Tag Archives: fall

Showers Bring Heavy Rain Tonight Before Cooler And Drier Conditions Early Week

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Hello everyone!

A cold front is incoming this evening and will cross the area tonight and early tomorrow morning. Showers will accompany this front with heavy rain and possibly a rumble or two in the far south. No severe weather is expected, just heavy rain. Rain will be heaviest in the north where up to an inch is expected. It will be lightest in the south where some areas may only pick up a quarter inch. Rain races NE Monday morning with clearing skies and gusty NW winds Monday during the day. Those NW winds will bring much cooler and much drier air in for Tuesday and Wednesday. An approaching front will bring SW winds and warmer air for late week with showers possible by the upcoming weekend. Just as a reminder, current information on tropical weather is now on the new tropical weather page.

4:00 PM Observations Verifying Today's Forecast
4:00 PM Observations Verifying Today’s Forecast

Today’s forecast worked out pretty well and the only glaring error was that there was more sunshine than expected. So far I haven’t received any complaints about that! Clouds are still slowly filtering in from the west while the Midcoast got their predicted marine fog. Temps look good with the only glaring error being lower temps (60’s) along the midcoast where the fog hasn’t let up. I have doubts about the 88 degree reading in Concord as no other station in that area is above the low 80’s but if that is actually accurate, that would be the other mistake as far as temps go. Overall, I’m pretty pleased with today’s forecast.

8 AM Upper Air Observations Showing The Overall Pattern. Image Credit: Meteocentre
8 AM Upper Air Observations Showing The Overall Pattern. Image Credit: Meteocentre

A deep trough is located over the Great Lakes this evening with an associated surface low near the SE corner of Hudson Bay. Ahead of the trough, strong blocking ridging exists over the Canadian Maritimes. In between, SW flow is bringing warm moist air northward. Strong NW flow behind the trough and attendant front will bring cool, dry air sourced from Northern Canada before SW winds ahead of the digging trough in the Pacific NW bring warmer air for the upcoming weekend.

HRRR With An Idea Of What The Radar Might Look Like Early Tomorrow Morning. Image Credit: Weatherbell
HRRR With An Idea Of What The Radar Might Look Like Early Tomorrow Morning. Image Credit: Weatherbell

In terms of what to expect tonight, showers are just now moving into far Western VT which means that western NH will start to see drops in 2-3 hours. It won’t be until well after dark that western Maine starts to see the rain move in. The rain will be associated with a single N/S band containing heavy rain and possibly a rumble or two in the far south. The band will be wider and heavier in northern areas resulting in higher totals there. The HRRR map above illustrates the setup well. The map is valid at 4:00 tomorrow morning. Rain will move out of Portland by 6 AM and out of the midcoast by 8. Clearing will follow.

12Z GFS Showing Gusty NW Winds Tomorrow. Image Credit: Weatherbell
12Z GFS Showing Gusty NW Winds Tomorrow. Image Credit: Weatherbell

Behind the front, gusty NW winds are forecast to develop. Winds could gust over 30mph at times as cooler and drier air works into the region. Look for these winds to quickly downslope the coast to sunny skies while upsloping may postpone sunshine for the mountains. Eventually, the air will become so dry that even with upsloping, the mountains will become sunny by afternoon. Dew points are forecast to drop to near 40 by tomorrow night. As winds settle down tomorrow night, temps will fall too. By Tuesday morning, the first fall like chills will be felt with temps bottoming out right around 40 in the north and 50 in the south with very dry air.

12Z GFS Showing Warm SW Winds Ahead Of An Approaching Front Late Next Week. Image Credit: Weatherbell
12Z GFS Showing Warm SW Winds Ahead Of An Approaching Front Late This Week. Image Credit: Weatherbell

Not ready for fall? Not to worry. By late in the week a front will be approaching from the NW and ahead of it SW winds will bring in slowly increasing warmth as well as humidity. While conditions won’t be stifling, the word sticky will once again come to mind by the upcoming weekend. As far as precip goes, the front won’t have a lot of dynamics associated with it and so scattered showers/storms are likely the most we’ll get from that front. After that, dry and warm conditions are likely to kick off next week.

Be sure to check out the new tropical weather page to keep tabs on the Atlantic disturbances 90L and 99L without the hype you may see on social media. The official NHC forecast, my forecast, and links to all the tropical weather information you need to take your own look at the tropics is all there. Check it out!

-Jack

The First Snow Of The Season Arrives Late Tonight After A Cold Rain

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Hello everyone!

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4:15PM Radar Shows Rain Slowly Expanding NW. Image Credit: Accuweather, Annotations By Me

Rain is already spreading across the area this afternoon as a plume of moisture moves north. The immediate coastline and the inland portion of the midcoast is currently seeing light to moderate rain and this will continue through the evening with rain slowly expanding NW.  Light to moderate rain should continue throughout most of the early part of the night mainly east of the Turnpike.

12Z GFS Giving Us An Overview Of The Storm, Map Credit: Weatherbell, Annotations By Me.
12Z GFS Giving Us An Overview Of The Storm, Map Credit: Weatherbell, Annotations By Me.

The main feature of this storm will be a sharp gradient on the back side of the system with 5 or 10 miles making up the difference between a few sprinkles and a half inch of rain ending as an inch of snow. As a result, the forecast is especially touchy for areas west of the Midcoast where 1-4″ is likely depending on elevation. Once you get to the I-295/I-95 corridor, a very sharp dropoff in snow totals is likely with some areas seeing up to 2″ and others but a few midnight flakes.

20Z HRRR Model IDEA On How The Storm Winds Down Tomorrow Morning. Map Credit: Weatherbell, Annotations By Me
20Z HRRR Model IDEA On How The Storm Winds Down Tomorrow Morning. Map Credit: Weatherbell, Annotations By Me

 

All precip, rain or snow, comes to an end early tomorrow morning with everyone west of I-95 dry by sunup and everyone else soon thereafter. The rest of tomorrow looks cool but nice with clearing skies and NW winds bringing in cooler and drier air.

18Z NAM Showing The Negatively Tilted Trough And The Winds Out Ahead Of It Directing The Storm Westward Up The Coast. Map Credit: Weatherbell, Annotations By Me
18Z NAM Showing The Negatively Tilted Trough And The Winds Out Ahead Of It Directing The Storm Westward Up The Coast. Map Credit: Weatherbell, Annotations By Me

Every storm has a surprise and by virtue of surprises, they largely remain unknown but if there was one place I had to guess there would be a surprise, it’s where there’s been one already. There were indications that the trough at the 500mb level would be negatively tilted with this storm for days. Finally, the surface forecasts caught up to that and in the past 24 hours the forecast has gone from ‘chance of a flurry midcoast’ to ‘many people get their first accumulating snow’. This trend has smoothed out with the afternoon guidance today but don’t be surprised if this thing comes a tad farther west and instead of a dusting, you end up with 2″ of snow. After all, it would really only take 25 miles to make that big of a difference for some.

12Z GFS Showing NW Winds Bringing In Colder (And Drier) Air Which Could Shut Off Precip Early
12Z GFS Showing NW Winds Bringing In Colder (And Drier) Air Which Could Shut Off Precip Early

The other, equally possible surprise is that the same cold NW winds bringing in the cold air to change things over to snow also come with enough dry air to shut off the precip early, especially because NW winds downslope off the mountains which dries the air even more. For a full explanation of downsloping in relation to temperature, check out my neat weather tidbit from a few weeks ago. While that post talks specifically about temperature, the same principle applies to moisture in that when air rises, moisture condenses and forms clouds/precip etc. just like it cools and when it sinks, the opposite happens. The post also includes a general overview on downsloping which applies to this forecast.

While the last two paragraphs could reasonably be perceived as me covering myself in case the forecast goes wrong, my hope is that in case it does, you can at least know why. As I’ve said several times, part of my goal here is to educate you about why weather happens as well as to tell you what’s likely to happen.

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Speaking of what’s likely to happen, here’s a look at how much snow to expect when all is said and done. All in all, not a big deal but it still will be nice to see the flakes flying in November.

I’ll have another update on tomorrow’s weather in the morning.

-Jack

Neat Weather Tidbit: The Mysterious Midnight Temp Spike

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Hello everyone!

PWM Temperature Graph Showing An Abnormal Spike In Temps At Around 8:30 Last Night.
PWM Temperature Graph Showing An Abnormal Spike In Temps At Around 8:30 Last Night.

Last night between 8 and 9 PM, something really cool happened all across southern Maine. Several hours after dark and following the passage of a cold front, temps spiked between 4 and 6 degrees in less than an hour going against all logic that temps should fall after dark especially without any large scale weather system to draw warm air north. Let’s see what happened.

8PM Surface Analysis Off The SPC Mesoanalysis Page Showing A Cold Front Stretched Across The Area.
8PM Surface Analysis Off The SPC Mesoanalysis Page Showing A Cold Front Stretched Across The Area.

At 8:00 last night, a cold front was crossing the area from west to east with SW winds ahead of it and W winds behind it. Temps were already pretty warm, in the 60’s, as southerly winds ahead of the front brought warm air into the region. Colder air lurked behind the front and temps in the 30’s were being reported in the upper Great Lakes with west winds bringing those temps right to us. So what happened? Shouldn’t temps have dropped after the passage of a cold front with an actual cold airmass behind it?

A General Explainer Of Upslope/Downslope Winds In Maine. All Crude Graphics Design Credit Goes To Me.
A General Explainer Of Upslope/Downslope Winds In Maine. All Terrible Graphics Design Credit Goes To Me 🙂

The answer lies in downsloping. This is a term I’ve used a lot but really want to explain here. Winds after the cold front were

westerly/northwesterly and thus the air over southern Maine came from New York/Quebec and then up and over the Appalachian Mountains. When the air rose up the west side of the Appalachians, it cooled but not a lot of the moisture was rung out as shown by the lack of precip at the time.

Because the air was still pretty saturated at the time, the sinking air on the east side of the mountains warmed at the saturated adiabatic lapse rate of roughly 5.5F for every thousand feet. The 5.5 degrees per 1,000 feet figure is for fully saturated air with relative humidity of 100%. The relative humidity in Portland at the time was 73% so the air could be expected to warm at 73% of the moist (partially saturated) adiabatic lapse rate. 73% of 5.5 degrees is 4.015 degrees, very close to the 4 degree rise measured at PWM.

At Augusta, the same calculation works. The temperature rose 5 degrees from 59 degrees at 9 PM to 64 degrees at 11PM. With a relative humidity at 9PM of 90%, that works out to a moist adiabatic lapse rate of 4.95 degrees, again, darn close to the 5 degrees observed in actuality.

0Z (7PM) Sounding From Gray Shoiwng Very Warm Air Just Above The Surface. Credit: SPC
0Z (7PM) Sounding From Gray Showing Very Warm Air Just Above The Surface. Credit: SPC

Another contributing factor to the suddenness of the spike in temps was warm air aloft suddenly being mixed down to the surface. The 7PM sounding up in Gray showed warm air just above the surface which promptly mixed down with the turbulence caused by the passage of the front.

The air just above the surface was being downsloped to just the right temperature with westerly winds just above the surface and when the surface front came through, the turbulence broke the inversion and sent those warm temps crashing to the ground.

I’ll be back in the morning with tomorrow’s weather. A sneak peek reveals cooler but still not chilly temps in the 50’s with mainly sunny skies.

-Jack

Heavy Rain And Wind Moves In Tomorrow Evening

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Hello everyone!

Not too much has changed since yesterday in terms of our upcoming heavy rain event. Here’s a quick updated rundown of what to expect.

Rain

12Z Canadian HRDPS Model Showing Deep Mositure Flooding Into The Area On Strong SE Winds. Map Valid 6AM Thursday. Credit: Weatherbell
12Z Canadian HRDPS Model Showing Deep Moisture Flooding Into The Area On Strong SE Winds. Map Valid 6AM Thursday. Credit: Weatherbell

Rain moves in during the evening hours tomorrow arriving in SW areas around 5 or 6 tomorrow evening with most of the area seeing rain by 7 or 8 PM. The heavier rain will hold off until later in the evening beginning in the west around 9 and spreading east through midnight. Between midnight and 6 AM or so, expect the worst conditions to occur with heavy rain being driven by strong winds.

NWS WPC Total Rainfall Forecast Through Thursday. Tan/Orange Areas Show 1-2″ Amounts While The Red Colors In The Mountains Show 2-2.5″ Totals. Credit: Weatherbell

While available moisture (Precipitable Water, shown above) is quite high, as well as forcing for wringing out that moisture, the ideal parameters are only really in place for about 6 hours early Thursday morning. As a result, total rainfall will be limited somewhat compared to if this was a more slowly moving system. A total of 1-1.5″ of rain is likely with 2-2.5″ amounts on south-facing mountain slopes.

Wind

12Z GFS BUFKIT Plot Showing 50kt Winds Below The Mixing Layer Early Thursday Morning.
12Z GFS BUFKIT Plot Showing 50kt Winds Below The Mixing Layer Early Thursday Morning.

Winds will become gusty tomorrow afternoon out of the SE as the front approaches. Expect winds building throughout the day with peak gusts arriving in the same 6 hour window as the heaviest rain from 12-6 AM Thursday. Most areas should see 15-25 mph winds with gusts to 35mph while the coast sees 25-35 mph winds gusting to near 60 mph. The plot above shows winds (everything but the yellow line, in knots) and the mixing layer (yellow line). Any winds below the yellow line are eligible to mix down to the surface in heavy precip. In heavy precip early Thursday morning, someone along the coast is likely to see some of those intense winds aloft mixed down on the order of 50-60 mph. The greatest threat for this is the NE coast closer to Penobscot Bay where a wind Advisory is up. All coastal areas should be prepared for strong winds, the chart above is for Portland.

Takeaway

Rain begins tomorrow evening becoming heavy late at night. Winds will also be on the increase out of the SE. Peak rain and wind occurs 12-6 AM Thursday with wind gusts approaching 60 mph along the coast. A total of 1-1.5″ of rain is likely with more on the south-facing mountain slopes where 2-2.5″ is likely.

I’ll have more updates tomorrow in a similar patter to today’s updates.

-Jack

Evening Update On Midweek Heavy Rain Event

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Hello everyone!

Our midweek heavy rain event is still very much on track for Wednesday afternoon through Thursday morning. Tonight’s update will focus more on specific impacts rather than larger scale setups.

Rain

NWS WPC Forecast Rainfall Amounts Through Thursday Afternoon. Credit: WPC/Weatherbell

Heavy rainfall is likely to be the main threat from this storm as Patricia’s moisture streams northward and interacts with the approaching cold front. A general 1-2″ is likely (Tan-Orange shadings on the map) with some 2-3″ amounts likely in the favored upslope areas (reddish shadings on the map). The fast moving nature of this system is what will keep precip amounts relatively low and given the quick arrival of dry air from the west Thursday morning, heavy precip should be centered in the 8PM-6AM timeframe which will limit total rainfall. Rain is likely to arrive earlier in the evening Wednesday likely closer to 5 or 6PM. These details will continue to be refined in the coming days.

Wind

12Z GFS Showing Very Strong Winds Just Above The Surface Early Thursday Morning.
12Z GFS Showing Very Strong Winds Just Above The Surface Early Thursday Morning.

With a strong cold front comes strong winds and this time is no different. A SE gradient will sharpen up during the day Wednesday leading to very strong winds by Wednesday afternoon into the evening. On the map above, the yellow line is the mixing layer and the red/green/blue contours are wind speeds. Elevation is the y-axis and time is the x-axis but read from right to left (I didn’t make the graph I promise! (credit to that goes to BUFKIT)). The takeaway is that any wind under the mixing layer is ‘eligible for a ride to the surface in heavy rain. Given the likely heavy rain early Thursday morning which coincides with the strongest winds just above the surface, very high winds are definitely a concern from midnight Thursday to 6-7AM or so. Expect the highest winds along the coast 20-30 mph with gusts to 55 mph or so. Lesser winds are expected elsewhere. With this kind of wind, saturated ground from the heavy rain, and some leaves definitely still on the trees, scattered power outages are likely especially along the coast.

The tides don’t look to line up particularly well for coastal flooding but some minor splashover is possible in the usually suspect areas.

I’ll follow today’s update pattern again tomorrow with daily weather in the morning and then a storm update in the evening.

-Jack