Thursday, November 26, 2015

Long Range Forecast (Posted 11/26/15)

This is the long range forecast, published on 11/26/15.

 The 500mb pattern over the last week showed a dominating ridge in the Gulf of Alaska, leading to negative geopotential height anomalies in central North America. This was exhibited by the strong storm system(s) that passed through the region since our last outlook.

 500-millibar chart shows a strong upper level low stationed over the Southwest, as the closed blue contours indicate. Southerly lower-level winds are advecting moisture northward into the Plains and Midwest, which will serve to kick off wintry weather on Thanksgiving.

 Polar water vapor imagery shows an active pattern in the North Hemisphere. We see two upper level lows with a Rossby Wave signature in the Gulf of Alaska, as well as another upper level low impacting the Aleutian Islands. Hurricane Sandra is shown near Mexico, and this will deliver moisture to the US later on.

 Analysis of the jet stream shows how the upper level low to the southwest of the Gulf of Alaska will likely be cut off from the jet stream in the near future, while a strong jet streak plows into the Pacific Northwest. Another jet streak pressing northwest of Arizona to the southeast of the trough tells us the upper level low in the Southwest is preparing to eject eastward. We also see another jet streak ribbon exiting Japan, which should provide us with a storm opportunity about 7-10 days down the road.

 Current tropical forcing across the globe shows upper level divergence from the area east of Madagascar, as well as northeast of Australia. This forcing pattern in the central Pacific is typically favorable for warmer weather, although additional convection near Africa helps dilute its influence so forcing is not too useful in its current position.

 Expecting a re-amplification of the pattern over the next 7-10 days as we see increased storm chances. Watch for a moderation in temperatures over the next several days, as tropical forcing indicates the atmosphere will be favorable for generally warmer than normal weather.

Storm concerns … potential storm monitored for 12/2 – 12/6. Increased risk for stormier than normal pattern about 12/5 – 12/15, though confidence is low.

 Continuing with previous outlook, conditions do still look somewhat cooler and stormier around the Christmas timeframe. New Years Day and the first week of 2016 should see a departure from this cooler/wetter pattern back into more moderated temperatures.

The Next Long Range Outlook will be published on December 2nd, 2015 at 5:00 PM CDT.