12/18 11:20 AM winter storm update

Band of precip will move into the region within the hour bringing a mix of rain, snow and sleet. The precip could initially fall as rain as the column saturates and cools. This band of precip is associated with the strong 850 mb low... Expect precip rates to continue to increase as this low skirts south of the region. Current RUC sounding show a 0c isothermal layer throughout the column this afternoon. Surface wet bulb is currently at at or slightly below zero in the triangle. Chance of moderate to heavy snow/Sleet during rush hour looks like a real possibility in the triangle.kk

12/18 winter storm update

Just a quick update on the timing of the snow/mix/rain transition. The transition gradient will be very tight. Greensboro/Winston Salem may see all snow with up to a foot of snow possible. Durham will likely see moderate snow transition to zr later tonight, and those just SW of Raleigh will see very little snow at all.

So my forecast for the triangle is difficult, because depending on where you live in the triangle will depend on how much winter weather you see. The NW will see more snow.. and the SE will see less snow. If the High pressure had been stronger and holding steady the whole region would've seen a historic snow storm... But instead it's this:


Friday afternoon: Snow, possibly mixed with light rain. The snow could be moderate at times in the afernoon. High 36

Friday night: Snow changing to sleet and ZR between 7 PM and 9PM and then all rain after 9PM. The snow could be heavy during the evening. Low 30

Saturday: A chance of freezing drizzle/drizzle and flurries. High 35

Possible snow accumulation totals within the triangle this evening:

Chapel Hill: 2-4 inches
Durham: 2-4 inches
Cary: 1-2 inches
Raleigh: 1 inch
SW of Raleigh: < 1inch

The models are all over the place with the Christmas Eve/Christmas storm.... Showing it as an all rain event at this time. But I can't out rule a major winter storm with this system.

12/17 Weekend winter storm update

Not much of an update is really needed, but I did want to mention the chance of moderate to heavy snow potential Friday afternoon until sometime Friday night/early Saturday morning. GFS Bufkit is showing a dry layer at around 850. The GFS may be having a difficult time handling diabatic cooling due to evaporation. Therefore, I believe an isothermal layer may exist during the evening hours. I think it may be a situation in which light precip will fall as rain (less evap cooling) and more heavier precip (more evap cooling) will fall as snow up until a certain point during the night. Significant snowfall during rush hour is not out of the question. The timing may need to be updated tomorrow on the exact timing of the changeover to rain. I believe that any changeover to ZR will be brief due to latent heat release caused by freezing. Temps will be borderline for ZR to begin with so expect the ZR itself to lead to enough of a temp increase to change the precip to rain over night. Also, most of the precip should end early Saturday morning with some light freezing drizzle and flurries possible through the afternoon.

Will need to really look into the Christmas eve storm as well. Could be anything from all rain to mostly snow to a historic ice storm.... stay tuned. Starting to gain some confidence though that someone will say a major Christmas eve/Christmas storm.

New Forecast:

Friday afternoon: Snow, possibly mixed with the light rain. The snow could be moderate to heavy at times in the afernoon. High 36

Friday night: Snow changing to sleet and ZR between 10 PM and 1AM and then all rain after 1. The snow could be heavy during the evening. Low 30

Saturday: A chance of freezing drizzle and flurries. High 35

12/16 - Weekend Winter Storm Forecast for the Triangle:

Synopsis: A low pressure will form along the gulf coast and move northeast off the North Carolina coast this weekend. Cold air will be in place as the low pressure nears the region which will likely bring wintery precip to the triangle. Forecast confidence is very low.

Discussion: A Miller A low will move up the North Carolina coast increasing moisture flux from the Atlantic into the triangle by Friday afternoon. This low will exit the area slowly first bringing in a round of precip due to overrunning warm advection over a fairly strong cold pool at the surface. A 2nd round of precip affiliated with the deformation band will occur later in the weekend. The GFS and ECMWF are in decently good agreement on the general location and timing of the low pressure. I am looking at GFS Bufkit soundings to determine first guess precip type. Forecast confidence is very low due to precip type remaining near the mixed bag region of the nomogram. Diabatic processes could play a large part in the precip type especially Friday afternoon as the precip begins. Also, this is a cold air damming scenario with cold air filtering in between a fairly weak high to the Northwest and a Low to the northeast. NWS RAH mentioned that this storm compares generally well with a storm in 05 in which very little wintery precip fell in the region. With that in mind this is a completely different storm. GFS and every other model for that matter tends to warm temps too much during a CAD event. This fact makes me want to go with an icier/snowier scenario for the triangle as the GFS already predicting a decent amount of ice and snow, especially in the deformation. Climatology however does not support this type of system as a major winter event however, which is why my confidence is so low. On top of that there will be a tight gradient between the rain/mix/snow lines. Also, diabatic processes will turn borderline temps for freezing rain into temps for rain. Right now it's too far out to truly pinpoint the exact location of the low and the strength of the cold air.

But I will forecast what I see as of now... This is likely to change!

Friday afternoon: A 60% chance of snow possibly mixed with rain

Friday night: 70% chance of snow mixing with freezing rain/rain and sleet by 8PM and then changing to all rain/freezing rain/sleet mix.

Saturday: Rain quickly changing over to freezing rain/drizzle before ending.