WEDNESDAY: 16-DEC-15 / 2:30 PM CDT
NEXT FULL WX UPDATE ON FRIDAY
MAJOR STORMS WITH RECORD WARMTH IN THE EAST 
Some of the most consistent and potentially reliable model forecasts in recent memory continue to call for another round of extended warmth in the East as 3 major storms impact the nation over the next 2 weeks. At the same time, however, considerably colder Temps are likely over much of the West - especially over the interior west.
A series of strong short wave TROFs will carve out a full latitude, long wave TROF over western North America by early next week – sending progressively colder air into the Western states while pumping up a ridge – and Temps in the east – along with a strong storm event likely in the east just before XMAS. Above normal Temps in the East should continue into at least the start of the New Year. To be sure, there will be some colder days following each storm passage – though only down to near normal levels. With the major storm track running from the southern Rockies to Great Lakes and Northeast region, most Precip east of the Mississippi will fall as rain.
With absolutely no model indications of a significant pattern change for the next 2 or more weeks, there is very high Confidence in the forecast Temp anomalies shown below. In fact, I cannot recall so many consecutive very strong signals for the continuation of the current pattern - and such good agreement between all global model suites – with only insignificant differences from one model run to the next. This has resulted in the highest Confidence Level (5 on a scale of 1 to 5) I have ever had for both Week 1 AND Week 2 Temp anomaly forecasts.
Fig 1: 2015 High Temporal Resolution Surface Height (SSH) Anomalies from the JASON (NASA) Satellite platform highlighting changes since JAN 1, 2015: The above looped imagery is assembled EVERY day (the highest temporal resolution available), showing the evolution of El Niño into the strongest warm episode since the all-time Super El Niño of 1997 (some ENSO related metrics exceeded those observed in 1997). 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 ocean waters correlate with lower than normal SSH’s. Keep in mind that actual SST anomalies do NOT always correspond on a one-to-one basis with Total Ocean Heat Content (OHC) of the entire corresponding column of water, which is generally represented by the JASON SSH anomalies. Note the impact of the powerful oceanic Kelvin Waves that crossed the equatorial Pacific during MAR/APR, late MAY/JUN, and again later in JUN and JUL which can be seen with the eastward expansion of the ‘white’ colored region that then retreats on its' western edge until the end of the summer and thru the fall when heat content was so high, that the entire equatorial EPAC lit up to the MAX height shown by the white shading. Also note that the well above normal heights off the Mexican West coast decreased in aerial extent – though anomalies re-intensified off the Central American & SW coast of Mexico during the past few weeks.
Figs 2a/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). The strong and amplified TROF in the central US will move quickly eastward and weaken as the next strong upstream short wave now approaching the GOA deepens and moves SE into the western US – with subsequent short waves following closely behind it - carving out a full latitude, long wave TROF in western North America by early next week. This major TROF – and 1 more that should follow it about 5-7 days later - will trigger a strong rain storm over the eastern US by the middle of next week thru XMAS day, with another strong storm just prior to New Year’s Eve. It’s worth noting that since yesterday, the GFS has called for a significant weakening of the flow pattern over the EPAC on into the US by the start of the New Year – with an implied zonal-like flow for at least a few days during the first week in JAN. This should result in a more tranquil pattern at the start of the New Year– though Temps will almost certainly still average above seasonal levels due to the westerly flow of mild air off the Pacific.
Fig 3: 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.Well Above normal Temps will continue on average for the next 7-days – despite a 2-day cool down to near normal levels early in the week ahead, with anomalies of 20˚ t near 30˚ possible in parts of the east next week. Overall Confidence in the forecast anomaly and Magnitude is well above average with readings of ‘5’ for the pattern and anomaly magnitudes - on a Scale from 1 to 5.
Fig 4: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (90%) integrated with the 12Z GFS Ensemble (5%) (ECMWF 5%) 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.Primarily due to several storm passages during the period, above normal (Absolute) Temps will not be as extreme as they were this past week in the eastern states, but will remain well above normal over the eastern half of the nation. Much colder conditions is still expected to develop in the west under the strong, upper level TROF, with a mean position over the far West. Confidence in the anomaly pattern is far above average for the season, with a reading of 5 on a scale of 1 to 5. However, though greater than its been in months, Confidence in actual anomaly values is near average levels, with a reading of ‘3’ on a scale of 1 to 5, primarily due to the possibility of being even warmer in the far east, and colder over the West.
Fig 5: GFS 15-Day Precipitation Pattern Loop (for mounts greater than 0.10” only)Three major storms will occur during the next 2 weeks, with the two strongest storms likely next week (surrounding XMAS) and heading into New Years. Some very heavy snowfalls likely in the west – including the Sierras - and heavy rains in the SE US and near the (East) coastal Plain.
Fig 6: Total Precip over next 15-Days. GFS Precip projection for amounts over 0.25”. Primary storm impacts with above to much above normal totals will be felt in the PAC NW and SE US – with near to locally above normal totals possible as far south as SOCAL – and near to above normal totals from the lower Mississippi Valley to the Great Lakes and Northeast.
✭ NEXT *FULL* WEATHER UPDATE ON FRIDAY✭
Posting Schedule: ‘FULL’ UPDATES ON MONDAYS & FRIDAYS … WX FORECAST CHARTS ON WEDNESDAYS AND WHEN WARRANTED
Want to be alerted when I post an Update? Then follow me on Twitter!
Steve
No comments:
Post a Comment