Category Archives: Thunderstorms

NYC Weekend Weather – Apr 19, 2019

Flooding, Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , , , ,

A slow-moving storm system will impact the area with potentially heavy rain that could trigger flash flooding overnight into the first part of Saturday. Precipitation chances die down significantly with the passage of this round of rain as a dry slot works into the area. However, lingering chances for showers still exist as this storm makes a slow exit to the east. Temperatures during this period are forecast to be at or above normal.

Rest of today – cloudy, but still warm with temperatures rising to about 70°F. We will be in the warm sector with the influence of southerly winds during the day. Rain chances increasing during the evening hours. Steady rain is forecast late into the overnight hours with temperatures. Some of the rain could be heavy. Thunderstorms are also possible, and these would increase the risk of flash flooding. Overnight lows around 60°F.

Weather Prediction Center surface forecast for 8AM Saturday

Saturday – the north-south orientation of the cold front that will provide lift for these storms overnight will align well with the prevailing southerly flow through most of the atmosphere. The slow eastward progression of this front will allow storm cells to train leading to more flooding potential as rain continues Saturday morning. The cold front associated with this slow-moving low should push through by the afternoon. A dry slot should cut off any precipitation for a while during this time frame. High temperatures should be in the low-60s. Overnight lows should fall into the low-50s behind the cold front.

GFS model output of 850 mb winds and relative humidity for 2PM Saturday, notice the pronounced area of browns, indicating very dry air. This is what is referred to as a “dry slot“, which can often follow on the heels of cold fronts associated with mature mid-latitude cyclones.

Sunday – the upper low associated with this storm system is expected to cutoff (become detached from primary westerly steering currents), resulting in a system that will meander and take a long while to exit the region. As such, Sunday is expected to remain cloudy, with a chance for some showers. High temperatures should be similar to Saturday in the low-60s. Overnight lows will again be around the low-50s.

Monday – temperatures warming up into the upper-60s, but yes, that cutoff low still lingers! Chance for showers continues in the morning. Clouds finally decreasing later and overnight lows in the mid-50s.

NYC Weekend Weather – Apr 12, 2019

NYC, Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , ,

Two distinct storms will affect weather in the area this weekend going into next week. The first is the remnant of the once mighty “bomb” cyclone that brought an abrupt return of winter conditions to the northern Plains states and Upper Midwest. The second will be a storm developing over Texas that could be a severe weather threat down South. Neither should result in a washout as the bulk of precipitation associated with these storms is timed to fall later in the day or overnight. Temperatures will be largely above normal during this period.

Rest of today – cloudy with chance of drizzle early. High temperatures around 60°F. Overnight lows in the mid-50s. Winds are forecast to turn to the south ahead of an anticipated cold front and in the wake of a warm front passing. Rain should accompany this frontal passage overnight.

Weather Prediction Center surface forecast for 2AM Saturday

Saturday – warm day in store with highs reaching into the low-70s despite mostly cloudy skies as the cold front passing overnight is forecast to stall and become stationary during the day. Overnight lows in the mid-50s again.

Sunday – shower chances increase as the next storm approaches. Temperatures will be cooler with highs in the low-60s due to clouds and rain. A second, more vigorous cold front is forecast to pass overnight into Monday. Rain, heavy at times, possibly with thunderstorms as overnight lows fall into the mid-50s.

GFS model output for 8PM Sunday

Monday – rain associated with this second storm should clear out around lunchtime. Cloudy day forecast now, but could see more breaks in the clouds and warmer temperatures in the upper-60s.

NYC Weekend Weather – Mar 15, 2019

NYC, Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , , , , ,

This weekend will see a warm start but then a cool down into the below normal range going into next week. A rumble of thunder and showers will precede this cool down. Weather looks pleasant for St. Patrick’s Day festivities and the NYC Half Marathon this weekend. 

Rest of today – mostly cloudy with some breaks of sun after a warm front passes over shortly and we sit in the warm sector of the same storm that tore through the central US earlier this week. As the trailing cold front pulls through this evening, it could provide enough lift for some additional showers and possibly a couple thunderstorms. High temperatures will be above average in the low-60s, mid-60s if some sun breaks through while we’re in the warm sector. Overnight lows behind the cold front should be in the low-40s.

Weather Prediction Center surface forecast for 8PM Friday

Saturday – bright, sunny day with high pressure building behind the cold front. Temperatures cooler, around 50°F. Overnight lows much cooler in the low-30s.

Sunday – cold start to the NYC Half Marathon in the low-30s but high temperatures will end up in the mid-40s with lots of sun. Overnight lows again around the freezing mark

Monday – increasing clouds with a possibility for some precipitation but chances are too low now to call. Highs in the mid-40s and overnight lows back down in the low-30s again.  

WxChallenge for Omaha, Nebraska (KOMA) | Oct 9-12

Outside of NYC, Rain, Thunderstorms, Weather Update, WxChallenge, , , , , , , , ,

A couple days into the forecast period for the second WxChallenge city for this fall, and I’ve experienced my worst forecast bust (for yesterday). Highlights in the post-mortem section. It has been a week of transitions for Omaha, which started off with relatively mild conditions but will end the week with possibility for patchy frost!

Synoptic Set Up

A 500 mb longwave trough will with multiple attendant vorticity maxima will pivot through the KOMA region during the first half of the forecast period before flow becomes more zonal. At the 300 mb level, multiple jet streaks could boost divergence with these 500 mb vorticity maxima. This enhanced lift, and strong wind shear profile could lead to some isolated strong-severe thunderstorms. The 850 mb shows evidence of a decently robust LLJ that would should bring a continuous supply of Gulf moisture up the Missouri Valley into the area. At the surface, a warm front looks to lift through Monday, then stall as a cold front in the vicinity of KOMA through late Wednesday due to the deep unidirectional winds parallel to the front boundary.

Notes

The potential for flash flooding, and bouts of heavy rain, is duly noted in the AFD during the first half of the weak. The synoptic ingredients for a long duration rainfall event are certainly evident. Soils in the area are already quite moist, given that flood warnings were present for stretches of the Missouri last week. GFS MOS QPF range on Sunday for 06Z Tuesday to 06Z Wednesday was 1.75-4.46”. NAM MOS QPF range for this time was 1.35-2.71”, consensus was 1.55-3.59”. Records around this time of year for QPF show that 1-2” can easily occur, despite the normal being only a mere 0.07”. SREF probabilities of >= 0.50” were above 90% for this period, and >= 1.00” was 50-70%, but over 2.00” of QPF probabilities were less than 10%. SREF mean was 2.73”, with a pretty large spread, from 0.69-5.54”. GFS mean was 3.93” with spread of 1.82-5.16”. For now, going with a superblend of the low-end of the ranges of MOS and plumes: 1.40”.

As of Monday, SREF and GEFs means had become much better aligned, with SREF mean at 2.83” and GEFs mean 2.95”. SREF spread was 1.34-4.46”, GEFs was 1.43-4.43”. QPF forecast shows KOMA a pretty large QPF gradient, and that uncertainty seems borne out well in the ensemble forecasts. SREF probabilities of >= 2.00” increased to the 10-30% with KOMA lying right on the fringe of 30-50% probabilities of this amount. >= 1.00” probabilities increased to 70-90%. Official NWS forecast as of 10Z Monday called for 1.65” during the forecast period Tuesday. GFS MOS QPF range was 2.10-4.21”, NAM 1.01-2.06”, consensus here is 1.55-3.13”. Based on these updates, I’m increasing my forecast to 1.85” – I’m hedging down below the SREF and GEFS means because I’m still not sure where the stationary/slow-moving surface front will set up in relation to KOMA, and where the best lift will be for heavy rain/thunderstorms as a result. Also, if the 850 mb LLJ fails to materialize close to KOMA, we could be looking at lower overall totals. Low SREF probabilities of over 2.00” also help justify this call. Looking at Wednesday, rain chances diminish considerably after the front moves through, but the story then becomes strong winds possible, with MOS pointing at 17-20 knot synoptic winds.

Ensembles continue to trend upwards as of Monday afternoon with QPF, SREF mean now 2.96” and GEFS mean is 3.16”. SREF probabilities are close to placing KOMA in the 50% >= 2.00” QPF. Will take one more look at 18Z MOS guidance and some other factors before finalizing, but am leaning towards increasing the precip forecast again, this time to maybe 1.90” I’m wary of going for 3” of QPF or higher, given that the entire month’s single-day QPF record is 3.09”. Even beyond 2” still seems unlikely.

On Tuesday, looking ahead at Wednesday and Thursday, the passage of a cold front is quite evident. Temperatures are forecast to drop considerably compared with the beginning of the weak, and precipitation will end, too. The forecast for Wednesday still retains a slight chance for some measurable QPF on the tail end of the main precipitation event Tuesday. Models have backed down from up to 0.25” of precip to less than 0.10”. SREF and GEFS means show approximately 0.04” on Wednesday. SREF probabilities showed that KOMA had a greater than 90% chance of receiving precipitation >= 0.01”, but less than 10% of >= 0.10”, going to go straight up with the ensemble means here. The other story for Wednesday will be stiff winds from the northwest, with MOS synoptic winds of 17-18 knots. This suggests even stronger sustained winds, and will aid in cold advection, keeping high temperatures suppressed. These blustery conditions are forecast to gradually abate by late in the day Thursday, such that the strongest winds Thursday should occur early in the overnight hours. Cold temperatures overnight into Thursday should be somewhat tempered by decent vertical mixing and overcast skies.

Forecasts Submitted

This only reflects finalized forecasts, I’ve made small adjustments to the forecast based on checking MOS daily.

Forecast Day Max Temp (°F) Min Temp (°F) Max Sustained Wind (kts) Precipitation (inches)
10/09/2018 62 57 14 1.91
10/10/2018 48 44 20 0.02
10/11/2018 48 34 17 0.00
10/12/2018 48 35 9 0.10

Post-Mortem

Day 1: Major bust across the board. Was off by more 5 degrees or more on both the high and low. This made up about half of the error points. The rest came from being off on max precipitation by more than 1.20”. MOS was considerably off the mark with temperatures – though NAM was closer. This was all due to the fact that a stationary frontal boundary never made it close enough to KOMA to realize warmer temperatures, and heavier precip. The axis of the 850 mb LLJ stayed south and east, along with the best surface convergence. As a result, nearly all of the model guidance was horribly wrong. The closest forecast in the class was still nearly 0.50” too high. I put too much credence into the upwards trends on the models – there were some indications already that KOMA was trending to be on the drier side of this event. Still, even if I had nailed the precipitation forecast, I would have still busted hard on the temperatures. Need to be a lot more cautious going forward about situations where a frontal boundary and precipitation are around, and probably hedge down on temperatures during transitional season when a forecast site could be on the cold side of a front with rain.

NYC Weather Update – Sept 26, 2018

NYC, Rain, Severe Weather, Thunderstorms, Weather Update, , , , , , , , , ,

Severe thunderstorms could impact the area later today ahead of an approaching cold front. Following the passage of this cold front, conditions will begin to improve, setting us up for a weekend with pleasant, cooler, classic autumn weather.

Rest of today – Storm Prediction Center in Norman, OK has placed parts of the NYC Tri-State (the city, north and west) under a slight risk of severe weather today. Warm, moist air (read: unstable, theta-e rich) is in place with the area in the warm sector of an advancing low pressure center located in Ontario/Quebec. Some rain/thunderstorm activity could take place along a weak warm front this morning. The main focus of activity will occur later today with a cold front approaching from the west.

This cold front will be accompanied by a streak of strong upper level winds (40-50 knots), which will be capable of providing the magnitude of vertical wind shear necessary for some strong to severe thunderstorms to organize. Given the direction of the winds at upper levels being largely parallel to the advancing frontal boundary, expect that the primary storm format will be a QLCS (quasi-lineary convective system) – a line or broken line of storms. High Resolution Rapid Refresh models depict the bulk of storm activity approaching the city around 8PM this evening. Given this storm format and synoptic set up, the most likely severe threat will be damaging wind gusts. Heavy rain could trigger flash flooding as well, since the ground is still quite saturated from yesterday’s rain.

The biggest limiting factor to storm strength today will be overcast skies limiting daytime destabilization from solar heating. As is often the case, I would expect the storms to be weakening somewhat as they approach a more stable marine air layer near NYC. Overall, expect a cloudy day with high temperatures in the low-80s and a muggy feel.

Storm Prediction Center Day 1 Convective Outlook

Weather Prediction Center forecast surface conditions at 8PM EDT

High Resolution Rapid Refresh simulated 1-km radar for 8PM EDT

NAM forecast for 500 mb winds and height valid 8PM EDT

Thursday – the cold front that brings us this possibly severe today will slow down as it pushes south of us, such that it remains close enough that a weak disturbance moving along it could bring us some additional showers late in the day. Skies will be partly sunny with much cooler high temperatures in the upper-60s.

Friday – easterly onshore flow on the back side of this cold front forecast to be to our south will keep skies cloudy with high temperatures around 70°F – chance for showers lingers.

Saturday – high pressure finally starts to take control of sensible weather and should produce a mostly sunny day with crisp conditions and high temperatures in the low-70s.

NYC Weekend Weather – Sept 21, 2018

NYC, Rain, Thunderstorms, Weather Update, Weekend, , , , , , ,

Cooler weather arrives just in time for the astronomical start of autumn. Cloudy conditions have been persistent, and will continue today. A chance for rain and scattered thunderstorms tonight going into Saturday from a passing cold front. These will not be drenching rains like with the remnants of Florence. High pressure returns Saturday, and should give us a dry weekend, though we may continue to see more clouds than sun.

Rest of today – cool, and cloudy, with high temperatures in the low-70s. Chance for showers and thunderstorms overnight with a passing cold front.

Saturday – sunnier with high temperatures in the mid-70s. The autumnal equinox will take place at 9:54PM EDT.

Sunday – partly sunny with high temperatures in the low-70s.

Monday (Mid-Autumn Festival) – partly sunny with high temperatures again in the low-70s.

NYC Weather Update – Sept 17, 2018

NYC, Rain, Thunderstorms, Weather Update, , , , , , , ,

We had some great late-summer weather this past weekend with high temperatures in the low-80s and lots of sun. Most of this week will be quite nice as well, with the notable exception of Tuesday, when remnants of Florence impact the region and bring around a day of heavy rain. Fortunately, this wet weather will be short-lived, and the remainder of the week should see a return to mostly sunny conditions.

Rest of today – increasing clouds and humidity as remnants of Florence approach from the south. High temperature around 80°F.

Tuesday – periods of rain, heavy at time, with scattered thunderstorms possible. Otherwise cloudy, with high temperatures around 80°F again.

Wednesday – conditions improve as the remnants of Florence quicly move off to the east. A return to mostly sunny weather with cooler highs in the upper-70s as the back side of the cyclonic rotation of the remnants of Florence brings a cold front through.

Thursday – another mostly sunny day with high temperatures in the low-70s, high pressure building should continue to keep things dry for the region.

NYC Weather + Special Tropical Update – Sept 10, 2018

Cool Images, NYC, Rain, Storms, Thunderstorms, Tropical/Hurricanes, Weather Update, , , , , , , , , , , , , , , , ,

This week kicks off with a prolonged period of unsettled weather as a warm front and a cold front both impact the area. Chances for rain will be with us through Wednesday. Conditions finally improve late in the week. We luckily will avoid direct impacts (aside from high surf) from what will be an extremely dangerous Hurricane Florence, which looks set to make landfall on North Carolina late this week. Aside from Florence, two other storms pose threats to US territories this week.

Rest of today – cloudy, with periods of rain, heavy at times, especially later in the day towards the overnight hours. High temperatures will be in the upper-60s with cool, persistent onshore flow from the east. Ahead of an approaching warm front.

Tuesday – chances for thunderstorms will persist into Tuesday, with this slow-moving warm front finally pushing through. There could be thunderstorms overnight. Then, later in the day, as the trailing cold front moves through. Once the warm front passes over, we’ll be within the warm sector of the parent low pressure system, which will allow temperatures to climb into the low-80s with a marked increase in humidity.

Wednesday – the cold front mentioned above will slow down as it approaches us and dissipate. This will lead to continuing chances for rain, and thunderstorms with temperatures again in the low-80s.

Thursday – high pressure will finally begin to build in to our north by Thursday behind the cold front above. This will lead to better conditions, with partly sunny skies and temperatures in the low-80s.

Friday – partly sunny skies with high temperatures in the low-80s again with high pressure to our north.

Florence, Isaac, and Olivia All Pose a Threat to the US

These three storms have the potential to impact the Southeastern US, Puerto Rico, and Hawaii respectively within the next week. Among these, Florence is by far the most dangerous, as it could make landfall on North Carolina as a Category 4 storm with maximum sustained winds of 145 mph.

Hurricane Florence

Over the past day or so, the picture for Florence has become much clearer. Various forecast models have come into remarkable alignment on both the overall track and intensity of Florence over the next 5 days, which means bad news for the Carolinas. The picture looks grim, with Florence set to make landfall as a very strong Category 4 storm packing sustained winds of 145 mph. Florence has nothing but warm water ahead of it, and there should be minimal impact ot this storm from vertical wind shear. Even if the storm weakens due to eyewall replacement cycles prior to landfall, that would only serve to increase the radius of its damaging winds. No matter how you slice it, Florence is likely to bring deadly storm surge and risk of life-threatening flash flooding and inland flooding. The fact that its forecast track slows to a crawl after landfall makes the flooding risk inland especially serious.

Hurricane Isaac

Isaac is a compact storm, which is leading to some uncertainty regarding both its track and intensity forecast. Small tropical cyclones are subject to wild swings in intensity both ways, which can be unpredictable at times. As of now, Isaac is forecast to cross the Windward Islands of the Lesser Antilles as a Category 1 storm, then continue into the Caribbean where hostile shear conditions should cause it to weaken. It is worth noting, despite the UKMET model being an outlier, that there are some signals that the storm could turn to the northwest later in the period, which could mean a threat to Hispaniola and Puerto Rico.

Hurricane Olivia

This storm continues to track towards Hawaii. Although weakening due to the influence of moderate wind shear, it is still set to hit Hawaii later this week as a strong tropical storm. The primary threat to Hawaii from Olivia will be in the form of heavy rain and flash flooding regardless of whether it makes direct landfall on one of the main islands.

NYC Weather Update – Sep 4, 2018

NYC, Rain, Storms, Thunderstorms, Tropical/Hurricanes, Weather Update, Weekend, , , , , , , , , , , , ,

A brief break in the heat over the weekend has led back into another warm spell to begin this week. This latest blast of heat will be short-lived as a backdoor cold front sweeps through tomorrow, followed by another, stronger cold front later this week. Temperatures for the upcoming weekend will once again be comfortable, seasonable to below average. In the tropics, things are starting to get busy with tropical storms Florence and Gordon active and another tropical wave poised to become a tropical cyclone off the coast of Africa. Gordon will make landfall overnight on the Gulf Coast east of New Orleans.

Rest of today – hot and humid with temperatures in the low-90s, mostly sunny skies.

Wednesday – cooler, though still warm with high temperatures in the upper-80s and partly sunny skies. A backdoor cold front will bring cooling onshore southeasterly breezes that help keep a lid on temperatures.

Thursday – temperatures rise back a couple degrees into the low-90s ahead of an approaching cold front from the northwest. The warm air ahead of the cold front could help set the stage for a few scattered strong thunderstorms as the front passes through.

Friday – temperatures cool off quite a bit into the low-80s under mostly cloudy skies. Chance of showers during the day with the cold front lingering south of the area.

Tropics Heating Up

We have 2 active tropical cyclones (Florence, Gordon), and another incipient one in the Atlantic Basin. Tropical Storm Gordon could strengthen into a hurricane before landfall on the Gulf Coast between Mississippi/Alabama overnight into Wednesday. Heavy rain could induce flash flooding in southern portions of these states. The immediate coastline will be at risk of storm surge flooding. Florence doesn’t pose an threat to land. The disturbance shown below that’s furthest east is a tropical wave that’s just emerged off the coast of Africa. This is worth watching as it has a high chance of becoming a tropical cyclone and its eventual track could pose a threat to portions of the Lesser Antilles.

NYC Labor Day Weekend Weather – Aug 31, 2018

NYC, Rain, Thunderstorms, Weather Update, Weekend, , , , , , , , , , ,

After a week of sweltering temperatures, the weekend brings some welcome relief from the heat. The downside is that these cooler temperatures come with mostly cloudy conditions and chances for rain. Labor Day marks the traditional end of summer, and it will feel like that this weekend, but temperatures will rise right back into the upper-80s and low-90s next week.

Rest of today – mostly cloudy with onshore easterly flow keeping temperatures suppressed in the mid-70s. This easterly onshore flow is happening on the back side of a cold front that passed through yesterday. This front will stall out and become stationary south of us over the Delmarva Peninsula. As impulses of energy move along this front, there will be chances for rain. However, it does appear the best chances for rain stay south of us.

Saturday – mostly cloudy still with slightly warmer temperatures in the upper-70s. Easterly onshore winds continue along with some chances for rain in the afternoon and more chances for showers and thunderstorms overnight.

Sunday – warming up into the mid-80s with scattered chances for showers and thunderstorms. Partly sunny skies otherwise.

Monday (Labor Day) – conditions improve just in time for the West Indian Day Parade festivities with high temperatures in the upper-80s and partly sunny skies.