More Beneficial Rain This Week

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

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s