IS FORECAST TO BE OFF OF VANCOUVER 
ISLAND AT THE START OF THE FORECAST PERIOD, WITH MID-LEVEL HIGH PRESSURE 
FORECAST INITIALLY ACROSS THE EAST. OVER THE COURSE OF THE WEEK THE 
AFOREMENTIONED LOW IS FORECAST TO TRACK INTO THE ROCKIES, WITH ANOTHER 
MID-LEVEL LOW APPROACHING NORTH AMERICA IN ITS WAKE. THE FORMER MID-LEVEL 
DISTURBANCE IS FORECAST TO HELP DEVELOP A SURFACE CYCLONE OVER THE CENTRAL 
PLAINS THAT IS ANTICIPATED TO TRACK TOWARDS THE GREAT LAKES. TRANSITIONING, 
INTO WEEK-2 A TENDENCY TOWARDS MID-LEVEL LOW PRESSURE OVER ALASKA AND THE WEST 
IS FORECAST, WITH MID-LEVEL HIGH PRESSURE ANTICIPATED OVER THE EAST.
HAZARDS
HEAVY PRECIPITATION ACROSS PORTIONS OF THE GREAT BASIN, THE NORTHERN ROCKIES, 
CALIFORNIA, THE PACIFIC NORTHWEST, AND THE SOUTHWEST, FRI-MON, JAN 19-JAN 22.
HIGH WINDS ACROSS COASTAL PORTIONS OF THE PACIFIC NORTHWEST, SAT, JAN 20.
HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL PLAINS, AND THE 
CENTRAL GREAT BASIN, SAT, JAN 20.
HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN AND CENTRAL PLAINS, THE UPPER AND 
MIDDLE MISSISSIPPI VALLEY, AND THE GREAT LAKES, SUN, JAN 21.
HIGH WINDS ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, THE CENTRAL AND 
SOUTHERN ROCKIES, AND THE SOUTHWEST, SAT, JAN 20.
MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHEAST AND THE LOWER 
MISSISSIPPI VALLEY, FRI, JAN 19.
MUCH BELOW-NORMAL TEMPERATURES ACROSS MUCH OF WESTERN AND INTERIOR MAINLAND 
ALASKA, SUN-TUE, JAN 21-23.
HIGH WINDS ACROSS PORTIONS OF THE BROOKS RANGE AND AREAS IMMEDIATELY TO ITS 
SOUTHWEST, FRI-TUE, JAN 19-JAN 23.
HIGH WINDS ACROSS PORTIONS OF THE ALEUTIAN AND ALASKA RANGES AND AREAS 
IMMEDIATELY TO THEIR SOUTH, SAT-TUE, JAN 20-23.
HIGH WINDS AND POTENTIAL FREEZING SPRAY FOR ST. LAWRENCE ISLAND, FRI-TUE, JAN 
19-23.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF CALIFORNIA, 
OREGON, AND NEVADA, WED-THU, JAN 24-JAN 25.
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR WESTERN AND INTERIOR 
MAINLAND ALASKA, WED-FRI, JAN 24-26.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR ALASKA WITH THE EXCEPTION OF 
THE WESTERN ALEUTIANS, WED-TUE, JAN 24-JAN 30.
SLIGHT RISK OF HEAVY PRECIPITATION EXTENDING FROM SOUTHEAST TEXAS THROUGH 
GEORGIA, WED-FRI, JAN 24-JAN 26.
SEVERE DROUGHT FOR PARTS OF THE GREAT PLAINS, THE SOUTHWEST, THE CENTRAL AND 
SOUTHERN MISSISSIPPI VALLEY, THE SOUTHEAST, AND HAWAII.
DETAILED SUMMARY
FOR FRIDAY JANUARY 19 - TUESDAY JANUARY 23: A PAIR OF CLOSED 500-HPA LOWS ARE 
FORECAST TO APPROACH THE PACIFIC NORTHWEST DURING THE COURSE OF WEEK-1. THE 
FIRST IS ANTICIPATED TO OPEN UP OVER THE GREAT BASIN AS A POSITIVELY-TILTED 
TROUGH, AND SHIFT INTO THE GREAT PLAINS DURING THE NEXT FEW DAYS. AS THIS 
FEATURE APPROACHES THE ROCKIES, SURFACE CYCLOGENESIS IS FORECAST OVER THE 
CENTRAL PLAINS. THIS SURFACE LOW IS FORECAST TO DEEPEN AS THE MID-LEVEL TROUGH 
TAKES ON A SLIGHTLY NEGATIVE TILT, AND TRACK TOWARDS THE GREAT LAKES. THE 
SECOND MID-LEVEL LOW IS FORECAST TO APPROACH THE WEST COAST LATER IN WEEK-1, 
BRINGING ANOTHER SHOT OF PACIFIC MOISTURE INTO THE WEST.
PERIODIC HEAVY PRECIPITATION (DAILY TOTALS EXCEEDING 2 INCHES OF LIQUID 
EQUIVALENT, WITH SNOW AT HIGHER ELEVATIONS AND RAIN ELSEWHERE) IS FORECAST IN 
ASSOCIATION WITH EACH OF THE MID-LEVEL FEATURES FROM THE PREVIOUS PARAGRAPH FOR 
NORTHERN CALIFORNIA, THE SIERRA-NEVADAS, WESTERN OREGON, AND WESTERN AND 
NORTHERN WASHINGTON INTO EXTREME NORTHERN IDAHO ON JANUARY 19-22. SNOW LEVELS 
ARE LIKELY TO BEGIN HIGH, AND DROP WITH TIME AS THE COLD-CORE SYSTEMS MOVE OVER 
THE REGION. RAINFALL AMOUNTS IN EXCESS OF 6 INCHES ARE POSSIBLE WITH THIS 
SYSTEM ALONG THE COAST THAT COULD HELP TRIGGER MUDSLIDES IN AREAS SUSCEPTIBLE 
FROM FIRES OVER THE PAST SEVERAL MONTHS. SNOW TOTALS IN THE SIERRA-NEVADAS AND 
CASCADES WITH THIS EVENT COULD EXCEED 3 FEET IN MANY PLACES. THE INITIAL SURGE 
OF MOISTURE ON THE 19TH AND 20TH APPEARS LIKELY TO BE FURTHER NORTH (OVER 
OREGON AND WASHINGTON) THAN THE SECOND PERIOD OF PACIFIC MOISTURE COMING ASHORE 
ON THE 21ST AND 22ND (OVER NORTHERN CALIFORNIA AND OREGON). IN ASSOCIATION WITH 
THE FIRST TROUGH MOVING INLAND, A PERIOD OF HIGH WINDS (SUSTAINED AT 35 MPH OR 
GREATER) IS LIKELY ACROSS THE FOUR CORNERS REGION INTO THE SOUTHERN AND CENTRAL 
PLAINS ON THE 20TH. MARGINALLY ELEVATED FIRE WEATHER CONDITIONS, THOUGH NOT 
DEPICTED ON THE MAP, ARE ALSO FORECAST ACROSS PORTIONS OF EASTERN NEW MEXICO 
AND WEST TEXAS ON THE 19TH AND 20TH DUE TO THE POTENTIAL FOR DRY AND BREEZY 
CONDITIONS.
WITH THE FIRST TROUGH MOVING INLAND, A SURGE OF PACIFIC MOISTURE INTO THE 
ROCKIES APPEARS LIKELY ON THE 20TH. THIS MAY LEAD TO HEAVY SNOW (EXCEEDING 8 
INCHES IN 24 HOURS) ON THE 20TH ACROSS PORTIONS OF COLORADO, WYOMING, AND 
NEBRASKA. AROUND THIS SAME TIME, SURFACE CYCLOGENESIS IS LIKELY TO BE OCCURRING 
OVER THE CENTRAL PLAINS. THIS SYSTEM IS FORECAST TO LIFT TOWARDS THE GREAT 
LAKES ON THE 21ST. THE GFS HAS TRENDED FURTHER NORTH TOWARDS THE ECMWF SINCE 
YESTERDAY, LIMITING ANY POTENTIAL ICING IMPACTS FOR NEW ENGLAND AS OPPOSED TO 
YESTERDAY'S OUTLOOK. A ROUND OF HEAVY SNOW (TOTALS UP TO A FOOT) REMAINS 
POSSIBLE FROM EASTERN NEBRASKA THROUGH THE GREAT LAKES ON THE 21ST AS THE 
TROWAL BECOMES DEFINED WITH THE DEEPENING LOW PRESSURE. GULF MOISTURE 
AVAILABILITY FOR THIS SYSTEM APPEARS SOMEWHAT LIMITED BY THE ANTECEDENT COLD 
AIR OUTBREAK OVER THE EAST KEEPING CONDITIONS DRY OVER THE EASTERN U.S., THUS 
NO HEAVY RAIN OR SEVERE WEATHER THREATS ARE ANTICIPATED AT THIS TIME WITH THE 
COLD FRONT OF THIS SYSTEM. THIS COLD AIR OUTBREAK IS LIKELY TO RESULT IN A 
BRIEF PERIOD OF MUCH BELOW-NORMAL TEMPERATURES (MINIMUM TEMPERATURE ANOMALIES 
OF -12 DEGREES F OR GREATER) FOR A SMALL REGION NEAR THE GULF OF MEXICO ON THE 
19TH BEFORE CONDITIONS BEGIN TO MODERATE.
SURFACE CYCLONES ARE FORECAST IN THE BERING SEA AND NORTHEAST PACIFIC DURING 
THE COURSE OF WEEK-1, BUT THEIR OVERALL IMPACTS ON ALASKA ARE LIKELY TO BE 
MUTED. INSTEAD, A SHIFT TO NORTHEASTERLY FLOW OUT OF THE ARCTIC CIRCLE AND 
YUKON APPEARS TO BE A MORE LIKELY THREAT AS COLD AIR SETTLES ACROSS THE STATE. 
MODELS SUGGEST THE POTENTIAL FOR A HIGH WIND EVENT ALONG AND DOWNWIND OF THE 
BROOKS RANGE ON THE 19TH THROUGH 23RD IN ASSOCIATION WITH NORTHEASTERLY FLOW 
THAT COULD INDUCE KATABATIC EFFECTS. SIMILAR GAP WINDS ARE POSSIBLE FURTHER 
SOUTH ALONG THE ALEUTIAN AND ALASKAN RANGES BEGINNING ON THE 20TH AND 21ST 
RESPECTIVELY AND LASTING THROUGH THE 23RD, WITH WINDS POTENTIALLY GUSTING TO 
NEAR 100 MPH FOR YAKUTAT. THESE HIGH WINDS ARE LIKELY TO BE FUELED BY MUCH 
BELOW-NORMAL TEMPERATURES (MINIMUM TEMPERATURE ANOMALIES OF -25 DEGREES F OR 
GREATER) BUILDING ACROSS THE STATE AS COLD AIR FILTERS SOUTHWESTWARD DURING THE 
21ST THROUGH 23RD. THE GEFS AND CANADIAN MODEL GUIDANCE IS MOST BULLISH ON THE 
COLD, WHILE THE 0Z ECMWF ENSEMBLE DEPICTS A MARGINAL EVENT. LASTLY, HIGH WINDS 
COULD ALSO IMPACT ST. LAWRENCE ISLAND ON THE 19TH THROUGH 23RD, AS THE BERING 
SEA HAS NOT FROZEN IN THE VICINITY OF THE ISLAND YET THIS SEASON, AND FREEZING 
SPRAY FROM THE STRONG NORTHEAST WINDS COULD DEVASTATE COASTAL COMMUNITIES ALONG 
THE WINDWARD SHORE.
FOR WEDNESDAY JANUARY 24 - TUESDAY JANUARY 30: DURING WEEK-2, ANOMALOUS 500-HPA 
TROUGHING IS FORECAST TO EXTEND FROM ALASKA THROUGH THE GREAT BASIN, 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 ENHANCED 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 FOR THE 24TH AND 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 MODERATE RISK OF MUCH BELOW-NORMAL 
TEMPERATURES IS FORECAST FOR PORTIONS OF WESTERN AND INTERIOR MAINLAND ALASKA 
DURING THE 24TH THROUGH 26TH DUE TO ENSEMBLE MEAN FORECASTS OF MINIMUM 
TEMPERATURE ANOMALIES FROM THE 12Z GEFS AND 12Z DETERMINISTIC EUROPEAN 
GENERALLY BEING 25 TO 30 DEGREES F BELOW NORMAL.
A SLIGHT RISK OF MUCH ABOVE-NORMAL PRECIPITATION IS FORECAST FOR PARTS OF THE 
GULF STATES ON THE 24TH THROUGH 26TH. THIS AREA IS ISOLATED BY THE ECMWF 
PROBABILISTIC EXTREMES TOOL WHERE AT LEAST A 40% CHANCE OF AN INCH AND A HALF 
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 
$$