Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 222018
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 22 2014

SYNOPSIS: A VERY PROGRESSIVE PATTERN IS EXPECTED DURING THIS OUTLOOK PERIOD.
ANY PRECIPITATION HAZARDS DURING THE DAY 3-7 PERIOD WILL BE BRIEF AND
TEMPERATURES ARE EXPECTED TO BE EITHER NEAR OR ABOVE NORMAL.  FOR THE DAY 8-14
PERIOD, A MORE AMPLIFIED PATTERN IS ANTICIPATED, WHICH INCREASES THE CHANCES OF
COLD AIR AND PRECIPITATION HAZARDS, MOSTLY IN THE MIDDLE OF THE COUNTRY.

HAZARDS

HEAVY SNOW IS EXPECTED FROM THE NORTH-CENTRAL ROCKIES TO THE HIGH PLAINS AND
UPPER MIDWEST, THU-FRI, DEC 25-26.

HIGH WINDS FOR PARTS OF THE UPPER MIDWEST, FRI-SAT, DEC 26-27.

HIGH WINDS AND SIGNIFICANT WAVES FOR THE ALEUTIANS, FRI-SAT, DEC 26-27.

HIGH WINDS FOR THE WEST COAST OF ALASKA, SAT-MON, DEC 27-29.

FLOODING LIKELY IN SOUTHWEST WASHINGTON AND NORTHWEST OREGON, THU-FRI, DEC
25-26.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FROM THE NORTHERN AND CENTRAL
ROCKIES TO UPPER MIDWEST, TUE-WED, DEC 30-31.

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

DETAILED SUMMARY

FOR THURSDAY DECEMBER 25 - MONDAY DECEMBER 29: AS THIS FORECAST PERIOD BEGINS,
AN AMPLIFIED TROUGH IS FORECAST TO MOVE OFF THE EAST COAST.  ANY HAZARDOUS
WEATHER ASSOCIATED WITH THIS SYSTEM IS EXPECTED TO OCCUR BEFORE THIS OUTLOOK
PERIOD BEGINS.  CONCURRENTLY, AN UPPER-LEVEL SHORTWAVE TROUGH IS EXPECTED TO
MOVE ACROSS THE CENTRAL ROCKIES.  AS IT PASSES OVER THE MOUNTAINS, SURFACE LEE
CYCLOGENESIS IS PREDICTED TO OCCUR.  THIS WILL HELP FOCUS THE PRECIPITATION
INTO AN AREA OF HEAVY SNOW FROM THE NORTH-CENTRAL ROCKIES TO THE UPPER MIDWEST.
 AREAL SNOWFALL TOTALS OF 4-6 INCHES IS POSSIBLE DURING THE 25TH AND 26TH, WITH
MORE THAN THAT LIKELY IN THE HIGHER ELEVATIONS. ON THE BACKSIDE OF THIS SYSTEM,
THE SURFACE PRESSURE GRADIENT IS EXPECTED TO INCREASE, LEADING TO HIGH WINDS
FOR THE UPPER MIDWEST FOR THE 26TH AND 27TH, WITH WINDS OF 20-30 KNOTS
ANTICIPATED.



INTENSIFYING PRESSURE GRADIENT AT THE SURFACE TO THE SOUTH AND WEST OF ALASKA
AHEAD OF A STRONG STORM IS EXPECTED TO LEAD TO HIGH WINDS AND SIGNIFICANT WAVES
FOR THE ALEUTIANS DURING THE 26TH AND 27TH.  WINDS IN EXCESS OF 40 KNOTS AND
WAVES OF 6-10 METERS ARE LIKELY ALONG THE ISLANDS DURING THIS TIME PERIOD.
THEREAFTER, AN UPPER-LEVEL RIDGE AMPLIFIES ALONG THE EASTERN PART OF THE STATE
INTO THE EASTERN PACIFIC, ALLOWING THE STORM TO MOVE NORTH AND THEN
NORTHWESTWARDS INTO THE BERING SEA.  AT THIS TIME, THE ONLY HAZARDOUS WEATHER
EXPECTED WITH THIS SYSTEM IS HIGH WINDS FOR PORTIONS OF THE ALASKAN WEST COAST.



AS THE EASTERN PACIFIC RIDGE AMPLIFIES, A STRONG SHORTWAVE IS PREDICTED TO DIG
DOWN INTO THE WESTERN CONUS.  THIS PATTERN FAVORS SIGNIFICANT SNOWFALL IN PARTS
OF THE NORTHWEST AND INTERMOUNTAIN WEST.  AT THIS TIME THOUGH, IT IS UNCERTAIN
HOW MUCH MOISTURE WILL BE PRESENT, AND THUS, WHAT SNOWFALL ACCUMULATIONS WILL
BE.  BECAUSE OF THIS UNCERTAINTY, NO HAZARDS ARE PLACED ON THE MAP AT THIS
TIME.

FOR TUESDAY DECEMBER 30 - MONDAY JANUARY 05: AS THE EASTERN PACIFIC RIDGE AND
WESTERN TROUGH CONTINUE TO DEEPEN, COLD AIR IS FORECAST TO MOVE SOUTH OUT OF
CANADA INTO THE MIDDLE OF THE COUNTRY.  A SLIGHT RISK OF MUCH BELOW NORMAL
TEMPERATURES EXISTS WITH DAILY NIGHTTIME TEMPERATURES OF 0 DEGREES FAHRENHEIT
OR LESS NOT OUT OF THE QUESTION.  HOWEVER, THIS FORECAST IS HIGHLY UNCERTAIN,
AND IN FACT, IS NOT IN AGREEMENT WITH IMPACTS THAT WOULD BE OBSERVED FROM A MJO
PATTERN THAT IS IN ITS CURRENT PHASE.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED ON DECEMBER 18, INDICATES A VERY
SLIGHT INCREASE IN THE AREAL COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2 TO
D4) FROM 17.09 TO 17.27 PERCENT ACROSS THE CONTINENTAL U.S. PERHAPS THE LARGEST
AND MOST SIGNIFICANT CHANGE FROM LAST WEEK`S DROUGHT MONITOR IS THE ONE-CLASS
IMPROVEMENT (FROM D4 TO D3) ACROSS NORTHERN CALIFORNIA AND THE SAN FRANCISCO
AREA IN RESPONSE TO THE RECENT HEAVY RAINS IN THAT REGION.





FORECASTER: KENNETH PELMAN

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