MONDAY: 23-NOV-15 / 4:40 PM CST
(NEXT WX/TEMP CHART UPDATE ON WEDNESDAY)
MAJOR STORM WITH POTENTIAL FLASH FLOODING, BLIZZARD CONDITIONS IN NEW MEXICO, TEXAS & OKLAHOMAThe upper air pattern is rapidly returning to the basic flow of earlier this month with a broad, zonal-like flow re-developing across much of North America, with strong short wave TROFs embedded within the flow pattern. Admittedly, the pattern 'reversion' is occurring even sooner than I anticipated, greatly limiting and even eliminating much of the arctic air intrusion into the US that was still forecast as late as last Friday to continue into the opening days of DEC. Indeed, the re-development of a broad, zonal-like flow will essentially cutoff the advection or development of any major arctic air into the US for at least the next 2 weeks – and probably much longer than that. But while deep, arctic air will be in short supply - strong storm systems won’t be.
A strong short-wave now approaching the PAC NW will amplify quickly over the next 2 days as it digs S/SE into California, bringing locally heavy coastal rains from northern CA northward - and potentially up to a foot of snow to the Sierras. And instead of the entire system moving quickly eastward to the southern Plains as was originally expected, the normally very weak sub-tropical High over Mexico is forecast to strengthen some over the next 72 hours, and in combination with changes to the strength and orientation of the polar Jetstream, will result in the upper level TROF becoming quasi-stationary for a couple days before it finally gets kicked out to the east as the next strong, upstream short wave approaches the PAC NW from the Gulf of Alaska (GOA). Despite these forecast changes, enough ‘energy’ will initially be ejected out towards the east to force the outbreak of mainly widespread and locally heavy rain from the upper Midwest southward to Texas on Thursday, which will then move slowly eastward, with the attendant cold front extending from New England southwest to central Texas on Friday. By that time, the ‘main event’ will begin.
TROPICAL STORM & COLD FRONT TO ‘COMBINE’ - WITH A BULLSEYE OVER PORTIONS OF NM, TX AND OKLatest satellite imagery indicates an extremely unusual late season tropical cyclone formation is imminent over the EPAC, about 650NM to the SSE of Baja. The global and specialized hurricane models are in very good agreement that this system will intensify into a Strong CAT 2 Hurricane by Thursday as it first moves towards the NW before recurving northeastward - likely coming ashore over western Mexico about 100NM to the SE of Baja early Saturday. While the cyclone will weaken rapidly after making landfall, abundant upper level moisture – riding on the approaching sub-tropical jet stream - will already be streaming rapidly northeastward towards New Mexico and Texas – and will interact with the upper level TROF and cold front approaching from the west.
While forecasts so far in advance have limited skill, it now appears that by the time most of the storm ends late Sunday – rainfall totals of 1” to 2” are possible over eastern New Mexico, with 4 to 6” possible in portions of Texas and Oklahoma - with isolated, T-Storm related totals up to 8”. In addition, 1 to 2 feet of snow is POSSIBLE in the TX/OK Panhandle. Stay Tuned…
EL NIÑO TO DOMINATE THE WINTER AHEAD With one of the strongest (if not THE strongest) El Niño events just now near its peak intensity – a mainly ‘warm’ and dry winter appears most likely across the northern tier of states – with increasingly colder and much wetter conditions across the southern states. Unless there is a “Sudden Stratospheric Warming” (SSW) event, this general pattern can be expected to last through the entire winter, even with SST Anomalies which are forecast to decline to around +1.5˚C by February, from the just set weekly record high of an amazing +3.1˚C (in the benchmark Niño 3.4 region) with isolated readings of +4˚C !
Major winter storms are expected to begin impacting all of California during the first half of DEC – and critically – including all of the southern watershed Sierras. It is not likely that these storms will completely end the extreme drought, but they COULD come close. While there has already been some rainfall in SOCAL, it now appears that it will be another couple weeks before the first chance for a truly big storm in southern California.
Fig 1: The most recent Weekly SST Anomaly Analysis for the Niño 3.4 Region SST anomalies continued to tick upward over the past week, with Anomalies exceeding 3.5˚C in the eastern portion of the benchmark Niño 3.4 region, and several isolated +4˚C anomalies! Critically, this results in absolute SST’s above 28˚C across ALL of the primary Niño regions – a level typically able to sustain convective activity (think SST’s typically required for Tropical Cyclone formation.), This is one of the most critical aspects of a warm ENSO event, enabling it to have a major impact on the overall WX pattern across the EPAC and North America.
Fig 2: 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 flow taking on a very broad west to east pattern, with embedded short wave TROFs moving quickly thru the primary flow pattern. At the start of the period, an innocuous appearing TROF off the British Columbia coast digs S/SE and intensifies rapidly, with a very slow eastward movement beginning at the end of the week just as the potential EPAC Hurricane comes ashore in SW Mexico. The TROF ends up with a closed Low near the Great Lakes by early next week before the next TROF moves inland at the end of next week - taking a similar course towards the Great Lakes by the end of Week 2 – just as another major TROF approaches the west coast. While forecasts beyond 10 days at times quite poor - especially so lately – it’s worth noting that by the end of Week 2, the approaching West coast TROF has a powerful jet stream behind it – which may lead to a very strong storm system event in the west during what would be ‘Week 3’.
Fig 3: GFS 15-Day Precipitation Pattern Loop (for amounts 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. Clearly, the ‘Big Event’ will be across NM, TX and OK at the end of this week, but widespread and locally heavy Precip also appears likely in the northeast and eastern states during the first half of next week. Note the heavy rain approaching the Mexican coast later this week - associated with the tropical cyclone expected to form by this evening.
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 and 8. Above normal Temps will redevelop across the entire eastern half of the nation during Week 1, with almost ‘hot’ conditions in south Texas. While well below normal Temps will dominate 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 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 forecast Temp anomaly pattern will essentially remain unchanged from Week 1, with above normal Temps across the eastern half of the nation, and below normal in the west. However, Temp anomalies across the Gulf coast region will likely start out much warmer than shown – but will end much colder by the end of the Week. Despite the drastic change in the forecast pattern during the past few days – excellent overall agreement between the GFS, ECMWF and their respective ensembles is good enough to raise my overall confidence in the forecast to about average for Week 2 forecasts at this time of year, with readings of ‘3’ for both the anomaly pattern and magnitude on a scale of 1-5.
Fig 6: Temperature ANOMALY forecast for December through February. Confidence in the above forecast is very good for the first half of the period (thru mid-JAN) – but is about ‘average’ for the last half of the winter due to the potential for a SSW event combined with the expected weakening of El Niño. In addition, with the area of warm water in the NE GOA persisting (against all odds – and my original forecasts!), there is significant risk that Temps could be colder than forecast in the Northeast – but overall, should still average above normal.
Fig 7: Precipitation ANOMALY forecast for December through February As described extensively over the past 6 months – the first truly stormy weather in at least 4 years is expected to occur across California, with the primary storm track extending from the southern portions of the West coast eastward into the southeastern US. Reference the above mentioned warm waters in the GOA, the chances of major storms along the east coast – including New England – is significant.
POSTING SCHEDULE: ‘FULL’ UPDATES ON MONDAYS / FRIDAYS … TEMP FORECAST CHARTS ON WEDNESDAYS AND WHEN WARRANTED
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Steve
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