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Rain Heavy At Times Tonight

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Hello everyone!

Showers are moving in this evening and will continue to do so through the overnight hours. Rain will be heavy at times and steadiest in the northern part of the mountains. The rest of the area will see more scattered heavy rain with thunder and gusty winds possible in the stronger cells. Showers and storms sweep east tomorrow morning with clearing in the afternoon. A few showers are possible Thursday with the passage of a cold front but otherwise the end of the week and the weekend look warm and dry. Another threat for heavy rain arrives early next week with significant heat relief likely following for the rest of next week.

4:30 PM Observations Verifying Today's Forecast. Credit: EDD
4:30 PM Observations Verifying Today’s Forecast. Credit: EDD

Today’s forecast was fairly good. Morning sun slowly faded behind increasing clouds and showers began encroaching from the west this afternoon. Temps stayed mainly in the 70’s as forecast with only a few low 80’s in far southern NH. The showers arrived a hair earlier than forecast and continue to do so this evening but the margin of error there was fairly small. Again, there is no such thing as a perfect forecast but today’s was fairly solid.

4PM Surface Observations Showing The Surface Setup For Tonight. Image Credit: SPC Mesoscale Analysis
4PM Surface Observations Showing The Surface Setup For Tonight. Image Credit: SPC Mesoanalysis

A round of rain ahead of a warm front is moving NE through the area currently. The warm front will lift north before stalling right around Portland tonight. Meanwhile, low pressure will track through the mountains during the same overnight timeframe before pushing a cold front south early tomorrow morning. This is the surface setup and is shown with the 4PM surface analysis map from the SPC mesoanalysis page. The biggest forecast challenge for tonight will be pinpointing exactly where that warm front sets up. North of it, steady heavy rains will put a noticeable dent in the drought. South of it, heavy rains will be hit or miss in a more convective format with some towns getting a much needed drink and others staying more or less completely dry.

4PM Middle Atmosphere (850mb) Analysis Showing A Plume Of Moisture Headed Our Way. Image Credit: SPC Mesoanalysis
4PM Middle Atmosphere (850mb) Analysis Showing A Plume Of Moisture Headed Our Way. Credit: SPC Mesoanalysis

Aloft, a disturbance over the Eastern Great Lakes will move rapidly NE tonight. SW winds ahead of this disturbance will pump a warm moist airmass into the region. This airmass will feature more Precipitable Water values in excess of 2″ which will support very heavy rain. Pictured is the 850mb moisture field (RH) and vectors showing where that moisture is going (arrows). Notice all the arrows pointing in our direction. This shows that the moisture is headed our way overnight tonight.

HRRR Showing One Idea As To How Things Play Out Tonight. Credit: Weatherbell
HRRR Showing One Idea As To How Things Play Out Tonight. Credit: Weatherbell

So what does this all mean for the forecast tonight into tomorrow morning? The HRRR model does a fairly good job summing it up. Rain will continue to overspread the region from SW to NE this evening and will become heavy at times. The heaviest rain will be concentrated over northern areas with the cutoff somewhere between Portland and Lewiston. North of that cutoff point, steady rain, heavy at times, can be expected with storm totals of 1-2″. Some areas have a shot at seeing up to 3″ if they can manage to sit under a downpour for a while. South of that cutoff, heavy rain will be more scattered with those same 1-2″ amounts falling only where the heaviest downpours track. Those that don’t see individual storms track overhead are likely to miss out on any substantial rain. Most areas in this southern region will see between a tenth and a third of an inch of rain with some spots under the heaviest downpours seeing amounts closer to an inch or two.

Some of the downpours over southern areas could feature thunder and gusty winds as some marginal instability tries to work in aloft. This will not be a widespread severe event but some gusty winds are possible especially across SW NH. The bigger severe threat is to our SW over SNE and NY but we will get some of those storms in a much weakened state. Be aware and have a plan if a warning is issued for your area but otherwise, this won’t be a significant event. Showers and storms sweep NE tomorrow morning with just a few showers left along the coast by sunrise.

12Z GFS Showing A Weak Cold Front Passing Overhead Thursday
12Z GFS Showing A Weak Cold Front Passing Overhead Thursday

The rest of Wednesday will be mostly dry with just an isolated pop up shower here or there. Temps will be warm but not hot and dew points will be sticky but not oppressive. Another cold front will approach the area Thursday which will bring the chance for some more showers and possibly a storm or two. Notice the two low pressure systems back to the west on this map valid Thursday afternoon. Those will slowly work east during the weekend and will end up near us by Monday with a slow moving cold front in tow.

This Morning's Surface Analysis Showing All The Players For This Week's Weather. Image Credit: Meteocentre
This Morning’s Surface Analysis Showing All The Players For This Week’s Weather. Image Credit: Meteocentre

Next week’s rain threat will be centered around Monday. The upper level pattern will shift by then and the seeds of that shift are being sown today. The thick black line is tonight’s disturbance. Thursday’s disturbance is the red line. The lines for the next heavy rainfall threat are the blue one in the top left over NW Canada, the green one south of Bermuda, and the pink one over the Rockies. The blue disturbance will drop south in the coming days and carve out a deep trough. The pink ridge will move offshore by Monday and will end up evolving into a large block off of Nova Scotia. The southerly flow around this block and ahead of the Canadian disturbance will drag tropical moisture provided by the green disturbance northward. There is no reason to change from last night’s forecast anything except the timing. The amplified pattern means that the forward (eastward) progress of each feature will be slowed. Last night, it looked like the heavy rain threat was primarily Sunday into Monday, now guidance indicates it’s more of a Monday/Tuesday affair. Based on the pattern and guidance trends, don’t be surprised if this ends up being more of a middle of next week event. It is still far too early for specifics but if you have plans around this time, keep updated with latest forecasts both from me as well as the NWS and local media.

The deep trough over the Central US that will be providing the focus for this rain threat looks to move east by late next week with more substantial heat relief. How long will that last? It’s anyone’s guess at this point but that should become clearer as we get closer. There is plenty of weather to figure out between now and then.

-Jack

More Beneficial Rain This Week

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Hello everyone!

After a weekend of on and off storms and heavy rain, we finally got a break from the heat, humidity, and storms today. Enjoy the drier air while it lasts because it won’t last long. Warm, sticky air will again flood the region tomorrow as a warm front tries to drive north. After heavy rain for many tomorrow evening, rain will become lighter and more scattered for the rest of this week with more dry hours than wet. That changes by this upcoming weekend when a deep trough to our west will bring more tropical moisture and accordingly more heavy rain.

5:00 PM Observations Verifying Today's Forecast
5:00 PM Observations Verifying Today’s Forecast

Today’s forecast worked out fairly well with the exception of cloud cover. In typical upslope/downslope situations, the clouds would reside over the mountains while the sun would be over the southern part of the area. Today, however, warm air advection aloft brought clouds to the south while the atmosphere dried out so much (and was still so warm aloft) that no widespread clouds were observed over northern areas. The cloud cover aside, everyone stayed dry as forecast and forecast temps panned out well with mid/upper 70’s north and low to mid 80’s south. Overall, not a disaster, but as always, it could’ve been better.

12Z GFS Showing The Upper Level Setup Tomorrow Evening
12Z GFS Showing The Upper Level Setup Tomorrow Evening

Tomorrow will feature the return of tropical moisture to the area as a disturbance passes through Northern VT and into Northern ME. A low pressure system will move right through the middle of the area tomorrow as well. This means that SW winds aloft and at the surface will again bring tropical moisture to the area. Tomorrow’s forecast will be basically split up into three parts, the delineation between them being location. The first part will be fairly heavy, fairly steady rain across the north.

12Z GFS Showing Tropical Moisture To Fuel Heavy Rains Tomorrow. Credit: Weatherbell
12Z GFS Showing Tropical Moisture To Fuel Heavy Rains Tomorrow. Credit: Weatherbell

Tropical moisture will once again be present across the region by tomorrow afternoon and evening and Precipitable Water values will be running near or over 2″ which is about as loaded as it gets here in Maine in terms of tropical moisture. Low pressure will pass right through the middle of the area leaving the northern part of the area to the north and eventually north west of the low. This is where steady precip is most likely, The tropical moisture will encounter some residual low level cool air leftover from today’s airmass and rise, cool, and condense, causing rain. Areas mainly north of route 2 could see 1-3″ of rain from this event.

12Z 4km NAM Showing One Idea As To How The Storm Could Play Out Tomorrow. Image Credit: Weatherbell
12Z 4km NAM Showing One Idea As To How The Storm Could Play Out Tomorrow. Image Credit: Weatherbell

The middle part of the area, north of a Portland/Hanover NH line, but south of route 2, will see more scattered showers and possibly a storm or two. This is the area through which the low itself will track which means that it will be missing both the instability from the warm sector south of the low, and the forcing for steady rain north of the low. This area will see the least amount of precip overall because it is neither here nor there so to speak. The precip for this middle stripe will range from a quarter to a half inch and will come from showers and storms that form farther south tracking NE.

12Z GFS Showing More Than Enough Shear For Severe Potential Tomorrow. Credit: Accuweather
12Z GFS Showing More Than Enough Shear For Severe Potential Tomorrow. Credit: Accuweather

Southern areas, south of that Portland/Hanover NH line, will see showers and storms with torrential rains and also with some limited severe potential. The nearby low, strong upper level disturbance, and warm front/cold front combo will provide the trigger. Strong shear associated with the developing low (pictured above) will provide the organizer, but the big question will, as per the norm here in Maine, be instability which, right now, looks limited at best. Due to the lack of instability and the presence of an inversion aloft which will help keep strong winds high in the sky, the severe threat looks limited. That being said, the SPC has this southern area in a marginal risk for severe weather and a stray strong wind gust can’t be ruled out. This severe threat will be least small overnight Tuesday into early Wednesday morning. Some scattered showers and possibly a stray storm is possible Wednesday morning before afternoon drying and clearing. Southern areas will see rainfall amounts vary widely depending on exactly where storms set up going into the evening hours. Some places could see over 1-2″ if storms train over a specific location while it is possible others struggle to see even a quarter of an inch of rain. There is no way of knowing exactly where storms will set up this far in advance.

Highs Tuesday look to remain cooler as clouds and showers overspread the area from west to east. Look for temps largely in the 70’s with a few low 80’s possible in SW NH.

Thursday and Friday at least look warm but not hot with some scattered showers in the afternoon but no organized rain. By the beginning of next weekend, however, a deep trough will be present over the Central US with deep S/SE flow from the tropics over our area out ahead of it.

12Z GFS Showing The Pattern For Our Next Rain Threat This Coming Weekend
12Z GFS Showing The Pattern For Our Next Rain Threat This Coming Weekend

There are several important factors for next weekend’s rainfall potential. The pattern looks a lot like last winter’s with a big trough just to our west flanked by large blocking ridges. Warm S/SE flow ahead of the trough looks to bring another threat for heavy rain, just like it did so many times last winter. At this point, all that seems clear is that another heavy rain threat exists and must be watched between 6 and 8 days from now. The pattern supports it as does all available guidance that I’ve seen. Specifics are still uncertain at this point but they will become less so as the week goes on. I’ll have more updates as those details become clearer.

Following that heavy rain threat, more significant heat relief seems likely as we look to move into the third and fourth weeks of August.

One last note, this Wednesday (8/17) at 6:30 PM, I will be giving a presentation at the Freeport Community Library where I will discuss me and my background, some of the quirks of Maine weather, how to be a better informed consumer of weather information, and finally what you can do to help meteorologists make better forecasts. For more details, click on over to the FB event page that the folks at the Freeport Library created. I hope to see you there!

-Jack

Heavy Rain Possible This Weekend Following Oppressive Heat Tomorrow

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Hello everyone

Current Conditions This Afternoon (4:30 PM) Verifying Today's Forecast
Current Conditions This Afternoon (4:30 PM) Verifying Today’s Forecast

This morning’s showers are now well offshore as an upper level disturbance rotates eastward. Looking at the forecast verification, temps worked out fairly well with widespread 70’s under cloudy skies. Some 80’s were reported in SW NH as expected. I didn’t think clouds would clear out enough in the far north for 80’s but by the looks of obs across SE Quebec, some warmer temps likely found their way into those areas. This morning’s showers evolved as forecast but so far no storms have been reported in NE areas though some leftover convection from Quebec could still find its way in later this evening. Overall, today was a pretty good forecast.

4km NAM Showing Oppressive Dew Points Tomorrow. Image Credit: Weatherbell
4km NAM Showing Oppressive Dew Points Tomorrow. Image Credit: Weatherbell

Tomorrow will begin a two-day sufferfest as we sit to the south of a frontal boundary. Look for highs to climb into the low to mid 90’s for most SW areas with upper 80’s elsewhere. SW winds will keep any sea breeze attempts at bay. Humidity will be the big story with dew points rising into the low 70’s for most with some upper 60’s north and east. The heat and humidity will combine to offer up heat index values near or over 100. Heat advisories are up for SW NH and York County ME due to this dangerous heat.

12Z 4km NAM Showing Widely Scattered Showers Possible Tomorrow. Image Credit: Weatherbell
12Z 4km NAM Showing Widely Scattered Showers Possible Tomorrow. Image Credit: Weatherbell

While there is no organized trigger for showers or storms tomorrow, there will be plenty of moisture around and as a result, even the differences in heating of the mountains could be enough to trigger a spot shower or two tomorrow afternoon. Again, this does not look widespread by any means but don’t be surprised to see a few drops if you’re out and about in the mountains. Most of the area looks to bake under the hot sun with no relief from clouds or precip.

12Z 4km NAM Showing More Dangerous Heat Friday. Image Credit: Weatherbell
12Z 4km NAM Showing More Dangerous Heat Friday. Image Credit: Weatherbell

More dangerous heat is on tap for Friday as we continue to sit south of the front. Temps are likely to be only slightly cooler than Thursday but dew points are likely to soar even higher. Temps in the low to mid 90’s combined with dew points in the 70’s will result in heat indexes exceeding 100 for much of the SW portion of the area. This is astronomical for Northern New England and nothing to take lightly. Be sure to take proper precautions such as hydration and limiting outside activity during the hottest part of the day. By evening, storms will be rumbling into the area from the NW and will begin to bring relief along with heavy rain, gusty winds, and frequent lightning.

12Z GFS Showing Sufficient Shear For Severe Storms Friday. Image Credit: Accuweather
12Z GFS Showing Sufficient Shear For Severe Storms Friday. Image Credit: Accuweather

The hot temps and oppressive humidity will result in a very unstable atmosphere Friday. Remember the three severe weather ingredients? We will have plenty of fuel. The approaching cold front will be our trigger and indications are that there will be more than enough shear to organize storms. This means that there is a threat for severe storms tomorrow with gusty winds being the main threat. This threat is greatest in the mountains where the front will be closer during peak daytime heating.

Current Water Vapor Satellite Showing All The Players For The Weekend Rain Event. Image Credit: COD Nexlab
Current Water Vapor Satellite Showing All The Players For The Weekend Rain Event. Image Credit: COD Nexlab

The pattern change I’ve been talking about for almost a week is finally here. A strong area of high pressure is setting up over the Western Atlantic as a trough is digging into the Western US. The SW flow on the periphery of the high and on the eastern side of the trough is directing a pool of tropical moisture associated with the tropical disturbance over Florida our way. Meanwhile, a powerful storm over Hudson Bay is pushing a cold front SE. Energy will eject from the Western trough and move east combining with the front and the moisture to bring rounds of showers and storms beginning Friday evening and wrapping up Monday.

12Z GFS Showing The Pattern For The Weekend
12Z GFS Showing The Pattern For The Weekend

I show the GFS 500mb vorticity (energy) and SLP map as it gives a general overview of what the pattern will be like from Friday evening through Monday morning. A front will be stalled overhead with several disturbances aloft and waves of low pressure at the surface promoting heavy rainfall. A final upper level disturbance and associated surface low will move east Monday bringing a final round of heavy rain. The exact location of this rain is still a bit up in the air. Some guidance suggests it will be right over us while some suggest we only see the far northern fringes of it. Those details should come into more clarity as that part of the event draws closer.

12Z GFS Showing The Moisture Plume Being Forced Offshore Monday
12Z GFS Showing The Moisture Plume Being Forced Offshore Monday

The front will continue to provide the focus for showers Sunday before the whole Western trough swings through with one final round of heavy rain Sunday night into Monday morning. This round is the most uncertain as there are some indications that it will primarily impact Southern New England leaving us dry. After this round passes out to sea, either via us or SNE, drier air looks to move in for the beginning of next week.

12Z GFS With This Week's Overview
12Z GFS With This Week’s Overview

The trend for this week will be a stifling start tomorrow and Friday before clouds and showers bring gradual cooling through the beginning of next week. Rounds of showers and storms could be heavy at times with flash flooding possible. Each round of rain will remove some moisture from the atmosphere so that by the beginning of next week we are left with a fairly dry and comfortable airmass. The pattern supports more rain by the middle or latter part of next week but there are no significant signals for a specific event yet.

I will have another update tomorrow morning. As a reminder, I will be gone from Friday afternoon through Sunday afternoon. I will post Friday morning but not again until Monday morning (there is the low potential I will return in time for a post Sunday evening but alas that depends on the weather). During this time, please revert to your primary source for weather information, such as the NWS or local media.

-Jack