Written by Sig Silber
The NOAA Update agrees with the recent short-term forecasts but is very different from the Early Outlook issued on October 19, 2017. It seems like the ongoing process of catching up with the imminent La Nina. But that is not how NOAA describes it. The role of the MJO is downplayed but that is not surprising in that the MJO is a fairly short-term pattern with impacts from the Active Phase generally lasting just three to four weeks. In this update report, we compare the new forecast with the prior forecast made just twelve days ago.
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NOAA Update of their Outlook for November
NOAA has, as usual, issued an update for the month following the last day of the prior month. This update was issued on October 31. In this Update Report, we present the Updated Outlook and compare it to the Early Outlook for November issued on October 19, 2017 just twelve days ago.
Temperature
Prior Outlook Issued on October 19, 2017
Updated Outlook Issued on October 31, 2017
Precipitation
Prior Outlook Issued on October 19, 2017
Updated Precipitation Outlook Issued on October 31, 2017
Here is the NOAA Discussion released with the November Update.
30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2017
THE UPDATED NOVEMBER OUTLOOK SHARES MANY SIMILARITIES WITH THE 0.5-MONTH LEAD OUTLOOK FROM EARLIER IN THE MONTH, SUGGESTING THAT THE BROAD LOW-FREQUENCY PATTERN FAVORED IN THE ORIGINAL OUTLOOK IS CONSISTENT WITH THE FORECAST EVOLUTION OVER THE NEXT FEW WEEKS. THE MJO HAS BEEN ACTIVE, AND THE RECENT EVOLUTION OVER THE NORTH PACIFIC AND FORECAST EVOLUTION OVER THE NEXT SEVERAL DAYS OVER NORTH AMERICA IS CONSISTENT WITH WHAT ONE WOULD EXPECT FROM MJO FORCING. HOWEVER THE MJO IS FORECAST TO BREAK DOWN AND NO LONGER PROJECT ONTO A FAVORABLE TROPICAL FORCING PATTERN DURING THE NEXT WEEK, LIMITING ITS USEFULNESS AT THIS TIME.
A HIGH-AMPLITUDE PATTERN IS FORECAST EARLY IN THE PERIOD, WITH ANOMALOUS RIDGING (TROUGHING) FAVORED OVER PARTS OF THE NORTH PACIFIC (WEST-CENTRAL CANADA). THIS PATTERN FAVORS THE DEVELOPMENT OF COLD, CONTINENTAL AIR MASSES OVER WESTERN CANADA WHICH IN TURN ARE EXPECTED TO SURGE SOUTHWARD INTO THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS. THE MEAN FRONTAL ZONE IS FORECAST TO RESIDE NEAR THE GREAT LAKES, EXTENDING SOUTHWESTWARD FROM THERE. AS A RESULT A GENERAL COLD NORTHWEST-WARM SOUTHEAST PATTERN IS DEPICTED WITH FAIRLY HIGH CONFIDENCE GIVEN THE HIGH-AMPLITUDE PATTERN FORECAST DURING THE FIRST TWO WEEKS OF THE MONTH. THIS PATTERN PROJECTS STRONGLY ONTO THE WINTERTIME PNA PATTERN (NEGATIVE PHASE), AND A POSITIVE AO/NAO PATTERN IS FAVORED BY VARIOUS MODELS EARLY IN THE MONTH. THE LATEST WEEK 3-4 GUIDANCE FROM THE CFS AND ECMWF ARE IN BROAD AGREEMENT DEPICTING A CONTINUED TILT TOWARD BELOW-NORMAL TEMPERATURES OVER THE NORTHWEST, BUT DIFFER FARTHER EAST. THE ECMWF FAVORS NEAR-NORMAL TEMPERATURES OVER THE GREAT LAKES, FOR INSTANCE, MORE CONSISTENT WITH THE FORECAST NEGATIVE PHASE OF THE NPO-WP TELECONNECTION PATTERN THROUGH THE FIRST TWO-THIRDS OF THE MONTH. THE ECMWF SOLUTION IS ALSO MORE CONSISTENT WITH THE EVOLUTION OF THE GEFS THROUGH DAY 16, AND SO IS WEIGHTED MORE IN THIS UPDATED OUTLOOK.
THE PRECIPITATION OUTLOOK IS UPDATED TO REFLECT THE INCREASED CONFIDENCE GAINED FROM EARLY MONTH PRECIPITATION ACROSS PARTS OF THE WEST AND, TO LESSER EXTENT, THE OHIO VALLEY AND GREAT LAKES. BELOW-NORMAL RAINFALL IS LIKELY ACROSS MUCH OF THE SOUTHEAST AND SOUTHERN PLAINS, WITH THE VARIOUS FORECAST TOOLS LINING UP IN AGREEMENT. HIGH AMPLITUDE RIDGING OVER THE BERING SEA DURING AT LEAST THE FIRST HALF OF THE MONTH FAVORS BELOW-NORMAL PRECIPITATION FOR SOUTHERN ALASKA INCLUDING THE PANHANDLE.
Sometimes it is useful to compare the present month outlook to the three-month outlook
November Plus November – January 2017/2018 Outlook
One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.
*The concept is that the probabilities of a deviation from climatology in the First Month and the combined Month Two and Three forecast that one derives must average out to the probabilities shown in the three-month maps.
For those who missed the Weekly Report which provides a lot more detail on how this will unfold with respect to the Days 6 – 10, 8 – 14 and weeks 3 and 4, you can access that report here.
