MONDAY: 09-NOV-15 / 3:40 PM CDT
(NEXT TEMP FORECAST CHART UPDATE WEDNESDAY )POSTING SCHEDULE: ‘FULL’ UPDATES ON MONDAYS & FRIDAYS … TEMP FORECAST CHARTS ON WEDNESDAYS AND WHEN WARRANTED
STRONG STORMS THIS WEEK AND NEXT – BUT LONG TERM GFS HAS NO CLUE
Heavy rains in portions of the east associated with a strong cold front will move out to sea during the next day or so as relatively mild Temps once again develops east of the Rockies during the week - along with the development of a fairly strong storm system over the lower Plains mid-week. This storm will then spread rain from TX northward to the Great Lakes, with strong winds also impacting the Midwest/Great Lakes as the storm moves thru the region on into Canada by the end of the week. (T.S. KATE – an extremely small cyclone with minimal tropical storm force winds near the NW Bahamas will be turning NE and will pass well east of the US coast during the next 48 hrs as it heads for the North Atlantic - merging with a non-tropical storm and frontal system.)
As the storm and associated cold front move east of the US, a brief shot of colder air will quickly be followed by much milder air next week as the next big TROF digs into the western US, leading to the formation of another storm in the center of the nation later next week. This is when things become quite uncertain due to huge model forecast differences between model runs exhibited over the last 3 days – including one model run that called for a 968 mb Low in NY state and arctic air plunge into the eastern US at the very end of Week 2 – while the latest model runs have essentially reverted back to the current pattern – albeit with increasingly more powerful TROF’s and associated surface storm systems towards the very end of Week 2. Longer term continuity, persistence, and global model ensembles have shown much better agreement between model run, strongly suggesting no major change in the overall pattern, but with increasingly stronger TROFs moving from the NORPAC / GOA into the western US and then on across the nation - with the pattern repeating every 6-8 days. To be sure, with each storm system passage, Temps will turn significantly colder – but with the rapid west to east movement of major TROFS and a generally zonal-like flow across Canada, preventing any cross-polar flow, overall, Temps will likely average above normal east of the Rockies and below normal to the west
While there remains great uncertainty in the details – the latest GFS model run still suggests TROFs will become strong enough for significant Precip to reach into SOCAL during the last week in NOV or first week in DEC (assuming the current pattern continues).
STRONG MJO SIGNAL BEGINS WEAKENING AS EL NINO INTENSIFIES YET AGAINThe strong MJO in the Indian Ocean began to slow over the weekend, and has now begun to weaken. Model forecasts continue to show the system weakening rather quickly over the next week as it begins to retrograde towards the west. As mentioned last week, a strong MJO in the Indian Ocean (‘Phase 2’ region) tends to result in colder conditions in portions of the eastern half of the nation – and to some degree this is happening - though with a weakening of the signal and combined with very strong forcing associated with El Nino, it appears this correlation is being ‘over-ridden’ to some degree.
Indeed, El Niño remains extremely strong, with the latest weekly anomaly reading for the Niño 3.4 region now up to 2.8˚C – tying the all-time record set during the last Super El Niño of 1997. While the various ‘ocean metrics’ having continued to increase (albeit slowly now), there has been a SLIGHT weakening in the upper tropospheric anomalies at 200mb and a small decrease in cloudiness/convection near the Dateline. This MIGHT be the first indications of a weakening El Niño – but it is far too soon to call it. But even if it is – there is no doubt that El Niño conditions will impact the upcoming winter pattern in a manner typical of a strong event.
Fig 1: GFS 10-Day Forecast for the Primary Teleconnections The overnight GFS ensemble forecasts for the NAO, PNA, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation) are all supportive of above normal Temps in the eastern Half of the country during the next 10-days. (The composites at the top of the image shows the 500mb pattern anomalies during a ‘Positive Phase’ for each Teleconnection, with the corresponding Surface Temp anomalies just below each one.)
Fig 2: SST and Depth Anomalies in the Equatorial Pacific. SST anomalies remain much above normal across much of the eastern Pacific, with some SSTA’s over 3.5˚C.
Fig 3: MJO Analysis and Global Model Forecasts The still strong MJO is now in the eastern Indian Ocean and its forward motion has come to a screeching halt. The models are in generally good agreement on the MJO weakening through the week as it begins to turn westward – with a couple model suggesting a new cycle will ‘restart’ by the end of the month in the far western Indian Ocean.
Fig 4: 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 190Kts 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 jet stream pattern just off the west coast at the end of the forecast period which, if it verifies, suggests a significant storm event in SOCAL during the last week of the month. (For more general info on the Jet Stream chart – see the last few blog posts.)
Fig 5: 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 along the mid and north Atlantic coast during the next 36 hours be followed by a fairly impressive storm in the central US later this week. A brief lull in the wet pattern early next week will be followed by another storm late next week. However, just how strong - and where it will track - is highly uncertain.
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. Above normal Temps east of the Rockies and below normal in the west will dominate the upcoming week – though not nearly as mild as the prior 2 weeks. Confidence in the forecast anomaly Pattern and Magnitude remains above average for this time of year due to very good model continuity through DAY 6 - with readings of ‘4’ on a Scale from 1 to 5.
Fig 7: 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 it ‘fits’ with the EURO and GFS Ensembles – while it is in poor agreement with the ECMWF operational model - resulting in below average confidence, with overall Confidence in the anomaly Pattern and magnitude still 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 8: Temperature Anomaly Forecast for Alaska during Week 1 Above normal Temps are going to decline thru the week – especially over central and southern portions of the mainland. Well below normal readings are likely through most of Week 2, with some moderation by the end of the week. ,
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Steve
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