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 thunderstorms...an 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. 

SUMMARY NOTES:

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. ***

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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. 

Friday, December 8, 2017

Winter Weather Advisory - First Snow of Season

Well folks...I'll eat my words from yesterday.

Yesterday morning I had posted that the chances of snow looked pretty slim and prospects were pretty muddy going forward.

Well...yesterday, the models trended west with the system that is expected to slide off the east coast. For this reason, a more "significant" snowfall is seemingly likely. While this won't be an outright snowstorm, a light to moderate event is likely. One thing to note is that the cutoff will be quite sharp. In other words, you will not have to go far to go from 4 inches of snow to nothing. We'll get into the specifics below.

As mentioned above, a coastal storm system will track off of the east coast later tonight and tomorrow. With the storm track now expected to be a little to the west of prior forecasts, snow will become likely very late tonight and throughout the day tomorrow. The upper level portions of this storm system have improved a lot over the past 24 hours. Snow will become likely by the wee hours of Saturday morning. The National Weather Service has issued a Winter Weather Advisory, which is in effect from tonight until 4:00pm Saturday afternoon.

The purple areas are under a Winter Weather Advisory for this potential storm. This *may* be extended farther to the west with more model data arriving later this morning/this afternoon.
Heavy snow is NOT expected. However, light to at times moderate snow will be likely. The best chance at a little more snow will be to the south and east of the metro areas (this much has not changed). What HAS changed is the expected western extent. Light snowfall may make it as far west as the Blue Ridge. There may also be some upslope farther west over the mountainous areas of the area.


The 06z GFS model forecast for the storm. You can see the snow backs pretty far to the west on this model.
Road accumulations should be minor due to temperatures hovering around or just above freezing - but slick conditions are still possible...especially given the low sun angle at this time of year.

Total snow accumulations south and east of the area will be 2-4 inches in spots. In the immediate I-95 corridor, 1 inch to as much as 3 inches may be possible. Farther west, the accumulations will taper down to an inch or less or a coating in the farthest west areas.

The 06z run of the 3km NAM model shows a bit more of an eastern snow profile. However, snow still gets into most areas...except for the far western zones.
The RGEM (Canadian regional model) is showing a very robust solution. I'm not sure this will happen. 
What's the potential of this being a busted forecast?

I would say that we are probably pretty close to the "maximum potential" for this snow event. It's a fairly quick hitting event, which prevents it from being a more significant event. There IS, however, the potential for the storm to cut east again, which would reduce totals significantly. SNow is notoriously hard to get in this area.

Will post updates as we draw closer. Stay tuned!

Thursday, December 7, 2017

Models Backing West a Bit w/Snow Potential

The model runs today have given a bit of a welcome surprise for snow lovers! They have come west a bit with the edge of the precipitation for the Friday night and Saturday morning snowfall. The cutoff will be sharp from east to west - but the potential now exists for an inch or two of snow around and to the east of the metro areas. Accumulation on roads would likely be very limited. 

A full update will be posted (with images tomorrow morning).