Prognostic Meteorological Discussion
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FXUS21 KWNC 172135
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST JANUARY 17 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 (EXCLUDING THE
ALEUTIANS), THE GREAT BASIN, SOUTHWEST AND GREAT PLAINS IS FORECAST, WITH
MID-LEVEL HIGH PRESSURE ANTICIPATED OVER THE EAST.

HAZARDS

HEAVY PRECIPITATION ACROSS PORTIONS OF THE GREAT BASIN, THE NORTHERN ROCKIES,
CALIFORNIA, AND THE PACIFIC NORTHWEST, SAT-MON, JAN 20-JAN 22.

HIGH WINDS ACROSS COASTAL PORTIONS OF THE PACIFIC NORTHWEST, SUN, JAN 21.

HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF CALIFORNIA AND THE
PACIFIC NORTHWEST, SAT-SUN, JAN 20-JAN 21.

HIGH WINDS ACROSS PORTIONS OF THE CENTRAL PLAINS, THE CENTRAL ROCKIES, THE
CENTRAL GREAT BASIN, THE SOUTHERN ROCKIES, THE SOUTHERN PLAINS, AND THE
SOUTHWEST, SAT-SUN, JAN 20-JAN 21.

HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL PLAINS, THE
CENTRAL GREAT BASIN, AND THE NORTHERN PLAINS, SAT, JAN 20.

HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI
VALLEY, THE GREAT LAKES, THE UPPER MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS,
SUN, JAN 21.

HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER MISSISSIPPI VALLEY,
SUN-TUE, JAN 21-JAN 23.

HEAVY PRECIPITATION ACROSS PORTIONS OF THE NORTHEAST AND THE GREAT LAKES,
MON-TUE, JAN 22-JAN 23.

HIGH WINDS ACROSS COASTAL PORTIONS OF THE MID-ATLANTIC AND THE NORTHEAST,
MON-WED, JAN 22-JAN 24.

HIGH WINDS ACROSS PORTIONS OF SOUTHERN INTERIOR ALASKA, THE SOUTH COAST OF
ALASKA, AND KODIAK ISLAND, SUN-WED, JAN 21-JAN 24.

HIGH WINDS ACROSS PARTS OF THE BROOKS RANGE AND ST. LAWRENCE, SAT-TUE, JAN
20-JAN 23.

MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF MAINLAND ALASKA, SUN-WED, JAN
21-JAN 24.

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHWESTERN
QUARTER OF THE CONUS, THU-SAT, JAN 25-JAN 27.

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF NEW MEXICO AND
WESTERN TEXAS, SUN-MON, JAN 28-JAN 29.

SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST, THE SOUTHERN
APPALACHIANS, THE LOWER MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE
TENNESSEE VALLEY, THU-MON, JAN 25-JAN 29.

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF MAINLAND ALASKA
AND THE ALEUTIANS, THU-SUN, JAN 25-JAN 28.

MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF MAINLAND
ALASKA, THU-SAT, JAN 25-JAN 27.

HIGH WINDS ACROSS PORTIONS OF THE SOUTH COAST OF ALASKA, 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 SATURDAY JANUARY 20 - WEDNESDAY JANUARY 24: 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 NORTHERN IDAHO ON JANUARY 20-22. 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 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). HIGH WINDS (40 KNOTS OR
GREATER) ARE POSSIBLE ACROSS COASTAL PARTS OF THE PACIFIC NORTHWEST ON JAN 21,
AS WELL AS HIGH SIGNIFICANT WAVE HEIGHTS (18 FEET OR GREATER) ALONG COASTAL
PARTS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, JAN 20-21.



IN ASSOCIATION WITH THE FIRST TROUGH MOVING INLAND, A PERIOD OF HIGH WINDS
(SUSTAINED AT 30 KNOTS OR GREATER) IS LIKELY ACROSS THE CENTRAL PLAINS, THE
CENTRAL ROCKIES, THE CENTRAL GREAT BASIN, THE SOUTHERN ROCKIES, THE SOUTHERN
PLAINS, AND THE SOUTHWEST JAN 20 TO 21. MARGINALLY ELEVATED FIRE WEATHER
CONDITIONS, THOUGH NOT DEPICTED ON THE MAP, ARE ALSO FORECAST ACROSS PORTIONS
OF EASTERN NEW MEXICO AND WEST TEXAS ON JAN 20 AND WEST-CENTRAL TEXAS ON JAN 21
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 CENTRAL ROCKIES, THE CENTRAL
PLAINS, THE CENTRAL GREAT BASIN, AND THE NORTHERN PLAINS. 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. 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. AS THIS LOW MOVES NORTHEASTWARD TOWARD NEW ENGLAND BY JAN 23,
PARTS OF THE GREAT LAKES MAY RECEIVE HEAVY SNOW JAN 21 TO 23, AND PARTS OF NEW
ENGLAND MAY RECEIVE HEAVY SNOW WITH LOCALIZED AREAS OF ICING AND FREEZING RAIN.
THESE AREAS MAY RECEIVE UP TO A FOOT OF SNOW OR GREATER IN 24-HOURS. THE
POTENTIAL FOR ICING IMPACTS FOR NEW ENGLAND ARE STILL EXPECTED TO BE LIMITED AT
THIS TIME. 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.



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 JAN 20 TO 23, 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 21ST AND LASTING THROUGH THE
24TH, 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. LASTLY, HIGH WINDS
COULD ALSO IMPACT ST. LAWRENCE ISLAND ON JAN 20 TO 23, 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 THURSDAY JANUARY 25 - WEDNESDAY JANUARY 31: MID-LEVEL TROUGHING IS
ANTICIPATED TO DEVELOP ACROSS MAINLAND ALASKA AND THE ALASKA PANHANDLE AS WELL
AS THE WESTERN HALF OF THE CONUS FROM THE BEGINNING TO MIDDLE OF WEEK-2. A
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES IS FORECAST ACROSS MAINLAND
ALASKA AND THE ALEUTIANS JAN 25 TO 28 AND THE NORTHWESTERN QUARTER OF THE CONUS
JAN 25 TO 27. IN THESE HIGHLIGHTED REGIONS, THE GEFS PROBABILISTIC EXTREMES
TOOL GIVES AT LEAST A 20% CHANCE OF THE DAILY MINIMUM TEMPERATURES BEING BELOW
THE 15TH CLIMATOLOGICAL PERCENTILE. 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 JAN 25 TO
27 DUE TO MODEL ENSEMBLE MEAN FORECASTS INDICATING MINIMUM TEMPERATURE
ANOMALIES 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 JAN 25 TO 29. THIS AREA IS ISOLATED BY THE ECMWF PROBABILISTIC
EXTREMES TOOL WHERE AT LEAST A 20% CHANCE OF AN INCH OF RAIN OVER 3-DAYS IS
POSSIBLE, AND GENERALLY WHERE THERE IS A 20% CHANCE OF THE 3-DAY TOTAL REACHING
THE 85TH PERCENTILE OR GREATER. 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: MELISSA OU

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