WEDNESDAY: 25-NOV-15 / 2:20 PM CDT
NOTE: Due to the Holiday, the next FULL Weather Update will be next Monday.
HEAVY RAINS / ICE / SNOW - BUT MILD TEMPS 
A strong and complex storm system over the inter-mountain west will spread Precip out across the southern Plains with Precip developing northward to the Great Lakes on Thanksgiving Day. Precipitation totals will be very heavy in some at times - in the south as deep layered moisture streams rapidly northeastward from the EPAC associated with the all-time record late season CAT 2 Hurricane SANDRA - expected to make landfall near or just east of Baja, California early SAT. Widespread rainfall of 2 to 4 inches is expected across portions of TX & OK – with isolated totals of 6”-9” possible in northern TX and eastern OK. Snow and icing conditions are likely from the TX/OK panhandle N/NE to the uppermost Mississippi Valley, while up to 1” of rain may fall from the mid-Mississippi Valley into the lower Great Lakes region – including the Chicagoland area. Very mild air will dominate the eastern half of the nation while well below normal dominate the west during Week 1.
While the storm system will weaken during the weekend, it will continue to bring unsettled conditions to much of the eastern US into early next week before a second impulse of energy triggers intensification of the storm system around the middle of next week in the central US. The models have diverged some on where the heaviest Precip will be with this mid-week system, but widespread Precip can be expected from the Great Lakes to Gulf coast before the whole system moves off the east coast later in the week.
The global models are in good agreement that another Pacific storm will hit the west coast starting around the end of next week – and MAY represent the start of a more frequent and further south storm track out west – with significant Precip reaching into SOCAL during the second week of DEC. In addition, Temps across much of the nation will rise to above normal levels – with the possible exception of the Gulf coast region where an unsettled pattern may persist - keeping a lid on daytime high Temps.
Fig 1: 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 location of TROF’s and Ridges. The strong TROF / closed Low in the west will move eastward and eventually across the Great Lakes into SE Canada later next week as the mean TROF continues to be anchored over the EPAC and western US. A strong system will move onshore at the end of next week and will cross the nation during Week 2, with yet another strong system coming onshore in about 12 days, reaching the central US at the end of Week 2.
Fig 2: 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 take hold across the entire eastern half of the nation, with below normal Temps out west. Overall Confidence in the forecast anomaly Pattern and Magnitude is now above average with readings of ‘4’ for the pattern and anomaly magnitudes - on a Scale from 1 to 5.
Fig 3: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (80%) integrated with the 12Z GFS Ensemble (10%) & ECMWF (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.Above normal heights and Temps will begin to dominate much of the nation during Week 2, with the exception of the Gulf coast due to lower heights and OCNL: Precip – typical of strong El Niños winters. Confidence has increased to near average with good overall model agreement and consistency between model runs and additional confirmation from longer range forecast tools. Overall Confidence is now near ‘3’ on a scale of 1 to 5.
Fig 4: GFS 15-Day Precipitation Pattern Loop (for mounts greater than 0.10” only) The major storm out west will move to the central US, with heavy rains developing from TX to the lower Great Lakes as snow and ice affects the TX/OK Panhandle northward towards the upper most Midwest. Note Hurricane SANDRA coming onshore on SAT, adding to the potential for very heavy Precip in TX/OK.
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Steve
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