One, Two Punch of Rain For Texas as Temps Remain Well Above Normal

By: Steve Gregory , 8:01PM,GMT on October 26,2015

MONDAY: 26-OCT-15 / 3:00 PM CDT
(NEXT UPDATE: THURSDAY - OCT 29)

ANOTHER HEAVY RAIN EVENT FOR TEXAS

Just as the rains have eased off across Texas (after flash flooding from rainfall totals exceeded 20” in several locations in Texas) – another deepening TROF approaching the western US coast will eventually trigger another round of locally heavy Precip to portions of the SW and especially Texas next Weekend. Pumping up the anticipated rainfall totals of 3” or more inches will be another surge of tropical moisture from the equatorial EPAC as El Niño continues to trigger unseasonable levels of convection in the EPAC.

Meanwhile, the upper level TROF that interacted with the remnants of Hurricane PATRICIA - resulting in the extraordinary (and well forecast) weekend rains in TX - is now heading E/NE across the Gulf coast region with a developing non-tropical cyclone near the LA coast expected to move rapidly NE to the Great Lakes, spreading locally heavy rains north and eastward into the Midwest and eastern US during the next several days.

STORMIER PATTERN & POSSIBLY WARMEST FIRST WEEK IN NOV SINCE 1997
Synoptic (large) -scale TROFs will continue moving into the western US and progressing to the eastern US every 5-7 days, with above normal Temps likely to continue over the eastern US for the next 2 or more weeks. In fact, the latest GFS model run is calling for the warmest nationwide opening week of November since the super El Niño event of 1997 - with only 62 total Heating Degree days (HDD) compared to the normal average of 100 HDD.

To be sure, there will be periodic cool downs over the next few weeks - especially in the Northeast - along with considerably stormier conditions. But with a mean (average location) TROF expected to evolve over the western US, Temps are likely to average below normal in the West starting next week with above normal Temps in the east - and this general pattern appears likely to continue into mid-November – and probably beyond then.

While it’s too early to know exactly when the first big storm will hit southern California global model trends point to significant rainfall reaching into southern California by mid-November.

MJO INTENSIFIES – BUT EL NIÑO MAY ‘OVERPOWER’ IT
As the global models have been forecasting, the first significant MJO event in 3 months began emerging late last week in the far western Indian Ocean and has intensified rapidly over the weekend while remaining essentially stationary. The signal is quickly approaching a Strong intensity; but all global models have begun to change their tune as to the longer range evolution for it.

Until yesterday, the models had been calling for the Oscillation to begin propagating slowly eastward by the upcoming weekend while remaining at moderate to strong intensity. However, the latest global model runs are pointing towards an oscillation that will only shift slightly towards the east before ‘collapsing’ in about 2 weeks. Besides being incorrect, it is quite possible that the current super El Niño base state of the atmosphere is simply too entrenched to allow the signal to propagate across the Pacific – or – it will be ‘hidden from 'view’ by the overriding El Niño flow pattern. We should, however, be able to discern an oceanic response in SST’s and total ocean heat content if the MJO does actually move across the equatorial Pacific.

Finally, the very latest CPC report indicates that the ONI (SST anomaly value in the Niño 3.4 region) has ticked up to a very strong +2.5˚C.

NOTE: I will be posting a 2 Year Animation of Sea Surface Height Anomalies in my Next post on Thursday




Fig 1: 15-Day 250mb ( ≈35,000 Ft) Wind Forecast Loop The Polar Jetstream (which typically is found around the 250mb level on average) continues to strengthen (as is typical for the season) with embedded TROFs remaining highly progressive. (I have drawn the mean position of the primary TROF’s (dashed re lines) and upper level High Pressure systems at the start and end of the forecast period – AND at Day 10.) Note the steady progression of TROFs as they move from the Gulf of Alaska into the western US - with amplification of a major TROF over the interior West before it weakens and advances towards the east coast. While no overly impressive storm system is expected to hit the east – widespread Precip is expected as the western TROF moves across the US. If the very broad TROF over the EPAC and western US at the very end of Week 2 verifies, stormy weather could reach into SOCAL during ‘Week 3’.


Fig 2: GFS 10-Day Forecast for the Primary Teleconnections The overnight GFS ensemble forecast for the AO, NAO and PNA Teleconnections are all pointing to a warmer than normal Temp pattern over the eastern US - with a positive AO and NAO – along with a negative PNA. While there is significant divergence of individual ensemble members towards the end of the forecast period – almost all members are on the ‘warm’ side of normal with the only significant difference being in the magnitude of each teleconnection forecast.


Fig 3: MJO Analysis and Global Model Forecasts A new MJO cycle began last week near the far western Indian Ocean and is approaching a ‘strong’ intensity. However, unlike last week’s forecasts for it, the latest global model forecast solutions show the signal weakening rapidly in 10-14 days while advancing very slowly across the Indian Ocean. However, unless the forecast is simply wrong – it's quite possible that the signal will be ‘hidden’ from analytic view by the extremely strong El Niño atmospheric flow pattern in the equatorial Pacific.


Fig 4: 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 -8. Above normal Temps are expected to continue nationwide during Week 1 – with rainfall east of the Mississippi Valley the only thing keeping Temps from reaching near record warmth levels. Overall, Confidence in the forecast anomaly Pattern and Magnitude is near average for this time of year, with a reading of ‘3’ on a Scale from 1 to 5.


Fig 5: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (80%) integrated with the 12Z GFS Ensemble (10%) 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 forecasts over the past 4 days has once again begun to swing ‘wildly’ for the Week 2 forecast period, but the majority of model runs – especially over the last 2 days - have pointed to a continuation of very warm anomalies during the first week in November as a strong TROF in the west forces Temps to fall below normal over the western half of the nation and stay above normal in the east. (An extremely warm period is forecast between OCT 31 and NOV 6th.) Because of the strong swings in Week 2 Forecast Temps, Confidence in the anomaly Pattern and magnitude remains below average, with readings of ‘2’ on a Scale of 1 to 5.


Fig 6: GFS 10-Day Total Precipitation Loop (for mounts greater than 0.25” only) Locally heavy to torrential rainfall is likely from TX north and eastward during the next 7 days – with the heaviest Precip along portions of the Gulf coast states, eastern Midwest and Northeastern US. As the next TROF develops near the west coast later this week, significant Precip will likely impact much of the western US – except for southern California – though Precip is possible in SOCAL towards the very end of Week 2 (but more likely during Week 3).


Fig 7: Temperature Anomaly Forecast for Alaska during Week 1 MUCH above normal Temps (which is still pretty cold by ‘lower 48’ standards) is expected to continue across the entire state - though the models are still calling for the magnitude of warm anomalies to fall off during Week 2 (something they have incorrectly forecast for the last 3 weeks!).

✭ The Next Update will be on THURSDAY OCTOBER 29 ✭

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Steve