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February 2014

Winter Storm Threat: Feb 14-15 (Final Call)

A trough will traverse the Ohio Valley today and will start to take on a negative tilt as it reaches the East Coast, with a nice vort max developing over the Carolinas that will allow for a rapid strengthening of the surface low once it moves off the coast. Cold air aloft and the upper-level dynamics will be fairly supportive of snow, but somewhat-limited moisture and a warm boundary layer (despite the snowpack) will prevent a bigger snowfall within the forecast region.


Risks are more towards the lower side across the region with this system, though there is some upside potential near the coast if the low can strengthen faster. A little event to top off this snowy period before temperatures jump well above normal next week.

Winter Storm Threat: Feb 12-13 (Final Call)

Only real notable adjustment for the final map was the expansion of the 12-18 contour and addition of locally 12+ over northern Maryland and into Pennsylvania. Expanded the 8-12 contour eastward slightly near I-95 and bumped the higher totals in North Carolina eastward a bit. Small changes to the western cut-off of the system as well.


There is more risk to the higher side west of I-95 and equal risks along and east of I-95. I will be in D.C. tonight into tomorrow to cover the storm!

Winter Storm Threat: Feb 12-13 (Second Call)

Not incredibly different from my initial forecast… still uncertainty with the low track, which could cause more/less sleet and rain along the coast and could move the western edge of accumulation west/east. Also have to watch that band on the west side of the storm for possible higher totals. Hard to tell if I should lean more GFS, Euro or just split the solutions.


Notable differences are 1) eastward shift of the 4-8 and 8-12 contours from central Maryland through northern North Carolina, 2) eastward shift of the western cut-off, and 3) addition of 12-18 contour in Virginia and extreme northern North Carolina. I think there is still more upward potential than downward west of I-95, but I am unsure of which way to lean along and east of I-95, where mixing could cut down totals but banding on the back side of the storm could boost totals.

Significant icing (0.25″+) is also possible in the Carolinas with this event, which could cut down on snow totals around Raleigh and Charlotte.

Even though the event will be underway in southern North Carolina tomorrow morning, I plan on issuing a quick update in the early afternoon tomorrow because Virginia northward could still see some decent shifts and I want to leave room to adjust if needed.

Winter Storm Threat: Feb 12-13 (Initial Call)

A big coastal storm will be ramping up in the Southeast Tuesday into Wednesday and will deepen along the Mid-Atlantic Coast Wednesday into Thursday, bringing significant snowfall to a large portion of the East Coast. My initial forecast leans mostly towards the Euro model, but there is some compromise with the GFS solution, which is also keeping confidence moderate at best. The Euro has been holding steady while the GFS keeps trending towards it, but the Euro may be over-amplified as it can be with these big coastal storms.

Sleet and rain mixing in along the coast should cut into totals, though how far inland the changeover goes is still up for debate. Likewise, the western edge could still see some notable shifts if the Euro track is way off (which I don’t believe to be the case). A strong area of banding is expected on the northwestern and western side of the storm, which could significantly boost totals if it can stall over an area for several hours.


I’m fairly confident that I will need to add a 12-18 inch contour in the next update, but I don’t have enough certainty in the forecast to place it at this time.

Winter Storm Threat: Feb 5 (Only/Final Call)

Heavy snow is expected across the northernmost parts of the forecast region, with lesser amounts the further south you go as snow at the onset of the storm battles with warming mid-levels as the storm pushes through the Mid-Atlantic. Timing of the changeover to sleet/freezing rain/rain will be critical from central PA roughly from I-80 (or even a little north of that) southward… so yeah, that’s a large area to watch for the changeover. After the storm passes, some residual moisture playing the upslope on the west side of the Appalachians could bring 1-2 inches of snow into the higher elevations of WV and the WV/MD panhandles.


Significant (damaging) icing is possible in southern OH, southern PA, WV, VA, western MD and western NJ, which is not shown on the map. For the DC area, places around I-95 and points east should have little to no icing, but west of I-95 up to 0.25-0.5 inches of ice is possible. Further north into PA/NJ, more notable ice is possible east of I-95. My forecast map includes snow+sleet accumulation, but not ice from freezing rain.

NEW! I added a confidence bar to my map, with a scale of 1 (low) to 5 (high). I almost always write out my forecast confidence in these blog posts, but those who just look at the forecast image will miss it, so I figured I would fill in some of the negative space with some useful information. The confidence in this forecast is 2 out of 5 (low-medium).

Here is the latest ice accumulation forecast from the NWS for the LWX forecast region:


Winter Storm Threat: Feb 3 (Final Call)

Brought things northward with this update due to that pesky “warm” layer aloft. This is a considerably tough forecast across the southern areas near the 1″ line as the models generally have isothermal temperatures along the freezing line between about 850mb-750mb. Temperatures at the surface are also around freezing, with sub-freezing temperatures in most of the layer just above the surface to about 850mb. So yeah, a lot of potential for the southern areas to either bust high or low with this event.


I included the “locally 8-12″ because it’s really hard to pinpoint where the places that get it might be. My best guess for spots of 8-12” would be in the MD/WV panhandles into south-central PA, and if the European model is correct, possibly into central NJ.

Winter Storm Threat: Feb 3 (Initial Call)

This is one of the more classic snow storms that we’re used to in the Mid-Atlantic: Temperature issues, wet (low ratio) snow and a mostly N+W of DC event. And of course there’s Philly getting in on the good stuff again like they have been basically all season.

The most uncertainty with this forecast lies in the southern edge of the accumulation zones where surface temperatures at or slightly above freezing will battle against the snow rates at least at the onset of precipitation. Most of the snow is expected to fall during 12z-18z, so it will have that pesky Sun to deal with as well. Despite what’s working against the storm, the snow rates look pretty good between 12z-18z, with the areas in and around D.C. currently expected to get about 0.5″ of QPF just within that six hour window. The northern edge of the higher totals is also a concern given the amount of disagreement and shifting the models are still doing at this juncture.


There’s still plenty of time for all this to shift north or south, and the gradient between snow totals may be tighter than what I have now across the southern areas. I’ll do some fine-tuning around this time tomorrow, but the overall theme of a nice 2-8″ swath across a good chunk of the region seems likely to hold.