Thursday, January 29, 2015

Icy Surprise Ahead?

Icy Surprise Ahead?

WINTER WEATHER ADVISORIES EXTENDED EAST TO 
BALTIMORE & NORTH DC METRO AREAS FOR SNOW & SLEET THURSDAY PM


1:10 PM 1/29 - Another Icy Surprise? We hope not, but atmospheric forces and ground temperature may have a different plan.

Our analysis of the enclosed image from the NOAA Storm Prediction Center indicates there is rising potential for a more widespread wintry mix event this afternoon across the region than may be expected. 


A fast-moving cold front is forcing a notable amount of moisture ahead of it. This moisture will be moving into a stubborn surface layer of cold air with ground temperatures at or below freezing. 

This may result in snow and sleet during the PM commute, starting between 3-4 PM in Frederick and Carroll County, moving to the Baltimore Metro areas between 4-5 PM, and tapering after 7 PM. 

Since a surprise ice event on Sunday 1/18 was produced by less than one-TENTH of an inch of ice (0.10"), this heightens concerns for areas along the I-95 corridor on west, especially for any untreated roads.

3 comments:

Mike Cheuvront said...

FYI- I read some conflicting definitions of a Miller A - Miller B storm. Here is what they mean.


Miller A- A classic Nor'easter. This type of Nor'easter forms along a deep trough in the Gulf Coast normally along a cold front. A area of low pressure moves along the trough out of the Rockies or Southwest U.S. The low pressure area moves over the Gulf and sucks up all that moisture. The primary Low Pressure moves off the Carolina coast and follows the jet stream along the coast moving north and east, sucking up more moisture and intensifying as it goes. A miller A is much easier to forecast, due to the fact there is only one area of low pressure.

Miller B- This type of Nor'easter has two areas of low pressure. one along the southern sub tropical stream, and an inland low along the northern polar stream. The northern storm rides up the Midwest (up the Ohio Valley). As the two areas of low pressure approach each other , they allow the southern and northern Jets to phase. These storms produce precipitation in the Midwest/Ohio Valley. As the primary low approaches the Appalachian Mountains; the primary storm loses its low pressure center, this leads to an energy transfer to the coast to the secondary Low along the coast. This allows the coastal low to grow in size and quickly intensity (undergoes cyclogenesis / bombogenesis ) . Miller B's a harder to forecast than a Miller A... Speed and energy transfer is key as to what the storm will do.

Andy, Southern York County Pa said...
This comment has been removed by the author.
Andy, Southern York County Pa said...

ALRIGHT BACK IN BUSINESS!

Been pulling too many long 12-14 hour days lately, heading into peak snow season. Never good when it's not snow related! Thought I might have been fired back in the winter of 2009/2010 but no one forced me out of the building, money kept showing up in the account, so I kept a low profile and the powers that be must have forgotten. Now I am still a faceless cog in the relentless sweat shop that is work. Slaving 12 hours a day over a hot photo copier, enduring deep paper cuts, and master minding office pranks takes a lot of mojo away from storm tracking.

My limited 2 cents around 72 hours out. Now that the last Boston blizzard has cleared the radar screens, clipper is clipping away as we speak, and the NAO is cruising to neutral crossing negative, we have a snow threat.

Right now there is a high probability of 4-8 inches of snow Sunday evening into Monday afternoon.

This will be a relatively fast moving system with a narrow band of high QPF of around an inch. Where that area sets up in the cold zone which is from Northern VA north, someone could get a foot.

I am more confident in a moderate snow right now, and won't pull the trigger on anything major yet.

Simply put, we are at 72 hours from the threat and there is a lot of time to shift the band of heavy QPF south. Confluence can be your friend or squash your snow. Models sometimes underestimate confluence until inside 48 hours and trend precip south. If that happens we are on the northern fringe of the qpf.

Right now we are tracking in my book a 4-8 event, with a larger upside possible. Good agreement in guidance the we will have a plowable snow. If the models were correct today and never shifted then we are near the QPF bulls eye. I like this threat, Manwich and martini worthy (gotta mix the red neck and bourgeoisie sometimes).

Nevertheless, a lot can change in a fast flow so what I am looking at or concerned about is suppression of heavy precip more than anything. We have the NAO on our side and the models are in agreement so that is a big big win in the powder hound playbook. The last storm guidance was all over and a raging positive NAO to keep it progressive.

This time will we stay in the high QPF zone, will FOOT KICK OUT a FOOT of SNOW in his FORECAST? TIME WILL TELL!