MONDAY: 18-JAN-16 / 3:00 PM CDT
NEXT WX UPDATE ON WEDNESDAY
MAJOR WINTER STORM POTENTIAL FOR NORTHEAST AND STORMS CONTINUE IN THE WEST
Those wishing for a major snow storm in the Northeast may get to celebrate by this coming weekend – and again next week - as 2 major storms forming over the Gulf coast region head northeastward. Not to be outdone, storminess will continue across much of the West coast for the next 2 weeks while Temps moderate back to or slightly above normal in the central US.
The first storm will be triggered later this week as a strong short wave now bringing heavy Precip to the PAC NW crosses the Rockies and heads for the Gulf coast region. A complex surface storm should form in the SE US by the end of the week and will likely track towards Cape Cod over the weekend. Temperatures should be cold enough for snow inland from the coast with ‘borderline’ readings in the big Northeast coastal cities. At this time, the potential exists for 6”-12” snow totals in the Washington DC to Boston corridor. (This outlook could easily change as we get closer to the event!)
As this first storm is impacting the mid and north Atlantic region, the next powerful Pacific storm will be coming onshore in the west, and a second major storm is likely to form over the southern states and take a similar track towards the Northeast during the middle of next week, with the potential for another 6” or more of snow in the Northeast.
The very active pattern is seen continuing into FEB, and this is leading to some significant run-to-run model differences beyond 10 days out, with the latest GFS model run MUCH COLDER in the central US (including the Midwest) than the past week of model runs had indicated. While the day to day specifics may be in question for Week 2, the OVERWHELMING model consensus calls for significantly warmer conditions in the central and ultimately eastern US during the last week of the month and into early FEB. Both the GFS and ECMWF have been calling for Temps to average 6˚ to 12˚ ABOVE normal by the end of the month – but - the very latest GFS 12Z run suddenly shows Temps averaging 5 to 10 degrees below normal in the Midwest during Week 2 – but points towards warmer conditions to develop during the first week in FEB. While I consider this latest run to be ‘BOGUS’ – in deference to it, I’ve modified the Week 2 forecast below to show near normal Temps on average in the central US – while forecast Temp anomalies for the eastern and western states remain essentially unchanged. (It's worth noting the latest ECMWF that just came in is still forecasting above normal Temps during Week 2.)
Fig 1: GFS 10 & 14 Day Forecasts for Primary Teleconnections that impact North American Weather The latest forecasts for the primary Teleconnection indices (AO, NAO, EPO (eastern Pacific Oscillation) and WPO (Western Pacific Oscillation)) are trending back towards a significantly milder pattern as the AO, NAO, WPO and EPO all move towards neutral and then into positive phases. The PNA remains in a positive phase until next week when it too shifts towards a milder phase around the end of the month. While there has been EXCELLENT agreement from both the GFS and ECMWF on this trend, a few GFS Ensemble members diverge from the consensus, with both the AO and NAO shown moving back into a slightly negative (cold) phase in 10-14 days. (The large uncertainty can likely be traced back to forecast variations for several tropical forcing mechanisms in the ENSO region where forecasts for SST anomalies and resulting convection are difficult for the models to handle accurately.)
Fig 2: 850MB Wind, SST Anomalies and Ocean Heat Content for Equatorial Pacific The latest Hovmöller chart of 850MB (~5,000 Ft.) westerly wind anomalies shows the powerful Westerly Wind Burst (WWB) that occurred last week and the subsequent development of a new Kelvin Wave – and the down-welling that has resulted across the equatorial Pacific. The down-welling has warmed SST’s by nearly 1/3 of a degree – raising the benchmark Niño 3.4 region anomaly back up to +2.8˚C. Unless there is another WWB, SST anomalies should level off by next week and then resume a slow, but steady decline during FEB.
Fig 3: us Average Temp Anomaly first half of JAN Despite the much colder Temps since New Years’, mean Temps for the first half of JAN have still managed to remain above normal across most of the northern half of the nation.
Fig 4a/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 jet stream winds (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). The polar vortex NE of the Great Lakes that brought the bitter cold to the upper Midwest since yesterday is moving quickly eastward towards Maine and out to sea as a potent short wave TROF in the PAC NW moves towards the SE US and deepens rapidly, taking on a negative tilt that should lead to a strong surface storm formation later this week. Another strong system will move into the PAC NW this weekend and will also plunge towards the SE US next week – raising the prospect for yet another strong Nor’easter during the middle of next week. By the end of the month into the start of FEB, a long wave TROF should develop across the western US – with warmer Temps developing ahead of it across the central and eastern US.
Fig 5: GFS 15-Day Precipitation Pattern Loop (for mounts greater than 0.10” only)Stormy conditions will continue to dominate much of the nation, though little Precip is expected across the north central US as storm systems hit the western states and then reform over the southern US/Gulf coast region, and then track northeastward. Storms in the PAC NW will drop another 3” to 6” of rain during the next 2 weeks, with Precip totals of 1” to 3” possible across the Northeast; with much of it being in the form of snow (especially away from the coast).
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. Temps will be moderating back to normal or slightly above across the central US during Week 1, with a bit colder conditions in the Northeast (primarily due to the impending weekend storm and colder air flowing in behind it). Overall Confidence in the forecast anomaly and Magnitude remains above average with a reading of ‘4’ for the anomaly pattern and magnitudes on a Scale from 1 to 5 due to excellent agreement and run-to-run consistency among both the GFS and ECMWF global models.
Fig 7: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (60%) integrated with the 12Z GFS Ensemble (10%), (ECMWF 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. Colder Temps will redevelop across most the western US as a deep, upper level TROF develops across the region. The SECOND storm now forecast across the eastern US during the start of Week 2 – assuming it verifies – will keep Temps down near normal over most of the east. The biggest uncertainty is now over the central US where 5+ days in a row of model runs called for much warmer conditions in the central US – but this mornings’ GFS run has totally reversed itself, with much colder Temps shown in the Midwest. However, with so many runs – including the ECMWF – all showing much warmer conditions, it’s likely this AM’s GFS has gone over the deep end on the forecast for colder conditions in the central states. In deference to both ‘opposite’ solutions, I’ve opted to forecast ‘near normal’ Temps on average in the Midwest region for Week 2. Due to the sharp differences between recent runs, overall confidence in the anomaly pattern is a bit below normal with a reading of ‘2’, but well below average with a reading of ‘1’ for the actual anomaly magnitudes (most notably in the central US).
✭ NEXT WEATHER UPDATE WILL BE ON WEDNESDAY✭
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Steve
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