Fair Warm Weather to Continue through Thursday….Cooler Weather this Weekend….Forecast Continues to be dry in the short term….
Tuesday February 17, 2015
Posted at 8:43 am by Howard
Good News.. According to the Jamstec (Japanese model) The AMO is crashing and the Atlantic will be cooling the next 6 months… This may very well help the drought over the far west and CA.
Our hemispheric planetary wave pattern will be going through some significant changes over the next two weeks. Although, it is doubtful that it will mean a significant precipitation event during the month of February, it will certainly be cooler with the chance of showers or some light snowfall by this weeks end. There will be other light snowfall opportunities again before the end of the month.
Looking at the 3, 5, 8 and 11 day means….The 500MB hemi pattern in the mean, remains unchanged over the next 3 days with it being highly amplified between the Eastern Atlantic, westward to near the Central Pacific. The main anomalies that continues to affect our weather is the strong upper height anomaly near 130W and the equally strong negative height anomaly over the Great Lakes. The day 5 means show our Eastern Pac upper ridge sharpening a bit at 130W and allowing some upper jet energy to spill more westward. Additionally, there is evidence of some weak UVM will be over our region this weekend caused by a weak upper jet spinning up over or near the sierra.. Over the Great Basin the progs are pretty dry at 700MB this weekend. With that said there is enough confidence to note that temperatures will pull back a good 20 to 25 degrees, from where they are today Tuesday. And again we may get some snow showers or light snow…….
Beyond this weekend, the models continue to go in the right direction. During week 2, the “GFS means” for days 8 and 11 suggest that a more important transition will take place, especially after the 25th. The Atlantic ridge flattens and the flow out over the Atlantic becomes more zonal off the Eastern Atlantic, allowing the flushing of cold air out off the east coast. At the same time, the big trough in the mid pacific retrogrades west to near Korea and the largest height rises are now located near the Date Line. This opens the wave length quite a bit hemispherically, and according the GFS means, allows for at least the potential of a mid latitude WNW upper jet across the eastern pacific by Day 11, the end of the month. That may be the beginning of a pattern change for the Sierra that will be for the better.
Although it is still too early to know exactly the pattern that we will evolve to, the ECMWF model has a cold trof over the Pacific NW south to the Great Basin by the end of the month. This is not typically a wet pattern but it would bring snow and quite colder weather.
The GFS is much more mixed with its results showing a retrogression of the cold westward first, then more West Northwest flow which might be wetter. More time is needed…Better Visibility will occur the next week. What is certain is that it will be much colder this weekend and there will be at the least, the possibility of light snowfall.
GFS and ECMWF
PNA goes negative after the 25th of February after being positive the past week….