Browse Tag

2016

SPC issues a moderate risk for tornadoes

http://www.spc.noaa.gov/products/outlook/archive/2016/day1otlk_20161129_2000.html

Summary:

After yesterday’s mostly-failed setup in which tornadoes were more scarce than expected in the Deep South, much higher instability today will likely result in stronger discrete storms that can mature enough to become tornadic. The SPC is targeting the 00z-04z time frame as the most dangerous as the low-level jet picks up, meaning nighttime tornadoes will be a big concern.

Opinion:

The Deep South is no stranger to these after-dark tornado setups, and I agree with the SPC’s forecast. With moisture and energy available right next door in the Gulf of Mexico, all you need is a proper storm system to move through to create a tornado threat. The winds associated with this system are fairly strong, and now the CAPE/shear combo is balanced enough where supercells can more reliably become organized enough to produce tornadoes. There are already multiple classic-looking supercells in Louisiana that are tornado-warned, and it looks like the southern Mississippi Valley will be in for a long night.

Winter Storm Threat: February 8-10 (Only/Final Call)

This storm has a complicated setup. You have multiple surface lows within a broader upper-level trough, marginal surface temperatures, and large discrepancies in QPF placement between the models.

Temperatures along and east of I-95 are the most uncertain, which are expected to be in the low-to-mid 30s through most of the event. Areas north and west of I-95 will start above freezing, and will cool to at or below freezing depending on how strong the snowfall rates are tonight.

Snowfall rates will be one of the most important factors in determining which areas see 4-8 inches, and which areas get 1-4 inches. The best rates are likely to be along the Maryland/Pennsylvania border into southern New Jersey.

20160208-09_MAsnow_final

The intensity of the initial coastal low, the secondary coastal low development, the strength of the low over the Great Lakes, and the timing of the strengthening and weakening of these lows are wreaking havoc on the QPF output on the various models.

I tried my best to offer a realistic compromise between the differences in QPF, while also accounting for the surface temperature and snowfall rate issues. I could definitely see a tighter gradient between accumulation amounts than what I have on the map.

Winter Storm Threat: January 22-24 (Final Call)

One final update before the frozen stuff starts to fall in the southwestern corner of my map. Made minor adjustments to the fringes in central/eastern North Carolina and up around NYC, with a slight expansion of the 18″+ contours.

20150122-24_MAsnow_final

Timing and impacts from this potential blizzard remain on track to what I said earlier today.

Winter Storm Threat: January 22-24 (Second Call)

The heavy snow in the core of the Mid-Atlantic remains on track, given the newest model data and latest trends. Two notable changes were made to the northern and southern fringes of the snow accumulation. General timing remains the same, with snow expected to start in the D.C. area between 3-6 p.m. Friday.

20150122-24_MAsnow_second

The northeastern edge of the snow accumulation was cut back as confidence increases in the storm track, leaving lower snow amounts across northeastern Pennsylvania into northern New Jersey. On the southern edge, western North Carolina into western Virginia and West Virginia saw snow increases due to better confidence in the QPF forecast and better temperature profiles. Further east, more warm air wrapping into the eastern side of the system made for lower snow forecasts across northeastern North Carolina, southeastern Virginia, and along the immediate Atlantic Coast.

Ice will also be an issue in the Southeast and in southwestern Virginia. Currently, areas in northern South Carolina and central North Carolina are forecast to receive 0.25-0.75″ of ice, according to the NWS.

20160121_RAH_Ice11am

At the moment, the NWS also has Blizzard Watches posted from the greater D.C. region up through Philadelphia and into NYC and Long Island.

20160121_BlizzardWatchesNoon

I will be posting a final forecast update this evening.

Winter Storm Threat: January 22-24 (Initial Call)

For those linked here from other sites, you can see my updated forecast here: Winter Storm Final Call

What can I say? This is a classic setup for feet of snow and possible/probable blizzard conditions across parts of the Mid-Atlantic. If you liked February 2010, then you’re gonna like this.

20150122-24_MAsnow_initial

The epicness that is this storm system will start on Friday and end Saturday night/Sunday morning. For the greater DC area, I’m expecting snow to start accumulating in the late afternoon or early evening on Friday. Once it starts, it won’t stop for quite some time, lasting through Saturday in most spots.

Temperatures won’t be frigid, so I-95 and areas south should see more of a dense, wet snow, while areas further north and west get into the drier, fluffier snow. Mixing issues with sleet and rain don’t really become a problem until you get south and east of I-95. The I-95 cities are expected to be at or below freezing at the surface throughout the storm.

On top of all this, strong winds will generate blizzard or close to blizzard conditions mainly in the DC/MD/Delmarva region. Persistent onshore flow will result in fairly high storm surge and beach erosion.

Get home early on Friday, because you won’t want to be out once it starts. Don’t plan on doing anything that involves going outside Friday night or Saturday… unless it’s sledding or a snowball fight.