Record Shattering Warmth and Very Stormy

By: Steve Gregory , 7:52PM,GMT on December 21,2015




 

MONDAY: 21-DEC-15 / 2:00 PM CDT

NOTE: DUE TO THE HOLIDAY, I WILL ONLY POST AN UPDATE OF THE TEMP ANOMALY CHARTS THIS WEDNESDAY

RECORD WARMTH EAST & STORMY WX AS PATTERN ‘SHIFTS’ FOR THE NEW YEAR

Daily, Weekly and potentially monthly Records will fall as 'The Big Warm’ continues thru the upcoming week across the eastern US – along with at 2 major storms. A period of more seasonal cold appears likely towards New Year’s and into the first Week of the New Year before a return to milder Temps emerges by the 2nd Week of JAN in the East – along with increasing chances for heavier Precip in Southern California (SOCAL).

Once the widespread Precip now in the central US moves off the east coast later tomorrow, a deepening TROF in the West and very strong ridging along the east coast will bring another surge of phenomenally warm Temps to the eastern US this week, with Temps reaching the 70’s as far north as NYC on XMAS Eve as another storm forms in the central US and moves to the Great Lakes by the end of the week. The western TROF then ejects eastward next weekend – heralding a transient pattern ‘shift’ and the formation of another major storm in the southern Rockies which also heads towards the Great Lakes region early next week. This storm will bring very heavy Precip to portions of the central and SE US – including with the potential for Blizzard-like conditions in eastern CO and the TX/OK Panhandle and one final surge of warmth to the east coast. A more tranquil pattern will likely develop during Week 2 as Temps warm in the West but turn colder in the central and eastern states.

MJO & EL NIÑO

The MJO continues to strengthen and is moving steadily eastward across the Maritime Continent and will reach the western Pacific (Phase 5 Location) later this week. Despite all global models calling for it to weaken rapidly – it has actually strengthened some as it moves somewhat faster towards the east. However, the location and intensity of convection associated with the extremely strong El Niño (the latest official ONI SST anomaly in the benchmark Niño 3.4 region is +2.9˚) is still the key player in the tropical Pacific - and the MJO may not be as strong as the automated Phase diagram below indicates. With model forecasts still calling for the MJO to weaken, I’m reluctant to believe the MJO will destructively interfere with El Niño or the convective pattern in the EPAC by holding itself together and moving towards the EPAC. For this reason, the odds are high that a classic El Niño pattern will re-assert itself during the 2nd and 3rd week in JAN. That said – we will need to monitor both the MJO and tropical convection patterns for any significant changes that could delay a return to a strong El Niño pattern as we’ve had for the last 6 weeks.

Finally, as mentioned last week, the very cold and strong polar vortex remains close to the North Pole, bottling up very cold air over the polar region, and none of the models show a change for at least 2 weeks – if at all. However, the ECMWF Ensembles are still showing significant stratospheric warming across the far eastern Pacific nosing into the westernmost portions of North America during early JAN. This, combined with strong tropical forcing from the EPAC (El Nino) is yet 1 more reason to believe it will lead to the redevelopment of a mean long wave TROF in the west during JAN – along with greater chances for major Precip in SOCAL by the 2nd week of JAN.




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Fig 1: MJO Analysis / Global Model Forecasts (left Panels) and Surface/850mb (~5,000 Ft) Temp Anomaly Composites (right panels) The latest MJO Phase diagram indicates it has reached strong intensity while moving at a faster rate across the Maritime Continent. However, as mentioned above, the convective pattern across the tropical Pacific associated with El Niño suggests the MJO may not be as strong as indicated above. While model forecasts still call for the MJO to weaken near term, it needs to be monitored closely this week to see if it continues crossing the Pacific at its current analyzed intensity which could destructively interfere with El Niño. As shown on the right hand panels, a strong ‘Phase 5’ signal teleconnects with an upper air pattern favoring very warm low level Temp anomalies over the eastern US – and a cooling trend over the SW US in~ 3 weeks (‘Lag 1’ – assuming it moves across region 5 next week.)


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Fig 2: GFS 10 & 14 Day Forecasts for the Primary Teleconnections that impact North American Weather The latest forecasts for the primary Teleconnection indices (AO, NAO, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation)) all support a warm East Temp pattern for the next 10 days – though a rising PNA into a positive phase suggests colder WX in the mid-Atlantic and SE US by late in Week 2, This is further evidenced by the latest GFS run showing much colder Temps spreading across the southern/Gulf coast states as well.


Fig 3: Jet Stream Forecast Valid JAN 4 (from the FIM’s Experimental model). The most important features to note is the TROF tracking across the far SW that will lead to wet and colder conditions (Classic El Niño) across the southern US starting during Week 2 into Week 3 (2nd week of JAN). More importantly, the location of the polar & sub-tropical jet streams over the Pacific that are orientated west-to-east, is over 600 miles further south than its generally been for the past month. Assuming it verifies, it implies wetter conditions returning to the West during the 2nd week in JAN, with the ‘core’ of heavier Precip shifting from the PAC NW southward into California. While this southward shift had been shown in previous extended range model forecasts, the latest forecasts have greater ‘technical support’ – including seasonality that normally shifts the heaviest Precip from the PAC NW in DEC southward to California during JAN.



Figs 4a/b: 500mb (≈ 18,000 Ft) Height Forecast Loop for the next 2 Weeks (Top) and corresponding 250mb ( ≈35,000 Ft) Wind Forecast Loop (Bottom) 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). A deepening long wave TROF in the West will eject 2 short waves towards the east this week before the primary TROF weakens and moves towards the eastern US by the end of Week 1, followed by some high level ridging in the PAC NW during Week 2. HOWEVER - unlike prior model runs since last THU, the latest GFS model run this AM shows less amplification of the TROF when it reaches the East during Week 2. Nonetheless, enuf cold air should move across the central and eastern US behind the TROF and storms to bring near seasonal cold during the first week of the New Year - before warmer Temps return.


Fig 5: GFS 15-Day Precipitation Pattern Loop (for mounts greater than 0.10” only). The animation shows total Precip forecasts during the preceding 24 hours in 3, 6 and then 12 hour time steps for the next 16 days. Precip will be heavy east of line from the western Great Lakes southwestward to the Lee of Rockies in NM while Precip in the West gradually ends during Week 2. Note the very heavy Precip in portions of the lower Plains on into the lower Midwest and SE US. Where very heavy Precip is shown (reddish tones) – Spring-like severe T-storms may also develop ahead of each storm system during the next week or so.


Fig 6: 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. EXTREMELY warm Temps in the east this week will begin easing off to ‘just’ above normal by the end of the Week in the central US. Confidence in the forecast anomaly Pattern and Magnitude is above average with readings of ‘5’ for the Pattern – and ‘4’ for the actual anomaly values which will be modulated by Precip - on a Scale from 1 to 5.


Fig 7: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (60%) integrated with: the 12Z GFS Ensemble mean (10%), the 00Z EURO model Ensemble (10%) AND CLIMATOLOGY (20%) 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.The GFS forecast anomaly pattern and magnitude has been followed closely due to reasonably good consistency between all models, however with any changing pattern, greater uncertainties emerge – especially with the Ensembles that are exhibiting greater solution spread now. For this reason, Confidence in the anomaly Pattern for Week 2 is now near average for this time period with a reading of ‘3’ on a scale of 1 to 5, while Confidence in actual anomaly magnitudes has declined to a bit below average with a reading of ‘2’ on a scale of 1 to 5.

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Steve