FRIDAY: 20-NOV-15 / 4:00 PM CST
(NEXT FULL WX UPDATE WITH SPECIAL WINTER WEATHER OUTLOOK ON MONDAY)
’TEMPORARY’ PATTERN CHANGE AND FAST MOVING SNOW SYSTEM
AS COLD AIR SPREADS ACROSS MOST – BUT NOT ALL – OF THE NATION The upper level pattern is in flux, with the development of a broad TROF across North America which will allow much colder conditions to continue developing in the interior West while gradually shifting eastward into the central and southern US over the next 10 days - while sparing the east coast from most of its ‘punch’.
A small but strong short wave TROF over the northern Rockies embedded in the larger scale flow will move rapidly eastward to the Great Lakes region during the weekend – which will lead to the development of a heavy snow band from Iowa into northern IL, Wisconsin and Michigan during the next 36-48 hours before weakening and moving into SE Canada. The system is expected to bring an unusually early heavy snow event to the Chicagoland region where 3”-8” of snow is likely by Saturday afternoon.
Temps will remain near or above normal across the upper Midwest, Great Lakes and much of the east coast states during the next 2 weeks, even as much below normal Temps develop over portions of the south central US - thanks in large part to forcing from the tropical Pacific (via the extremely strong El Niño and moderate but quasi-stationary MJO in the Indian Ocean).
MAJOR STORM FORMATION CENTRAL US NEXT WEEK – STAYS MILD IN THE EAST! All models continue to call for the development of a large storm system in the center of the nation by Thanksgiving, starting with a strong system hitting the PAC NW early next week - and then reforming into a large storm in the central US by Thanksgiving. At this time, it appears this storm will move relatively slowly towards the Great Lakes on into SE Canada; resulting in another heavy rain & T-Storm event across the entire Mississippi Valley through Thanksgiving weekend before weakening some as its associated cold front moves off the east coast by the end of the month (though the front is likely to ‘hang up’ over Florida resulting in more heavy Precip across that state).
MJO/TROPICAL FORCING WILL NIX ARCTIC AIR FROM REACHING EAST COASTThe still moderately strong MJO in the Indian Ocean is expected to remain in that region while generally maintaining its intensity. This, combined with the ongoing strong El Niño event – correlates with colder than normal Temps in the west and south, but warmer than normal Temps in the northeastern quadrant of the nation.
And while we're in the midst of a pattern ‘interruption’ (allowing an arctic outbreak in the west and south central US) , both the GFS and ECMWF models are in general agreement in showing the pattern reverting back towards a ‘TROF in the West and ridge in the East’ during the first week in DEC. This also increases the chances that stormy conditions will begin impacting ALL of the west coast – including SOCAL – in early DEC, with above normal Temps over the Midwest and eastern US.
Fig 1: MJO Analysis and Global Model Forecasts The moderate intensity MJO in the Indian Ocean has retrograded into the west central Indian Ocean – but is forecast to move slowly back towards the east during the next 2 weeks (Left Panel). The MJO Signal location/correlation (Right Panel) shows a ‘Phase 2’ MJO at 3 (LAG 1) to 6 (LAG 2) weeks after the MJO began – supports the current and near term forecast Temp anomalies over the US.
CLICK IMAGE To Open FULL Size image in a new window
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, PNA, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation) generally support a return to above normal Temps over the central-eastern portions of the nation with the EPO, WPO, AO & NAO going into a positive phase. The Positive PNA tends to support colder than normal conditions in the SE US – so these signals are not especially at odds with each other. While the individual Ensemble members show a fairly wide divergence (right panel) for each Teleconnection metric – they are all forecasting the same 'phase'.
Fig 3: 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 broad TROF over North America at the start of the Loop gradually trends back to a TROF over the EPAC and western US – and is the primary reason that my Week 2 forecast is warmer than the GFS solution (by about 2 degrees) – but especially supports my forecast for a return to significantly above normal Temps in the central and eastern states during early DEC. The jet stream forecast is decidedly ‘complicated’ – with several individual jet ‘streaks’. These wind speed maxima (jet stream wind ‘streaks’ or ‘segments’) are typically the driving force for strong storm systems and are associated with current modeling forecasts for numerous and strong, short wave TROFs. With the primary ‘action’ shifting into the EPAC and western US in 2 weeks, a turn to much stormier conditions out west in early DEC seems likely.
Fig 4: 2015 – High Temporal Resolution Surface Height (SSH) Anomalies from the JASON Satellite platform A ‘radar’ type system on a NASA satellite measures ocean surface heights, and the above image shows the departure from normal heights starting on JAN, 2015. The ‘movie’, using imagery from EVERY day of the year, shows the evolution of El Niño into one of, if not the, strongest El Niños on record. 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 waters correlate with lower than normal SSH’s. Note that the western 'edge' of the very warm waters (white shading) in the central Pacific has begun shifting slowly eastward - another indicator that El Niño is likely at MAX intensity. Keep in mind that actual SST anomalies do not always correlate highly or ‘one-to-one’ with total heat content of the corresponding entire column of water represented by SSH.
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. After the heavy snow event over the weekend in the Midwest/Great Lakes region – the storm that first appears in the PAC NW early next week shifts to the central US by Thanksgiving – with very heavy rainfall totals likely from this storm during the Holiday weekend.
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 will hang on across New England and Great Plains - with colder than normal readings in the SE and much of the west. Confidence in the forecast anomaly Pattern and Magnitude remains near average for this time of year with readings of ‘3’ on a Scale from 1 to 5.
Fig 7: 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 forecast Temp anomaly PATTERN has been followed closely due to very good consistency between model runs. And agreement with the ECMWF. However, I have warmed the forecast anomalies over the south central US and east coast by 1 to 3 degrees due to recent model TRENDS towards warmer solutions. Overall Confidence in the anomaly Pattern and magnitude is still low relative to average because of differences between the GFS and ECMWF and the unusual pattern of anomaly ‘intensities’ - with a reading of 2 for the pattern and anomaly magnitudes on a scale of 1 to 5.
POSTING SCHEDULE: ‘FULL’ UPDATES ON MONDAYS / FRIDAYS … TEMP FORECAST CHARTS ON WEDNESDAYS AND WHEN WARRANTED
✭ NEXT FULL WX UPDATE AND WINTER OUTLOOK ON MONDAY ✭
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Steve
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