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 1901Z Dec 03, 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
201 PM EST SUN DEC 03 2017

VALID 12Z THU DEC 07 2017 - 12Z MON DEC 11 2017

...STORMY PATTERN EXPECTED FOR SOUTHERN AND PORTIONS OF
SOUTHEASTERN ALASKA...

A BLOCKING FLOW PATTERN WILL KEEP THE WEATHER RATHER UNCHANGED
ACROSS ALASKA THROUGH THE MEDIUM RANGE. AN ANOMALOUS UPPER RIDGE
IS EXPECTED TO BUILD ACROSS WESTERN NORTH AMERICA DURING THE SHORT
RANGE, WITH 500 HPA HEIGHT ANOMALIES EXCEEDING +3 STANDARD
DEVIATIONS POSSIBLE BY DAY 4 (THU) ACROSS NORTHERN BRITISH
COLUMBIA. UPSTREAM OF THE RIDGE, PERSISTENT NEGATIVE HEIGHT
ANOMALIES ARE EXPECTED ACROSS THE NORTH/CENTRAL PACIFIC WITH AN
ACTIVE TRAIN OF SHORTWAVES ORIGINATING ACROSS EAST ASIA AND
QUICKLY AMPLIFYING AS THEY ENTER THE LARGER SCALE TROUGH. WHILE
CONFIDENCE IS ABOVE AVERAGE WITH RESPECT TO THIS LARGE SCALE FLOW
PATTERN, THE DETAILS ARE MUCH MURKIER. MODEL SPREAD SURROUNDING
THE SMALLER SCALE WAVES IS VERY HIGH, ESPECIALLY BY LATE IN THE
WEEK.

DETERMINISTIC SOLUTIONS SEEM TO SHOW SOME LEVEL OF AGREEMENT THAT
A RELATIVELY COMPACT AREA OF LOW PRESSURE WILL QUICKLY MOVE
NORTHWARD INTO SOUTHERN ALASKA ON THU, ALTHOUGH ENSEMBLE SPREAD IS
STILL SOMEWHAT HIGH AND MODEL RUN-TO-RUN TIMING DIFFERENCES REMAIN
(E.G. THE 12Z GFS WAS MUCH QUICKER WITH MOVING THIS SYSTEM INLAND
RELATIVE TO THE PREVIOUS CONSENSUS FROM OVERNIGHT). AFTER THU
MODEL SPREAD QUICKLY INCREASES EVEN FURTHER, BUT THERE IS A
GENERAL CONSENSUS (REPRESENTED BY THE ENSEMBLE MEANS) THAT AN AREA
OF LOW PRESSURE SHOULD LINGER SOUTH OF THE ALASKA PENINSULA
THROUGH DAYS 5-7. MULTIPLE SHORTWAVES WILL LIKELY PASS OVER THE
REGION DURING THIS TIME FRAME, WITH THE POTENTIAL FOR SMALL-SCALE
LOWS TO MOVE NEAR THE COAST OR EVEN ONSHORE, BUT FORECAST
CONFIDENCE FOR SUCH FEATURES IS VERY LOW AT THIS POINT. ANOTHER
MORE VIGOROUS SHORTWAVE LOOKS TO MOVE INTO THE BERING SEA BY LATE
SAT. WHILE MODELS GENERALLY AGREE ON THE EXISTENCE OF THIS FEATURE
AND THE ASSOCIATED SURFACE CYCLONE, THEY DIFFER SUBSTANTIALLY ON
THE STRUCTURE OF THE SYSTEM AS WELL AS THE TIMING. GIVEN THESE
CONSIDERATIONS, THE WPC FORECAST WAS INITIALLY BASED ON A
MULTI-MODEL DETERMINISTIC BLEND ON DAY 4, INCLUDING THE
ECMWF/CMC/GFS. THE FORECAST WAS QUICKLY TRENDED TO MAJORITY
ENSEMBLE (ECENS AND NAEFS) WEIGHTING FROM DAY 5 ONWARD, HOWEVER.
DETERMINISTIC MODELS WERE REMOVED FROM THE FORECAST BLEND ENTIRELY
BY DAY 8, GIVEN THE VERY LARGE SPREAD. EVEN THE ENSEMBLE MEANS
SHOULD BE USED WITH MUCH CAUTION BY THAT TIME AS ENSEMBLE SCATTER
PLOTS SHOW EXCEEDINGLY LARGE SPREAD AND LITTLE TO NO CLUSTERING OF
SOLUTIONS.

IN TERMS OF SENSIBLE WEATHER, THE IMPLICATIONS OF THIS PATTERN ARE
A BIT MORE CLEAR THAN THE DETAILS OF THE MASS FIELDS. A STORMY
PERIOD IS IN STORE FOR SOUTHERN AND SOUTHEASTERN ALASKA WITH
PERSISTENT AND DEEP SOUTHERLY FLOW TRANSPORTING COPIOUS AMOUNTS OF
PACIFIC MOISTURE NORTHWARD INTO THE REGION (PWAT ANOMALIES REACH
+2 TO +3 STANDARD DEVIATIONS THROUGH MUCH OF THE PERIOD), WITH THE
POTENTIAL FOR RELATIVELY HEAVY PRECIPITATION ACROSS MULTIPLE DAYS
(PARTICULARLY ACROSS FAVORED/WINDWARD TERRAIN). SNOW SHOULD BE A
BIT MORE SPARSE ACROSS CENTRAL/NORTHERN ALASKA, BUT SCATTERED SNOW
SHOWERS ARE STILL EXPECTED ESPECIALLY ACROSS THE BROOKS RANGE.
TEMPERATURES SHOULD GENERALLY BE NEAR OR SLIGHTLY ABOVE AVERAGE
GIVEN THE SOUTHERLY FLOW AS WELL AS THE UPPER RIDGING NOSING INTO
THE STATE.

RYAN