Isotherm Posted December 18, 2012 Share Posted December 18, 2012 However, IF the brand new Euro weeklies happen to be onto something, there could be a widespread and longlasting cold pattern over much of the U.S. for the subsequent 3+ weeks. I take with a grain of salt, but am admittedly paying attention. Stay tuned. If the EPO signal is in fact real, and sustained, I would tend to believe the idea of severe cold getting into the picture. We've already got 2/3 ducks lined up on the pond with the NAO and AO. The EPO has been our thorn in the side thus far, and if that remains on the neutral/neg side in January, the blocking "trifecta" will be complete and the flood gates will be opened. Link to comment Share on other sites More sharing options...
GaWx Posted December 18, 2012 Share Posted December 18, 2012 If the EPO signal is in fact real, and sustained, I would tend to believe the idea of severe cold getting into the picture. We've already got 2/3 ducks lined up on the pond with the NAO and AO. The EPO has been our thorn in the side thus far, and if that remains on the neutral/neg side in January, the blocking "trifecta" will be complete and the flood gates will be opened. The last four GFS runs have consistently made it cold from the western U.S. through the MW and into the NE by ~12/28-9 and extending into the first few days of Jan. Let's see if the dates start to slip or if we finally reach a consistently cold period then. If so, that would be consistent with the Euro weekly timing. The -NAO on the 0Z run was quite impressive! Edit: The 0Z GEFS is pretty chilly by 12/30 and is the coldest of at least the last four runs from 12/30 through 1/2 with it appearing entrenced then. Link to comment Share on other sites More sharing options...
Srain Posted December 18, 2012 Share Posted December 18, 2012 The overnight guidance and ensembles continue to advertise a major winter storm event potential cross the Southern Rockies/Southern Plains during the busy Christmas Holiday travel period. The Euro is a bit faster by 12-24 hours ejecting a powerful trough across Texas/Oklahoma, while the GFS suggests a meandering closed core 5H low taking a southern track across Central/SE Texas into Louisiana/Arkansas. Normally we see the GFS suggesting a more progressive pattern while the European guidance is slower. The Operational and ensembles paint a very interesting Winter Storm across a region that does not normally see this type of potential setup. Very cold air with wintry weather may extend as far S as Houston/Lake Charles with possible blizzard condition from N Cental TX/Oklahoma (Dallas/OKC) on E. Very cold sub freezing temps may reach as far S as the S Central Texas and on E along the Gulf Coast depending on the final storm track. The blocking regime does suggest abit more southerly track across the CONUS during the upcoming busy travel period. This feature may also offer a severe episode as well as it ejects from the Southern Rockies on Christmas Day. EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 159 AM EST TUE DEC 18 2012 VALID 12Z FRI DEC 21 2012 - 12Z TUE DEC 25 2012 ...A HIGHLY ACTIVE WINTER PATTERN REMAINS ON TAP... THE BULK OF GUIDANCE FROM MOST MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR LARGER SCALE PATTERN EVOLUTION FOR THE NEXT WEEK. THIS FLOW IS HIGHLIGHTED ALOFT THIS WEEKEND BY AN AMPLIFIED TROUGH JUST OFF/ALONG THE WEST COAST...AN AMPLIFIED RIDGE OVER THE W-CENTRAL US...AND ANOTHER AMPLIFIED TROUGH/CLOSED LOW CENTERED OVER THE NORTHEAST. THE LEAD SYSTEM AND ASSOCIATED DEEP SURFACE LOW/SYSTEM AND ASSOCIATED SENSIBLE WINTER WEATHER FOCUS SHOULD PROVE SLOW TO EXIT INTO THE CANADIAN MARITIMES WORKING INTO BLOCKED FLOW. THIS WILL LEAVE PLENTY OF ROOM FOR COOLING BACK ACROSS THE ERN AND CENTRAL US DOWN THROUGH THE SRN TIER STATES WELL IN ITS WAKE...INCLUDING PROTRACTED LAKE EFFECT SNOW POTENTIAL. UPSTREAM...ERN PACIFIC TROUGH ENERGIES AND ASSOCIATED UNSETTLED WEATHER/COOLING/PCPN ARE EXPECTED TO WORK INLAND ACROSS THE WRN US BY SUN/MON BEFORE EMERGING INTO THE CENTRAL US NEXT TUE WHERE SRN PLAINS CYCLOGENESIS/GULF INFLOW/DEVELOPING PCPN COULD OCCUR TUCKED UNDERNEATH A MID-HIGHER LATITUDE DOME OF COLDER HIGH PRESSURE. HPC OVERNIGHT MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS ALONG WITH ASSOCIATED NEW HPCGUIDE OVERNIGHT SENSIBLE WEATHER GRIDS WERE PRIMARILY DERIVED FROM A COMPOSITE BLEND OF GENERALLY COMPATABLE GUIDANCE...AT LEAST AT MID-LARGER SCALES...FROM THE GFS/ECMWF AND GEFS/ECMWF ENSEMBLE MEANS. Link to comment Share on other sites More sharing options...
usedtobe Posted December 18, 2012 Share Posted December 18, 2012 The pattern is still cutter prone even with that storm just after Christmas. It may still work out for areas further north into New England, but there isn't a big block or confluence to really force this off the Delmarva for example. We still have time so it isn't set in stone, just something I'm seeing. that is also what I see with another shortwave dropping into the southwest which may or may not repeat the process or the boxer day storm could set up a decent enough block to finally get the confluence right. Right now I've settled to looking at 2 week chunks and for mid atlantic, I don't like the coming chunk much until towards the 1st of the year when the ridging over Ak should start delivering more frequent shots of cold air but the neg PNA will still be battling it over the southeast and mid atlantic. You guys have lots more wiggle room. Link to comment Share on other sites More sharing options...
easternsnowman Posted December 18, 2012 Share Posted December 18, 2012 If you like cold and snow south it looks like south of the M/D line in the east coast may not be the place to be. Link to comment Share on other sites More sharing options...
Srain Posted December 18, 2012 Share Posted December 18, 2012 As Don and Wes (usetobe) as well as others have alluded to, the January time frame look rather impressive for sustained cold to even very cold for much Canada and the US as heights rise across Alaska and the very cold air that has been building across that Region heads S. Link to comment Share on other sites More sharing options...
usedtobe Posted December 18, 2012 Share Posted December 18, 2012 Steve, most of my thoughts have been in the 2 week range and I think for the mid atlantic the next 2 weeks will probably average near normal with a roller coaster in terms of temps. Beyond that time range, it depends on whether a nice ridge pokes into Ak like the ensemble mean and CFS2 are implying. The pattern showsn on the GEFS ens mean towards Jan 1with the ridge poking into AK but with lower than normal heights over the southwest is a tricky one. If they are right, the pattern will transition to cold even into the mid atlantic though we still may be dealing with a miller b type or southwesterly flow waa which usually aren't major snow events (more than 6 inches). MY guess is that probably will happen but I don't have a tremendous amount of confidence in how quickly that will happen. The CFS2 weeklies have not done that well this winter or at least that is my perception. Link to comment Share on other sites More sharing options...
Srain Posted December 18, 2012 Share Posted December 18, 2012 HPC Update regarding the Christmas Storm Complex: EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 936 AM EST TUE DEC 18 2012 VALID 12Z FRI DEC 21 2012 - 12Z TUE DEC 25 2012 ...A HIGHLY ACTIVE WINTER PATTERN REMAINS ON TAP... THE BULK OF GUIDANCE FROM MOST MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR LARGER SCALE PATTERN EVOLUTION FOR THE NEXT WEEK. THIS FLOW IS HIGHLIGHTED ALOFT THIS WEEKEND BY AN AMPLIFIED TROUGH JUST OFF/ALONG THE WEST COAST...AN AMPLIFIED RIDGE OVER THE W-CENTRAL US...AND ANOTHER AMPLIFIED TROUGH/CLOSED LOW CENTERED OVER THE NORTHEAST. THE LEAD SYSTEM AND ASSOCIATED DEEP SURFACE LOW/SYSTEM AND ASSOCIATED SENSIBLE WINTER WEATHER FOCUS SHOULD PROVE SLOW TO EXIT INTO THE CANADIAN MARITIMES WORKING INTO BLOCKED FLOW. THIS WILL LEAVE PLENTY OF ROOM FOR COOLING BACK ACROSS THE ERN AND CENTRAL US DOWN THROUGH THE SRN TIER STATES WELL IN ITS WAKE...INCLUDING PROTRACTED LAKE EFFECT SNOW POTENTIAL. UPSTREAM...ERN PACIFIC TROUGH ENERGIES AND ASSOCIATED UNSETTLED WEATHER/COOLING/PCPN ARE EXPECTED TO WORK INLAND ACROSS THE WRN US BY SUN/MON BEFORE EMERGING INTO THE CENTRAL US NEXT TUE WHERE SRN PLAINS CYCLOGENESIS/GULF INFLOW/DEVELOPING PCPN COULD OCCUR TUCKED UNDERNEATH A MID-HIGHER LATITUDE DOME OF COLDER HIGH PRESSURE. THE DAYTIME PACKAGE IS BASED ON THE 00Z/18 ECENS MEAN, THE ROBUSTNESS OF WHICH HAS STRENGTHENED CYCLE BY CYCLE OVER THE PAST FEW DAYS. BOTH THE 00Z/18 GFS AND ECMWF ARE SOLIDLY CORRELATED WITH THIS MEAN, AND SHOULD SERVE ADEQUATELY FOR LOCAL DETAILS THROUGH AT LEAST DAY 6. CISCO/SCHICHTEL Link to comment Share on other sites More sharing options...
HM Posted December 18, 2012 Share Posted December 18, 2012 A note about the CPC anomaly graphic and possible storm after Christmas I posted in the NE subforum: What you have here is above normal heights to begin with across Canada so that when you get some ridge from a Mid Latitude Wave, the anomaly charts appear to look amazing. This is a case where you actually have to look at the means and the anomalies. If you just look at the h5 anomalies, you'd think 2009 or 2010 was on the way or something. In reality, the Arctic Heights took a hike back to Asia and we are left with generally above normal heights throughout Canada, so any small ridge will appear like a huge block on anomaly charts. The thing about "models not realizing the strength of the 50-50 low and block" is usually when there is a strong cold air source / suppressive high / polar vortex. The situation after Christmas is another hybrid, bootleg scenario that could possibly benefit the interior Northeast and portions of Coastal New England. Link to comment Share on other sites More sharing options...
usedtobe Posted December 18, 2012 Share Posted December 18, 2012 A note about the CPC anomaly graphic and possible storm after Christmas I posted in the NE subforum: What you have here is above normal heights to begin with across Canada so that when you get some ridge from a Mid Latitude Wave, the anomaly charts appear to look amazing. This is a case where you actually have to look at the means and the anomalies. If you just look at the h5 anomalies, you'd think 2009 or 2010 was on the way or something. In reality, the Arctic Heights took a hike back to Asia and we are left with generally above normal heights throughout Canada, so any small ridge will appear like a huge block on anomaly charts. The thing about "models not realizing the strength of the 50-50 low and block" is usually when there is a strong cold air source / suppressive high / polar vortex. The situation after Christmas is another hybrid, bootleg scenario that could possibly benefit the interior Northeast and portions of Coastal New England. I agree and what little block that is there really gets crushed by the vortex that moves into the Baffin bay/Island area where you want a ridge. The pattern is not one in which you lock in the low towards the maritimes, Instead it moves eastward and allows a ridge to pop between it and the next shortwave coming out of the west. Thats a lakes cutter type scenario. The ridging on the ens mean across Ak and the northwest flow aloft over western Canada should help bring some cold air into the Conus especially the upper midwest. That may be the feature that eventually gives the east some snow chance in the form of either miller b events or southwesterly flow warm advectio type events overrunning the low level cold. Link to comment Share on other sites More sharing options...
HM Posted December 18, 2012 Share Posted December 18, 2012 I agree and what little block that is there really gets crushed by the vortex that moves into the Baffin bay/Island area where you want a ridge. The pattern is not one in which you lock in the low towards the maritimes, Instead it moves eastward and allows a ridge to pop between it and the next shortwave coming out of the west. Thats a lakes cutter type scenario. The ridging on the ens mean across Ak and the northwest flow aloft over western Canada should help bring some cold air into the Conus especially the upper midwest. That may be the feature that eventually gives the east some snow chance in the form of either miller b events or southwesterly flow warm advectio type events overrunning the low level cold. I, of course, agree with everything you posted. Consider it a "gift" if you get any type of wintry wx along the eastern seaboard before the EPO dislodges the cold air. It simply is not a classic 50-50 low / -NAO setup. By the way, if this same PV situation happened last winter, it would have meant 70s. So I think the cold, snow lovers should feel happy that we aren't torching to extreme levels (although we aren't far away either). Link to comment Share on other sites More sharing options...
uncle W Posted December 18, 2012 Share Posted December 18, 2012 what's disturbing about this warm December is nineteen of the top twenty warmest Decembers in NYC had below average seasonal snowfall...This year could make the top ten or five warmest Decembers the way it's going...My expectations of a snowy winter are low now...Yea we could get a major storm and wind up with above average snowfall but it's not happening until we get some cold air in here...We're at 29 for the low for December 2012...The record is 26 set in 1974...I'd like to see mid to low 20's like we had on this date last year...It can turn on a dime like 1984-85 or 1956-57...Those years had near average snowfall...As of now that's about all we can hope for in this area... Link to comment Share on other sites More sharing options...
easternsnowman Posted December 18, 2012 Share Posted December 18, 2012 what's disturbing about this warm December is nineteen of the top twenty warmest Decembers in NYC had below average seasonal snowfall...This year could make the top ten or five warmest Decembers the way it's going...My expectations of a snowy winter are low now...Yea we could get a major storm and wind up with above average snowfall but it's not happening until we get some cold air in here...We're at 29 for the low for December 2012...The record is 26 set in 1974...I'd like to see mid to low 20's like we had on this date last year...It can turn on a dime like 1984-85 or 1956-57...Those years had near average snowfall...As of now that's about all we can hope for in this area... Since 1990 less than a third of decembers have below normal, we got spoiled with 2009 and 2010. It looks like we're now back to our usual december weather. The trend since march 2010 cannot be ignored we have to expect above normal temps it seems and snowfall depends upon luck so perhaps since things are not the way they once were (weather wise) maybe snowfall will be different and past comparisons don't mean that much. Link to comment Share on other sites More sharing options...
uncle W Posted December 18, 2012 Share Posted December 18, 2012 Since 1990 less than a third of decembers have below normal, we got spoiled with 2009 and 2010. It looks like we're now back to our usual december weather. The trend since march 2010 cannot be ignored we have to expect above normal temps it seems and snowfall depends upon luck so perhaps since things are not the way they once were (weather wise) maybe snowfall will be different and past comparisons don't mean that much. was 2008, 2009 and 2010 usual December weather?...I used to feel this way in the late 1980's and early 1990's...Since 2000 snowfall in December is running above average thanks to Dec. 2000, 2002, 2003, 2005, 2008, 2009 and 2010...Two lousey Decembers in a row is not unusual...After all the good Decembers we had recently it's nature evening things out... Link to comment Share on other sites More sharing options...
easternsnowman Posted December 18, 2012 Share Posted December 18, 2012 was 2008, 2009 and 2010 usual December weather?...I used to feel this way in the late 1980's and early 1990's...Since 2000 snowfall in December is running above average thanks to Dec. 2000, 2002, 2003, 2005, 2008, 2009 and 2010...Two lousey Decembers in a row is not unusual...After all the good Decembers we had recently it's nature evening things out... I believe 2008 was slightly above normal and 2009 was slightly below and 2010 was well below normal .We must not forget that november had snow and so far is actually colder than december so far,I don't how that would fit in? Maybe we are in whole new terrority here. Link to comment Share on other sites More sharing options...
uncle W Posted December 18, 2012 Share Posted December 18, 2012 I believe 2008 was slightly above normal and 2009 was slightly below and 2010 was well below normal .We must not forget that november had snow and so far is actually colder than december so far,I don't how that would fit in? Maybe we are in whole new terrority here. November averaged 43.9 in NYC...It's averaging 44.8 so far this December...1996 averaged 43.0...December 1996 averaged 41.3...That's the closest it came to having a December warmer than November other than 1873...It was 37.0 and 36.5 back then for the two months... Link to comment Share on other sites More sharing options...
easternsnowman Posted December 18, 2012 Share Posted December 18, 2012 November averaged 43.9 in NYC...It's averaging 44.8 so far this December...1996 averaged 43.0...December 1996 averaged 41.3...That's the closest it came to having a December warmer than November other than 1873...It was 37.0 and 36.5 back then for the two months... I believe 1996-97 was also enso neutral. I grew up in nyc area but I have lived in western burbs of philly past 20 years or so....but do miss NY and planning on moving upstate in next couple of years. I remember that year we had over twice the snowfall philly had and some areas nearly 3 times as much, what saved us was the snowfall in early march and April fools day storm which brought nearly 8 inches by me and over 17 inches in the poconos where my wife and I were during that particular storm. Link to comment Share on other sites More sharing options...
SnowGoose69 Posted December 18, 2012 Share Posted December 18, 2012 I believe 1996-97 was also enso neutral. I grew up in nyc area but I have lived in western burbs of philly past 20 years or so....but do miss NY and planning on moving upstate in next couple of years. I remember that year we had over twice the snowfall philly had and some areas nearly 3 times as much, what saved us was the snowfall in early march and April fools day storm which brought nearly 8 inches by me and over 17 inches in the poconos where my wife and I were during that particular storm. Neutral ENSOs following La Ninas just do not seem good for the entire country as a whole, may be a small sample size but too often it seems you have that remnant La Nina pattern hanging on even if you do get the -NAO/AO. Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 18, 2012 Share Posted December 18, 2012 Some quick early evening thoughts... 1. The pattern change continues to evolve as anticipated at this point in time. 2. A major winter storm will impact the Plains States into the western Great Lakes region tomorrow and Thursday. Parts of the region could pick up more than a foot of snow with isolated amounts exceeding 15". Rain could end with accumulating snow in Chicago. 3. There is a growing prospect that the above-noted storm will bring a moderate to significant snowfall to the Ottawa area. 4. In the longer-range, the AO is likely to remain negative, the PNA should become neutral (and could head positive in January) and the EPO could become neutral or even negative. Prospects for a significant Arctic outbreak will likely increase at the start of January. 5. Storminess appears likely to continue for at least the next 2-3 weeks. Link to comment Share on other sites More sharing options...
WEATHER53 Posted December 18, 2012 Share Posted December 18, 2012 Some quick early evening thoughts... 1. The pattern change continues to evolve as anticipated at this point in time. 2. A major winter storm will impact the Plains States into the western Great Lakes region tomorrow and Thursday. Parts of the region could pick up more than a foot of snow with isolated amounts exceeding 15". Rain could end with accumulating snow in Chicago. 3. There is a growing prospect that the above-noted storm will bring a moderate to significant snowfall to the Ottawa area. 4. In the longer-range, the AO is likely to remain negative, the PNA should become neutral (and could head positive in January) and the EPO could become neutral or even negative. Prospects for a significant Arctic outbreak will likely increase at the start of January. 5. Storminess appears likely to continue for at least the next 2-3 weeks. I hope you are right sir because this smacks of a couple other winters where we chased the 10-15 days away well into Janaury before finally conceeding that it was not to be. Link to comment Share on other sites More sharing options...
Ottawa Blizzard Posted December 19, 2012 Share Posted December 19, 2012 Some quick early evening thoughts... 1. The pattern change continues to evolve as anticipated at this point in time. 2. A major winter storm will impact the Plains States into the western Great Lakes region tomorrow and Thursday. Parts of the region could pick up more than a foot of snow with isolated amounts exceeding 15". Rain could end with accumulating snow in Chicago. 3. There is a growing prospect that the above-noted storm will bring a moderate to significant snowfall to the Ottawa area. 4. In the longer-range, the AO is likely to remain negative, the PNA should become neutral (and could head positive in January) and the EPO could become neutral or even negative. Prospects for a significant Arctic outbreak will likely increase at the start of January. 5. Storminess appears likely to continue for at least the next 2-3 weeks. Don, the storm this week is certainly looking more promising for Ontario. It's looking like even Toronto could pick up a couple of inches. Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 19, 2012 Share Posted December 19, 2012 Don, the storm this week is certainly looking more promising for Ontario. It's looking like even Toronto could pick up a couple of inches. Certainly, things are looking better for Toronto than they did even a day ago. However, some of the guidance brings in excess of 30 cm of snow to Ottawa. If that guidance verifies, Ottaw could have its biggest snowfall since February 23-25, 2010 when 32.0 cm fell and biggest two-day snowfall since December 9-10, 2008 when 33.4 cm fell. There remains some uncertainty, so such a substantial snowfall is not yet assured. Nevertheless, odds of a moderate to significant snowfall have been increasing on the guidance. Link to comment Share on other sites More sharing options...
Heisy Posted December 19, 2012 Share Posted December 19, 2012 I am in absolute love with what I see for early January...just hope it isn't cold and dry, thanks for everything Don, it's a shame the Dec 26-28 storm looks to be a cutter, but I think it will help to keep the AO neg. Link to comment Share on other sites More sharing options...
Ottawa Blizzard Posted December 19, 2012 Share Posted December 19, 2012 Certainly, things are looking better for Toronto than they did even a day ago. However, some of the guidance brings in excess of 30 cm of snow to Ottawa. If that guidance verifies, Ottaw could have its biggest snowfall since February 23-25, 2010 when 32.0 cm fell and biggest two-day snowfall since December 9-10, 2008 when 33.4 cm fell. There remains some uncertainty, so such a substantial snowfall is not yet assured. Nevertheless, odds of a moderate to significant snowfall have been increasing on the guidance. The latest run of the NAM was definately good for Toronto and especially Ottawa. Perhaps this will be the storm that changes the pattern, just like the December 18,1993 storm changed everything that winter? Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 19, 2012 Share Posted December 19, 2012 In Message #243, I talked about why I believe winter 2012-13 is not likely to be a repeat of the non-winter of 2011-12. Last winter, week after week, most of the guidance and the ENSO-teleconnection analogs were painting warm outlooks. After a pause following November, the scenario is a cold one. Below are the latest monthly forecasts for January 2013 from the CFSv2 and also what's showing up on the analogs for January 1-7, 2013 coupled with the month as a whole for those analogs. Notice how similar the CFSv2 and analog ideas for January are. The ENSO-teleconnection analogs are based on ENSO Region 3.4 anomalies in the -0.35°C to +0.40°C range, AO in the -3 to -1 range, and the PNA in the -1 to 0 range for January 1-10, 1950-2012. The analog years that came up were 1960, 1969, 1979, 1982, 1994, and 2004. March 1960, February 1969, February 1979, April 1982, and February 1994 had KU snowstorms. January 2004 had a major snowstorm in the Plains States and a massive lake effect snowstorm. Link to comment Share on other sites More sharing options...
Srain Posted December 19, 2012 Share Posted December 19, 2012 EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 158 AM EST WED DEC 19 2012 VALID 12Z SAT DEC 22 2012 - 12Z WED DEC 26 2012 ...QUITE AN ACTIVE HOLIDAY WINTER WEATHER PATTERN... MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR LARGER SCALE PATTERN EVOLUTION INTO MONDAY. THE PATTERN REMAINS HIGHLIGHTED ALOFT THIS WEEKEND BY AN AMPLIFIED TROUGH JUST OFF/ALONG THE WET WEST COAST...AN AMPLIFIED RIDGE OVER THE W-CENTRAL US...AND ANOTHER AMPLIFIED TROUGH/CLOSED LOW CENTERED OVER THE WINTERY NERN US. THE LEAD SYSTEM AND ASSOCIATED DEEP SURFACE LOW/SYSTEM AND SENSIBLE WINTER WEATHER FOCUS SHOULD PROVE SLOW TO EXIT INTO THE CANADIAN MARITIMES WORKING INTO BLOCKED FLOW. THIS LEAVES PLENTY OF ROOM FOR COOLING BACK ACROSS THE ERN AND CENTRAL US DOWN THROUGH THE SRN TIER STATES WELL IN ITS WAKE...INCLUDING LINGERING WEEKEND LAKE EFFECT SNOW POTENTIAL. UPSTREAM...ERN PACIFIC TROUGH ENERGIES AND ASSOCIATED UNSETTLED WEATHER/COOLING/PCPN ARE EXPECTED TO WORK INLAND ACROSS MUCH OF THE WRN US INTO SUN/MON. FORECAST SPREAD BECOMES INCREASINGLY PROBLEMATIC MON-WED OF NEXT WEEK THOUGH. RECENT GFS RUNS OFFER THE LEAST PROGRESSIVE AND MOST STREAM SEPARATE FLOW. RECENT ECMWF RUNS ALSO HAVE STRONG SYSTEM POTENTIAL BUT ON THE MORE PROGRESSIVE SIDE OF THE FULL ENVELOPE OF GUIDANCE SOLUTIONS. IT SEEMS THE UPSTREAM/DOWNSTREAM FLOW AROUND THE LOWER 48 PATTERN COULD PLAUSIBLY SUPPORT EITHER SOLUTION CAMP. ACCORDINGLY...NEW HPC OVERNIGHT MEDIUM RANGE GUIDANCE WAS PRIMARILY DERIVED FROM A 50-50 BLEND OF MORE COMPATABLE GEFS/ECMWF ENSEMBLE MEANS. A COMPOSITE GEFS/ECMWF ENSEMBLE MEANS BLEND MAINTAINS DECENT HPC CONTINUITY AMID UNCERTAIN POTENT FLOW. THIS SOLUTION WOULD FOCUS ACTIVITY INTO THE CENTRAL US CHRISTMAS WHERE SRN PLAINS CYCLOGENESIS/DEEPENING GULF INFLOW/DEVELOPING HEAVIER PCPN TUCKS UNDERNEATH/INTO A MID-HIGHER LATITUDE DOME OF COLDER HIGH PRESSURE. THE DEEPENING WINTER LOW HAS AMPLE DYNAMIC POTENTIAL TO DEEPEN TO ANOTHER THREATENING MAJOR WINTER SYSTEM FOR THE E-CENTRAL US WED...GIVE OR TAKE A DAY. SCHICHTEL Link to comment Share on other sites More sharing options...
OUGrad05 Posted December 19, 2012 Share Posted December 19, 2012 Anyone have thoughts on what appears to be a significant system on the 25-27th? Specifically its impact on NE OK. Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 19, 2012 Share Posted December 19, 2012 Anyone have thoughts on what appears to be a significant system on the 25-27th? Specifically its impact on NE OK. At least for me, it's too soon to be confident in details. It does appear that a rain changing to snow scenario is probably more likely than all rain or all snow. At least some accumulations appear possible, but that's as far as I can go from this far out. Link to comment Share on other sites More sharing options...
Srain Posted December 20, 2012 Share Posted December 20, 2012 As has been previously mentioned, a potent Winter Storm appears on the horizon near the Christmas Holiday period. There may be some major societal/travel impacts that spread across a large portion of the CONUS during the period. While it is too soon to know the exact details, with the busy travel period ahead it does warrant monitoring. EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 200 AM EST THU DEC 20 2012 VALID 12Z SUN DEC 23 2012 - 12Z THU DEC 27 2012 ...MORE ACTIVE WINTER WEATHER COMING... MODELS AND ENSEMBLES IN GENERAL OFFER AN INCREASINGLY SIMILAR LARGER SCALE FLOW EVOLUTION FOR NEXT WEEK DESPITE CONTINUED DIFFERENCES WITH EMBEDDED SYSTEM TIMING AND INTERACTIONS. THIS PATTERN SEEMS HIGHLIGHTED BY LEAD MID-UPPER LEVEL TROUGH ENERGY FROM THE CENTRAL TO ERN US DAY CHRISTMAS EVE/CHRISTMAS ALONG WITH AN ASSOCIATED SURFACE SYSTEM REFLECTION AND PCPN FOCUS THAT THE MODELS TRENDS NOW BETTER FAVOR INTO THE COOLED AIRMASS IN WAKE OF THE DEEPER DOWNSTREAM CANADIAN MARITIME LOW. UPSTREAM...AMPLE MID-UPPER LEVEL TROUGH ENERGY DIGS FROM THE WEST COAST CHRISTMAS EVE TO THE S-CENTRAL ROCKIES/PLAINS BY CHRISTMAS WITH SURFACE LOW DEVELOPMENT AND PCPN UNDERNEATH AND OVER SWD SURGED PLAINS HIGH PRESSURE. THIS SYSTEM REALLY IS EXPECTED TO DEEPEN MID-LATE WEEK OVER THE E-CENTRAL THE ERN US INTO A MAJOR WINTER STORM WITH AN EXPANDING HEAVIER PCPN SHIELD. THERE IS AMPLE ROOM FOR COLD AIR TO SETTLE TO THE NORTH OF THE LOW AND DAMMED DOWN THROUGH THE MID-ATLANTIC IN ADVANCE OF THE SYSTEM. OVERALL...HPC OVERNIGHT MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS ALONG WITH NEW OVERNIGHT 00 UTC HPCGUIDE 5KM SENSIBLE WEATHER GRIDS HAVE BEEN PRIMARILY DERIVED FROM A BLEND OF THE 18 UTC GFS WITH THE 12 UTC ECMWF/GEFS ENSEMBLE MEAN/ECMWF ENSEMBLE MEAN. THESE MODELS OFFERED A REASONABLY SIMILAR LARGER SCALE PATTERN EVOLUTION ALOFT AND CLUSTER THE MAIN SURFACE FEATURES BETTER THAN OTHER AVAILABLE GUIDANCE. THE PURPOSE OF INCLUSION OF THE ENSEMBLE MEANS WAS TO SMOOTH THE LESS PREDICTABLE SMALLER SCALE DETAILS WHILE BLENDING IN THE GFS/ECMWF ALLOWS FOR BETTER FEATURE DEFINITION FOR SEEMINGLY THE MORE PREDICTABLE FEATURES GIVEN BROAD GUIDANCE SUPPORT. A QUICK LOOK AT THE LATER 00 UTC MODELS SHOWS CONTINUED VARIABILITY WITH TIMING/SPACING OF EMBEDDED INDIVIDUAL FEATURES BUT CONTINUED SUPPORT FOR THE OVERALL ACTIVE WINTER PATTERN. SCHICHTEL Link to comment Share on other sites More sharing options...
Srain Posted December 20, 2012 Share Posted December 20, 2012 EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 1044 AM EST THU DEC 20 2012 VALID 12Z SUN DEC 23 2012 - 12Z THU DEC 27 2012 ...STORM SYSTEM INCLUDING SOME HEAVY SNOW TO AFFECT MUCH OF THE NATION CHRISTMAS EVE TO THE 27TH... ...SYNOPSIS... THE LARGE SCALE PATTERN FEATURES A POTENT COMBINATION OF MODERATELY DEEP AND ENERGETIC SYSTEMS AND PROGRESSIVE FLOW AT MIDDLE LATITUDES. THIS YIELDS THE OPPORTUNITY FOR MODERATELY STRONG CYCLONES TO BRING SWATHS OF RAIN/SNOW/WIND TO MUCH OF THE U.S. OVER A SHORT PERIOD OF TIME. ONE SUCH STORM IS BECOMING INCREASINGLY LIKELY TO DEVELOP IN THE SOUTHWEST STATES ON THE 24TH AND INTENSIFY OVER THE PLAINS/MIDWEST ON THE 25TH AND 26TH. SEVERAL MODELS ALSO INDICATE THE POSSIBILITY THAT THIS STORM WILL HAND OFF TO A COASTAL LOW/NOR'EASTER BEGINNING AROUND DAY 7...THE 27TH. ...MODEL CHOICE... THE 00Z GFS LOOKS ENTIRELY PLAUSIBLE AND FITS WELL WITH BOTH THE 00Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN. THE LOW TRACK THE GFS DEPICTED FROM THE SOUTHERN PLAINS TO OHIO VALLEY ON DAYS 5-7 MATCHES CONTINUITY FROM THE OVERNIGHT PACKAGE AND IS IN THE MIDDLE OF THE BEST CLUSTERING OF ENSEMBLE LOW TRACKS. THIS GAVE US MODERATE TO STRONG CONFIDENCE IN USING THE 00Z GFS AS THE PRIMARY BASIS FOR OUR FRONTS/PRESSURES...WITH RELATIVELY LOWER WEIGHTING ON THE ENSEMBLE MEANS EVEN THROUGH DAY 7. WE ALSO GAVE SOME WEIGHT TO THE 00Z CANADIAN WHICH OFFERS A SIMILAR PROGRESSION. THE 00Z ECMWF WAS LARGELY DISCOUNTED AS BEING TOO AMPLIFIED AND SLOW WITH THE PLAINS/MIDWEST CYCLONE AND ALSO WITH A TROUGH APPROACHING THE WEST COAST LATE IN THE PERIOD. THE ECMWF WAS A CLEAR OUTLIER...ESPECIALLY WITH RESPECT TO DEPTH...COMPARED TO EVEN ITS OWN ENSEMBLE MEMBERS. ONE KEY POINT AT DAY 7...IS THAT OUR MODELS OF CHOICE...GFS/GEFS MEAN/CANADIAN...ALL POINT TOWARD A HAND-OFF FROM THE CYCLONE OVER THE OHIO VALLEY TO A DEVELOPING LOW ALONG THE MID ATLANTIC COAST. THIS IS NOW REFLECTED IN OUR FORECAST. ...IMPACTS... THE STORM SYSTEM OF INTEREST THIS PERIOD WILL ENTER THE WEST COAST ON DAY 3 AND DIG INTO THE SOUTHWEST ON DAY 4...BRINGING RAIN/SNOW/POTENTIAL WINTER STORM CONDITIONS TO THE MOUNTAINS. AT THE SAME TIME...BLOCKED FLOW AT HIGHER LATITUDES WILL ALLOW A STACKED CYCLONE OVER EASTERN CANADA TO FORCE MORE ARCTIC AND MODIFIED ARCTIC AIR DOWN INTO THE CENTRAL U.S...SETTING THE STAGE FOR ANOTHER SNOW EVENT WHEN THE STORM EJECTS FROM THE SOUTHWEST STATES. EXPECT THIS TIME THAT THE PERSISTENT BLOCK OVER EASTERN CANADA WILL SUPPRESS THE TRACK OF THE SURFACE LOW INTO THE OHIO VALLEY RATHER THAN THE GREAT LAKES. AT PRESENT TIME...THE MOST LIKELY SNOW SWATH APPEARS TO BE ACROSS NORTHWEST OK INTO KS/MO CHRISTMAS DAY AND NIGHT...CONTINUING TOWARD NORTHERN IL/IN. RAIN/THUNDER WILL OCCUR FARTHER SOUTH TO THE GULF COAST...SWEEPING EASTWARD. MODELS INDICATE COLD AIR DAMMED INTO THE MID ATLANTIC REGION IN ADVANCE OF THE SYSTEM...WHICH MAY RESULT IN A MIXTURE OF PRECIPITATION TYPES TOWARD DAYS 6/7. IF THE COASTAL LOW/NOR'EASTER WERE TO FORM AS FORECAST...IT APPEARS PER THE 00Z GFS/GEFS INFORMATION THAT THE SNOW LINE WOULD INDEED REACH THE COAST AND THE MAJOR CITIES IN NEW ENGLAND. THIS IS AT DAY 7...HOWEVER...AND THEREFORE IS LESS CERTAIN. THE ECMWF ENSEMBLE IS A BIT SLOWER AND FARTHER WEST...SUGGESTING MORE WARM ADVECTION WHICH WOULD PUSH THE RAIN/SNOW LINE INLAND. BURKE/RAUSCH Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.