Prognostic Meteorological Discussion
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FXUS21 KWNC 242008
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 24 2014

SYNOPSIS: HIGH PRESSURE ALONG THE ATLANTIC COAST AT THE START OF THE OUTLOOK
PERIOD IS PREDICTED TO MOVE OUT OVER THE ATLANTIC, GRADUALLY GIVING WAY TO A
COLD FRONT APPROACHING FROM THE MISSISSIPPI VALLEY. MOISTURE STREAMING UP FROM
THE SOUTHEAST MAY RESULT IN WET CONDITIONS ACROSS THE MID-ATLANTIC REGION
DURING LATE SUNDAY AND EARLY MONDAY. MUCH COLDER ARCTIC AIR IS EXPECTED TO MOVE
SOUTHWARD ACROSS THE WESTERN AND CENTRAL LOWER 48 STATES FROM THE BEGINNING OF
THE 3-7 DAY PERIOD INTO THE MIDDLE OF WEEK-2. STRONG, SOUTHERLY, ONSHORE FLOW
FROM THE GULF OF ALASKA IS ANTICIPATED TO BRING UNSETTLED WEATHER TO PARTS OF
THE ALASKA RANGE SATURDAY TO MONDAY AND WARMER TEMPERATURES TO MUCH OF ALASKA
FOR A PROLONGED PERIOD.

HAZARDS

HEAVY RAIN FOR PARTS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS, AND
SOUTHEAST, SAT-SUN, DEC 27-28.

HEAVY SNOW FOR PARTS OF THE CASCADES, SAT, DEC 27.

HEAVY SNOW FOR PARTS OF THE BITTERROOT RANGE, SAT, DEC 27.

MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE GREAT PLAINS AND ROCKIES,
SAT-TUE, DEC 27-31.

HIGH WINDS FOR THE WEST COAST OF ALASKA, AND SOUTH-CENTRAL ALASKA, SAT-SUN, DEC
27-28.

HEAVY PRECIPITATION FOR PARTS OF THE SOUTH COAST OF ALASKA, INCLUDING KODIAK
ISLAND, SUN-MON, DEC 28-29.

HIGH WINDS FOR THE NORTHERN SIDE OF THE ALASKA RANGE, SUN-MON, DEC 28-29.

MUCH ABOVE NORMAL TEMPERATURES ACROSS MUCH OF MAINLAND ALASKA, MON-FRI, DEC
29-JAN 2.

SLIGHT RISK FOR MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE GREAT BASIN,
ROCKIES, AND GREAT PLAINS, THU-SUN, JAN 1-4.

MODERATE RISK FOR MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE CENTRAL GREAT
BASIN, CENTRAL AND SOUTHERN ROCKIES, AND CENTRAL AND SOUTHERN PLAINS, THU, JAN
1.

MODERATE TO HIGH RISK FOR MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE
NORTHERN ROCKIES AND NORTHERN GREAT BASIN, THU-SAT, JAN 1-3.

POSSIBLE FLOODING FOR PARTS OF SOUTHERN GEORGIA, SAT-SUN, DEC 27-28.

SEVERE DROUGHT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, SOUTHEAST,
LOWER MISSISSIPPI VALLEY, PACIFIC NORTHWEST, GREAT BASIN, AND CALIFORNIA.

DETAILED SUMMARY

FOR SATURDAY DECEMBER 27 - WEDNESDAY DECEMBER 31: A COLD FRONT IS PREDICTED TO
SWEEP EASTWARD ACROSS THE CONUS FROM THE MISSISSIPPI VALLEY TO THE EAST COAST,
BRINGING HEAVY RAIN TO PARTS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS,
AND SOUTHEAST OVER THE WEEKEND. SOME AREAS MAY RECEIVE 2.5 INCHES OF RAINFALL
OR GREATER IN A 24-HOUR PERIOD.



A MODERATELY STRONG UPPER-LEVEL SHORT WAVE TROUGH IS FORECAST TO IMPACT THE
PACIFIC NORTHWEST, BRINGING HEAVY SNOW TO PARTS OF THE CASCADES ON SATURDAY
INTO SATURDAY NIGHT. SNOW LEVELS ARE EXPECTED TO RANGE FROM 1500 TO 2000 FEET,
WITH SOME AREAS POTENTIALLY RECEIVING SEVERAL INCHES OF SNOW.



LOW PRESSURE IS PREDICTED TO TRACK SOUTHEASTWARD OUT OF ALBERTA ACROSS THE
NORTHERN GREAT PLAINS AT THE BEGINNING OF THE PERIOD. THIS STORM SYSTEM IS
ANTICIPATED TO BRING HEAVY SNOW TO PARTS OF THE BITTERROOT RANGE ON SATURDAY,
WITH MODELS INDICATING THE POSSIBILITY OF SOME AREAS RECEIVING OVER AN INCH OF
LIQUID EQUIVALENT IN A 24-HOUR PERIOD. ARCTIC AIR IS EXPECTED TO FOLLOW IN ITS
WAKE ACROSS THE WESTERN AND CENTRAL CONUS, BRINGING MUCH BELOW NORMAL
TEMPERATURES TO A LARGE AREA OF THE GREAT PLAINS AND ROCKIES THIS PERIOD INTO
THE BEGINNING OF WEEK-2. DAILY MINIMUM TEMPERATURES ARE FORECAST TO REACH 20
DEGREES F BELOW NORMAL IN SOME AREAS. PORTIONS OF THE SAN JOAQUIN VALLEY IN
CALIFORNIA MAY REACH FREEZING TEMPERATURES AT THE BEGINNING OF THE PERIOD.
HOWEVER, DUE TO SIGNIFICANT MODEL UNCERTAINTY REGARDING HOW FAR SOUTH THIS COLD
AIR WILL REACH, AN ADDITIONAL TEMPERATURE HAZARD IS NOT DESIGNATED AT THIS TIME.



A STRONG STORM SYSTEM IS EXPECTED TO APPROACH WESTERN ALASKA FROM THE BERING
SEA AT THE BEGINNING OF THIS PERIOD, BRINGING HIGH WINDS TO PARTS OF THE WEST
COAST AND SOUTH-CENTRAL ALASKA OVER THE WEEKEND. SOME AREAS MAY EXPERIENCE
SUSTAINED WIND SPEEDS REACHING 40 KNOTS OR GREATER. STRONG, SOUTHERLY FLOW EAST
OF THIS STORM SYSTEM MAY BRING HIGH WINDS TO THE NORTHERN SIDE OF THE ALASKA
RANGE, AND HEAVY RAIN AND SNOW ALONG THE SOUTH COAST OF ALASKA, INCLUDING
KODIAK ISLAND, SUNDAY TO MONDAY. THIS AREA MAY EXPERIENCE SUSTAINED WIND SPEEDS
OF 35 KNOTS OR GREATER AND RECEIVE 3 INCHES OR GREATER OF LIQUID EQUIVALENT IN
A 24-HOUR PERIOD.



STRONG SOUTHERLY FLOW FROM THE GULF OF ALASKA IS ANTICIPATED TO BRING MUCH
ABOVE NORMAL TEMPERATURES TO MUCH OF MAINLAND ALASKA MONDAY TO THE MIDDLE OF
WEEK-2. MODELS SHOW DAILY MINIMUM TEMPERATURES REACHING 40 DEGREES F ABOVE
NORMAL OR GREATER. THIS INFLUX OF WARM, MOIST AIR ACROSS COLD, WET ROADS MAY BE
CONDUCIVE TO FROSTY, SLICK DRIVING CONDITIONS. ADDITIONALLY, ANY LIQUID
PRECIPITATION AWAY FROM THE COAST MAY LEAD TO A FREEZING RAIN HAZARD.

FOR THURSDAY JANUARY 01 - WEDNESDAY JANUARY 07: WARM, SOUTHERLY FLOW FROM THE
GULF OF ALASKA IS EXPECTED TO EXTEND INTO THE BEGINNING OF THE WEEK-2 PERIOD.
THIS PATTERN IS ANTICIPATED TO CONTINUE THE ENHANCED LIKELIHOOD FOR MUCH ABOVE
NORMAL TEMPERATURES ACROSS MUCH OF MAINLAND ALASKA ON JANUARY 1-2.



COLD, ARCTIC AIR ACROSS WESTERN AND CENTRAL CONUS IS PREDICTED TO PERSIST FROM
THE DAYS 3-7 PERIOD INTO MUCH OF THE WEEK-2 PERIOD. A SLIGHT RISK OF MUCH BELOW
NORMAL TEMPERATURES IS DESIGNATED FOR A LARGE AREA COVERING THE GREAT BASIN,
ROCKIES, AND GREAT PLAINS JANUARY 1 TO 4. MODERATE RISK AREAS FOR MUCH BELOW
NORMAL TEMPERATURES ARE ISSUED FOR PARTS OF THE CENTRAL GREAT BASIN, CENTRAL
AND SOUTHERN ROCKIES, AND CENTRAL AND SOUTHERN PLAINS ON JANUARY 1, AND ACROSS
THE NORTHERN ROCKIES AND NORTHERN GREAT BASIN JANUARY 1 TO 3. A HIGH RISK AREA
FOR MUCH BELOW NORMAL TEMPERATURES IS ALSO INCLUDED ACROSS PARTS OF THE IDAHO
PANHANDLE JANUARY 1. THESE AREAS HAVE THE POTENTIAL OF DAILY MINIMUM
TEMPERATURES REACHING BELOW THE 15TH PERCENTILE COMPARED TO CLIMATOLOGY, AND
FREEZING TO BELOW-FREEZING TEMPERATURES.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED ON DECEMBER 24, INDICATES A VERY
SLIGHT DECREASE IN THE AREAL COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2 TO
D4) FROM 17.27 TO 17.18 PERCENT ACROSS THE CONTINENTAL U.S.

FORECASTER: MELISSA OU

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