FRIDAY, 11-SEP-15 / 3:40 PM CDT
NO FULL UPDATES PLANNED UNTIL MONDAY - SEP 21ST DUE TO HARDWARE SWAP OUT ! 
I may complete the cutover sooner and also may be able to post Temperature Anomaly Forecast charts before then. I will send a ‘Tweet’ whenever I post an update. Sorry for the inconvenience!
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HIGHLY PROGRESSIVE FLOW PATTERN RAPIDLY TAKING HOLD An amplifying TROF is digging southeastward across the Midwest towards the eastern US this weekend, but will just as rapidly lift out to the northeast and be followed by building upper level heights early next week. At the same time, a rapidly amplifying TROF in the EPAC will move into the far west – and then weaken quickly into a short wave TROF that will move rapidly towards the Great Lakes by next weekend (SEP 19/20). Finally, (and somewhat surprisingly) the global models are in excellent agreement that this highly progressive pattern is likely to 'repeat' during Week 2 and right through the end of month.
Despite the periodic development of high amplitude TROFs in both the east and western US – from a Temperature anomaly standpoint - the very rapid changes will effectively be equivalent to a zonal-like flow. This will prevent the development or advection of significant cold air anywhere across the nation during the rest of the month. And while the rapid and frequent intensification of TROFs would typically result in significant rainfall along and ahead of associated fronts – these changes are expected to be so rapid, it will be difficult for moisture to build up ahead of each front - so most Precip will likely be found across the Gulf coast region where each cold front will ultimately go stationary, allowing the region to become the ‘focal point’ for the development of widespread and locally heavy Precip. The western Gulf region near TX will be especially vulnerable to heavy Precip this weekend into next week as remnant moisture from former Hurricane Linda is now streaming across Mexico and adds to the moisture 'buildup' in that region.
That said, significant rainfall is also likely this weekend in the Northeast as the first in the series of cold fronts moves across the region, with widespread Precip also likely in the PAC NW associated with each TROF and frontal passage. In addition, significant Precip is also likely in parts of the Midwest and Great Lakes region where upper level dynamics associated with each TROF will be sufficient to trigger locally heavy showers and isolated T-Storms ahead of each front.
TROPICAL ATLANTIC At first glance, the NHC ‘overview’ chart for the Atlantic makes it seem like there are a lot of disturbances that need to be followed. A closer look, however, reveals that they (NHC) give the odds of development near ZERO for most of these systems - with only the system now near the Cape Verde Islands given a chance of development later next week. None of these ‘areas of interest' have been designated as an INVEST yet.
The last several global model runs do show development of the Cape Verde’s system later next week as it moves across the central Atlantic towards the Leeward Islands. This is a ‘reasonable’ possibility as the widespread dry and stable air now in place is likely to ‘moisten up’ and become somewhat more unstable. The instability increase will partially be a result of SST’s that are now slightly above normal from the central ATL westward to the near the CARIB. In addition, wind shear, which is very high and hostile to cyclone development in the central Atlantic is expected to fall off next week, lending support for the development of a cyclone. However, even if a cyclone does form, the track for the system is likely to be ‘out to sea’ as the mid-latitude TROFs moving across the US and then out over the Atlantic are extending further south into the sub-tropics at times, increasing the chances that these TROFs will weaken the sub-tropical ridge - forcing any cyclones to recurve northward and ultimately out to sea.
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Fig 1: Overview of Tropical Atlantic BasinThe tiny, 'lopsided’ minimal tropical storm HENRI is heading northward and is of no concern, while remnant moisture/TROF from what was TS GRACE is moving slowly westward into the far eastern CARIB. Very high wind shears over 30Kts continue across the region, will prevent cyclone formation of the TW near the CARIB and the TW in central Atlantic near 40˚W longitude. The large tropical wave with deep / abundant moisture near the Cape Verde Islands is moving slowly westward - and while no rotation is evident, as the system moves westward this weekend, low to mid-level vorticity MAY ultimately prove sufficient for cyclone formation later next week as the system moves from the central Atlantic towards the Leeward Islands.
Fig 2: The TPW (Total Precipitable Water) Loop (Top) and latest image frame (bottom) with ‘V’ wind vector component analysis) highlights areas with deep layered moisture. ‘Bluish’ colors represent dryer air while the darker, ‘orange’ tones highlights areas of deep moisture in the column of air above the surface. The 72 hour looped imagery highlights the deep moisture associated with the TW near the eastern CARIB, the wave in the central Atlantic, and the large TW near the Cape Verde Islands. The ‘V’ component analysis of wind vectors shows possible rotation developing with the Cape Verde TW - and the large but very disorganized TW now over central Africa.
Fig 3: IR and SAL color enhanced image loop for the eastern ATL and western Africa. The 24 hour loop shows the wind ‘curvature’ around the axis of the TW as the system oved off the African coast overnight, but a ‘closed’ circulation has not yet developed. Dry and more stable air was pulled offshore to the north of the TW, but the dry /stable air is in a very thin layer, and should not be relevant to this system once it moves into the central Atlantic.
Fig 4: The mean 500mb Forecast from the GFS and EURO (ECMWF) model valid in ~8 Days There is truly excellent agreement between both of these models (and their ensemble members – not shown). The 500mb (~18,000’) zonal-like flow from the NORPAC across North America (NORAMER) belies the deep TROF’s that will be at their most amplified over the eastern US and near the West coast. With the mean, west-to-east flow across NORAMER, no significant cold air outbreaks is possible.
Fig 5: 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 7. Temps will average near to slightly below normal over the eastern third of the nation, but will still average above normal across New England. Well above normal Temps will continue across much of the west, except for the interior Valleys in California. Confidence in the forecast anomaly Pattern and Magnitude is above average for this time of year, with readings of ‘4’ for both the anomaly Pattern and Magnitude on a Scale from 1 to 5.
Fig 6: GFS Precipitation forecast for the next 7-days. The Heavy Precip in the Northeast this weekend is associated with the cold front moving thru the region right now, while the widespread, heavy Precip over Mexico is from the remnant moisture of former Hurricane LINDA.
Fig 7: 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 7. The stormy weather across Alaska is leading to below normal Temps over much of interior Alaska, with near or above normal Temps in the far south. While there will be significant day-to-day Temp swings over the next 2 weeks, no major cold formation (by Alaskan standards!) is expected through the end of the month.
Fig 8: 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 / expected anomalous thermal patterns & projected storm system passages. Above normal Temps are expected to continue during Week 2 (and right thru the end of the month) as the MEAN flow remains zonal-like. However, Temp anomalies of 5 to 10 degrees below normal may develop for 1 or 2 day periods at times – but these will be followed by equally warm anomalies for 2 or 3 days. Overall Confidence in the forecast anomaly Pattern is near average, but confidence in the anomaly Magnitude is below average for Week 2 due to the rapidity of Temp changes expected – resulting in a Confidence Level reading of ‘2’ on a Scale of 1 to 5.
✭ The Next WX Update is Scheduled for MONDAY, SEP 21ST ✭
Steve
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