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.