The storm track for the last few weeks has been more to the south than I would have expected. Temperatures this morning are far below normal and tonight the temperature for the Pinecone Drop will be significantly below zero. Temperatures across the Southeastern US, much of the Caribbean and most of Europe have been chilly, too. This can be attributed to the the negative phase of the Arctic Oscillation(AO) that has been in place since the middle of November.

Arctic Oscillation - Negative phase on right. Positive Phase on left. Negative phase drives the polar jet stream and storm track farther to the south.

The key characteristics of the negative phase are high pressure at high latitudes and lower pressure to the south near 45 degrees. This brings warmer than normal conditions to some places like Greenland, and colder temperatures like we have seen in the Eastern US. It is also responsible for the shift of the Western US storm track to the south, into Arizona. The question is: “Will it last?”

As I pointed out in the fall, I thought we would be moving toward a dry and potentially warm winter. December and November both started that way and shifted along the way. Here is the GFS model outlook for the AO.

Arctic Oscillation Outlook - Climate Prediction Center

The Climate Prediction Center has been fairly consistent in their outlook for the Southwest to be warm and dry this winter, even in their 6-14 day outlooks. But, with this outlook for a mostly negative AO, they seem to be changing their tune. Here are their 6-10 and 8-14 day outlooks.

Climate Prediction Center 6-10 day Precipitation Outlook

Climate Prediction Center 6-10 day Temperature Outlook

Climate Prediction Center 8-14 day Precipitation Outlook

Climate Prediction Center 8-14 day Temperature Outlook

In this outlook from yesterday afternoon, they are seeing a persistent storm pattern similar to the last couple weeks. What’s odd is that this morning just about every model has significantly altered the outlook to little chance of significant snow for the next couple weeks. This is a big shift. Joe Bastardi, at AccuWeather, seems to believe that this pattern is going to come to an end and we will see a return to conditions like we had in Early December.

Yesterday, I thought we were looking at a persistent storm pattern. Today, I am not so sure. But, I think the next few model runs will tell the tale. With the cooling in the North Atlantic. We could see more of an average overall winter for Flagstaff.

Well, here is my T-Model outlook for Friday to Thursday, December 5-11.

This is a very novel and proprietary model. The key to it is my confidential set of inputs.

Stu T-Model for precipitation probably, December 5-11, 2010

Given the inputs to the T-model, and current NOGAPS and NOAA computer models, it looks like there could be a good chance for a cut-off low pressure system to form off the coast of California next week and move over Northern Arizona. This could be a significant storm. However, cut-of low pressure systems are notoriously difficult to forecast.

On another note, if you read the Forecast Discussion from the National Weather Service, you should look for the discussion provided by Peterson. Here is one from this morning:

000
FXUS65 KFGZ 301028
AFDFGZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
330 AM MST TUE NOV 30 2010

.SYNOPSIS...COLD AND DRY CONDITIONS WILL PERSIST TODAY BEFORE A
WARMING TREND DEVELOPS FOR THE REMAINDER OF THE WEEK.

&&

.DISCUSSION...LOW-LEVEL EASTERLY WINDS WILL PERSIST TODAY...ALTHOUGH
THEY WILL BE QUITE LIGHT. THIS WILL KEEP COLDER AIR TRAPPED OVER
MUCH OF NORTHEASTERN ARIZONA...INCLUDING THE NORTH-FACING SLOPES OF
THE MOGOLLON RIM. THIS...COMBINED WITH A VERY COLD START TO THE
DAY...WILL MAKE FOR ANOTHER AFTERNOON OF BELOW NORMAL TEMPERATURES.
BY WEDNESDAY...THROUGH FRIDAY OR SATURDAY...HIGH PRESSURE WILL
AMPLIFY OVER ARIZONA...WITH LOW-LEVEL WINDS BECOMING SOUTHWESTERLY.
THIS WILL MAKE FOR A SUBSTANTIAL WARMING TREND AND CONTINUED DRY
CONDITIONS. MODELS STILL HINTING AT THE NEXT SYSTEM BEING LATE IN
THE WEEKEND...OR EARLY NEXT WEEK. STRENGTH...TIMING...AND LOCATION
ARE ALL OVER THE PLACE...SO LOW POPS AND MODEST COOLING ARE ALL WE
CAN REALLY GO WITH FOR NOW.

&&

.AVIATION...FOR THE 12Z PACKAGE...VFR CONDITIONS WILL PREVAIL
THROUGH THE TAF PERIOD...WITH MOSTLY CLEAR SKIES...AND WINDS
GENERALLY 10KT OR LESS. A FEW HIGHER GUSTS ARE POSSIBLE THIS
AFTERNOON AT KFLG AND KGCN. AVIATION DISCUSSION NOT UPDATED FOR
AMENDMENTS.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

$$

PUBLIC...........PETERSON