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posted on 01 November 2017

NOAA Updates November, 2017 Outlook

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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.

November Outlook Updated


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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

November Early Outlook Temperature Issued on October 21, 2017

Updated Outlook Issued on October 31, 2017

Temperature November, 2017 Outlook Updated on October 31, 2017

This is a big change for twelve days. We now have a large cool Northwest anomaly (extending north into the Alaskan Panhandle) in the forecast and the Southern Tier warm anomaly extends north joining the prior warm anomaly in New England.

Precipitation

Prior Outlook Issued on October 19, 2017

November Early Outlook Precipitation Outlook Issued on October 21,  2017

Updated Precipitation Outlook Issued on October 31, 2017

November  Precipitation Outlook Updated on October 31, 2017

The Northern Tier is a lot wetter. The Southern Tier dry anomaly is a lot more intense. Southern Alaska including the Panhandle is now shown as dry.

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

November and NDJ 2017 2017-2018 Updated on October 31, 2017

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.

For both temperature and precipitation if you assume the colors in the maps are assigned correctly, it is a simple algebra equation to solve the month two/three forecast probability for a given location = (3XThree-Month Probability - Month One Probability)/2*. So you can derive the month two/three forecast this way. You can do that calculation easily for where you live or for the entire map.

*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.

An issue with the above procedure when we do it at the end of a month is that we are comparing a three-month map produced for release on the third Thursday of the month with an updated Single-Month map issued on the last day of the month. So the question one has to deal with is whether the changes for the next month change what NOAA would have issued for the three-month period if they were updating that as well on the last day of the month.
Our conclusion is that this is indeed the case this month to some extent. So one needs to apply the above subtraction methodology will a liberal dose of caution since we believe NOAA is playing catch-up re the La Nina and correcting the previous overly optimistic view of the MJO as it applied to November. The former change might impact December and January but the MJO change most likely would not.

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

Click here for a list of Sig Silber's Weather Posts

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