WINTER EVENT #1
~11/15/2018~

RECAP

DMV WEATHER 4CAST
NWS MEASURED TOTALS

Annapolis BWI Dulles D.C.
4CAST 0.1" 0.2" 0.4" 0.1"
TOTALS 0.5" 1.7" 3.0" 1.4"

 

OFFICIAL 4cast
WINTER EVENT #1

(Wed, 11/14 @ 7:45p EST)

What better way to start off Winter 2018-2019 with (a) a wintry storm 17 days ahead of meteorological winter (12/1) and 6-7 weeks ahead of calendar winter (winter solstice on 12/21 and (b) a Nor'easter with marginal temps that involves just about everything falling from the sky except frogs, war propaganda pamphlets, and straight cash (where's D.B. Cooper when you need him???). But this is the DMV region, which includes a large area of low-lying coastal plains on the MD Eastern Shore, some in-between metropolitan areas of Annapolis/Baltimore/D.C. and every jammed-in city and suburb in between, and many other places like Frederick MD and Leesburg VA off to the N & W of the big cities and the I-95 corridor that have the benefit of elevation to provide them with the MOST IMPORTANT/NECESSARY ingredient for snowfall more often than most - cold air! And that means winter weather 4casts are almost always riddled with uncertainty and many precip types...this one being no different.

SO WHAT'S THE DEAL WITH THIS ONE?

Cold air will be in place, but it'll be marginal for many. Overnight temps in D.C. and Annapolis and points south and east likely will never drop to/below 32 degrees...and that's no bueno for snow (sort of...more on that in a few).

For others, temps will bottom out overnight tonight at maybe 30-32/33...so places like Bel Air MD, Towson MD, Dulles VA, Frederick MD and certainly more mountainous/higher elevation locations like Hagerstown MD and Winchester VA and beyond will have the key ingredient of cold(er) air to get some snow.

But this storm lacks on extra-nice component, which is a truly cold high pressure area to the N of the region to help drive/reinforce cold air into place so that when the storm comes from the south...the precip is almost definitely (and all) frozen. Instead, there's a high pressure center...but it's a bit out of perfect position and instead of delivering NNE winds...it'll likely deliver more ENE winds, if not E winds, and that's as much of a hindrance as a help as it'll either be a wash if not a slightly warming effect with air coming in somewhat off of the relatively warmer Atlantic Ocean (and at this point in the year, over a Chesapeake Bay with water temps still in the 50's, whereas it's not as big a deal in true winter when air temps are cold and bay temps are much lower).

SWEET DETAILS, BUT...WILL IT SNOW OR NOT?

The reality is this: many in the DMV region will likely see snow fall from the sky tomorrow morning, but the expectation will be that not much will stick to grassy surfaces/sidewalks and almost none will stick to roadways for areas along and S-E of Interstate 95...simply because the ground temps are too warm.

For those areas with colder air temps and colder surface temps (N & W of DC/Baltimore at higher elevations), there could be some sticking to grass and sidewalks and even roadways...and there could even be some freezing rain in the mix as cold air gets trapped at the surface in a shallow layer while warmer air comes in higher up in the sky, so for these places there could be some delays to schools in the morning and there could be some slick surfaces, as well. This would be for areas such as Montgomery County MD, Frederick County MD, Carroll County MD, Baltimore County MD, Washington County MD and Loudon and Faquier Counties in VA.

WAIT...HOW DOES IT SNOW IF TEMPS ARE ABOVE 32 DEGREES?

In simplest terms, if snow is falling in temps above 32 degrees and starts melting...it produces an effect called "evaporative cooling" where the evaporation of the melted snow cools the temps around it by absorbing heat (convenient, right!)...and therefore, the flakes are spared and allowed to fall all the way to the ground as...snow(flakes)! This effect doesn't typically last too long, but does at least give everyone a shot at seeing snow...even if short-lived. We think this effect will be in effect for many tomorrow where temps are 33-36+ in the AM when precip moves in...snow first, then a change to rain. Time will tell, as this is a very localized effect...so let's see what goes down across the region as things start to fall down from the sky.

OUR OFFICIAL SNOWFALL ACCUMULATION TOTALS 4CAST

  • Annapolis = 0.1"
  • Baltimore = 0.2"
  • Dulles, VA = 0.4"
  • Washington, D.C. = 0.1"
  • Frederick, MD = 1.1"
  • Winchester, VA = 3.3"
  • Waldorf, MD = 0.0"
  • Bel Air, MD = 0.3"
  • Bowie, MD = 0.1"
  • Gaithersburg, MD = 0.7"
  • Columbia, MD = 0.3"
  • Fredericksburg, VA = 0.0"
  • North East, MD = 0.3"
  • Easton, MD = 0.0"

Bottom line: this is a borderline temperature storm that could cause problems, though no real identifiable factors point to AM issues other than N & W of DC/Baltimore...so be prepared, stay informed, and be safe whether it's snow, sleet or plain old rain (and let's not forget: the rain could be heavy at times, with totals of 1-3" of rain possible in spots along with gusty winds of 20-30+ mph at times).

Enjoy this first (of what we expect to be 10 or more) winter weather events of the new cold weather season, but as always...have fun and be safe.

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