Tuesday, January 29, 2019

How about "Wish I Knew  Wednesday?"

UPDATE AS OF 4:20 AM WED 1/30/19

WEDNESDAY: Surprise Squall Line 10 AM - 2 PM
  • Did you know an Arctic front is coming? If not, you will feel it soon.  Short range computer models are depicting a literal white-out wall knifing through the entire region from 10 AM to 3 PM. Winds will spike to 25-35 mph with higher gusts of 45-50 mph in the mid afternoon, just as a near-instant burst of snow arrives with it. 
  • Wind Advisory in effect from 9 AM to 6 PM today for much of the region, and statements from NWS to expect "heavy snow at times" with reduced visibility and strong gusty winds creating power outages. This is especially concerned with single digit temperatures coming tonight and sub-zero wind chills much of Thursday.
  • On a 2-hour delay? You might be stuck facing an approaching squall line of snow, cold surfaces where salt is not working due to low temperatures, and wind-blown snow reducing visibility right at the time everyone is either heading into school or work, or heading home. This is what we call a multi-hazard high impact event. 

  • From the Sterling VA National Weather Service: "Strong winds may blow down trees and power lines which would result in power outages. Loss of power could be life threatening due to the very cold temperatures. Snow showers or snow squalls could enhance gusty winds and briefly lower visibility, resulting in very hazardous driving conditions, especially near and north of Highway 50."
So now you know, and it won't be a surprise for those like you whom have seen the latest "High Resolution Rapid Refresh" model, (HRRR) shown below. They KNOW how serious a winter squall line CAN be, and recognize it's not something to be dismissed. 

Squall line depicted on short range map for 12 PM Wed 1/30

Now, let's ask ourselves, how could the computer models  bother with depicting a seemingly tiny little stripe of snow around 12 Noon Wednesday? Wouldn't all the dry air squeeze it out to nothing? Since many of you were no doubt wondering that same thing this very evening, here's our answer.

Not if the moisture is traveling WITH the Arctic front, and is tapping high liquid to snow ratios of 20:1 or greater. In that case, just 0.01" of water can produce up to 1/2" of snow. Imagine if it all fell in just 1 hour. For fun, let's say...2 PM. Right before buses start to roll. Wish you knew about this on Tuesday? 

In our 15 years of forecasting here at Foots, we have learned there is ONE THING school districts and other organizations seek to avoid if at all possible when making an opening/closing decision:
  • To announce a 2 hour delay, only to realize after it's much too late, that conditions have conspired against you in the computer models, forcing your hand into an early dismissal, or a closing. 
It is a tricky call all the way around, but we are glad to help work the storms with you, and glad you have found the information useful over the years.

- Forecaster Foot & the Advisory Team
Let's Call It "Tricky Tuesday."
Update as of 5:30 AM ET TUE 1/29

  • AM TO AFTERNOON: The latitude of Interstate 70 in central Maryland expected to be dividing line between areas of mainly snow (Frederick, Carroll, Baltimore, Harford), with areas south of I-70 seeing a rain/snow mix until after 2 PM.
  • BETWEEN 12-2 PM: North of I-70, all precip changes to snow and becomes heavy, with up to 1/2" per hour at times after 2 PM to 4 PM. South of I-70, rain/snow mix will battle a few more hours, then convert to all snow starting 4 PM. If you are not home by 4 PM, consider staying where you are until after 7 PM. Remember the Jan 26, 2011 "Carmageddon" on the JFX? Need we say more.
  • PM COMMUTE: From 4-6 PM, once sun angle is lost, snow should become heavy in all areas from I-66 to central PA. Prepare for extended delays, hazardous travel anywhere north of I-66 in DC, snow-covered roads, plow trucks trying to treat roads, frazzled nerves and occasional hair loss. 
  • WHAT'S NEXT? It gets cold, really really cold. And windy through Thursday. A squall line of snow showers may push through the region Wednesday morning, creating a new round of potential delays and icy conditions, with temperatures around 15 F. See below for previous updates and details on timing.

"When can I see you again?"

Update as of 5:30 AM ET TUE 1/29
  • A three-day period of significant and potentially disruptive winter weather will produce widespread impacts on the Mid-Atlantic region from Tuesday 1/29 through Thursday 1/31. A combination of rain to snow, falling temperatures, Arctic conditions and sub zero wind chills may create hazardous travel conditions at times from Tue AM through Thu PM. Today would be a good day to get done as much as you can in advance of this winter resurgence.
  • TUE 1/29: Fast-moving cold front with ample moisture will cross the region, quickly changing rain to snow in all areas west of I-95 corridor by mid afternoon. Short range models show a period of high snowfall intensity up to 1.0" per hour is possible from northern Virginia through the DC metro and into central Maryland. Map below is generalized conditions expected from 4 PM on, with 00Z Wed = to 8 PM local time. 

  • WED 1/30: Region-wide temperatures holding in teens to low 20s, with winds gusting to 30 mph at times. Any residual water or snowmelt will quickly refreeze, possibly creating icy travel conditions for Wed AM commute.

  • THU 1/31: Arctic front sweeps across the region, with AM temps near 5 F in areas south of I-70, -5 F to 5 F north of I-70 into southern PA, and near 10 F on Eastern shore.  AM Wind Chills -10 F to 0 F for much of central MD, southern PA and 0 F to 5 F above for DC metro / northern Virginia. 

NWS Hourly for Sykesville, MD in Carroll County along I-70 as representative of the expected cold intrusion and wind chills

For readers in area school systems, now you have the explanation behind today's headline, so buckle up and get your schedule ready for a re-do. - Forecaster Foot & the FF Team

Tuesday, January 22, 2019

When is the next one?
  • An "intermission" of southern jet stream-enhanced mild air will overtake eastern third of the U.S. from midweek into Friday, with temperatures trending into the 40s. After this raucous cold, we're not sure if our hearts want to "come back from Havana" anyway until the thermometer at least crosses 32.
  • Brief periods of snow possible Thursday afternoon in the Mid-Atlantic at back edge of departing cold front. Little or no impact expected due to warm air & rainfall prior. Refreezing unlikely as snow should be light, intermittent and roadways mild.
  • By Friday afternoon, a new Arctic High pressure system will be reintroducing a fresh supply of much colder air into eastern U.S. This is a strong indicator for the next storm: Accumulating snow has a better chance when cold air is in place before a system develops. 
ABOVE: Probability that your area exceeds the liquid equivalent of 0.25" in snow or sleet, projected for the Sunday 1/27 into Monday 1/28 time period. A similar map is shown for Day 7, Monday into Tuesday.

BELOW:  Long range projection of general surface low position by early Monday morning 1/28 indicates the potential for a favorable setup of a classic "Nor'easter" type system. 

When you see the whiplash weather coming for February, you may look back on January with fondness for the days when temperatures would go above 32 F for more than one day. 

And, if you're a Powderhound, there is so much fun lurking in the long range, we are sure it will be a delight to behold once we can map out all the possibilities coming up. 

- Forecasters Foot and Wise