Skip Navigation Links weather.gov 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center

 
 

 

Follow the Weather Prediction Center on Facebook Follow the Weather Prediction Center on Twitter
NCEP Quarterly Newsletter
WPC Home
Analyses and Forecasts
   National High & Low
   WPC Discussions
   Surface Analysis
   Days ½-2½ CONUS
   Days 3-7 CONUS
   Days 4-8 Alaska
   QPF
   PQPF
   Flood Outlook
   Winter Weather
   Storm Summaries
   Heat Index
   Tropical Products
   Daily Weather Map
   GIS Products
Current Watches/
Warnings

Satellite and Radar Imagery
   Satellite Images
   National Radar
Product Archive
WPC Verification
   QPF
   Medium Range
   Model Diagnostics
   Event Reviews
   Winter Weather
International Desks
Development and Training
   Development
WPC Overview
   About the WPC
   Staff
   WPC History
   Accomplishments
   Other Sites
   FAQs
Meteorological Calculators
Contact Us
   About Our Site
 
USA.gov is the U.S. Government's official web portal to all federal, state, and local government web resources and services.
 
Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1929Z Dec 07, 2017)
 
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
 
Abbreviations and acronyms used in this product
 
View Alaska Map


ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM EST THU DEC 07 2017

VALID 12Z MON DEC 11 2017 - 12Z FRI DEC 15 2017

THE LARGE SCALE FLOW PATTERN ACROSS THE NORTH PACIFIC IS EXPECTED
TO REMAIN RELATIVELY STABLE THROUGH THE EXTENDED FORECAST PERIOD.
STRONG RIDGING IS EXPECTED TO PERSIST ALONG THE NORTH AMERICA WEST
COAST, WITH PERSISTENT NEGATIVE HEIGHT ANOMALIES CENTERED ACROSS
THE NORTH/CENTRAL PACIFIC, JUST NORTH OF HAWAII. A STREAM OF
SHORTWAVES WILL EJECT FROM THE BROADER AREA OF NEGATIVE HEIGHT
ANOMALIES AND MOVE NORTHWARD AROUND THE WESTERN SIDE OF THE RIDGE
INTO ALASKA THROUGH THE PERIOD. TELECONNECTIONS ASSOCIATED WITH
SEVERAL OF THE STRONGER NORTHERN HEMISPHERE 500 HPA HEIGHT
ANOMALIES SUPPORT A CONTINUATION OF THIS PATTERN AND MAINTENANCE
OF THE RIDGE THROUGH THE NEXT WEEK. GIVEN THE RELATIVELY HIGH
PREDICTABILITY OF THE LARGE-SCALE PATTERN, MODELS AND ENSEMBLES
SHOW ABOVE AVERAGE AGREEMENT ESPECIALLY EARLY IN THE FORECAST
PERIOD. BY MID TO LATE NEXT WEEK, MODEL SOLUTIONS CONTINUE TO SHOW
ABOVE AVERAGE AGREEMENT ON A BROAD SCALE, BUT WITH SOME INCREASING
DIFFERENCES RELATED TO THE DETAILS OF A SOMEWHAT CHAOTIC SMALL
SCALE FLOW PATTERN WITH MULTIPLE WAVES AND INTERACTIONS. MODELS
ALSO SHOW SOME DIFFERENCES WITH RESPECT TO IF AND HOW QUICKLY THE
UPPER RIDGE BEGINS TO BREAK DOWN. THE CMC HAS BEEN PERSISTENT WITH
BREAKING THE RIDGE DOWN QUICKLY NEXT WEEK, WHICH IS CONSIDERED
UNLIKELY GIVEN THE DESCRIBED HEMISPHERIC FLOW PATTERN AND
TELECONNECTION SUPPORT FOR THE RIDGE.

ON DAY 4 (MON) ONE SHORTWAVE AND SURFACE LOW ARE FORECAST BY MOST
GUIDANCE TO BE MOVING QUICKLY INLAND ACROSS SOUTHERN/CENTRAL AK.
THE GFS AND 00Z ECMWF SHOWED GOOD AGREEMENT WITH RESPECT TO THE
TIMING AND POSITION OF THIS FEATURES, AND THUS THESE TWO MODELS
COMPRISED A MAJORITY OF THE FORECAST BLEND DURING THE EARLY PART
OF THE FORECAST PERIOD. BY DAY 5 (TUE) ANOTHER IN THE RAPID
SUCCESSION OF SURFACE LOWS SHOULD BE LOCATED A COUPLE HUNDRED
MILES SOUTH OF THE ALEUTIANS AS IT ALSO MOVES QUICKLY NORTH AND
WEAKENS. ON DAY 6 (WED) YET ANOTHER SHORTWAVE/SURFACE LOW SHOULD
ENTER THE GULF OF AK AS IT MOVES NORTHWARD TOWARD MAINLAND AK.
SPREAD BEGINS TO INCREASE A BIT BY THIS TIME, BUT THE 00Z ECMWF
WAS RELATIVELY WELL-CENTERED WITHIN THE ENSEMBLE SPREAD AND THUS
WAS WEIGHTED A BIT MORE HEAVILY BY THIS TIME RELATIVE TO THE GFS
WHICH HAS SHOWN GREATER RUN-TO-RUN VARIABILITY. FINALLY, BY DAYS
7-8 (THU-FRI), A POTENTIALLY MORE SIGNIFICANT SHORTWAVE IS SHOWN
BY MOST GUIDANCE TO AMPLIFY ACROSS THE ALEUTIANS/BERING SEA WITH
LIKELY THE MOIST MATURE SURFACE CYCLONE OF THE PERIOD CROSSING THE
ALEUTIANS BY THU NIGHT. MODELS/ENSEMBLES ALL AGREE ON THE
EXISTENCE AND GENERAL NATURE OF THIS SYSTEM, BUT DIFFERENCES WITH
RESPECT TO DETAILS OF UPPER-LEVEL AND SURFACE CYCLONE STRUCTURE
RESULT ON MODERATELY DIFFERING TIMING/INTENSITY SCENARIOS. TO
ACCOUNT FOR THE GRADUALLY INCREASING UNCERTAINTY DURING DAYS 6-8,
A TREND TOWARD MAJORITY 00Z ECENS/06Z GEFS WEIGHTING WAS SHOWN
DURING THIS TIME FRAME. GIVEN THE DECENT LARGE SCALE AGREEMENT,
COMPONENTS OF DETERMINISTIC ECMWF/GFS WERE INCLUDED THROUGH DAY 8.

IN TERMS OF SENSIBLE WEATHER, THE PERSISTENT AND DEEP SOUTHERLY
FLOW AND RAPID TRAIN OF SHORTWAVES WILL RESULT IN A CONTINUED
STORMY PERIOD FOR SOUTHERN AND PORTIONS OF SOUTHEASTERN AK, WITH
HEAVY PRECIPITATION POSSIBLE ESPECIALLY IN FAVORED WINDWARD
TERRAIN AREAS. FARTHER NORTH, SOMEWHAT DRIER CONDITIONS WILL
PREVAIL NORTH OF THE ALASKA RANGE, BUT STILL EXPECT SCATTERED SNOW
SHOWERS THROUGH MUCH OF THE PERIOD AS ROUNDS OF SHORTWAVE ENERGY
PASS OVERHEAD. UPPER RIDGING AND SOUTHERLY FLOW WILL KEEP
TEMPERATURES NEAR TO SLIGHTLY ABOVE NORMAL FOR MUCH OF
SOUTHERN/CENTRAL AK. TEMPERATURES WILL BE CLOSE TO CLIMATOLOGICAL
NORMS NORTH OF THE BROOKS RANGE, WITH TEMPERATURES HOVERING FROM
THE SINGLE DIGITS ABOVE TO SINGLE DIGITS BELOW ZERO.

RYAN