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Unsettled weather expected this week with numerous showers and thunderstorms possible at times7/21/2024 An unsettled and rather wet weather pattern will take hold this week as a stationary/warm front lingers in the area through about Wednesday. This brings daily chances for showers, downpours, and thunderstorms. By Friday, a cold front will have passed through leaving less humid conditions along with meager rain chances and increasingly sunny skies.
MON: Warm and humid with highs in the low 80s for most areas. Dew points will be in the lower 70s so you definitely will feel the humidity outside. While not constant and not a washout, we do anticipate scattered to numerous showers and thunderstorms throughout the day. The greatest chance of rainfall should occur between noon and 9pm, but heavier downpours cant be ruled out earlier. It will not rain heavily everywhere, but some areas will see 1-3" of rain which could cause some flash flooding. There is a low, but not 0 risk of severe weather, including gusty winds and a brief tornado or 2 especially south of the DC metro area. TUE: Tuesday will feature less rain during the day, so temperatures will be higher as a result of more sun with highs in the upper 80s to low 90s and likely very humid. A few showers or storms cant be ruled out during the day, but the highest chance of rain will come in the evening and overnight hours when an additional inch or so of rain could fall in some areas. The overall risk for severe weather on Tuesday is low, but not 0 given warmer temperatures and the warm front still nearby. Storms will once again be capable of producing heavy rainfall rates, but may be less widespread than Monday. WED: Wednesday will be similar to Monday with periods of showers, downpours, and storms during the afternoon and evening. High temps will range from the mid 80s to low 90s with dew points in the low-mid 70s leading to very humid conditions. Locally heavy rainfall will be possible, especially east of I-95 where an additional half inch to inch of rain is possible. The risk of severe weather appears to be quite low at this time. THUR: On Thursday, a cold front will begin making its way though, bringing yet another round of at least scattered showers and storms. High temperatures will range from 85-90 degrees with periods of sun and clouds amongst the afternoon and evening showers and storms. Some storms could produce locally heavy rain, gusty winds, and lightning. The coverage of storms should be less than prior days. FRI: The cold front should move through fairly early on Friday, leaving us with only isolated chances for showers. High temps will once again be in the upper 80s to around 90 but with gradually lowering humidity and mainly sunny skies thanks to a change to NW winds. Overall, it likely will end up a pretty nice day considering what the rest of the week will be like. SAT: This is definitely the pick of the week with little to no chance of rain, sunny skies, and low humidity. It will be warm, with highs in the mid 80s to low 90s, but still not a bad day at all for outdoor activities. We need to soak in the lack of humidity and cooler temps Thursday and especially Friday because we're in for some seriously hot temps again next week.
For Thursday, expect partly sunny skies with highs in the upper 80s to low 90s. So still hot but not oppressive and the humidity will be lower as well. I don't expect any rain on Thursday. For Friday, it will be much cooler with highs only in the 80s. Widespread showers and thunderstorms are expected east of I-95, but its a bit uncertain how far west this rain goes. Areas between I-81 and I-95 have a 30-50% chance of rain but will probably only see a trace to 1/2". Areas east of I-95 have 60-80% chance of rain and could see 1-2" in isolated areas. Rain may be moderate to heavy at times with the bulk of it occurring south of Baltimore. We ramp up the heat immediately starting on Saturday with low-mid 90s likely under sunny skies (stray morning shower possible). Humidity remains manageable but definitely increasing. For Sunday, we shoot back into the mid and upper 90s to near 100 in some spots with heat index values over 100 likely. That said, I think we will fall just short of heat advisory criteria. Still, it will be dangerously hot. Temperatures continue to climb on Monday with highs nearing 100 in many areas (mainly 97-99) and heat index values around 105 which puts us right at advisory criteria. On Tuesday, I expect the heat to be near its peak with highs near or above 100 degrees along the urban corridor, and upper 90s area wide. Heat index values could exceed 105 degrees depending on how high the dew points get. Sun-Tues all feature a 10-20% chance of a pop up afternoon thunderstorm. With the lack of widespread rain, the drought WILL GET WORSE so please begin thinking about ways you can conserve water. Looking ahead towards mid-late week, the heat will likely peak on Wednesday with both the GFS and EURO showing temps at or above 100. This might be overdone, but not out of the questions. Following this, a cold front will move through on Thursday. Now its possible that a few strong storms could develop on Wednesday, but there is a better chance on Thursday since we actually have a trigger. And we always have to watch for severe weather when we end a heat wave around here. There remains some timing differences with the passage of the cold font so expect changes to the thunderstorm aspect of this forecast. Senior Forecaster Jack DANGEROUSLY HOT conditions are expected Monday-Wednesday with temps in the mid to upper 90s (near 100 in some areas), and heat index values of 100-110. There is a HEAT ADVISORY in effect for Monday, but this will be extended into both Tuesday and Wednesday. Depending on how hot we get on Wednesday, an EXCESSIVE HEAT WARNING may be required.
On Tuesday, there is a 20-30% chance of an afternoon downpour, but many areas wont see a drop. By Wednesday, a drastic increase in atmospheric moisture thanks to what will be left of Beryl will result in more scattered thunderstorms especially in the evening. This risk increases further on Thursday and especially Friday (50-60%) where numerous thunderstorms will be possible. It remains uncertain just how widespread the storms will be, or where exactly they will occur, but any storm could produce significant amounts of rainfall in a short period of time (1-3" rainfall rates) and this could lead to isolated flash flooding. Right now, the severe weather risk looks fairly low but we will have to monitor that. It remains very humid all week, but the intense heat breaks a bit Thursday-Saturday with temps in the 80s to low 90s at most thanks to the rain chances and cloud cover. Senior Forecaster Jack WED: Mostly sunny skies with increasing temps peaking in the upper 80s to around 90. Luckily the humidity holds off for one more day. Winds will turn to the SE sustained at 5-10mph and gust up to 20mph at times. No precipitation is expected on Wednesday. Lows will drop into the upper 60s to low 70s. THUR: Hot and humid with temps into the low-mid 90s under partly to mostly sunny skies. A few scattered showers and thunderstorms are likely during the afternoon and evening, a few of which could be severe and impact outdoor plans. With the humidity, the heat index will range from 97-102 in most spots. Chance of rain is 60% and low temps will only fall into the mid 70s in most areas. FRI: Another hot and humid day with sunny skies and heat index values around or over 100 degrees. An isolated afternoon storm is possible, but most areas will be dry. Any storm will produce heavy rain and lightning but severe weather is not currently expected. Chance of rain is 40%. Lows will fall into the 70s to perhaps near 80 in the city areas. SAT: Hot, humid, and stormy, but again not a washout. Highs in the 90s again. Similar to Thu/Fri, scattered afternoon storms are possible and these could be severe (see more on this below). Heat index values at or above 100 degrees seem likely given the humidity. Chance of rain is 60%. Low temps will fall into the low-mid 70s for most. SUN: Overall a nicer day than Saturday with sunny skies and slightly lower humidity. We cant rule out an isolated PM storm but chances are much lower only at about 20%. High temps will range from the upper 80s to lower 90s.Winds will be light and variable as a cold front slides through. Low temps Sunday night fall into the low-mid 70s so not much impact from the cold front. MON: Another hot day and humid one at that as well with a slight chance for afternoon thunderstorms. Highs will range from 90-95 degrees with a heat index around 100. That said, plenty of sunshine is also expected. The chance of rain is 30%, and low temps will fall into the 60s and 70s. For Thursday, subtle forcing from a cold front to our west and a lee trough over the I-81 corridor should spark a few scattered showers and thunderstorms across the area tracking west to east between the hours of 2pm and 8pm. Temperatures should reach the 90s with dew points in the low-mid 70s will lead to plenty of instability. The overall forcing and wind shear isn't to impressive, with less than 30kts of bulk shear and lapse rates are also poor. But some of the storms could produce isolated wind damage due to gusts in the 40-60mph range. For this reason, SPC has the entire area in a level 1/5 risk for severe weather. Thunderstorms will likely produce copious rainfall rates. While this could certainly have impacts to fireworks and celebrations, many areas wont see any rain at all.
On Saturday, an actual cold front will be moving through, colliding with a hot and humid airmass. Wind shear and forcing will both be stronger on Saturday, and there will be ample instability. While there is still some uncertainty, it seems likely that Saturday will have the best chance of severe weather this week. The above image is the SPC severe weather outlook for Saturday. They continue to highlight north central and western Maryland in a level 2/5 slight risk of severe weather, with a level 1/5 marginal risk for the rest of our viewing area. Most of Saturday will be dry and we expect very little if any storms during the daylight hours. This is due to the lack of a triggering mechanism to get storms to develop. That said, if by chance a storm were to form, it would likely be severe and capable of producing damaging winds or a tornado. The models have come into agreement that a line of showers and thunderstorms will move into southern PA and far northern MD between 8pm and midnight Saturday night. Its going to be a very humid night, so there will be at least some instability to work with, along with plenty of wind shear. Assuming that the line of storms maintains its intensity, there could be a risk of isolated wind damage and isolated tornadoes across southern PA and northern MD. Overall, the risk is fairly low but its not 0. In the image below, I've outlined the areas at highest risk for isolated tornadoes using the RRFS model from WeatherBell Maps: As far as hazards go, the ingredients favor primarily a risk of isolated damaging winds (gusts 50-60mph) as well as the chance for a few isolated tornadoes. Any thunderstorm will also produce dangerous lightning and very heavy rainfall rates as well. Hail is not really a concern in this situation. Again these will be isolated and not everyone will see the listed hazards. On Sunday, the threat shifts east. The image above is the SPC severe weather outlook for Sunday. A slight risk (level 2/5) for severe weather has been issued for areas east of Frederick, and a marginal risk (level 1/5) has been issued for areas west of there. A cold front will be sliding through during the afternoon. The atmosphere will be very unstable with 2000-3000 j/kg of cape and 30-40kts of wind shear. This will create an environment very favorable for severe thunderstorms. The question we have is the timing of the cold front. If it speeds up, the the threat of thunderstorms will be confined to areas east of I-95 and especially the eastern shore. If it slows down a bit, then the risk would extend further west and include much of our area. Right now, the highest confidence for severe weather is along and east of I-95. The main hazards on Sunday will be from damaging winds (gusts of 60-70mph possible) and large hail possibly the size of half dollars. There will also be a low end tornado threat in any supercell that can become established. And of course heavy rain and lighting will also occur in any storm. Storms should be more numerous on Sunday, but still not everyone will see these above hazards.
THURSDAY: A cold front moves through pre dawn, possibly triggering a few more light showers. But by late morning we clear out into sunny skies with lowering humidity and highs only in the mid-upper 80s. Winds will be light from the NW with occasional gusts around 15mph. Lows will drop into the 60s. FRIDAY: Even nicer than Thursday with highs in the low-mid 80s under mostly sunny skies and continued low humidity. Winds will switch to the SE but remain light with peak gusts only around 15mph. No rain is anticipated for Friday so be sure to spend time outdoors. Lows will fall into the mid 60s to low 70s. SATURDAY: A warm front will be lifting north through our area during the day on Saturday bringing showers and thunderstorms. High temperatures will be in the upper 80s to low 90s with very high humidity. Showers and thunderstorms may turn severe during the afternoon and evening (more on this below). Low temps will drop into the upper 70s and low 80s. There is a 60% chance of rain on Saturday. evaluating saturdays severe weather risk:Some of the model data shows a concerning look in terms of severe weather potential on Saturday. A warm front will be lifting north during the day and may stall somewhere nearby. Wherever this occurs will play a very important role in the risk level we receive. If the warm front lifts north in time, then the atmosphere will destabilize and be favorable for severe weather. If it stays south of us or is too slow to lift north, we wont have time to destabilize and the conditions will not favor severe weather. It is too early to know which one of these will occur, but the more reliable Euro model shows it to our north with a rather potent severe weather and flash flooding environment. As far as hazards go, the presence of a warm front increases wind shear on a local level. The high dew points means it wont take a lot of instability to produce severe weather. So, assuming the warm front lifts north of us, there will be a risk of damaging winds, tornadoes, and extremely heavy rainfall that could lead to localized flooding. Again this all depends on the exact track of the warm front. Also if we get any sun during the day, the threat will increase. Remember that if the warm front is too far south, we wont destabilize and there will be little to no severe weather. That is a totally reasonable outcome. Given we are still 3 days out, there is obviously some uncertainty still and details will need to be ironed out over the coming days. Truthfully, there are some similarities in some of the model data to the tornado outbreak we had in early June. That said, there are some models that just have us rainy and no severe weather. I am NOT saying this will be like that, but I do encourage you to closely monitor the forecast as this has at least some potential to be impactful and we want to give you the earliest heads up possible. Some risk of severe weather may also materialize on Sunday, but confidence is low.
We will have another full update like this sometime on Friday. Senior Forecaster Jack The map below may look a bit overwhelming so let me break it down for everyone. On Wednesday, high temperatures across the mid Atlantic will reach the low-mid 90s, with even a few upper 90s possible. Dew points are also expected to rise into the upper 60s to around 70, leading to moderate to high amounts of humidity. When combined with the hot temperatures, ample instability will develop (area outlined in brown). There will also be a belt of wind shear in the order of 25-40 kts across the northeast and mid Atlantic, which will overlap the area of instability across the mid Atlantic. The best overlap of these 2 favorable ingredients for severe weather is expected to occur across central/northern MD, central/southern PA, and NJ. To the west, a cold front will approach between 4 and 10pm, likely triggering thunderstorms along it. As they intersect this unstable airmass, they should become strong to severe. As of now, the SPC has expanded the slight risk (level 2/5) to include the entire area just as we were expecting. Model data on Monday came into better agreement in more widespread thunderstorms occurring between 4pm and 10pm, leading to higher confidence. Scattered to numerous strong/severe thunderstorms seem like an increasingly likely possibility. If confidence in more widespread thunderstorms increases, then an enhanced risk (level 3/5) may be issued, but confidence is too low at this time. The main hazards for Wednesday will be damaging winds that could reach or exceed 60-70mph. Model data shows a favorable environment for some pretty substantial wind gusts in any severe storms that develop. Some hail is also possible, but it should not exceed the size of quarters. The chance of tornadoes does exist, but its a very low risk and confined mainly north of the MD/PA state line where there will be stronger wind shear. Heavy rain is likely with any storm along with frequent lightning. There are some similarities with this event to July 12th 2022. But while this has potential to be a notable severe weather event, there are some things that could go wrong with the forecast leading to a lower risk of severe weather.
1: Cloud cover left over from thunderstorms in the Midwest may leak over the mountains into our area sometime Wednesday morning. If this occurs and they don't dissipate in time, we miss out on peak heating which will lower instability greatly reducing our severe weather threat. 2: Deep mixing of the lower atmosphere during the afternoon drops the dew points too low, inhibiting the development of robust thunderstorms and dropping the instability low enough to where the storms are weaker. 3: Scattered showers and storms form well ahead of the cold front between 2 and 4pm and drop our temperatures and leave behind a lid over the atmosphere known as convective inhibition. This would prevent any additional storms from becoming severe with the actual cold front. With that said, this certainly bears watching, but is not something to be overly worried about and I certainly wouldn't cancel any plans. Just keep an eye on the forecast and watch for changes and updates. Senior Forecaster Jack A refreshing airmass briefly overtakes the area Monday and Tuesday with temps mainly in the 80s on Monday and low 90s on Tuesday. Both days feature tolerable humidity and breezy-windy conditions with gusts possibly topping 30mph on Monday. No rain is expected either day. By Wednesday, we shoot right back into the middle and upper 90s with heat index values over 100 once again. Luckily this will be short live as a stronger cold front moves through late evening and overnight, bringing thunderstorms and a cooler and drier airmass to end the week. Thursday and Friday should be mainly dry with increasingly sunny skies as well as temps only in the 80 to around 90ish with tolerable humidity. severe weather chances on wednesdayThere is a good chance (a least 50%) of thunderstorms Wednesday late afternoon and evening, and its possible that some of these become severe. Temperatures along the east coast will rise well into the 90s, with middle and upper 90s likely in some areas. A belt of 20-30kts of wind shear also will overspread portions of the Northeast and Mid Atlantic states overlapping the northern portion of this hot airmass. Assuming dew points rise enough (they would need to reach the upper 60s at least), then there will be ample instability present. Since this instability will overlap this shear over portions of Maryland, Pennsylvania, and New Jersey, this is where a locally higher risk of perhaps some more widespread storms may occur. A cold front will approach from the west and as it intersects this modestly sheared and unstable airmass, thunderstorms will likely develop. Looking at the parameters in place, the primary risk should be damaging winds as storms grow into clusters or line segments. There's enough wind shear present and some steepened mid level lapse rates that some small to perhaps even large hail could occur on an isolated basis. We currently are not expecting tornadoes to a concern but that's something we will closely monitor. Any storm will also be capable of producing frequent lightning and heavy rainfall. Again, this will all depend on how much instability develops which is reliant on both how much cloud cover there is and how high the dew points get. We will be able to fine tune this as we get closer. There is no official outlook yet from the Storm Prediction Center, but I suspect that they will at least put us in a marginal risk (level 1/5) starting with the day 3 outlook issued at 3am Monday (for Wednesday).
High temperatures will once again reach the upper 90s to perhaps low 100s on Sunday, with heat index values of 103-107 degrees. This has prompted a heat advisory to be issued for the entire area. These remain dangerously high temperatures and we strongly discourage outdoor activities between 10am and 6pm. One thing that may keep temps down just a touch is increased cloud cover, but its uncertain how much cloud cover will develop. The above graphic was created using the NWS forecasted high temperatures off WeatherBell. The high heat and humidity will create a favorable thermodynamic environment for thunderstorms during the afternoon and evening hours. Wind shear is weak, as is forcing, so we are not expecting widespread severe weather. But any storm that develops with this much heat and humidity will pose a risk of locally damaging winds, hail, and flash flooding. The storms should remain isolated to scattered, so not everyone will see a storm and many areas will remain dry. Again, the main concern is localized microbursts capable of producing wind gusts on the order of 50-65mph in some spots. This is thanks to high surface instability, high DCAPE, and steep low level lapse rates. All of which are favorable for microbursts even with weak wind shear/forcing. That being said, there is a low end chance for an isolated tornado especially along and north of the Mason Dixon line where shear will be stronger, or where outflow boundaries interact with storms resulting in brief locally higher shear values.
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