FRIDAY: 13-NOV-15 / 4:15 PM CDT
(NEXT FULL WEATHER UPDATE ON MONDAY)POSTING SCHEDULE: ‘FULL’ UPDATES ON MONDAYS & FRIDAYS … TEMP FORECAST CHARTS ON WEDNESDAYS AND WHEN WARRANTED
ANOTHER STRONG STORM TO HIT NATION 
The next major storm to cross the country is now coming ashore in the PAC NW with heavy rains and high elevation snows. The strong upper level TROF is heading southeastward and will reach the lower Plains by Monday while winding up into a strong, closed off upper Low and surface storm system. Heavy snows with near blizzard conditions is possible at higher elevations of the front range of the Rockies (including Denver), while heavy rain and T-Storms – some locally severe – will break out across the Mississippi Valley. Since the storm is expected to become ‘cut-off’ aloft, its forward motion will slow as it heads northeast towards the Great Lakes. It will take until late next week before the associated cold front passes off the east coast. Precip totals of 1”-3” is possible from Texas to IL, with 1” totals quite possible along the east coast by the time the storm departs. At this point, it appears the nation will get a break from the very stormy conditions for 5-7 days, along with more seasonal Temps before a return to stormier conditions during Thanksgiving weekend.
The GFS has continued to swing wildly in its longer range (beyond 10 days) forecast solutions, and ‘normally’ this is indicative of a pattern change in the offing. However, while a bonafide pattern change cannot be ruled out, it is somewhat more likely that the poor model performance in the longer ranges is related to El Niño and the still highly progressive nature of the overall flow pattern. In addition, the GFS forecast solution is differing significantly from the ECMWF in a number of ways beyond 7 days out – leaving confidence in the Week 2 outlook quite uncertain.
STRONG MJO SIGNAL REFUSES TO WEAKEN – WHILE EL NIÑO SHOWS SIGNS OF ‘PEAKING’ (PART I) The strong MJO in the Indian Ocean continues to move across the Indian Ocean (‘Phase 2’ location) and remains relatively strong based on the latest analysis. This is in stark contrast to the multi-model forecast that has been consistently calling for it to weaken rapidly and retrograde to the west! Exactly why the forecasts have suddenly become so bad (from ALL models) is not clear – as is the continuing forecast for the signal to weaken rapidly and turn westward. There is likely some type of low frequency background signal from the tropics either ‘messing up’ the MJO analysis – or the forecast – or both! In either case, as can be seen in the below Figure, the Temp anomaly across North America is responding to a strong Phase 2 signal – implying that it is mainly the MJO forecasts that are being negatively impacted.
While SST anomalies in the ENSO regions continue to be indicative of an extremely strong El Niño – there are some signals emerging that El Niño may have 'peaked' - and is on the cusp of a slow weakening trend – in line with recent CFSv2 and NMME forecasts.
First of all, it appears that SSTA’s are no longer rising, and more importantly, westerly wind anomalies in the lower levels and easterly wind anomalies at high levels in the equatorial Pacific have begun weakening over the past 10-14 days. The latest SOI has begun rising, and cloudiness/convective activity near the dateline has also subsided. And even though the latest forecast for 850mb (~5,000 Ft) are calling for another surge in westerly anomalies during the next 7 days, the magnitude is unimpressive. In addition, it appears the below normal sub-surface ocean Temps in the tropical WPAC have finally begun to migrate towards the east – the typical pattern when El Niño is about to start weakening.
While it's certainly possible there may yet be another resurgence in the oceanic and atmospheric metrics supportive of El Niño (possibly due to another strong Westerly Wind Burst or a constructive MJO event for example), the odds favor a slow weakening. ALL THAT SAID – El Niño will almost certainly maintain a ‘strong’ intensity into FEB, and the winter weather pattern will continue to reflect a strong event through most if not all of the winter on into early spring. I’ll have more information on the current ‘path’ for El Niño in Monday’s Blog.
Fig 1: SST Anomalies across the Pacific Basin Much above normal SST’s continue in the equatorial Pacific, with some anomalies exceeding +3˚C within all ENSO regions. The benchmark 3.4 region anomaly remains close to +2.8˚C – but Temps have shown little change over the past 10 days. However, SST anomalies in the WPAC have warmed over the past 2 weeks, and are near normal levels – typical of a normalizing environment.
Fig 2: 200mb (~40,000 Ft.) Wind Anomalies The strong easterly wind anomalies in the upper atmosphere over the EPAC and Westerly anomalies in the WPAC (an important El Niño related characteristic) have weakened considerably during the past 2 weeks; and while this will typically occur to some extent during the winter – it is one sign of a possible weakening of El Niño.
Fig 3: 850mb (~5,000 Ft.) Wind Anomalies Likewise, the large region of strong Westerly wind component anomalies in the lower levels has also weakened significantly during the past couple weeks, while the easterly anomalies have weakened in the WPAC – though this may be partially be related to the MJO in the Indian Ocean.
Fig 4:) Hovmöller Chart for 850mb (~5,000 Ft.) Wind Anomalies with 7-Day Forecast As shown in the above (Fig. 2) westerly anomalies have weakened – with a weak albeit significant increase in westerly anomalies forecast during the next 7-days to the east of the Dateline. In addition, a more ‘chaotic’ wind anomaly pattern appears to be emerging in the EPAC.
Fig 5: CFSv2 Forecast for Niño 3.4 Region The latest CFSv2 Forecast for the 3.4 Niño region continues to indicate that SST anomalies have peaked - but importantly – note that it is forecast to remain ‘strong’ (SSTA of +1.7˚C or higher) through the winter.
Fig 6: NMME Ensemble Forecast for Niño 3.4 Region Likewise, the most recent NMME Ensemble Forecast is forecasting the peak intensity to be reached by the end of the month, but calls for it to maintain a ‘strong’ intensity into early FEB.
Fig 7: GFS 10-Day Forecast for the Primary Teleconnections The latest forecast for the primary Teleconnection indices affecting North America NAO, PNA, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation)) remain supportive of above normal Temps in the eastern Half of the country during the next 2 weeks – though noteworthy is the brief period that the NAO and EPO turn negative – implying somewhat colder conditions – and is in line with my Week 2 Temp anomaly forecast below. (The top composites show the 500mb pattern anomalies during a ‘Positive Phase’ for each Teleconnection, with the corresponding Surface Temp anomalies.)
Fig 8: MJO Analysis and Global Model Forecasts The STILL strong MJO in the eastern Indian Ocean continues moving eastward towards the South China – in sharp contrast to all global model forecasts of the past 10 days that called for it to weaken rapidly by now. Nonetheless, all models continue to insist that significant weakening and a turn towards the west (retrograde) is imminent. The MJO Signal Correlation with Temp anomalies over the US (Right Panel chart) – and is quite similar to the current real-time Temp anomaly pattern. It’s worth noting at this point that should the signal maintain itself and move into Phase 3 and/or 4 – correlation charts show a similar warm signal across North America.
Fig 9: ECMWF 500mb (~18,000 Ft) Forecast for the Northern Hemisphere for Day 10 The above forecast highlights the rather ‘chaotic’ upper air pattern across the hemisphere – with a number of cut-off Lows and numerous short waves embedded in an apparent ‘6-wave’ pattern – with little cross-polar flow anywhere (all indicative of a highly progressive flow - typical during a strong El Niño event).
Fig 10: 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 location of TROF’s and Ridges. The Polar Jetstream (which on average is typically found around the 250mb level during the winter) continues to intensify, with jet core MAX winds exceeding 190 Kts at times – with both the polar and sub-tropical jet seemingly ‘merging’ at times – a juxtaposition often seen as strong surface storms develop. Of special note is the strengthening of the sub-tropical jet from west of Hawaii eastward across the southern US.
Fig 11: GFS 15-Day Precipitation Pattern Loop (for mounts greater than 0.10” only) The animation shows total Precip forecasts during preceding 24 hours in 3, 6 and then 12 hour time steps for the next 16 days. Locally heavy rains will hit the PAC NW during the next couple days before the main storm winds up in the lower Plains early next week – with heavy Precip spreading northward into the Great Lakes
Fig 12: 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. MUCH Above normal Temps east of the front range will ease back towards normal following the major storm passage later next week. Confidence in the forecast anomaly Pattern and Magnitude remains above average for this time of year with readings of ‘4’ on a Scale from 1 to 5.
Fig 13: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (90%) integrated with the 12Z GFS Ensemble (10%) and the 00Z EURO model Ensemble (0%) 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 has been followed VERY closely – only because of rough consistently with prior 12Z model run cycles – and ensemble forecasts. Overall Confidence in the anomaly Pattern and magnitude remains below average – even for this time of year which is always somewhat uncertain – with readings of ‘2’ for both the anomaly pattern and magnitude - on a scale of 1 to 5.
Fig 14: Temperature Anomaly Forecast for Alaska during Week 1 It now appears Temps will average well below normal across much of the state through the end of the month, and teleconnects well with above normal Temps in the eastern US.
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Steve
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