Major Rains For SOCAL as Pattern Change To Bring Arctic Cold To East

By: Steve Gregory , 2:32PM,GMT on January 5,2016


 

MONDAY: 04-JAN-16 / 2:15 PM CDT

NEXT WX CHART UPDATE LL WILL BE ON WEDNESDAY

STORM SYSTEMS TO BRING HEAVY RAIN – MUD SLIDES TO SOCAL

A complex series of storm systems off the CA coast will bring the first major rains to SOCAL this week, with widespread 2” rainfall totals likely across the LAX basin southward to San Diego, with isolated T-Storms potentially bringing totals to 3”. Snowfall totals will generally be from 1 to 3 feet across the Sierras, with the snow level falling off to near 5,000’ over the southern mountains by mid-week. The heavy rains raise the prospect for major mud slides over SOCAL. Most of the heavier Precip will be over by late in the week, with only isolated, light showers likely during the weekend period – if at all. While there will be a break from the Precip during Week 2 (in SOCAL) – there is a significant chance of it returning during the last 6-10 days of JAN while Precip is likely to continue unabated thru the period in northern California.

As the storm systems move out over the lower Plains later this week, warmer air ahead of the storm will move northward into the Midwest and east as the storm heads to the Great Lakes by the weekend. The stormy WX will then spread to the east coast with much colder air moving into the Midwest – spreading to the eastern US later next week.

MJO AND ‘BLOCKY’ PATTERN TO BRING COLDER TEMPS TO CENTRAL-EASTERN US

The moderately strong MJO has reached the central Pacific and continues heading eastward. The strong signal should reach central America by next week and then across the tropical Atlantic as it weakens. The MJO, combined with the development of high pressure over the polar region (brought about in large part by the extremely powerful NORATL storm last week that sent Temps to 50˚F above normal at the North Pole !) caused upper level heights to soar over the North Pole region. This in turn will force heights to lower over the US and allow much colder air to develop over the central and eastern states next week.

El Niño remains very strong, with the latest ONI reading at +2.7˚C – though SST’s should drop off significantly over the next week as up-welling ahead of the MJO along with colder, sub-surface waters eat away at the warm, surface waters. However, this will be quickly followed by a down-welling Kelvin Wave to the west of the MJO (and a potential WWB) – and should stabilize SST’s – if not cause them to rise again during the second half of JAN (before resuming to fall in FEB.)

There are already indications from the Ensembles that after a 7-12 day period of very cold conditions (centered in the Midwest – not the Northeast) – the semi-blocking situation at higher latitudes (due to the loss of the polar vortex near the North Pole) – will begin dissipating due to the strong El Niño – and Temps will probably get back above normal in the Midwest and Northeast as we approach the end of JAN and head into FEB.

Note: During a typical (climatological) Chicago winter, Temps fall to Zero or below on 13 days. So far, we have not even fallen into single digits, let alone zero. There have only been 10 winters out of the last 143 that the Temp has failed to reach zero or lower. At this time, it appears we will drop into single digits later next week – though sub-zero readings are possible if there is a snow cover (not at all a certainty since mainly rain is expected before the colder air moves in).




Fig 1: Precipitation Forecasts from the ECMWF and GFS OIver 2” of rain are forecast across the LAX basin this week by ALL the models – implying 1-3 ft snow accumulations at higher elevations of the Sierras. As a very strong and cold upper Low moves across SOCAL this week – the chance of isolated T-Storms with heavy rain (and possibly hail) will be possible, raising rain totals in some locations to 3”.


Fig 2: Comparison of 500MB Forecasts from the ECMWF and GFS Global Models Overall, there is EXCELLENT agreement between the EURO ECMWF model and the GFS on the hemispheric pattern at mid-ranges.. It’s worth noting the GFS has handled longer range forecasts for the SW US BETTER than the EURO model for over a month now – and about the same over the rest of the nation.


CLICK IMAGE To Open FULL Size image in a new window

Fig 3: GFS 10 Day Forecasts for the Primary Teleconnections that impact North American Weather The latest forecasts for the primary Teleconnection indices (NAO, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation)) now support a turn towards somewhat colder conditions over the eastern half of the nation. The strongly positive PNA also supports colder Temps over the east as well. It’s worth noting that the EPO is shown rising back towards a positive phase in 2 weeks – and the PNA Ensembles (not shown) suggests the PNA may go negative in 2 weeks as well. These shifts support a moderating trend by late JAN – and is a result of the El Nino pattern re-asserting itself on the mid-latitude pattern.


CLICK IMAGE To Open FULL Size image in a new window

Fig 4: MJO Analysis / Global Model Forecasts (left Panels) and Surface/850mb (~5,000 Ft) Temp Anomaly Composites (right panels) The MJO continues moving westward into the West Pacific, – against all model forecasts for the past 3 weeks – and has actually strengthened a bit more. (Model forecasts had called for rapid weakening to near dissipation during the last few 3 weeks). As the MJO moves into the EPAC in 2 weeks, it should cause an increase in EASTERLIES over the ENSO region – causing SST’s to decline due to upwelling. Assuming the MJO remains robust, after it moves towards central America, a Westerly Wind burst may possible occur – temporarily stopping any ocean cooling. (It should be noted, however, that the models – while seemingly doing a better job now – still call for the MJO to weaken during the next 2 weeks – so the impact on the EPAC remains quite uncertain.) Note the projected 850mb Temp anomaly trends based on long-term ‘MJO Phase Composites’ that show the “See-Saw” type Temp anomaly pattern over the eastern half the nation that is certainly hinted at by the operational and Ensemble models.


Fig 5: Sub-Surface Temp Anomalies (top )and Sub-Surface Temp anomalies (bottom) across the Equatorial EPAC SST Anomalies over the ENSO regions remain very high, with the benchmark 3.4 region still near +2.7˚C. Note the continuing expansion of colder waters at depth into the EPAC which is undermining the ‘reservoir’ of warm sub-surface waters in the EPAC. The Total Heat content in the tropical Pacific has fallen sharply over the past few weeks to the lowest levels since the spring. Still, with a potential resurgence in SST’s in late JAN – a strong El Niño event is assured to last thru the winter. Looking WAY AHEAD – most models show a neutral ENSO state by next summer, with a potential La Niña developing by the Fall.



Figs 6a/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 deep upper air Low off the CA coast will move inland this week as several short wave TROFs rotate thru the flow, triggering heavy rains across SOCAL and heavy, mountain snows. As the deep TROF moves towards the central US later in the week, it will phase up with a strong short wave plunging southward out of Canada, carving out a deep TROF over the eastern half of the nation by next week – and bringing the first significant arctic air mass of the year to the central and eastern US. Towards the end of the forecast cycle (12-16 days) – the much above normal heights over northern Canada and the polar region begin to lower and a more zonal flow shows signs of returning to the continent, and especially over the US by the end of the period. A positive EPO is likely to develop by then, along with a more neutral PNA as a more typical El Niño re-establishes itself by the end of the month.


Fig 7: 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. Series of storm this week will bring widespread 2” totals to the SOCAL area – with locally 3” possible – along with 1-3 feet of snow in the Sierras. The storm complex will move into the central US later in the week before spreading to the eastern states over the weekend. Isolated showers but generally drier conditions develop in the West for a few days this weekend before another series of storms heads for the west coast. Widespread, locally heavy Precip is seen across the Gulf coast region during Week 2 – typical during a strong El Nino event.


Fig 8: 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. Temps will bounce back above normal later this week before colder air moves into the Midwest during the Weekend – and into the east next week. Confidence in the forecast anomaly Pattern remains above average with a reading of ‘4’ while the forecast Magnitudes are near average with a reading of ‘3’ on a Scale from 1 to 5 due to uncertainties with the snow extent in the Midwest as the late week storm moves towards the Great Lakes and the extent of cold air into the central US over the weekend.


Fig 9: 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 model forecast anomaly pattern and magnitude forecast has been followed closely due to very good agreement among all models. However with any changing pattern, greater uncertainties emerge – especially with the Ensembles exhibiting greater solution spread during the last few days of the forecast cycle. Confidence in the anomaly Pattern and magnitude for Week 2 is now a bit below average for this time period with readings of ‘2’ on a scale of 1 to 5.

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Steve