Monday, January 25, 2021

Taste of Winter On Tap

 Snow lovers will be disappointed by how the next two potential winter weather events have trended in the models. What appeared to be a week where winter might have roared back with a vengeance, has trended to a much more tame situation. We'll go in-depth below. 

Late in the work week last week, it appeared that a minor to moderate winter weather event would impact the area tonight into tomorrow. Additionally, it seemed that there was significant potential for a larger storm later in the week. However, due to some complex factors in the mid and upper levels of the atmosphere, both events have trended downwards. 

With regards to the winter weather event tonight and tomorrow - temperatures are quite marginal. While favored areas to the north and west (think the I-81 corridor) may see some icing and snowfall, the overall theme of this storm system is minor. There may be a a slushy inch or two even close to the metro area, along with a little dose of icing as well. However, I would think that by tomorrow afternoon, most areas will have safe travel close to the cities. This will be more of a nuisance storm than anything. 

High resolution NAM model showing potential snowfall primarily along and north of the Potomac River. This may even be a bit on the generous side. A slushy inch or two is certainly possible, however. (Source: College of Dupage)

You can see above that the high resolution NAM model shows a little snow accumulation focused north of the Potomac River. Even so, that accumulation should be relatively minor and slushy. 

Freezing rain forecast from the high resolution NAM model. A little icing is possible, especially to the west in the favored colder areas. (Source: College of Dupage)

Icing may be a story as well. Of course, even the tiniest amount of freezing rain accumulation can cause mayhem on the roads. The good news is that temperatures aren't frigid for this storm. Icing is still a concern, but as soon as temperatures rise above the freezing mark, things should improve. Perhaps the I-81 corridor will see a more prolonged period of icing conditions. Regardless, use caution on the roads during the precipitation, and be careful particularly on the bridges and overpasses. 

The attention will then turn to later this week. What appeared to be our first chance of a big snowstorm has petered out. Instead, a storm system looks likely to pass to the south. We may see some flurries around, but at the moment, the chances for substantial snow are going way down. Snow lovers will be stuck waiting again. 

The 06z GFS model run from Monday morning. You can see a low pressure area and its associated precipitation well off the coast. This storm system was forecast to be much closer to the coast a few days ago. (Source: TropicalTidbits)

There are indications that the overall Northern Hemispheric pattern may remain semi favorable for potential snow events going forward, but the problem so far has been a lack of cold air across the entire continent. We'll see where February takes us! 

Saturday, January 23, 2021

Winter May Make a Comeback

With the exception of a few flurries and the snow/mix event back in December, winter (other than some seasonably cold days and nights) has been largely absent this year. There have been multiple factors (and some bad luck) that have contributed to this. 

Technical Discussion

During the fall, the configuration of the upper level weather patterns over the Pacific Ocean caused warm air to essentially flood portions of North America. Our cold air "source" regions in Canada became essentially non-supportive to winter weather events. Even with storm systems tracking favorably for our region, there was simply no cold air to tap or drain into the area.

If you're a regular reader of weather blogs or discussions, you'll likely know that our best snowstorms tend to occur when certain atmospheric teleconnections are in the right configuration. Primarily, we look at the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), and the Pacific North American oscillation (PNA). In an ideal world for snow, we'd have a negative NAO, negative AO and a positive PNA. It's also important to remember that we are in a La Nina pattern this winter, which is generally not as favorable for snow as a weak to moderate El Nino. 

Interestingly enough, we've had those oscillations in our favored spots for large sections of the winter. The problem is, the cold air source regions are just not that cold. This is improving, and this is part of the reason why we now have some winter weather threats to track.

End of Technical Discussion

The first threat for winter weather will be from a storm system that will impact the area from Monday into Tuesday. As usual, the models will shift around until we are closer to the event start time. This particular system was "slipping away" as it appeared that it could be a very light event or a rain event (or both!). However, there has been some tendency in the past few model run cycles to bring the event back to a point where we could see some wintry precipitation. 

The last 12 runs of the GFS model for the Mon/Tue winter weather potential. (Source: TropicalTidbits)

You can see in the above animation that the winter precipitation threat has bounced around a fair amount. Areas that are typically favored (north and west of the metro area and into the I-81 corridor) could see the best shot at winter weather. The unfortunate thing is that those areas may also see a significant icing event caused by freezing rain. Freezing rain is a tricky precipitation type (ptype) to forecast, so this won't be clear until closer to the event. 

The Saturday, January 23 06z GFS model run showing potential freezing rain accumulation. (Source: College of Dupage)

The image above shows the 06z GFS run (the early Saturday morning model cycle) freezing rain accumulation. It shows very damaging amounts of icing for parts of the higher elevations to the west. Even some icing shows up closer in to the DC/Baltimore areas. 

The Saturday, January 23 06z GFS snowfall forecast. (Source: College of Dupage)

Meanwhile, you can see snow accumulations look A LOT less impressive based on this run of the GFS. Of course, this is all still a fluid forecast and a lot can still change. For now, if you are WELL to the west of the metro area, it wouldn't hurt to prepare for some icing. Any forecast for destructive levels of icing should hold off for now until certainty is higher with the storm system. 

Perhaps the more interesting aspect of the forecast is later in the week. Some model solutions suggest a another storm system will pass by to the west before transferring to the coast. This would be on or around Thursday. While the latest runs of the GFS model are showing a significant snowstorm for the region, other models are not yet biting on the event. Thus, we'll leave it as a note here - let's get through the Mon/Tue storm before we look too far into the next one. 

Stay tuned! 



Sunday, April 12, 2020

Hazardous Weather Expected Monday

Buckle up. Odds are increasing that a rather high impact weather system will cause several types of weather-related hazards across the region from tonight through tomorrow.

The trouble-making weather system is an area of low pressure that is currently developing and intensifying over the Plains. This system will track towards the Great Lakes region through tomorrow. The storm will be intensifying to a level that will cause significant impacts across large swaths of the nation (Ex: potential severe weather/tornado outbreak in the Dixie region today/tonight.

Sunday morning surface weather map from WPC.

Impacts for the DC/Baltimore region will begin later tonight. There is the potential for moderate to heavy rainfall as the system's effects approach the area. Some rainfall totals in the area will be in the 1-2 inch range. The local National Weather Service (NWS) office indicates that isolated instances of flooding may occur, but the probability or spotty nature of this is not enough to warrant a flood watch at the moment. This could change, so stay tuned. All eyes then turn to the potential for severe weather on Monday. 

Some uncertainty still exists about the amount of instability as well as the exact timing of the front/system. These factors will greatly impact the level of severe weather threat across the region. If the system is faster than anticipated, there will not be enough time for instability to develop ahead, and the severe storm threat may be muted or reduced. Currently, models are in decent agreement that there will be a window of time when instability can develop before the line of storms comes in. This would result in a decent threat for severe weather. If (this scenario is not particularly likely) the system slows a bit more than expected, a substantial threat for all modes of severe weather could transpire across the area. As it stands, areas in Virginia and into the Carolinas are already looking at this threat. Whether the best threat extends further north into our region remains to be seen. 

One measure of instability on the NAM 3km model for Mon afternoon. Notice the pockets of instability in the area. If this verifies, a higher risk level from the Storm Prediction Center could be issued.

Regardless of severe extreme wind field will be situated a few thousand feet off of the surface. Showers and heavy rainfall could mix these winds down to the surface even without strong storms. Winds at the 925mb level (a couple thousand feet up) and the 850mb level (about a mile up) are forecast to be anomalously strong. In fact, 925mb winds are 50-60 knots across the area for a time on Monday morning and early afternoon. 850mb winds approach 70-75 knots during the same time period. These winds could cause damage - and thus, the expectation is that the NWS will be posting wind advisories and/or high wind warnings to cover this threat. 

850mb winds from the NAM model for Monday morning. Credit: TropicalTidbits

One factor that could enhance any damage caused by the wind is the heavy rainfall threat overnight tonight. Saturated ground could make it much easier for trees to be toppled. Have a severe weather plan in place. 


Heavy rainfall threat tonight and into early AM tomorrow. 

Wind damage threat during the morning and along with the front. 

Conditional severe storm threat (dependent on instability levels)

Best odds for severe weather currently reside down into VA/Carolinas.

High impact event. Keep an eye on the sky. 

I will be providing updates throughout the day today if anything changes. 

Wednesday, May 22, 2019

Tough Forecast for Thursday - Storms Possible

Another pleasant day is on tap for today. Low humidity and temperatures a bit higher than yesterday will make for a nice day. Wind will be a lot less of an issue today with only light winds across the area. Enjoy today...tomorrow will mark a return of warmer and significantly more humid conditions.

By tomorrow morning, dewpoints will be on the rise as they head up to the upper 60s and potentially even the lower 70s. This type of humidity is quite uncomfortable. Highs tomorrow will be well into the 80s. The humidity will make it feel like it is even warmer as well.

During the afternoon and evening, there is a chance of thunderstorms across the area. However, the various computer models disagree significantly on the coverage of thunderstorms. The best threat for storms (potentially severe) will be well north of the area into Pennsylvania and New York state. However, storms will also be possible across the DC/Baltimore area. IF storms do form and move across the area, the ingredients are in place for a potentially significant severe weather event. Again, best odds being to the north.

There is an "Enhanced" risk for severe storms outlined by the NWS Storm Prediction Center for extreme Northern Maryland and Pennsylvania. A lower risk is in place for the rest of the area. Large hail and damaging winds would be the primary threats.

Tuesday, May 21, 2019

Strong Storms Possible Thursday

Beautiful weather is dominating the area today as Canadian high pressure is in control of our weather. Breezy conditions will persist throughout the day but winds will start to calm down towards sunset and into the evening. Low temperatures tonight will be in the 50s in the cooler suburbs to the low 60s in the urban centers.

The next chance at rainfall will be late Wednesday night and then on Thursday. Odds are not super high at this point...but there is a chance for severe weather. We are already outlooked in a day 3 risk for severe storms from the NWS Storm Prediction Center.

Moderate to strong instability will develop across the area on Thursday afternoon with warm air and dewpoints rising into the 60s. There will also be sufficient wind shear to sustain updrafts. However, forcing may be a bit limited and thus storm coverage is a big question mark. In fact, there are some models that leave our area mostly dry.

It is also worth noting, however, that sounding analogs indicate that there is an elevated risk for significant hail growth if storms are able to develop and grow upscale. It is too far out to say anything with any certainty.

The NAM model showing pockets of moderate to strong instability in the area for Thursday afternoon. 
Something to keep an eye on regardless of the end result. Memorial Day forecasts will come into focus in the next day or two as well.

Friday, December 15, 2017

12/15 Snow Event (LIVE Updates)

***Live updates will be posted here regarding the light snow event expected this afternoon - the latest updates will be at the top, while the older updates will fall to the bottom of this post. ***

3:34pm - 

Area roadways are slick in spots. However, the back edge of the snow is now moving through Northern Virginia and parts of Maryland. The snow should end from west to east over the next few hours. Use caution on the roads as black ice may have formed due to melting/refreezing of moisture. 

12:05pm - 

The radar is beginning to really blossom around the area. A large portion of the area is reporting either light flurries or very light snow at this time. A Winter Weather Advisory is in effect until 7:00pm tonight. Due to cold conditions, slick spots will be possible on roadways during the afternoon and evening rush. 

Additionally, several area school systems are closing early. However, Montgomery Co Schools are closing according to REGULAR schedules. 

Radar shows snow developing across the area. The area of blue radar returns has the steadiest snow at the current time. Expect increasing coverage of the snow throughout the early afternoon. 

Light Snow Expected This Afternoon

Light snow is expected to develop across the metro areas this afternoon. Flurries and very light snow are already being reported in northern parts of the area to as far south as Gaithersburg. 

While accumulations should be limited to mainly north and east of the Potomac River, an inch to two inches are certainly possible. Due to it being Friday, and the snowfall occurring during the afternoon, impacts to the evening commute are certainly possible. 

The highest accumulations will likely reside from Baltimore and to the north and east. But an inch or so of snow is possible as far south and west as the Potomac River. A coating may be possible in Northern Virginia. 

Be prepared for hazardous roadway conditions and give snow treatment vehicles plenty of room! Any additional updates will be posted as needed this afternoon and evening.

For this reason, a Winter Weather Advisory is in effect until 7:00pm this evening!

Howard County Schools have announced they are closing 90 minutes early. 

The radar around 10:45am. You can see snow beginning to develop to the north and west of the city centers.