The final part of the Winter 2016-17 forecast is here!
Here's our guess has to much snow to expect for Virginia and surrounding areas for the winter season:
2016-17 WINTER OUTLOOK: PART 4 - BREAKDOWN OF MONTHLY TEMPERATURES, OVERALL PRECIPITATION, AND U.S. WINTER HIGHLIGHTS
U.S. WINTER HIGHLIGHTS
For much of the week on our Facebook page, we talked about all of the factors that play into the seasonal outlook (NAO, AO, PDO, ENSO, etc.) We are approaching the final part of the winter outlook (Snowfall prediction at 5:00 PM Friday, October 28th). Here's our breakdown of monthly temperatures for the upcoming winter.
This is a huge turn from previous winters, where temperatures were mild to very warm for December. While we think there will be some up and down temperature swings, much of the Mid-Atlantic should end the month at least 1 to 2 degrees below average. The brutally cold air will be across portions of the Midwest and Great Lakes region. This will help push storms closer or along the East Coast. We think there will likely be a few wintry storms during the month. While it's impossible to predict when that will happen exactly, the odds for a "White Christmas" this year is much higher compared to recent years -- the chance is higher compared to recent years.
We think January will be the coldest month, with the Arctic Oscillation tanking at times, providing a pretty chilly cold period during the month of January. The PDO and PNA will likely remain dominant across the West and Southwest, which will put a trough across the East. There's a chance for at least one big storm. However, too much cold can suppress storms to the South, so we will need to watch how this plays out carefully. We do think there will be several clipper systems, and this will reinforce the cold.
If the current ENSO forecast is correct, and we continue to go from a borderline Weak La NIna to a La Nada, I think that the colder than normal temperature scheme will continue across the East, with very warm conditions across the Southwest and West. It may not be as chilly across the Southeast compared to January, but the Mid-Atlantic, Mid-West and Northeast will likely still have its share of cold. Sometimes, a fairly large storm is possible before a big pattern or temperature change. I would not be shocked if this happened in February across the Mid-Atlantic.
Below average precipitation is erected across potions of the Deep South and Southwest. Disturbances that enter the Pacific Northwest and Rockies will likely produce above average precipitation in these areas. Disturbances across the Midwest will be more on the wintry side, but we are highlighting this as "above" to give the general idea that we expect an active pattern in this area. Slightly above across coastal Northern-Mid Atlantic and New England with some disturbances being stronger than anticipated, or some lows that form off the Mid-Atlantic coast, producing snowy periods.
While no two winters are alike, we look at analogs from different years that helps us get some type of idea what the winter will be like. It's also based on different variables, including if each winter was a La Nina, El Niño or neutral (La Nada). Some of the analog years that stood out were 1960-61, 1961-62, 1984-85, 1985-86, 1993-94, 1995-96, 1996-97, 2013-14, and 2014-15. These analogs were a combination of La Nada or weak La Niñas, with many showing a warm PDO (huge blob we mention often in the Northern Pacific, south of Alaska) that often associates with a trough in the east (colder) and a ridge in the west (warmer). The Southwest will likely see very warm and dry conditions through much of the winter.
Based on the latest information, including increased Siberian snow cover and a pretty active Typhoon season in the Western Pacific that often plays a huge role with buckling the jet stream and sending cooler weather across the Eastern U.S., temperatures for much of the Mid-Atlantic will range anywhere from near average to below average. Some ridging across the Southeast will keep temperatures a bit warmer across the Carolina's, Georgia and Florida, but I think there will be cold shots as well as we head later into the winter, probably mid-winter.
It should also be noted that "too much cold" is a bad thing for snow. Very cold temperatures leads to very dry air, and that would tend to push storm tracks South and East. We think the really cold air will be across the Mid-West, Great Lakes, and portions of the Northeast, which would tend to push storm tracks closer to the coast.
For Virginia, we think December will likely have some swings in temperatures, but the cold will win overall. This theme should continue into January and possibly continue into February, depending on the state of La Naña or La Nada conditions. Although there's colder water temperatures near the Equatorial Pacific, the theme should still result in either a very Weak LaNiña to La Nada conditions. While we literally had La Nada in 2013-14 and 2014-15, where the winter started warm, long range continues to suggest more ridging in the West and through in the East.
Although the PDO has weakened a bit, it has been showing signs of getting its act together again, which should help to provide cold. With signs pointing to potential blocking (-NAO), this should also help favor some storm tracks that come up the East coast, or at least systems that come through the Tennessee River Valley or Carolina's, then lows that develop along the Carolina coast, resulting in a winter storm track.
Precipitation looks to be "normal" -- However, remember that if these systems are in the form of snow, 12 inches of snow is equivalent to 1 inch of rain.
Dangerous Heat Index Values Near 110 This Afternoon for Washington, D.C., Southern & Eastern Maryland, Delmarva, Northern Neck and Hampton Roads
Excessive Heat Warnings continue for Washington, D.C., Fredericksburg, and Southern Maryland. Once again, while there are no warnings issued south and east, please take the advisory seriously (heat advisory criteria index 105 to 109) as the heat index will likely be on the very high end of the threshold, if not 110 degrees or higher across Hampton Roads, the inland areas of the Delmarva and the Northern Neck. Not surprised (and hopefully) to see warnings expanded later this morning or early this afternoon.
Today's heat index values will be the highest near the coast. Dew points are in the upper 70's. While dew points are expected to drop a bit West of I-95, it may be difficult for the dew points to lower. Therefore, dew points in the mid to upper 70's and temperatures 95 to 99 degrees will result in heat indices of 108 to 112 degrees. Dew points may lower enough along I-95 for the heat index to be a few degrees cooler than yesterday ranging 106 to 109, however, the typical locations, such as heat island/urbanized areas will still see heat indices closer to the 108 - 109 range, at least for an hour or two. The Piedmont should see heat indices range 103 to 106 and mid-90's to around 100 for much of the Shenandoah Valley.
The latest HRRR model shows a line of thunderstorms trying to develop across Western Virginia and moving eastward into the Piedmont. However, with the ridge in control, this may be overdone and any storms that do make it across the Blue Ridge will fall gradually weaken and fall apart. Coverage for thunderstorms 20 percent across the Piedmont and Eastern Virginia, and 30 percent across Western Virginia.
SUNDAY: Excessive Heat Warning Continues for Washington, D.C. Metro; Warning Now Includes Fredericksburg and Southern Maryland
EXCESSIVE HEAT WARNING continues for Washington, D.C. Metro on Sunday. NWS Baltimore/Washington has expanded the Excessive Heat Warning to now include Fredericksburg and Southern Maryland. The Excessive Heat Warning is from 12 Noon Sunday until 8:00 PM Sunday Evening. The heat index is expected to hover around 110 degrees during the afternoon hours.
The peak heat index this afternoon at Washington-Dulles International Airport reached 114 degrees! While Richmond and Norfolk are only under a "Heat Advisory" on Sunday (criteria: 105 to 109), we will likely see urbanized areas reach the 110-degree mark. Since many areas along I-95 corridor will flirt with the warning criteria, please treat the Heat Advisory and Heat Warning the same (respectfully) and continue to use extreme caution if outdoors for any length of time.
Dew points are expected to drop a bit in the afternoon across the Piedmont and Valley.... therefore, heat index values will be a little lower, but still on the high side. Heat indices are expected to reach the 100 degree mark across the Southern Piedmont to as high as the mid-100's in the Central and Northern Piedmont. The Northern Valley will see heat indices around or a few degrees over 100, with mid to upper 90's across the Southern Valley areas.
Current NWS Warnings & Advisories
EXCESSIVE HEAT WARNING is in effect for the Washington, D.C. and Baltimore Metropolitan area. Heat index will likely exceed 110 degrees this afternoon with the actual air temperature around 100 degrees. HEAT ADVISORY for Central and Eastern Virginia. This means the heat index will range 105 to 109 degrees, however, some of the latest data suggests maximum heat indices a bit higher (109 to 112), especially across urban areas.
An Excessive Heat Watch is also in effect for Washington, D.C. and Baltimore Metropolitan area on Sunday. The heat index could reach or exceed 110 degrees for two days in a row.
Maximum Heat Index -- This Afternoon
We combined the latest model data and the NWS maximum peak heat index and came up with the heat index forecast shown above for this afternoon. Temperatures will be at least 2 or 3 degrees higher compared to yesterday. Dew points may have difficulty lowering this afternoon. Therefore, dew points will likely range from the low to mid 70's....and possibly upper 70's along the coast. With a southwest flow and the Bermuda High still in control, there's at least 75% confidence that we will see heat indices across Metro Richmond near 110 degrees, especially in the city. The same goes for Norfolk and portions of Hampton Roads with the heat index around 110 degrees. The Piedmont and valley will also experience high heat index values, however, not as high compared to the I-95 corridor and Eastern Virginia.
Forecast Highs -- This Afternoon
Actual air temperatures this afternoon will be near 100 degrees across Washington, D.C. and Baltimore. Upper 90's can be expected across Metro Richmond and Norfolk, and low to mid 90's across the Southern Piedmont. While it will still be humid in the mountains, at least actual air temperatures will only reach the upper 80's!
Sunday gets no better...
Temperatures on Sunday will be about the same as today with heat index values once again near 110 degrees in urban areas. However, there will be a slightly better chance for showers and thunderstorms across Northern Virginia (30 percent chance).
Changes ARE on the way...
Here's the 850 mean temperature anomaly as we go into Wednesday of this week. A clipper system and arctic front will push through the area late Tuesday into Wednesday. Some models support some snow showers or flurries, but the more important thing to look at is how cold it will be. Models are showing highs mainly around freezing on Wednesday, which is very similar to the high of 31 degrees at Richmond International last Tuesday!
Here's the GFS ensemble (12z) that shows different low pressure plots. This is late next weekend into early next week. You can see where even more colder air from the Northern Plains and Midwest starts to advance eastward. This is basically a trough setting up. So, the ensembles are clearing seeing the energy, but it all comes down to how cold it will be and where the storm system sets up at.
While you need cold to produce snow, in many cases "too" cold can suppress systems and limit formation. Very cold means very dry air. After the late weekend or early week storm leaves the picture, evidence of strong blocking, and another batch of very cold air reloads across the East Coast.
The NAO and AO (arctic oscillation) is expected to remain in a very negative position, however, in time, it appears the AO may trend more on the neutral side by the end of the month. The PNA should remain positive, which means a ridge across the West. West based negative NAO is normally the key to most systems in regards to colder air and storms. When it goes really negative, it disrupts the polar jet stream, causing it to buckle and send colder air to the east. It can usually cause interactions with the northern and southern jet, resulting in storminess.
The last image on the left shows that the West based NAO looks to stay pretty negative through for the next week... Which is why I think that one of these storms coming up could be a hit for the Mid-Atlantic and into the Northeast.
The bottom line is, don't get "bent out of shape" if you are looking for snow and operational runs go from a lot to nothing. There continues to be pretty strong supporting evidence of cold and stormier weather on the horizon.