MONDAY: 16-NOV-15 / 4:15 PM CDT
(NEXT TEMP CHART UPDATE ON WEDNESDAY)POSTING SCHEDULE: ‘FULL’ UPDATES ON MONDAYS & FRIDAYS … TEMP FORECAST CHARTS ON WEDNESDAYS AND WHEN WARRANTED
STRONG STORM BRINGS BLIZZARD - SEVERE T-STORMS – HEAVY RAINS TO CENTRAL US 
As a strong and deep TROF over the SW US moves out over the lower Plains, heavy snow with near Blizzard conditions will hit portions of the Front Range – including the Denver metro area where 4”-8” of snow is likely with totals of 8”-15” possible near the foothills. As the surface storm center intensifies tonight and Tuesday beneath a cut-off upper low, very heavy rains will spread northward from Texas to the central Midwest with locally severe T-Storms and possibly isolated Tornadoes in NE Texas, eastern OK and Arkansas – with the risk of severe storms spreading into LA and MS Tuesday as the overall storm system moves eastward. Because the system is expected to cut-off into a closed, upper level Low, it will move somewhat slower towards the east – with the storm system not clearing the coast until Friday – with locally heavy Precip possibly persisting across Florida through the weekend as the cold front stalls out.
After what may be a 6-10 day period of generally more tranquil conditions, the next major storm is expected to hit the PAC NW and move across the intermountain west before overspreading the central US as we head into the Thanksgiving weekend. Beyond this general outlook, the details for this storm and its track is extremely uncertain as the GFS and EURO global models are at loggerheads over the general upper air pattern beyond 10 days out – with the GFS showing much colder conditions over the eastern US compared to the ECMWF model for the end of the month and opening days of DEC.
STRONG MJO FINALLY MATCHES FORECAST AS EL NIÑO SSTA's REACHES RECORD HIGH The strong MJO in the Indian Ocean finally began to weaken over the weekend, with all global models continuing to show additional weakening and a westward retrograde motion thru the next 10 days. This all but assures that it (MJO) will have no major impact on EPAC wind and Precip anomalies and El Niño SST anomalies for at least the next 7-10 days.
After 2 weeks in which atmospheric metrics such as upper and lower level wind anomalies weakened in the tropical Pacific, there was a slight uptick in the last 5 days. However, with a strong oceanic Kelvin Wave moving slowly across the EPAC, SST anomalies in the EPAC have surged during the past week, with the official ONI (SST anomaly) hitting a weekly record high of +3.0˚C in the benchmark Nino 3.4 region, beating the +2.8˚C record set during the Super El Niño of 1997. In addition, total upper ocean heat anomalies have increased to the highest levels of the year – assuring us of a strong El Niño weather pattern thru much if not all of the winter.
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Fig 1: SST Anomalies Comparison for the Same Week during the 3 Strongest El Niño Events The SST ANOMALY IN the BENCHMARK NINO 3.4 REGION SET a RECORD HIGH OF +3.0C. this week (Lower panel). The Max SST anomalies across the tropical EPAC are of similar magnitude for the 3 strongest El Niño events of the last 60 years (1982, 1997 and 2015). However, SST anomalies across the rest of the Pacific basin differ significantly this year compared to 1982 and 1997, with much sharper SST gradients during prior events compared to this year. It is fair to say that this will likely lead to a noticeably different WX pattern response over North America compared to the 1982/83 and 1997/98 winters – but in what way it will differ is not at all clear. That said, with warmer waters over much of the EPAC this year, it’s reasonable to surmise that storm systems could be generally ‘wetter’ this year compared to the prior El Niño years - especially during the first half of winter – and possibly warmer conditions in the west, most critically in the form of higher snow levels in the western mountains. However, this is pure conjecture on my part with no analogs found in the modern records to lend support to this.
Fig 2: MJO Analysis and Global Model Forecasts The strong MJO in the eastern Indian Ocean finally began to weaken and has turned westward – and move back across the Indian Ocean during the upcoming week while weakening slowly. The MJO Signal location correlates with generally above normal Temps over the central and northeastern US.
Fig 3: Upper Ocean Heat Content Anomaly Analysis The above charts highlight the changes in heat content during the past year across the tropical Pacific and the impact of 4 major Kelvin Waves that crossed the Pacific during since last Winter. As each Oceanic KW moved eastward, down welling along and ahead of each ‘wave crest’ (black dashed lines) led to warming – while the trailing portion of each wave (black dots) led to upwelling and some cooling of the upper ocean layer. Clearly, net warming far exceeded the cooling effect as each the time period between waves was relatively short, thereby limiting the time spent in an upwelling (cooling) mode. (In contrast to the short wavelength KW's, the KW passage that completed last DEC with over a 3 month break before the next powerful Kelvin Wave arrived in March – allowed the ocean to cool during JAN and FEB.)
Fig 4: Subsurface Temperature Anomalies during the past 2 months Note the extremely warm sub-surface readings in the EPAC, with further warming (associated with the latest Kelvin Wave) during the latest 2 weeks. However, the cold anomalies in the WPAC which have essentially remained in place since the summer has shown some eastward migration during the last few weeks. This is typically among the first indicators that El Niño has reached its max intensity.
Fig 5: 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. Note how the strong 500mb LOW in the SW US at the start of the forecast period moves somewhat slower to the east- slowing the eastward movement of the heavy Precip across the Mississippi Valley and eastern US. In addition, note the overall mean amplitude of the major TROFs remain relatively low for this time of year – and is indicative of a fairly progressive wind/weather system pattern.
Fig 6: GFS and (Top) versus ECMWF (Bottom) 500mb (~18,000 Ft) The above charts are from the overnight run of the 2 major global models and highlight the extremely divergent forecasts foir the week 2 period – with the European model showing much warmer conditions across the eastern half of the nation for Week 2 compared to the GFS. In addition, the ECMWF implies the development of a much stronger storm event towards the end of Week 2 due to the highly amplified TROF over the western US. (I would be remiss not to mention that the latest GFS model run from this AM has trended closer to the ECMWF solution – but is still a MUCH colder solution).
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Fig 7: GFS 10-14 Day Forecasts for the Primary Teleconnections that impact North American Weather The latest forecasts for the primary Teleconnection indices (AO, NAO, PNA, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation)) generally call for above normal Temps during Week 1 – with conflicting signals for Week 2. (The top composites show the 500mb pattern anomalies during a ‘Positive Phase’ for each Teleconnection, with the corresponding Surface Temp anomalies.) Note the Ensemble forecasts (right panels) diverge significantly towards the end of the forecast period (divergent red lines). Of significant note is the forecast for a Negative NAO during Week 1 – yet Temps are expected to remain above normal this week. This is an unusual situation. OTH, the negative PNA and positive WPO and EPO appear to be well correlated with actual surface Temps during the upcoming week.
Fig 8: Latest CFSv2 Temperature Anomaly forecast for December While not the most accurate of models – the extent of warmth forecast for North America in December is nothing short of amazing!
Fig 9: 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. Very heavy rainfall totals are expected along and just ahead of the cold front associated with the strong storm developing in the lower Plains – followed by at least a week of more tranquil conditions nationwide.
Fig 10: 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. Nationwide above normal Temps are expected this week – despite the near blizzard conditions in portions of the front range at the start of the period. 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 11: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (70%) integrated with the 12Z GFS Ensemble (20%) and the 00Z EURO model Ensemble (10%) 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 forecastTemp anomaly PATTERN has been followed closely – due to the still quite good consistency between model runs. However, in deference to the much warmer solution of the ECMWF (European model) – I have warmed the forecast anomalies over the eastern half of the nation by 2 to 4 degrees. (The explicit GFS Heating Degree Total for the week is 195 versus my forecast for 175 HDD’s. Overall Confidence in the anomaly Pattern and magnitude is very low because of differences between the GFS and ECMWF – with a reading of 1 on a scale of 1 to 5, and a reading of 2 for the magnitude of the anomalies on a scale of 1 to 5.
Fig 12: Temperature Anomaly Forecast for Alaska during Week 1 The arctic air over Alaska will be rapidly shifting into Southwest Canada later this week as MUCH ABOVE normal Temps surge back across the state during Week 2.
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Steve
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