WEDNESDAY: 06-JAN-16 / 2:25 PM CDT
NEXT *FULL* WX UPDATE ON FRIDAY
SOCAL RAIN CONTINUES WITH INCREASING CHANCES FOR MAJOR WINTER STORMS EAST
A series of storms will continue thru the weekend in the SW US – with another 1”-2” of rain in SOCAL and 1-2 ft. of additional snow in the Sierras – and more mud slide potential. (This will bring the Week storm total to 2”-5” in SOCAL and Sierra snowpack totals of 2 to 5 ft.) Precip will become more scattered and lighter during the weekend across SOCAL before drier and milder conditions return to the region by the end of Week 1 as the main Pacific storm track starts shifting back to the PAC NW (though it is likely to return to the SW US towards the end of JAN).
As the western system moves to the Plains tomorrow, a surface storm will form and head for the Great Lakes with a surge of warmer air ahead of it to the east of the Mississippi Valley. The storm will bring locally heavy Precip of 1”-2” to the mid-Mississippi Valley – exacerbating the record flooding on the Mississippi. Mostly rain is expected in Chicago – rather unusual for mid-winter – which will also may total more than 1” making this a VERY unusual event. The storm/Precip will be followed by much colder conditions in the Midwest during the weekend, with a second surge of arctic air during the middle of next week. Precip reaches the eastern US where rain is expected in all the large coastal cities this weekend before colder WX moves in next week. However, along with the colder air next week in the east – there is increasing potential for 1 or even 2 major winter storms in the Northeast US during Week 2 as a powerful sub-tropical jet stream interacts with vigorous TROFS in the SE US.
The ‘blocky’ high latitude pattern is expected to gradually weaken towards the end of Week 2, after which milder Temps may overspread the northern tier of states in late JAN and well into FEB as El Niño re-exerts itself on the mid-latitude weather pattern.
Fig 1: 2015 High Temporal Resolution Surface Height (SSH) Anomalies from the JASON (NASA) Satellite platform highlighting changes since JAN 1, 2015: The above looped imagery is assembled EVERY day (the highest temporal resolution available), showing the evolution of El Niño into the strongest warm episode since the all-time Super El Niño of 1997/98. Since warmer water occupies greater volumes than cold water, higher than normal Sea Surface Heights (SSH) correlate with warmer than normal ocean Temps – while colder ocean waters correlate with lower than normal SSH’s. Keep in mind that actual SST anomalies do NOT always correspond on a one-to-one basis with Total Ocean Heat Content (OHC) of the entire corresponding column of water, which is generally represented by the JASON SSH anomalies. Note the impact of the powerful oceanic Kelvin Waves that crossed the equatorial Pacific during MAR/APR, late MAY/JUN, and again later in JUN and JUL which can be seen with the eastward expansion of the ‘white’ colored region. By the end of the summer and thru the fall – heat content was so high, that the entire equatorial EPAC was above the MAX height shown by the White shading. As colder sub-surface waters spread into the EPAC during the past month, total heat content has dropped considerably just North of the Equator with the highest heat content waters located to the south of Equator and off the west coast of Mexico.
Fig 2: MJO Analysis / Forecast for Next 30 Days The latest MJO Phase diagram (Left panel) indicates it remains moderately strong as it heads moves across the EPAC towards the Atlantic and then Africa later next week. As conjectured over the past few weeks, the MJO has triggered another Westerly Wind Burst (WWB) – and this should help stabilize SST anomalies in the key ENSO regions during the rest of JAN before they begin to decline again during FEB. The extended outlook from the ECMWF Ensembles (Right panel) anticipates the MJO will remain quite active with a new ‘cycle’ starting by the start of FEB. strong while steadily moving eastward into the West Pacific. This implies the MJO will continue to be a major player for North American Weather along with El Niño for most of the winter – though how it will moderate the pattern in FEB is uncertain, and highly dependent on exactly where the strongest forcing from El Niño ends up being during late JAN and FEB.
Fig 3: 850MB Wind Anomaly Outlook for Equatorial Pacific As previously conjectured, the Hovmöller chart of 850MB westerly wind anomalies shows the development of a VERY STRONG Westerly Wind Burst (WWB) during the last couple days that is going to intensify further this week as the MJO moves across the Atlantic towards the Indian Ocean (where a new cycle is forecast to begin based on the long range ECMWF Ensemble forecast model). This should halt the decline in SST anomalies in the ENSO region thru the end of JAN before it begins to decline again in FEB. However, El Niño is expected to remain ‘strong’ thru most of FEB before it falls off to neutral territory during the summer (POSSIBLY shifting to a La Niña state in the Fall.)
Fig 4: GFS 10 Day Forecasts for Primary Teleconnections that impact North American Weather The latest forecasts for the primary Teleconnection indices (NAO, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation)) initially support colder than normal Temps in the East – but most indicators are expected to trend towards a more neutral phase – with support for a moderation in Temps to near or above normal during last 8-10 days of the month.
Fig 5: 500mb (≈ 18,000 Ft) Height Forecast Loop for the next 2 Weeks The above loops show the wind patterns and jet stream wind speeds (250mb chart) and the location of TROF’s, Ridges, and anomalous 500MB heights (implied Temps – with bluish shading for below normal, and reddish shades for above normal heights). The highly progressive pattern continues, though a more northerly wind component over the northern US and higher amplitude TROFS will colder conditions to move into the northern and eastern US at times. The storm track shifts towards the PAC NW during Week 2 like it was in DEC) while a strong sub-tropical jet keeps the weather pattern wet and quite active across the southern state. The chances for major winter storms in the east and especially NE US will increase during Week 2 – though with a changing pattern, track forecasts can be notoriously bad this far in advance.
Fig 6: GFS 15-Day Precipitation Pattern Loop (for mounts greater than 0.10” only)Stormy conditions will persist this week in SOCAL as a series of disturbances move from the Pacific eastward across the SW US and then towards the NE US. Heavy rains in the Mid-Mississippi Valley later this week spread into the NE over the weekend – and should end early next week. By then, Precip will begin to re-develop across the Gulf coast and SE US, raising the CHANCE for a snow event in the NE later next week. Another 1 or potentially 2 major winter storms are possible in the east during Week 2.
Fig 7: Temperature ANOMALY forecast for Week 1 is based STRICTLY on the MOS data forecasts from the todays 12Z operational GFS model run with only minor adjustments towards the raw model data points for Days 6 and 8. Temps will continue to AVERAGE Above normal during Week 1 in the east with warming Temps in the Midwest and east this week and much colder conditions following behind the storm system in the Midwest over the Weekend and in the east next week. (There will be a few mornings next week with Temps that may average 15 degrees below normal in the upper Midwest – typical during JAN – but not even remotely close to setting any records.) Overall Confidence in the forecast anomaly and Magnitude is near to above average with a reading of ‘4’ for the anomaly pattern and ‘3’ for the magnitudes - on a Scale from 1 to 5.
Fig 8: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (90%) integrated with the 12Z GFS Ensemble (5%) (ECMWF 5%) using the projected pattern along with explicit surface and 850mb (~5,000 FT) Temp forecasts. Some Temps are adjusted for known or expected anomalous thermal patterns & projected storm system passages. There is high uncertainty on just how cold the arctic outbreak next week will be – but all indications are that it will primarily impact the Midwest, but will not be extreme or last very long since a somewhat zonal-like flow over Canada continues to limit the development of deep, arctic cold. Nonetheless, I have LOWERED the projected Temps across much of the nation by 1˚ to 2˚. Confidence in the anomaly pattern is below average with readings of ‘2’ for the anomaly pattern and magnitudes on a scale of 1 to 5 due to the frequent swings in Temps every few days that will accompany storm systems crossing the nation.
✭ NEXT *FULL* WEATHER UPDATE WILL BE ON FRIDAY✭
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Steve
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